Associations of invasive cyanobacterial species and phytoplankton community structure with abiotic influences in post-glacial temperate lakes under climate change

Associations of invasive cyanobacterial species and phytoplankton community structure with abiotic influences in post-glacial temperate lakes under climate change | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Associations of invasive cyanobacterial species and phytoplankton community structure with abiotic influences in post-glacial temperate lakes under climate change Tümer Orhun Aykut, Robin Michael Crucitti-Thoo, Agnieszka Rudak, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5679541/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study conducted in Mazurian and Suwałki Lakelands (Poland), investigated the composition and distribution of phytoplankton species, currently existing invasive Cyanobacteria, and their linkages with various environmental parameters. Water and phytoplankton samples were collected from twenty-five lakes in the summer of 2023 to achieve the aims. In the study, crucial ecological influences such as pH, conductivity, dissolved oxygen, nutrient concentrations, and water temperature values were measured and their associations with phytoplankton community structure were described. In addition, the Shannon diversity index, Pielou’s evenness, Euclidean distance analysis, frequency analysis, and redundancy analysis have been applied to interpret the obtained data. In total 325 phytoplankton species were recorded, with the most abundant class being Cyanophyceae represented by 170 taxa. Although they had relatively low biomass, all of the investigated invasive cyanobacterial species ( Raphidiopsis raciborskii , Chrysosporum bergii , and Sphaerospermopsis aphanizomenoides ) have been identified in several water bodies. The Shannon diversity index showed that the highest diversity was found in one of the most eutrophic lake (Rekąty). Euclidean distance analysis described the highest similarity between two lakes with similar trophic status in Suwałki Lakeland (Przerośl and Hołny). RDA analysis revealed the positive correlations between Chlorophyceae and pH; Cyanophyceae and dissolved oxygen concentration. Biodiversity environmental parameters invasive Cyanobacteria phytoplankton structure Raphidiopsis raciborskii Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 INTRODUCTION Natural ecosystems together with lakes all over the World are increasingly influenced by anthropogenic disturbances, including habitat loss and degradation, different types of pollution, invasive or alien species, and overuse of sources (Cottingham and Carpenter 1998). In freshwater bodies, phytoplankton is the most prevailing, unicellular and microscopic life forms (Giripunje et al. 2013) which are the main element of the aquatic food web and have global significance for ecosystem services and continuity (Winder and Sommer 2012). Although they account for 1% of the photosynthetic biomass on Earth, they are responsible for more than 50% of global net primary production. They are the essential energy source for every single aquatic ecosystem (Field et al. 1998), in addition to facilitating the persistence of biogeochemical processes (Arrigo 2005). For these reasons, they are considered a core aspect of a healthy aquatic ecosystem (Xu et al. 2001). Several factors influence the composition and abundance of phytoplankton in aquatic environments with any changes in these factors directly affecting the phytoplankton community structure to some extent. Principally, factors affecting phytoplankton growth can be described as pH, water temperature, light conditions, nutrient concentrations, and predation by zooplankton and fish (Domingues and Galvao 2007). Phytoplankton algae are often used as bioindicators and biomonitoring organisms to determine the ecological status and disturbance effects of chemical pollutants in water bodies (Xu 1997; Xu et al. 2001). That’s because their short life cycles allow the organisms to respond swiftly to environmental changes, which is reflected in the composition and structure of phytoplankton (Domingues and Galvao 2007; Wu et al. 2014). Three leading features merit their use in ecosystem biomonitoring (Hötzel and Croome 1999): (i) they have high sensitivity to environmental (abiotic and biotic) changes, (ii) they are easier to collect and analyze in comparison to other aquatic organisms, and (iii) most species are cosmopolitan with well-known autecology (Van Dam et al. 1994). Additionally, surveys that have been conducted based on phytoplankton community analysis are frequently used as a tool for biomonitoring to help generate early warnings of water problems (Thiébaut et al. 2006). As a result, different evaluation approaches based on microalgae have been developed in several countries and regions (Siddig et al. 2016). Biological invasions in lakes are a serious threat to biodiversity and ecosystem functioning, with successful invasions depending on relationships between multiple abiotic and biotic factors (Bolius et al. 2019). In recent years, the number of species spreading to new latitudes has increased and the introduction of invasive species can have several, generally negative ecological consequences. Invasive species are common in nearly every type of ecosystem, but aquatic ecosystems are especially at risk because of a combination of different factors (Sala et al. 2000). The three key factors that contribute towards a successful invasion have been determined (Lonsdale 1999; Litchman 2010) as i) the identity and genetic variation of the invader, (ii) the characteristics of the local community (Stachowicz and Byrnes 2006), and (iii) the optimal level of abiotic parameters of the habitat for the certain phytoplankton species, such as temperature (Seifert et al. 2015), light access (Conroy et al. 2007; Vidal et al. 2008) and nutrient content (De Meester et al. 2002; Yang et al. 2008). If these factors occur, the invaders often outcompete local species and become the new dominant species in the ecosystem (Lonsdale 1999; Litchman 2010). The presence of ice cover determines the existence of multiple specific conditions that influence physical and chemical changes that affect the community structure (Ptak 2013b). This matter's importance has increased since global warming's effect on freshwater bodies was described. Correspondingly, considerable changes are encountered in the elements of lakes. The increase in water temperature (Austin and Colman 2008; Hampton et al. 2008) and the decrease in time of ice season are particularly crucial examples (Magnuson et al. 2000). Lake Śniardwy is one of the most important lakes in this study as it is the largest one in Poland, but also because of its potential to be a reference to the other lakes investigated in this study. While the recorded mean water temperature in this lake was 9.0°C between 1972–1987, it was 10.4°C between 2004–2019. In the same periods (1972–1987 and 2004–2019), the duration of the ice cover (days) decreased from 103 days to 73 days (Ptak et al. 2020). Analysis proved that these differences were significant for observing a change in the lake's physical, chemical, and biological processes (Ptak et al. 2020). As cyanobacterial invasive species, especially Raphidiopsis raciborskii can be favored by different temperature levels, they also can adapt themselves to it (Silva et al. 2022; Zheng et al. 2023; Meriggi et al. 2024; Zheng et al. 2024). Therefore, it is essential to not only consider changes in temperature and ice cover in this region but also to evaluate how these changes impact invasive cyanobacterial species and the phytoplankton structure. Freshwater ecosystems such as lakes, rivers, and ponds have larger biodiversity per surface area than marine and terrestrial ecosystems (Dudgeon et al. 2006) and they have an operating role that impacts human societies positively, which are nutrient and water cycling (Wetzel 2001). However, non-indigenous species strongly modify these ecosystems by introducing different taxonomic groups (Strayer 2010; Simberloff et al. 2013). Even though some well-studied invasive species such as Daphnia lumholtzii do not have a great negative impact on the environment, most of the aquatic invasive species have already harmed the ecosystems and humans in various ways (Havel et al. 2005a; Havel et al. 2005b). This is why understanding the species’ invasion progress and reproduction strategies is crucial (Havel et al. 2015). Potentially harmful blooms caused by Cyanobacteria are extensive in freshwater ecosystems globally and are enforced by climate change and anthropological elements (Huisman et al. 2018). Among tropical and subtropical invasive species noted in temperate Europe, Raphidiopsis raciborskii , Raphidiopsis mediterranea , Chrysosporum bergii , and Sphaerospermopsis aphanizomenoides are considered a growing threat (Stüken et al. 2006). R . raciborskii being the most important, which is already known as a highly invasive species in Western Poland, is a freshwater, planktonic, filamentous, potentially toxic, and nitrogen-fixing Cyanobacteria (Antunes et al. 2015). In addition, the presence and the formed blooms of this Cyanobacteria have swiftly increased in tropical and subtropical lakes and reservoirs globally (Haande et al. 2008; Yang et al. 2017; Sidelev et al. 2020). Cylindrospermopsins (CYNs) can be produced by R . raciborskii , which poses health risks to both humans and other organisms, although no European strains have been found to produce this toxin (Rzymski and Poniedzialek 2014; Sidelev et al. 2020). Polymethoxy-1-alkenes (PMAs) are another compound with potential toxicity to organisms in freshwater bodies (Rzymski and Poniedzialek 2014). Similar to cylindrospermopsin (CYNs), PMAs may exhibit geographical differences, with Australian strains of R . raciborskii capable of producing them, in contrast to strains found in Europe (Jaja-Chimedza et al. 2015). Some South American strains of this species are reported to be able to produce saxitoxins (STX) that are hazardous (Ferrão-Filho and Silva 2020). The aims of this study carried out in twenty-four lakes that are going through major changes due to climate change in ice cover duration and water temperature in the Mazurian and Suwałki Lakelands of Poland which are the post-glacial ones as well as in one lake in Central Poland, in Warsaw, are i) to observe the occurrence of potentially toxic, invasive cyanobacterial species in geographical gradient from the central towards North-eastern Poland, ii) reveal the composition and distribution of different classes of phytoplankton assemblages in studied lakes, and to iii) describe their associations with numerous environmental parameters. The chosen geographical gradient is important to compare the cyanobacterial invasion based on temperature values as it is claimed to be one of the most important influencing variables. MATERIALS AND METHODS Sampling region and period The following lakes have been chosen and examined to determine the phytoplankton communities and the occurrence of invasive cyanobacterial species: Suskie (1), Piłag (2), Szczęśliwickie (3), Probarskie (4), Zjadły (5), Majcz Wielki (6), Inulec (7), Głebokie (8), Mikołajskie (9), Sztynorckie (10), Mamry (11), Brzozolasek (12), Niegocin (13), Śniardwy (14), Żabinki (15), Rekąty (16), Przerośl (17), Hańcza (18), Pobondzie (19), Długie Wigierskie (20), Leszczewek (21), Wigry (22), Dowcień (23), Zelwa (24), and Hołny (25) (Fig. 1). Among these water bodies, only Szczęśliwickie (Warsaw, Central Poland) is not part of the Mazurian or Suwałki Lakelands (post-glacial lakes) which are located in Northeastern Poland. This artificial lake situated in Central Poland was inspected due to its hypereutrophic character and potential for comparison with the north-eastern lakes. However, even though lakes were evaluated based on geographical gradient, it must be noted that the climate in Central Poland is milder than in Northeastern Poland. Structural information about the lakes is available in Table 1. Period of collecting the samples and analysis of biotic and abiotic variables To reveal the associations between phytoplankton structures and environmental variables, water and phytoplankton samples from the Mazurian and Suwałki Lakelands were collected between 13–17 August 2023 and Szczęśliwickie on 28 August 2023. The key environmental factors were selected as water temperature (°C), Secchi depth (cm), conductivity (µS/cm), dissolved oxygen (mg/L, %), pH, and nutrients such as non-purgeable organic carbon (NPOC, mg/L), total nitrogen (TN, mg/L), total phosphorus (TP, mg/L), ammonium (N-NH 4 + , mg/L), nitrate (N-NO 3- , mg/L), phosphate (P-PO 4 3- , mg/L), and sulfate (S-SO 4 2- , mg/L). Apart from nutrient analyses, all parameters were checked in the field. Secchi depth was measured with a Secchi disk while the rest of the environmental factors were with a YSI 556 multiprobe. Dissolved oxygen (DO) values and water temperature values were measured at different depths (0–30 cm to 9 m) depending on the lake. NPOC and TN values were detected with the combustion method by using the Multi N/C 3100 apparatus (Wakley and Black 1934) while TP values were found by nitric acid digestion method in temperature up to 230°C followed by measurements using continuous flow analyzer SAN + + Skalar (MEWAM 1981). The values of remaining nutrients (N-NH 4 + , N-NO 3 - , P-PO 4 3- , and S-SO 4 2- ) were detected with the spectrophotometric method by using a continuous flow analyzer SAN + + Skalar (Gray et al. 2006). For the collection of phytoplankton samples, water from three different places in the studied lake was obtained with a water sampler. After mixing collected water in a bucket a one-liter subsample was collected in plastic containers for every lake. Fixation of the samples was accomplished by Lugol’s solution with an addition of 38% formaldehyde to the final concentration of 1.5%. All measurements and sample collections were done in most of the lakes in the middle point of the lakes, except Lakes Zjadły and Probarskie in which the samples were collected from the jetties protruding into the lakes. The samples were kept at + 5°C in a dark place immediately after sampling. Identification of phytoplankton species Phytoplankton samples were identified according to Pliński and Komárek (2007), Komárek and Anagnostidis (2007), Pliński and Hindák (2010), Pliński and Owsianny (2011), Komárek (2013), and Pliński and Witkowski (2013) with Utermöhl method using inverted light microscope (Utermöhl 1958). The biomass of each species was determined by volumetric analysis of cells using the geometric approach and expressed as wet weight (Wetzel and Likens 2000). Statistical analysis of the biotic and abiotic parameters All of the statistical analyses were performed in R (v4.4.1) (R Core Team, 2024) using the “vegan” package (VCEP et al. 2022). In every statistical analysis, the water temperature and dissolved oxygen values are the values measured within the top 0–30 cm of the surface. Before the analysis of the environmental variables, data was standardized using the function “decostand” to avoid false grouping due to different units of measurement of each factor. Pearson correlation analysis was performed to remove collinear environmental factors. For values below the measurement range, it was assumed the lowest range limit was the measured value for calculation purposes. We have also performed Hellinger transformation to species data because of the high fraction (> 85%) of zero values due to the absence of certain species. Transformed data was used for RDA analysis combining species and environmental factors data sets. Species richness and the Shannon diversity index were calculated to reveal the diversity of the phytoplankton in lakes (Shannon 1948). Pielou’s evenness index was applied to have more critical remarks about the distribution of taxa of the phytoplankton in the lakes (Pielou 1964). Euclidean distance analysis (ED) was used in determining the similarity of lakes in terms of abiotic variables (Clarke and Warwick 2001). Frequency analysis was performed to understand the percentage of the presence of the phytoplankton species in the lakes, regardless of their abundance. The phytoplankton species were divided into five different groups according to this analysis based on their presence in the lakes, defined as follows: Rare (1–20%), Uncommon (21–40%), Common (41–60%), Very Common (61–80%) and Abundant (81–100%) (Kocataş 1996). Two lakes which are Probarskie and Zjadły were not included in ED due to incomplete environmental data. RESULTS Environmental variables Measurements of abiotic parameters found at twenty-five lakes in Mazurian and Suwałki Lakelands are given in Fig. 2 . The important points are highlighted below. Values for water temperature and dissolved oxygen have been measured from various ranges of depth depending on the characteristics of the lake. The values for temperature gradually decreased with the depth as was expected in every lake and the thermocline of stratified lakes was found at around 5 m depth. However, this distinction was not as clear with the values of DO. The water temperature at the surface (0–50 cm) in the studied lake varied between 21.4°C (Śniardwy) and 27.0°C (Piłag). Meanwhile, at the same depth, DO was varied between 15.17 mg/L (Rekąty) and 7.02 mg/L (Zjadły). The thermocline for Inulec occurred at 7 m, Głebokie at 6 m, Żabinki at 5 m, Przerośl 6 m, Pobondzie at 5 m, Długie Wigierskie at 6 m, Wigry at 7 m, and Hołny 4 m. On the other hand, DO values significantly lowered at 1 m for Piłag, at 4 m for Inulec, at 6 m for Głebokie, at 2 m for Sztynorckie, at 4 m for Żabinki, at 2 m for Rekąty, at 6 m for Przerośl, at 3 m for Hańcza, at 5 m for Pobondzie, at 7 m for Długie Wigierskie, at 3 m for Leszczewek, at 6 m for Wigry, at 4 m for Dowcień, at 6 m for Zelwa, and 4 m for Hołny. The measurements in twenty-three lakes revealed that the maximum value of SD was in Lake Hańcza (710 cm). There was a wide difference between this value and the second-highest value (410 cm) which was observed in two lakes: Wigry and Majcz Wielki. The lowest values were noted in Sztynorckie with 60 cm, followed by Suskie (70 cm) and Szczęśliwickie (75 cm). Because samples from Lake Zjadły and Probarskie were collected from a pier protruding to the lake, we were not able to measure the Secchi depth as it exceeded the depth at the bottom sediments under the pier by 1.5 and 2 m respectively. The highest conductivity value was found in Szczęśliwickie (593 µS/cm) followed by Leszczewek (501 µS/cm). The lowest value was observed in Probarskie with 168 µS/cm. Except for Lake Zjadły, the studied lakes were slightly basic. The highest pH values were observed in five lakes, respectively: Probarskie (8.58), Majcz Wielki (8.55), Szczęśliwickie (8.54), Głebokie (8.53), and Niegocin (8.50). The lowest value was observed in Zjadły (6.84). The highest TN value was found in Piłag with 2.75 mg/L while the lowest was in Zelwa. For TP the most enriched lake was Sztynorckie (0.55 mg/L) but for fourteen lakes the values were lower than 0.025 mg/L although in Szczęśliwickie the lowest identified TP value was 0.03 mg/L. When it comes to N-NH₄⁺ the maximum value was found in Rekąty (0.09 mg/L) and the minimum detectable value in Piłag (0.07 mg/L), but in all other lakes the values were lower than 0.05 mg/L which was the threshold value for the chosen method. In the case of N-NO 3 - , the highest was found in Długie Wigierskie (0.13 mg/L). For P-PO₄³-, in all lakes, values were found to be lower than 0.025 mg/L. Lastly, the maximum S-SO₄²- value was observed in Suskie (22.20 mg/L) while the lowest was in Inulec (2.40 mg/L). Phytoplankton communities In this study conducted in the Mazurian and Suwałki Lakelands, 325 phytoplankton species were identified altogether. The most abundant class was Cyanophyceae with 170 taxa (52.3% of all taxa), 34 of which were identified to genus level. The numbers of the species found in the classes Bacillariophyceae (69 taxa, 19 of which were identified down to genus level) (21.2% of all taxa) and Chlorophyceae (68 taxa, 22 of which were identified down to genus level) (20.9% of all taxa) were close to each other. In addition, there were respectively 13 (4.0% of all taxa) (4 of which were identified down to genus level), 3 (0.9% of all taxa), and 2 (0.6% of all taxa) taxa were obtained in the classes of Dinophyceae, Cryptophyceae, and Chrysopyceae (1 of which was identified down to genus level). On a lake basis, the highest number of taxa were identified in Rekąty with 66 taxa, and 41 of them belonged to Cyanophyceae. This was followed by Pobondzie (59 taxa), and Niegocin (59 taxa). The lowest numbers of taxa were observed in Długie Wigierskie (34 taxa), Leszczewek (35 taxa), and Wigry (36 taxa). Additionally, there was no lake found without representatives of Cyanophyceae, Chlorophyceae, and Bacillariophyceae. The lowest number of Chlorophyceae members were found in Majcz Wielki and Głebokie with 2 taxa while for Bacillarophyceae the minimum number of taxa was observed in Suskie, Probarskie, Głebokie, Sztynorckie, Rekąty, Pobondzie, Długie Wigierskie, and Leszczewek with 3 taxa. In the class Cyanophyceae, the maximum number of species belonged to the genera Dolichospermum (13 taxa), Aphanocapsa (11 taxa), and Microcystis (10 taxa). In the class of Chlorophyceae, Cosmarium (6 taxa) and Staurastrum (5 taxa) were the genera with the highest number of species while in Bacillariophyceae these genera were Navicula (9 taxa) and Cymbella (6 taxa). In addition, the genus Ceratium (5 taxa) was obtained to have the highest number of species in the class Dinophyceae. According to performed analyses, the presence of R . raciborskii was recorded in five lakes: Szczęśliwickie, Mikołajskie, Rekąty, Sztynorckie, and Pobondzie. Additionally, C . bergii was found in three lakes: Rekąty, Żabinki, and Pobondzie, S . aphanizomenoides only in Pobondzie while R . mediterranea in two lakes: Mikołajskie and Śniardwy. The phytoplankton community of Mazurian Lakes varied a lot. There were 49 species identified in Suskie which is the lake with the highest total biomass. Chlorophyceae accounted for 46.0% of the total phytoplankton biomass. Trichodesmium lacustre and Desmodesmus opoliensis were the species reported only from here. In Lake Piłag, the species richness was low, only 38 species were identified. Chlorophyceae was the dominating class with a 51.1% percentage of the biomass. It was followed by Cyanophycae (28.7%) and other classes were nearly evenly distributed compared to other lakes. Pseudopediastrum boryanum and Dolichospermum circinale found to have dominant species. Tetraedron sp., Ulnaria sp., and Ulnaria ulna were found only in Piłag. Szczęśliwickie is a lake studied in the sense of hydrobiology, but no phytoplankton study published from there yet. In our study, this lake also had quite a low species richness with only 37 identified species. Chlorophyceae accounted for 45.8% of the total biomass while Cyanophyceae had 40.7%. However, the significance of this lake is the occurrence of Raphidiopsis raciborskii which appeared in low numbers (only one individual). There were also two taxa: Geitlerinema sp. and Nodularia sp. identified up to the genus level only in this lake. Throughout almost all summer period, the surface of Lake Szczęśliwickie was covered with gelatinous clumps of Aphanocapsa . During the phytoplankton identification A . incerta was the only species found here belonging to this genus. Probarskie and Zjadły are geographically close lakes with unrevealed phytoplankton community structure. According to our study, 41.3% of the biomass of Probarskie was formed by Chlorophyceae while Zjadły was dominated by Dinophycae by 33.7%. In addition, the species richness in Probarskie (56 species) was higher than in Zjadły (41 species). Pediastrum biradiatum in Probarskie and Ceratium hirundinella in Zjadły were the most abundant species. Jaaginema sp., Oscillatoria limosa , Pediastrum sp., and Tetrastrum elegans were identified only in Probarskie while Leptolyngbya thermobia , Oscillatoria sp., Radiocystis fernandoi , and Gomphonema minutum were in Zjadły. Majcz Wielki had low species with only 40 identified species. Cyanophyceae had the biggest share in biomass with 27.4% but Ceratium hirundinella was found to be the species with the most biomass. Anagnostidinema ionicum , Epithemia sp., Nitzschia inconspicua , and Synedra sp. were encountered only in this lake. In Inulec, there were only 42 species identified, and Cyanophyceae was the dominating class with 40.3% of the biomass. However, on the species level, Cosmarium joshuae and Ceratium hirundinella were the ones with the highest biomass, respectively. Aphanocapsa rivularis , Spirulina subtilissima , Ankistrodesmus arcuatus , Staurastrum manfeldtii , and Tetraedron trigonum were the species found only in Inulec. In Głebokie, Chlorophyceae had the biggest share in total biomass (50.4%) and Pseudopediastrum boryanum contributed the most to it. However, species richness here was low with only 39 identified species. Dolichospermum minisporum , Nostoc commune , Nostoc paludosum , Trichodesmium sp., and Cocconeis pediculus were found only here. Compared to the other lakes, Lake Mikołajskie had a relatively high biomass of the Dinophyceae (27.8%) but the biomass of Chlorophyceae was the most (42.1%). There were 56 species identified from this lake. Glaucospira laxissima , Leptolyngbya carnea , Pseudanabaena galeata , Spirulina baltica , Tetrastrum sp., Aulacoseira sp., and Cymbella tumida were identified only in Mikołajskie. Also, the Raphidiopsis raciborskii was reported from this lake and its number (2) was higher than in Szczęśliwickie. Lake Sztynorckie had relatively high species richness with 47 identified species. Cyanophyceae had the biggest share in biomass with a 70.8% contribution. Additionally, Microcystis aeruginosa and Anagnostidinema amphibium were the most dominant cyanobacterial species in this lake. Most importantly, the Raphidiopsis raciborskii occurring in Lake Sztynorckie reached the highest biomass in the whole study. Cyanobium sp., Gomphosphaeria aponina , Jaaginema quadripunctulatum , Leptolyngbya angusta , Merismopedia elegans , and Fragilaria perminuta were reported only from this lake. Species richness in Mamry was quite high with 49 identified species. Chlorophyceae and Cyanophyceae were co-dominating phytoplankton classes in this lake. Compared to other lakes Dinophyceae also had a large contribution to the total biomass with 14.9%. There were many species identified only from Mamry: Aphanocapsa nubila , Aphanothece floccosa , Microcystis firma , Planktolyngbya undulata , Pseudanabaena thermalis , Romeria gracilis , Romeria leopoliensis , Trichocoleus sp., Gymnodinium fuscum , Microspora abbreviata , Amphora copulata , Cymbella neocistula , Diploneis elliptica , Epithemia turgida , and Nitzschia amphibia . There was no information found about the phytoplankton community of Brzozolasek. In our study, 43 species were identified from this lake and the biomass of Cyanophyceae was dominating by 52.9% which was followed by Dinophyceae by 29.0%. The contribution to the total biomass of the Chlorophyceae (6.2%) was the second lowest in this lake in the entire study. Anabaena elegans , Anabaena ellipsoidea , Limnolyngbya circumcreta , Microcystis natans , Synechocystis sp., Amphora ovalis , Encyonema ventricosum , and Planothidium frequentissimum were reported only from Brzozolasek. Lake Niegocin had very high species richness with 59 identified species. Chlorophyceae had the biggest share in the total biomass with a 62.8% contribution. Pediastrum duplex and Cosmarium reniforme were the species with the highest biomass, respectively. Dolichospermum fuscum , Gomphosphaeria sp., Komvophoron schmidlei , Nodularia spumigena , Planktolyngbya crassa , Spirulina meneghiniana , Navigeia decussis , Odontidium mesodon , and Stephanodiscus sp. were described only from Niegocin. In Lake Śniardwy, the largest lake in Poland species richness was found to be high with 53 identified species. 64.5% of the total phytoplankton biomass in this lake was contributed by Chlorophyceae. Pseudopediastrum boryanum was the species with the highest biomass. Leptolyngbya boryana , Chlamydomonas ehrenbergii , Chlamydomonas sp., and Surirella brebissonii were the species reported only from here. In Lake Żabinki, 45 species were identified including the invasive Chrysosporum bergii. 62.3% of the total phytoplankton structure was formed by Cyanophyeae, which is the second-highest percentage of Cyanophyceae in a single lake. It has been followed by Dinophyceae (15.8%). Total biomass was found to be 5.5 mg/L and the biggest contributor to this was Ceratium hirundinella and Limnothrix redekei . Pseudanabaena articulata , Spirulina major , Synechocystis septentrionalis , Chlamydomonas reinhardtii , Pinnularia sp., and Surirella librile were found only here. Lake Rekąty was characterized by the highest species richness with 66 identified species including invasive Chrysosporum bergii and Raphidiopsis raciborskii . 48.3% of the phytoplankton structure was formed by Cyanophyceae. Many cyanobacterial species that occurred only in this lake such as Anabaena sedovii , Anabaenopsis cunningtonii , Anabaenopsis knipowitschii , Dolichospermum sigmoideum , Microcoleus autumnalis , Microcystis panniformis , Rhabdogloea linearis . In addition, other phytoplankton classes were represented by species occurring only in this lake, such as Gonyaulax apiculata , and Oocystis lacustris . In Suwałki Lakeland there were also big differences in the composition and structure of the phytoplankton community. In Lake Przerośl, species richness was found to be high with 53 species and the class Cyanophyceae formed the structure by 45.9% biomass. On the other hand, the phytoplankton class Cryptophyceae had one of the lowest biomasses (0.2%). Anabaena echinospora , Anathece clathrata , Microcystis botrys , Oscillatoria tenuis , Peridinium willei , Gonatozygon monotaenium , Teilingia sp., Eunotia sp., and Gyrosigma kuetzingii were identified only from Przerośl. There were merely 39 species identified in the deepest lake in Poland, Hańcza which means the species richness was quite low here. 35.7% of the total biomass was formed by Cyanophyceae while 30.2% by Dinophyceae making the two classes’ subdominants in this lake. It is also worth mentioning that with 7.9% the share of the Chlorophyceae was one of the lowest here in the whole study. Snowella sp., Diploneis separanda , Hantzschia sp., and Pantocsekiella ocellata were identified only from here. Lake Pobondzie was one of the most important lakes in this study as all three aimed-to-find cyanobacterial invasive species ( R . raciborskii , C . bergii , and S . aphanizomenoides ) were found here even though they had very low biomasses. Unfortunately, no available phytoplankton data was found but, in this study, Cyanophyceae was dominating (40.8%) class followed by Chlorophyceae (29.8%). Species richness in Pobondzie was the second-highest in the whole study with 59 taxa. There were quite a lot of species reported only from Pobondzie: Anathece sp., Dolichospermum viguieri , Nostoc passerinianum , Nostoc undulatum , Sphaerospermopsis aphanizomenoides , Sphaerospermopsis sp., Synechocystis sallensis , Peridiniopsis polonicum , Cosmarium granatum , and Willea apiculata . Długie Wigierskie had one of the lowest species richness in this study with 34 taxa. The phytoplankton structure in this lake was dominated by Dinophyceae with 51.5% and it was the highest percentage of biomass for Dinophyceae in the entire study. Ceratium cornutum and Ceratium hirundinella were the main representatives of the phytoplankton class Dinophyceae. The total biomass was 1.00 mg/L, which was one of the lowest in the whole study. There were only two species from Bacillariophyceae encountered only from this lake which are Diatoma sp. and Eunotia bilunaris . There were only 35 species identified from Lake Leszczewek. The biggest share of the total biomass was formed by Chrysophyceae with 34.7%. Leptolyngbya ectocarpi , Synechococcus sp., Koliella longiseta , and Neidium sp. were reported only from Leszczewek. Lake Wigry, the largest lake in Suwałki Lakeland and the third-largest lake in Poland had relatively low species richness (36 taxa), Cyanophyceae was the dominating phytoplankton class accounting for 39.0% of total phytoplankton biomass followed by Dinophyceae with 23.2%. Wigry was one of the lakes where no Cryptophyceae were found during biomass calculation. Biomass of Chrysophyceae was found to be 16.1% and it was the second highest in the entire study. There were two taxa ( Gloeocapsa sp. and Placoneis sp.) identified down to genus level in Wigry which are found only in this lake. In Lake Dowcień, there was no Dinophyceae representative were encountered during the biomass calculation. The highest part of the biomass was formed by Chlorophyceae with 39.2% and it has been followed by Cyanophyceae with 37.1%. On the other hand, species richness was average (46 taxa). Cosmarium turpinii , Treubaria sp., and Ulothrix tenerrima , Cymbella lange - bertalotii , and Navicula capitatoradiata were found only here. The phytoplankton community structure of Lake Zelwa was strongly formed by Cyanophyceae with 45.2% and the rest of the phytoplankton classes were relatively evenly distributed except Cryptophyceae (2.2% and Chrysophyceae (5.6%). Species richness here was also average (45 taxa). Dolichospermum danicum , Microcystis sp., Rhabdoderma sp., Desmodesmus denticulatus , Asterionella formosa , Eunotia rhomboidea , and Gomphonema micropus were present only in Zelwa. Lake Hołny, located the most to the east of the studied lakes, was dominated by Chlorophyceae with 42.8% of the biomass. Caloneis budensis was encountered only here. The biomass of Cyanophycea (22.7%) and Dinophyceae (22.7%) were very close to each other. Species richness was relatively high with 50 taxa. Borzia trilocularis , Chroococcus cumulatus , Dolichospermum mucosum , Eucapsis aphanocapsoides , Botryococcus sp., Hariotina reticulata , Caloneis budensis , and Nitzschia dissipata were described only from Hołny. Statistical Evaluation of Data Biomass rates of the phytoplankton communities The mean value of total biomass in all lakes was calculated as 6.7 mg/L. The highest biomass was found in Lake Suskie with 56.2 mg/L followed by Sztynorckie (23.8 mg/L) and Szczęśliwickie (11.6 mg/L). The lowest biomass was found in Brzozolasek (0.8 mg/L) followed by Hańcza, Majcz Wielki, and Zjadły in which the total phytoplankton biomass was 0.9 mg/L (Fig. 3 ). Considering the phytoplankton classes, Cyanophyceae had the highest mean value for the biomass with 2.8 mg/L (42.3%) followed by Chlorophyceae at 2.5 mg/L (37.8%) and Dinophyceae at 0.8 mg/L (11.5%). Cryptophyceae (0.2 mg/L, 3.6%) and Bacillariophyceae (0.2 mg/L, 3.5%) had quite close values to each other while Chrysophyceae was 0.1 mg/L (1.4%) (Fig. 4 ). Evaluating the lakes among each other, all of the biomass values of the other phytoplankton classes were found to be the highest in Suskie; except for Chrysophyceae in Leszczewek. However, this was because of the high biomass in the Suskie. When the lakes are evaluated on their own, the highest biomass rate of Cyanophyceae was in Sztynorckie (70.8%), Chlorophyceae in Śniardwy (64.5%), Bacillarophyceae in Hańcza (17.3%), Dinophyceae in Długie Wigierskie (51.5%), Cryptophyceae in Majcz Wielki (9.1%), and Chrysophyceae in Leszczewek (34.7%). Monactinus simplex was the species with the highest biomass (23.5 mg/L) and it made 37.2% of the whole Chlorophyceae (Fig. 5 ). On the other hand, Anagnostidinema amphibium was found to have the highest biomass (13.7 mg/L) in Cyanophyceae. The biomass values of the invasive species R . raciborskii (0.39 mg/L), C . bergii (0.09 mg/L), and S . aphanizomenoides (0.02 mg/L) were quite low in the entire study. In addition, the highest biomass of R . raciborskii was found in Sztynorckie (0.26 mg/L). In total, 11 lakes were dominated by Cyanophyceae, 10 by Chlorophyceae, two by Dinophyceae, and only one by Chrysophyceae. Species richness, Shannon diversity index, and Pielou’s evenness To reveal the diversity of phytoplankton community structure, species richness, and the Shannon diversity index were employed based on the presence and biomass of the identified species in all lakes. Considering every lake, it was determined that the Shannon diversity index varied between 1.79 (Mikołajskie) and 2.84 (Rekąty) (Table 2 ). Species richness, which reflects the number of identified species in lakes regardless of their biomass, showed the highest richness in Rekąty (66 taxa) and the lowest in Długie Wigierskie (34 taxa). Pielou’s evenness was also applied to reveal how evenly the species are distributed and to verify diversity. Accordingly, the highest evenness was found in Leszczewek (0.92) and the lowest in Niegocin (0.57). Euclidean distance analysis Clustering analysis was used to determine the similarities of the freshwater bodies investigated in Northeastern Poland. Using Euclidean distance analysis (ED) the similarity between the lakes in terms of ecological variables was identified. Accordingly, Piłag and Hańcza (ED = 8.51) were found to have the lowest similarity. On the other hand, Przerośl and Hołny (ED = 1.11) were found to have the highest similarity (Fig. 6 ). Euclidean distance analysis also revealed the closeness among Rekąty, Szczęśliwickie, Leszczewek, Sztynorckie, Suskie, and Piłag which formed a cluster separated from all other lakes. The second large cluster was divided into a small cluster grouping Lakes Hańcza and Długie Wigierskie and the other to which the rest of the lakes were assigned. The smaller groups with higher similarity can also be distinguished here. Therefore, Pobondzie, Dowcień, Przerośl, Hołny, Wigry, Mamry, Zelwa, Brzozolasek, Inulec, and Żabinki formed one cluster while Majcz Wielki, Głebokie, Niegocin, Mikołajskie, and Śniardwy the second which are oligotrophic and oligo-mesotrophic lakes with similar nutrient content. The last two clusters were among Brzozolasek, Inulec, and Żabinki and Majcz Wielki, Głebokie, Niegocin, Mikołajskie, and Śniardwy. All of these lakes are located in Mazurian Lakeland (ML) and they have similar main abiotic variables such as temperature, conductivity, pH, and dissolved oxygen. Brzozolasek was an interesting lake in this cluster, even though geographically it is located in the same area, the nutrient content and other abiotic variables of this lake were different than the others. It also had very low phytoplankton biomass. Frequency analysis The most frequent species defined was Aphanizomenon gracile , which was not encountered only in Lake Piłag. A . gracile was followed by Limnothrix redekei and Planktolyngbya limnetica which were noted in 22 lakes. Although this analysis is not related to abundance, all of the frequently found species had relatively high biomass. 269 of 325 species were described as belonging to "Rarely Found Species", 29 to "Seldomly Found Species", 12 to "Commonly Found Species", 9 to "Frequently Found Species", and six to "Continuously Found Species". Moreover, all three ( R . raciborskii, C . bergii , and S . aphanizomenoides ) of the invasive cyanobacterial species in Poland also belong to "Rarely Found Species" (Fig. 7 ). Additionally, frequency analysis showed only six species that could be classified as "Continuously Found Species" which were Aphanizomenon gracile , Anagnostidinema amphibium , Limnothrix redekei , Planktolyngbya limnetica , Cryptomonas sp . and Rhodomonas sp. as they have been encountered in more than 20 lakes. Redundancy analysis (RDA) According to the RDA results, environmental variables included in the analysis explain 37.63% of the variation in algae composition across lakes (Fig. 8 ). It was observed that water transparency was negatively correlated with pH. DO, TP, TN, and pH were placed together in the same quarter, opposite to transparency. In addition, it was revealed that Chlorophyceae had a positive correlation with pH and TN while they had a negative correlation with transparency, Cyanophyceae positively correlated with DO, whereas Chrysophyceae negatively correlated with DO. Bacillariophyceae, Cryptophyceae, and Dinophyceae did not have any strong relationship with environmental parameters. However, Bacillariophyceae exhibited a slight positive correlation with transparency and a negative with TN, TP, and pH (p < 0.05) while Cryptophyceae showed a slightly positive with TP and TN, whereas Dinophyceae negative relationship with electrical conductivity (EC) (Fig. 8 ). DISCUSSION Throughout the whole sampling period, the phytoplankton community structure in Mazurian and Suwałki Lakelands showed a notable difference. The phytoplankton communities in twenty-five lakes were dominated by Chlorophyceae and Cyanophyceae representatives except Zjadły (Dinophyceae), Długie Wigierskie (Dinophyceae), and Leszczewek (Chrysophyceae). Mazurian and Suwałki Lakelands can be considered as well-studied areas. Therefore, spatial and temporal changes in the phytoplankton community structures will be discussed. Moreover, some lakes that have never been studied before in terms of phytoplankton and their community structure will be revealed. According to the study performed in Suskie (Lossow et al. 2004), authors reported that this lake has been dominated by Cyanophyceae and the contribution of other phytoplankton classes was quite low except in November. In our study, there was no strict domination of a single class. Lossow et al. (2004) also reported Planktothrix agardhii (formerly known as Oscillatoria agardhii ) and Limnothrix redekei (formerly known as Oscillatoria redekei ) were quite abundant in the class of Cyanophyceae. In support of this, P . agardhii and L . redekei were both encountered in this lake in our study. However, only P . agardhii had a biomass worth mentioning. Trichodesmium lacustre and Desmodesmus opoliensis were found only in this lake. Even though there is no study about the whole phytoplankton community of Lake Majcz Wielki, this mesotrophic lake in Mazurian Lakeland has been studied in terms of various communities of phytoplankton (Gliwicz et al. 1981; Hillbricht-Ilkowska et al. 1984), picophytoplankton (Jasser 1997; Jasser 2002) zooplankton, and zoobenthos (Kołodziejczyk and Lewandowski 2009). The lake was one of 24 lakes included in a study of plankton seasonal changes summarized in the PEG model (Sommer et al. 1985). Gliwicz et al. (1981) stated that Dinobryon had a higher biomass share in this lake. Similarly, Hillbricht-Ilkowska et al. (1984) also reported that Majcz Wielki was dominated by Dinobryon . In support of this, our study revealed also that although Dinobryon divergens was not dominating in Majcz Wielki, it was the second most abundant species after Ceratium hirundinella . In addition, it was the third lake that Chrysophyceae reached this much of high biomass (13.0%) in the entire study. Pasztaleniec et al. (2010) reported that Cyanophyceae with dominant Microcystis sp., Woronichiniana naegeliana , and Aphanizomenon issatschenkoi ) had the largest biomass in Lake Głebokie in the whole year while in May the phytoplankton was dominated by Chlorophyceae ( Pandorina morum , Staurastrum cuspidatum , Eutetramorus planctonicus , and Coelastrum microporum ). In our study, this lake was highly dominated by Chlorophyceae. However, none of the mentioned species were encountered in this lake in August 2023. Pasztaleniec et al. (2010) also stated that in July, the lake was dominated by Ceratium hirundinella , which is when we also performed sampling, and in our study C . hirundinella and C . cornutum were found in this period as well. Even though they were not dominating, their biomass was considerably high. Lake Mikołajskie is another lake that has been very frequently analyzed in terms of various organisms and it was another Polish lake included in the PEG model of seasonal plankton changes (Sommer et al. 1985). Spodniewska (1976) studying phytoplankton in Mikołajskie in the seventies stated that Dinophyceae was the most dominant phytoplankton class in the summer season, and they formed 90.0% of algal biomass. In the same study, Ceratium hirundinella was found to be the most abundant species. In a study almost 40 years later (Ochocka and Pasztaleniec 2016) Cyanophyceae had the biggest share of phytoplankton biomass in Mikołajskie both in 2012 and 2013 when the study was conducted. However, Dinophyeae was the second most abundant phytoplankton class in 2012. In our study, the biomass of the Dinophyceae was also very high, but the Chlorophyceae was the most dominant phytoplankton class. Contrary to the earlier studies Cyanophyceae was the third class of phytoplankton with a contribution of only about 25% of total biomass. In addition, C . hirundinella was the second most abundant species in this lake. Napiórkowska-Krzebietke et al. (2023) studying Lake Sztynorckie reported that Limnothrix redekei , Pseudanabaena limnetica , Planktolyngbya limnetica were the most abundant species during their sampling in summer while Aphanizomenon gracile , Raphidiopsis raciborskii , and Planktothrix agardhii were occurring with relatively low biomass. They also stated that Cyanophyceae was the most abundant phytoplankton class during their summertime sampling both in June and August of 2021. In the present study, Cyanophyceae also had the biggest share in the total biomass, and it was the highest percentage in the entire study. Moreover, all of the species mentioned were found in our study as well as invasive R . raciborskii with low biomass. Napiórkowska-Krzebietke and Hutorowicz (2005) analyzing phytoplankton in Lake Mamry stated that Bacillarophyceae and Chrysophyceae had the highest diversity in this between 1986–2001. In our study, Cyanophyceae was the most diverse phytoplankton class in this lake, even though the lake was found to have relatively low diversity when compared with other surveyed lakes. It was also reported between 1986–1989 that Bacillariophyceae, Cryptophyceae, and Dinophyceae were the dominant phytoplankton classes (Napiórkowska-Krzebietke and Hutorowicz 2005) and another study (Półtoracka 1963) stated the dominance of Bacillariophyceae as well. It was also mentioned that the genus Dinobryon was abundant during the summer (Napiórkowska-Krzebietke and Hutorowicz 2005). In our study, Chlorophyceae and Cyanophyceae shared the total biomass almost equally and it has been followed by Dinophyceae. The genus Dinobryon was found in this lake with relatively high biomass compared to others. Bukowska et al. (2017) reported that Cyanophyceae accounted for 91.0% of the total biomass in August 2011. In our study, Chlorophyceae had a slightly bigger share (32.3%) in Mamry while Chlorophyceae had (31.8%). In a study of Lake Niegocin, high levels of total phytoplankton biomass (8.20 mg/L) were recorded up to 1994 and this amount is quite similar to the biomass we found in this study (8.80 mg/L) (Napiórkowska-Krzebietke and Hutorowicz 2006). In 2000, Dinophyceae, Cyanophycae, and Cryptophyceae were reported as the three co-dominant classes (Napiórkowska-Krzebietke and Hutorowicz 2006). Meanwhile, in our study, this lake was dominated by Chlorophyceae. In several studies, (Napiórkowska-Krzebietke and Hutorowicz 2006; Bukowska et al. 2017) mentioned that in 1991, this lake was dominated by Planktothrix agardhii . In the present study, this species was reported from this lake, but it did not have significant biomass. According to a study by Napiórkowska-Krzebietke et al. (2020), it was stated in Śniardwy which is the largest lake in Poland, 70.0% of the phytoplankton biomass was formed by Bacillariophyceae in spring and summer. However, in the present study, the dominating phytoplankton class was Chlorophyceae. Moreover, this percentage was the highest one covered by Chlorophyceae in this survey. According to several studies (Haider et al. 2003; Zagajewski et al. 2009; Ballot et al. 2010), Pseudanabaena limnetica , An abaenopsis sp., and Anabaenopsis elenkini were found in Rekąty. In our study, A . elenkinii was found in this lake with high biomass. On the other hand, P . limnetica which was one of the most frequent species was not encountered here, even though this lake had the highest species richness. In addition, Anabaenopsis sp. was not reported from this lake either. Moreover, in another study, Aphanizomenon flos-aquae , Chroococcus minimus , Chroococcus turgidus , Limnothrix redekei , Microcystis aeruginosa , and Planktolyngbya limnetica were reported from this lake (Jakubowska et al. 2013). They were all described in this study as well except A . flos-aquae and C . turgidus . On the other hand, Jakubowska et al. (2013) reported the occurrence of R . raciborskii from this lake. Hańcza is one of the most well-studied lakes and the deepest lake in Poland, but also one of the least oligotrophic lakes in the study. According to a study, in August 1973, the dominating phytoplankton classes in the lake were Dinophyceae and Cyanophyceae (Spodniewska 1978). A later study reported that in the summer of 1994, Ceratium hirundinella and Peridinium sp. shared the highest biomass, and the Cyanophyceae contributed less (Jasser 2002). In a relatively current study (Napiórkowska-Krzebietke and Hutorowicz 2013), it was mentioned that 114 taxa were identified while in the present study, it was 39. They also claimed that the main dominating class was Bacillariophyceae representatives ( Cyclotella sp. and Asterionella formosa ), which were not encountered in our study. However, the biomass of pennate C . placentula was quite high. Interestingly, Napiórkowska-Krzebietke and Hutorowicz (2013) also mentioned Aphanocapsa and Aphanothece were the major phytoplankton biomass contributors in August 2006, 2007, and 2008, but in our study, these genera' were not encountered in Hańcza and Anagnostidinema amphibium was the dominating Cyanophyceaen species. In a study about the genus Pediastrum (Lenarczyk et al. 2015), it was claimed that in Leszczewek Stauridium tetras (formerly known as Pediastrum tetras ) and Pseudopediastrum boryanum (formerly known as Pediastrum boryanum ) were encountered. In our study, Chlorophyceae formed a quite low percentage of biomass and the mentioned species were not found. The importance of this lake is the high percentage of biomass was formed by Chrysophyceae ( Dinobryon divergens ) which was also the maximum in the study. It has been followed by Cyanophyceae. Szczęśliwickie is a highly eutrophic lake and the only lake in this study that was not part of Mazurian and Suwałki Lakelands. It had the third-highest biomass in the entire study with 11.6 mg/L of fresh biomass. This lake's phytoplankton structure was formed almost the same as Suskie which is the lake with the highest phytoplankton biomass. The phytoplankton was dominated by Chlorophyceae with a share of 45.8% and Cyanophyceae with 40.7%. It was observed that according to RDA, Szczęśliwickie had a slightly positive correlation with NPOC, and in Euclidean distance analysis (ED) it clustered with other eutrophic lakes (Rekąty, Leszczewek, Sztynorckie, Suskie, and Piłag) as an expected result. This closeness mainly came from their low Secchi depth which varied between 60–150, and high nutrient concentrations. Their Secchi depth values were one of the lowest in the study and dissolved oxygen concentrations in these two lakes were quite similar. In addition, except S-SO₄²-, the nutrient concentrations were very low in Hańcza and Długie Wigierskie. In addition, compared to other studied lakes, they had higher temperatures (23.2–27°C) and pH (8.05–8.54). Hańcza and Długie Wigierskie were also clustered and they are both narrow and deep lakes with lower trophic status. Lakes Probarskie and Zjadły were not included in RDA and ED, because of a lack of measured environmental parameters. These lakes that are located in Mazurian Lakeland had comparably high species richness and Zjadły was notable in the sense of having the second-highest Dinophyceae share (33.7%) in total biomass. Based on ED, Lake Inulec was closely clustered with Żabinki as they have similar nutrient content and trophic characteristics. According to RDA, Inulec had a slight positive association with both DO and TP. ED showed that Lake Brzozolasek clustered with Inulec and Żabinki. This result is interesting as both lakes mentioned had higher nutrient content than Brzozolasek. In Brzozolasek, the biomass of Chlorophyceae was very low unlike in most of the lakes. In Lake Żabinki, Chlorophyceae formed only 4% of the whole phytoplankton community structure, which was the lowest percentage in the entire study, and just as Brzozolasek, RDA revealed this lake did not exhibit any strong relationship with any abiotic influences. Lake Przerośl also did not have any strong relationship based on RDA, but a very slight positive relationship with conductivity existed. This lake had the lowest ED value which means it has the highest similarity with another lake (Hołny). They were also clustered with Lakes Dowcień and Pobondzie which are the lakes in Suwałki Lakeland with similar environmental variables. Pobondzie was one of the most interesting lakes in terms of invasive cyanobacterial species. All three alien species that were aimed at were found here, which are R . raciborskii , C . bergii , and S . aphanizomenoides . However, all of their biomass’ was very low and almost unimpactful. RDA showed this lake also has a slight positive correlation with conductivity. Długie Wigierskie was interesting in terms of Dinophyceae forming more than half of the total biomass and it has a strong negative association with conductivity based on RDA. Based on RDA, Wigry with Majcz Wielki, Zelwa, and Mamry were located together in the quarter along with TR and opposite to TP, TN as four lakes were found to have very similar pH, temperature, and dissolved oxygen values. According to the results of RDA, while Dowcień had a strong positive relationship with conductivity Lake Hołny had a strong positive correlation with DO and it had the closest similarity to Przerośl on ED. Numerous phytoplankton species can be suggested as eutrophic lake indicators while few of them appear to indicate oligotrophic waters (Rawson 1956). Järnefelt (1952), in a comprehensive study, listed many plankters for eutrophic lakes while there were only 6 which were limited to oligotrophic waters. As suggested also by Rodhe (1948), Dinobryon divergens is one of these acknowledged and well-known oligotrophy indicators. In our study, this species could not be reported only from 5 lakes (Piłag, Mikołajskie, Brzozolasek, Hańcza, and Zelwa) out of twenty-five, and within these lakes, only Hańcza can be considered as oligotrophic. However, in Lake Leszczewek (mesotrophic) this species was found to have the highest biomass (0.740 mg/L) which does not correlate with the claim. It also needs to be noted that in this lake the contribution of the Chrysophyceae to total phytoplankton biomass was the most (34.7%) in the entire study. Rawson (1956) also suggested that the globally widespread species might develop ecotypes so we might have difficulty identifying them correctly. It has been also claimed that Tabellaria flocculosa is indicator species for oligotrophic status, Ceratium hirundinella , Pediastrum duplex , and Pseudopediastrum boryanum (formerly known as Pediastrum boryanum ) for mesotrophic while Microcystis aeruginosa and M . flos-aquae for eutrophic (Rawson 1956). In our study, even though these species were encountered in various water bodies, T . flocculosa was in Lake Mamry (0.23 mg/L) (mesotrophic). In addition, both C . hirundinella (3.10 mg/L) and P . boryanum reached the highest biomass in Lake Mikołajskie (4.45 mg/L) while P . duplex in Niegocin (4.70 mg/L). Both of these lakes can be considered as eutrophic. Lastly, M . aeuruginosa was found to have the highest biomass respectively in Sztynorckie (4.05 mg/L) and Suskie (2.48 mg/L) which were both hypereutrophic lakes, while M . flos-aquae in Przerośl (0.49 mg/L) (eutrophic). General literature knowledge suggests genus Cyclotella is a common indicator for oligotrophic water bodies (Scheffler and Padisák 1997; Saros and Anderson 2015; Ossyssek et al. 2020). According to Stoermer (1978), abundant occurrence of this genus does not strongly indicate an oligotrophic, low to moderate productivity environment. In their study, this genus was found in the most excessively disturbed and polluted regions, as with the oligotrophic ones. In our study, from this genus, only Stephanocyclus meneghinianus (formerly known as Cyclotella meneghiniana ) was identified from eight lakes. The trophic statuses of these lakes varied from eutrophic to oligotrophic. However, Stephanocyclus meneghinianus reached the maximum abundance (0.08 mg/L) in Lake Suskie which is a hypereutrophic lake in ML. Aphanizomenon flos-aquae was claimed as a Cyanobacteria indicating mesotrophic and eutrophic water by Komárek and Anagnostidis (1989). In our study, this species was identified from 6 lakes (Inulec, Mikołajskie, Sztynorckie, Żabinki, Pobondize, and Dowcień) which can be classified in this spectrum. The larger phytoplankton less subject to grazing losses (Burns 1968) such as Ceratium hirundinella are usually a summer bloom species in eutrophic lakes. Even though cyanobacterial species receive the most attention in these productive lakes, the high increase of large Dinophyceae domination is assuredly important (Reynolds 1973; Reynolds 1973; Pollinger and Berman 1975). In the presented study, C . hirundinella was encountered in twenty lakes. However, the biomass of this species was the highest (3.05 mg/L) in Lake Mikołajskie which is an eutrophic water body. On the other hand, C . hirundinella was also claimed to be the determinant phytoplankter for mesotrophic and oligotrophic waters (Rawson 1956; Reynolds et al. 2002). Another Dinophyceae representative, Peridinium cinctum was also claimed to be common for mesotrophic lake species (Reynolds et al. 2002). During our study, this species was not reported but Peridinium bipes , Peridinium willei , and Peridinium sp. were identified in 4 lakes (Probarskie, Żabinki, Długie Wigierskie, and Dowcień). However, this genus had the highest biomass in Lake Żabinki which is a highly eutrophic lake. Palmer (1969) stated that Coelastrum and Pediastrum can be indications of eutrophic waters as they have strong resistance to organic pollution. Even though all of these genera were encountered in nearly every lake in our study, two species from Coelastrum ( Coelastrum astroideum and C . microsporum ) reached their maximum biomass (1.64 mg/L) in Lake Suskie which is the most eutrophic lake in the entire study. Monoactinus simplex (formerly known as Pediastrum simplex ) was also found to have the highest biomass (18.75 mg/L) in the same lake (Palmer 1969). Lastly, Desmodesmus communis (formerly known as Scenedesmus communis ) and Tetradesmus obliquus (formerly known as Scenedesmus obliquus ) from Scenedesmus had the highest biomass (1.35) in Lake Sztynorckie which was also a hypereutrophic. Chlamydomonas is also a genus claimed to be an eutrophic water indicator (Peerapornpisal et al. 1999). In our study, even though this genus was not very commonly found, 3 species ( Chlamydomonas ehrenbergii , Chlamydomonas reinhardtii , and Chlamydomonas sp.) were identified from 2 lakes: Śniardwy (eutrophic) and Żabinki (eutrophic). Therefore, Chlorophyceae representatives showed a correct correlation with trophic status in this study. Raphidiopsis raciborskii is one of the most interesting cyanobacterial species as it has expanded its geographical range from tropical and subtropical regions to temperate regions during the last decades (Antunes et al. 2015). Based on the comprehensive study of the occurrence of R . raciborskii in Poland (101) and Lithuania (16) in 117 lakes, Kokociński et al. (2017) revealed its presence in 25 lakes. However, even though they investigated the lakes in Northeastern Poland, 24 of the lakes in which they reported R . raciborskii were located in Western Poland while one was in Lithuania. This supports the previous findings (Kokociński and Soininen 2012) that claim R . raciborskii occurs mostly in lakes of Western Poland where they revealed the occurrence of this species in 20 lakes. In that study lakes Piłąg and Rekąty have not been investigated. In the present study, twenty-four lakes in Northeastern Poland and one in the Warsaw area were explored, and R . raciborskii was detected in five of them which are Szczęśliwickie (Warsaw, Central Poland), Mikołajskie, Sztynorckie, Rekąty (Mazurian Lakeland – ML), and Pobondzie (Suwałki Lakeland - SL). In addition, C . bergii were also found in three lakes Żabinki, Rekąty (ML), and Pobondzie (SL) while S . aphanizomenoides only in Pobondzie. The biomass of the R . raciborskii was calculated as 0.03 mg/L in Szczęśliwickie, 0.04 mg/L in Mikołajskie, 0.26 mg/L in Sztynorckie, 0.05 mg/L in Rekąty, and 0.01 mg/L in Pobondzie which are strongly low amounts except Lake Sztynorckie. Kokociński and Soininen (2012) reported the contribution of this species varied between 0.07% (Jelonek) and 13.89% (Żabiniec) in Western Poland lakes. In addition, they found out that the R . raciborskii was not occurring in deep lakes, while it was in lakes with high TN and conductivity and large surface area. In our study, in lakes where R . raciborskii was found, Secchi depth varied between 75 (Szczęśliwickie) – 130 cm (Pobondzie). Additionally, both of these lakes can be considered small-sized lakes with low mean depth. In a recent study (Napiórkowska-Krzebietke et al. 2023), R . raciborskii was reported from Sztynorckie in August 2021 and it accounted for 8.0% of the total phytoplankton community biomass. In our study, this species was encountered in the same lake and obtained there the highest biomass among the lakes where it occurred as well as the highest percentage in total phytoplankton biomass (1.1%). This suggests that Lake Sztynorckie is a lake in which the invasion of R . raciborskii is best established, although the contribution of this species is still largely varying. Additionally, Chrysosporum bergii and Sphaerospermopsis aphanizomenoides were other tracked invasive cyanobacterial species in our study. C . bergii was encountered in three lakes which are Żabinki, Rekąty, and Pobondzie while S . aphanizomenoides was found only in Pobondzie. Total biomass of both invasive species was low: 0.088 mg/L ( C . bergii ) and 0.023 mg/L ( S . aphanizomenoides ). C . bergii reached its maximum biomass in Lake Żabinki which was 0.048 mg/L. Another well-known invasive species we aimed at was Raphidiopsis mediterranea , found only in two lakes which are Mikołajskie and Śniardwy with low total biomass as well. In a study, C . bergii was reported in seven out of 19 investigated lakes in Poland, but their biomass varied between 0.03 and 0.55 mg/L (Kokociński and Soininen 2019). According to a former study in Western Poland (Kokociński et al. 2013), they did not observe this species at all or only in single localities with low biomass. To conclude, even though cyanobacterial invasion is faster in Western Poland, the findings do not support the term invasive for these species ( R . raciborskii , R . mediterranea , C . bergi, and S . aphanizomenoides ) in these lakes while we can name them as alien species which are at the beginning of their invasion progress. In this situation, monitoring the existence and the biomass of the mentioned species is crucial. Moreover, in a study concerning alien algae in European waters, Wilk-Woźniak and Najberek (2013), identified 14 alien and three cryptogenic species. Within Cyanophyceae, Anabaenopsis cunningtonii , Anabaena minderi , Cuspidothrix issatschenkoi , Raphidiopsis mediterranea ; from Chlorophyceae, Coelastrum polychordum and Pediastrum simplex ; from Bacillariophyceae, Conticribra guillardii , Cyclostephanos delicatus , Discostella woltereckii , Gyrosigma fasciola , Skeletonema potamos , Thalassiosira duostra ; from Dinophyceae Peridiniopsis kevei and Peridinium gatunense were described as invasive species for European freshwater bodies. In the present study, A . cunningtonii (Rekąty), R . mediterranea (Mikołajskie and Śniardwy), and Monoactinus simplex (formerly known as P . simplex ) (Suskie, Piłag, Szczęśliwickie, Inulec, Mikołajskie, Niegocin, Śniardwy, Rekąty, and Wigry) were found while no alien Bacillarophyceae and Dinophyceae species were identified. In Suskie (56.2 mg/L) and Sztynorckie (23.8), the total biomass was found to be the highest, respectively. Suskie was dominated in terms of filament numbers by Anagnostidinema amphibium and Aphanizomenon gracile but as these filamentous cyanobacterial species have low cell biomass, the biggest contributor to the total biomass was identified as Monoactinus simplex (18.8 mg/L). In addition, in Lake Sztynorckie, two Cyanobacteria contributed the most: Microcystis aeruginosa (4.0 mg/L) and A . amphibium (3.9 mg/L). The lowest total biomass (0.8 mg/L) was found in Brzozolasek and the largest part came from the Ceratium cornutum (0.2 mg/L). Considering the phytoplankton classes, Cyanophyceae (71.0 mg/L, 42.3%) and Chlorophyceae (63.4 mg/L, 37.8%) had the highest share. For Cyanophyceae, this amount came from Suskie (23.1 mg/L), Sztynorckie (16.9 mg/L), and Szczęśliwickie (4.7 mg/L) while for Chlorophyceae it was Suskie (25.8 mg/L), Niegocin (5.5 mg/L), and Szczęśliwickie (5.3 mg/L). Chrysopyceae only formed 1.4% (2.3 mg/L) of the total biomass and the biggest contributor were Leszczewek (0.7 mg/L) and Szczęśliwickie (0.3 mg/L). CONCLUSION This research aimed to describe the phytoplankton community structure and reveal the occurrence of possible invasive cyanobacterial species in twenty-four lakes located in Mazurian and Suwałki Lakeland, Northeastern Poland, and one in Central Poland. Total phytoplankton biomass was found to be the highest in Suskie while considering the phytoplankton classes Cyanophyceae was the biggest contributor. 170 of them being Cyanophyceae representatives, 325 phytoplankton species were identified. The presence of Raphidiopsis raciborskii was found in five lakes, Chrysosporum bergii in three lakes, and Sphaerospermopsis aphanizomenoides in just one lake. However, the low biomass of these species in all the lakes raises the question of whether they are truly invasive or simply new to the region. On the other hand, it is concerning that these cyanobacterial species, which are already established in Western Poland, are now starting to appear in Eastern Poland as well even though they do not have high biomass. This shift could be a result of a decrease in ice cover duration and an increase in water temperature caused by climate change. Aphanizomenon gracile was found to be the most frequent species since it has been found in twenty-four lakes while Monoactinus simplex had the largest biomass as a single species. As a result, we think that it is crucial to continue the studies on invasive cyanobacterial species in Mazurian and Suwałki Lakelands as they can produce toxic compounds that can risk human health and influence native phytoplankton assemblages. Declarations Funding: This work was supported by the 2nd edition of Microgrants, the Comprehensive support program for the University of Warsaw's doctoral students. Author Contribution T.O.A. : Data collection, writing and editing of the manuscript, statistical analysis.R.M.C.T. : Data collection, English check of the manuscript.A.R. : Statistical analysis, data curation, critical revision of the manuscript.I.J. : Data collection, supervision, project administration, critical revision of manuscript. Acknowledgement The completion of my research study would not have been possible without the support and guidance of Prof. Dr. Iwona Jasser. I want to extend my sincere gratitude to Robin Michael Crucitti-Thoo and Agnieszka Rudak for their support and collaboration. In addition, we all appreciate the help and assistance of the local people of Mazurian and Suwałki Lakelands. References Antunes JT, Leão PN, Vasconcelos VM (2015) Cylindrospermopsis raciborskii : Review of the distribution, phylogeography, and ecophysiology of a global invasive species. Frontiers in Microbiology 6(2015): 473. 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Vidal L, Kruk C (2008) Cylindrospermopsis raciborskii (Cyanobacteria) extends its distribution to latitude 34 53’S: Taxonomical and ecological features in Uruguayan eutrophic lakes. Pan-American Journal of Aquatic Sciences 3(2): 142–151. Wakley A, Black IA (1934) An examination of the Degthareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Science 37(1): 29–38. Wetzel RG (2001) Fundamental processes within natural and constructed wetland ecosystems: short-term versus long-term objectives. Water Science and Technology 44(11–12): 1–8. Wetzel RG, Likens G (2000) Lake basin characteristics and morphometry: Limnological analyses. Springer Science & Business Media, New York, 430 pp. Wilk-Woźniak E, Najberek K (2013) Towards clarifying the presence of alien algae in inland waters—can we predict places of their occurrence? Biologia 68: 838–844. Winder M, Sommer U (2012) Phytoplankton response to a changing climate. 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Oceanological and Hydrobiological Studies 38(2): 113–120. Zheng B, He S, Zhao L, Li J, Du Y, Li Y, Shi J, ... & Wu Z (2023) Does temperature favour the spread of Raphidiopsis raciborskii , an invasive bloom-forming cyanobacterium, by altering cellular trade-offs? Harmful Algae 124: 102406. Zheng B, Zhou L, Wang J, Dong P, Zhao T, Deng Y, Song L, ... & Wu Z (2024) The shifts in microbial interactions and gene expression caused by temperature and nutrient loading influence Raphidiopsis raciborskii blooms. Water Research 268: 122725. Tables Table 1. Structural information about the investigated lakes. Lakes Latitude Longitude Mean depth (m) Maximum depth (m) Area (ha 2 ) Suskie 53°42'48.38"N 19°20'36.85"E 2.4 5.3 55.7 Piłag 53°52'47.63"N 19°59'20.17"E N/A N/A 4.7 Szczęśliwickie 52°12'10.25"N 20°57'30.51"E 3.0 9.4 2.3 Probarskie 53°49'43.11"N 21°22'58.02"E N/A N/A 163.9 Zjadły 53°48'40.84"N 21°23'14.94"E N/A N/A 82.2 Majcz Wielki 53°46'51.31"N 21°27'29.57"E 6.0 16.4 162.5 Inulec 53°48'24.22"N 21°28'33.56"E N/A N/A 178.3 Głebokie 53°49'0.41"N 21°30'22.27"E N/A N/A 25.3 Mikołajskie 53°46'39.41"N 21°35'57.53"E 11.2 25.9 500.0 Sztynorckie 54° 7'49.76"N 21°40'38.54"E 2.0 3.0 47.3 Mamry 54°10'27.07"N 21°42'59.97"E 9.8 43.8 2504.4 Brzozolasek 53°36'59.19"N 21°44'38.78"E N/A N/A 155.9 Niegocin 53°59'14.17"N 21°45'42.00"E 9.9 39.7 2600.0 Śniardwy 53°46'57.56"N 21°46'39.02"E 5.8 23.4 11340.5 Żabinki 54° 8'3.29"N 21°58'49.26"E N/A N/A 890.6 Rekąty 53°55'4.08"N 22°11'3.34"E N/A N/A 53.5 Przerośl 54°17'1.32"N 22°35'52.64"E 9.0 28.0 62.05 Hańcza 54°16'21.74"N 22°49'22.35"E 38.7 108.5 305.0 Pobondzie 54°18'45.37"N 22°57'6.68"E 3.6 27.0 53.0 Długie Wigierskie 54° 1'33.26"N 23° 1'41.91"E 6.4 14.9 77.6 Leszczewek 54° 4'22.10"N 23° 3'53.44"E 3.6 6.5 21.5 Wigry 54° 2'57.67"N 23° 6'15.73"E 15.4 73.0 217 Dowcień 54° 4'51.12"N 23° 7'36.89"E N/A N/A 59.9 Zelwa 54° 1'28.46"N 23°25'15.89"E 5.8 12.3 81.8 Hołny 54° 8'39.66"N 23°27'43.15"E 5.8 15.2 158.1 Table 2. Species richness, diversity, and evenness of the lakes. Lakes Species richness Shannon diversity index Pielou’s evenness Suskie 49 2.13 0.68 Piłag 38 2.01 0.65 Szczęśliwickie 37 2.24 0.72 Probarskie 56 2.27 0.77 Zjadły 41 1.95 0.78 Majcz Wielki 40 2.38 0.81 Inulec 42 2.30 0.78 Głebokie 39 1.88 0.61 Mikołajskie 56 1.79 0.60 Sztynorckie 47 2.51 0.83 Mamry 49 2.32 0.75 Brzozolasek 43 1.90 0.72 Niegocin 59 1.83 0.57 Śniardwy 53 1.81 0.60 Żabinki 45 2.31 0.82 Rekąty 66 2.84 0.82 Przerośl 53 2.61 0.78 Hańcza 39 2.42 0.81 Pobondzie 59 2.58 0.82 Długie Wigierskie 34 2.33 0.78 Leszczewek 35 2.61 0.92 Wigry 36 2.63 0.84 Dowcień 46 2.54 0.85 Zelwa 45 2.41 0.79 Hołny 50 2.03 0.68 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5679541","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":393223059,"identity":"40d57cb1-84ca-40d6-8e5c-a37dc7b6fbef","order_by":0,"name":"Tümer Orhun 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Rudak","email":"","orcid":"","institution":"University of Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Agnieszka","middleName":"","lastName":"Rudak","suffix":""},{"id":393223062,"identity":"5d2f71c7-0d2c-475f-ba1f-98b5ce49fa7b","order_by":3,"name":"Iwona Jasser","email":"","orcid":"","institution":"University of Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Iwona","middleName":"","lastName":"Jasser","suffix":""}],"badges":[],"createdAt":"2024-12-19 21:53:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5679541/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5679541/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":72194742,"identity":"a67fecee-3e79-4bc0-968f-c7fc5bdcc8ff","added_by":"auto","created_at":"2024-12-23 14:44:41","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1162156,"visible":true,"origin":"","legend":"\u003cp\u003eLakes where the study was carried out were numbered by geographical gradient (West to east).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/40c23e281beff1cb0e6ad01a.png"},{"id":72193120,"identity":"9d758230-c39b-4151-8fd9-aefe7fbe1876","added_by":"auto","created_at":"2024-12-23 14:36:41","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":178902,"visible":true,"origin":"","legend":"\u003cp\u003eEnvironmental parameters that have been measured in Northeastern Polish temperate lakes.\u003c/p\u003e","description":"","filename":"floatimage210.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/2814cd7b50604987cbe780d8.png"},{"id":72193118,"identity":"13440498-5a55-4080-a47d-5235a53e34d3","added_by":"auto","created_at":"2024-12-23 14:36:41","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":60808,"visible":true,"origin":"","legend":"\u003cp\u003eTotal phytoplankton biomass in studied lakes (Mind the biomass of Lake Suskie).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/4f708a427fa1f7726b39366d.png"},{"id":72194741,"identity":"1e4491d3-2ea9-4ba9-82bf-e30c3962761d","added_by":"auto","created_at":"2024-12-23 14:44:41","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":30778,"visible":true,"origin":"","legend":"\u003cp\u003ePercentages of total biomass of phytoplankton classes in the whole study.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/ec35709ce0a29191d88e40cd.png"},{"id":72193124,"identity":"632a410b-26fd-4355-8528-09107a029a31","added_by":"auto","created_at":"2024-12-23 14:36:41","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":145929,"visible":true,"origin":"","legend":"\u003cp\u003ePercentages of phytoplankton classes.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/6ba273cb1e75fcdd6f570a06.png"},{"id":72193121,"identity":"f7886cec-be3c-4eec-ae5c-4bb5f609d161","added_by":"auto","created_at":"2024-12-23 14:36:41","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":36345,"visible":true,"origin":"","legend":"\u003cp\u003eDendograms of euclidean distance analysis based on the following abiotic variables: Secchi depth, pH, conductivity, temperature, dissolved oxygen, NPOC, TN, TP, N-NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, N-NO\u003csub\u003e3-\u003c/sub\u003e, P-PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e, and S-SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/86c940fca7ba7b140c48e36b.png"},{"id":72193129,"identity":"d2492a6f-7ade-4f6a-bfb1-31c634d2eeee","added_by":"auto","created_at":"2024-12-23 14:36:41","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":113118,"visible":true,"origin":"","legend":"\u003cp\u003eFrequency analysis to reveal the percentage of occurrence of the phytoplankton species.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/cea9d824d9b61d91d5d268b5.png"},{"id":72193127,"identity":"0e51dc59-ece6-4b14-a944-7f6b290d6f0f","added_by":"auto","created_at":"2024-12-23 14:36:41","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":167370,"visible":true,"origin":"","legend":"\u003cp\u003eRDA results showing relationships between environmental variables and phytoplankton classes in selected lakes (DO: Dissolved oxygen concentration, TP: Total phosphorus, TN: Total nitrogen, NPOC: Non-purgeable organic carbon, CD: Electrical conductivity, and TR: Transparency).\u003c/p\u003e","description":"","filename":"floatimage83.png","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/8f013ac1a4fccd2ad6291b9e.png"},{"id":73471897,"identity":"c3b05e5d-cbef-484b-a0c1-f239b945d8d9","added_by":"auto","created_at":"2025-01-10 09:39:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2989758,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5679541/v1/f18a35e5-38d5-42c6-9041-4ad5c1661aee.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Associations of invasive cyanobacterial species and phytoplankton community structure with abiotic influences in post-glacial temperate lakes under climate change","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eNatural ecosystems together with lakes all over the World are increasingly influenced by anthropogenic disturbances, including habitat loss and degradation, different types of pollution, invasive or alien species, and overuse of sources (Cottingham and Carpenter 1998). In freshwater bodies, phytoplankton is the most prevailing, unicellular and microscopic life forms (Giripunje et al. 2013) which are the main element of the aquatic food web and have global significance for ecosystem services and continuity (Winder and Sommer 2012). Although they account for 1% of the photosynthetic biomass on Earth, they are responsible for more than 50% of global net primary production. They are the essential energy source for every single aquatic ecosystem (Field et al. 1998), in addition to facilitating the persistence of biogeochemical processes (Arrigo 2005). For these reasons, they are considered a core aspect of a healthy aquatic ecosystem (Xu et al. 2001).\u003c/p\u003e \u003cp\u003eSeveral factors influence the composition and abundance of phytoplankton in aquatic environments with any changes in these factors directly affecting the phytoplankton community structure to some extent. Principally, factors affecting phytoplankton growth can be described as pH, water temperature, light conditions, nutrient concentrations, and predation by zooplankton and fish (Domingues and Galvao 2007). Phytoplankton algae are often used as bioindicators and biomonitoring organisms to determine the ecological status and disturbance effects of chemical pollutants in water bodies (Xu 1997; Xu et al. 2001). That\u0026rsquo;s because their short life cycles allow the organisms to respond swiftly to environmental changes, which is reflected in the composition and structure of phytoplankton (Domingues and Galvao 2007; Wu et al. 2014). Three leading features merit their use in ecosystem biomonitoring (H\u0026ouml;tzel and Croome 1999): (i) they have high sensitivity to environmental (abiotic and biotic) changes, (ii) they are easier to collect and analyze in comparison to other aquatic organisms, and (iii) most species are cosmopolitan with well-known autecology (Van Dam et al. 1994). Additionally, surveys that have been conducted based on phytoplankton community analysis are frequently used as a tool for biomonitoring to help generate early warnings of water problems (Thi\u0026eacute;baut et al. 2006). As a result, different evaluation approaches based on microalgae have been developed in several countries and regions (Siddig et al. 2016).\u003c/p\u003e \u003cp\u003eBiological invasions in lakes are a serious threat to biodiversity and ecosystem functioning, with successful invasions depending on relationships between multiple abiotic and biotic factors (Bolius et al. 2019). In recent years, the number of species spreading to new latitudes has increased and the introduction of invasive species can have several, generally negative ecological consequences. Invasive species are common in nearly every type of ecosystem, but aquatic ecosystems are especially at risk because of a combination of different factors (Sala et al. 2000). The three key factors that contribute towards a successful invasion have been determined (Lonsdale 1999; Litchman 2010) as i) the identity and genetic variation of the invader, (ii) the characteristics of the local community (Stachowicz and Byrnes 2006), and (iii) the optimal level of abiotic parameters of the habitat for the certain phytoplankton species, such as temperature (Seifert et al. 2015), light access (Conroy et al. 2007; Vidal et al. 2008) and nutrient content (De Meester et al. 2002; Yang et al. 2008). If these factors occur, the invaders often outcompete local species and become the new dominant species in the ecosystem (Lonsdale 1999; Litchman 2010).\u003c/p\u003e \u003cp\u003eThe presence of ice cover determines the existence of multiple specific conditions that influence physical and chemical changes that affect the community structure (Ptak 2013b). This matter's importance has increased since global warming's effect on freshwater bodies was described. Correspondingly, considerable changes are encountered in the elements of lakes. The increase in water temperature (Austin and Colman 2008; Hampton et al. 2008) and the decrease in time of ice season are particularly crucial examples (Magnuson et al. 2000). Lake Śniardwy is one of the most important lakes in this study as it is the largest one in Poland, but also because of its potential to be a reference to the other lakes investigated in this study. While the recorded mean water temperature in this lake was 9.0\u0026deg;C between 1972\u0026ndash;1987, it was 10.4\u0026deg;C between 2004\u0026ndash;2019. In the same periods (1972\u0026ndash;1987 and 2004\u0026ndash;2019), the duration of the ice cover (days) decreased from 103 days to 73 days (Ptak et al. 2020). Analysis proved that these differences were significant for observing a change in the lake's physical, chemical, and biological processes (Ptak et al. 2020). As cyanobacterial invasive species, especially \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e can be favored by different temperature levels, they also can adapt themselves to it (Silva et al. 2022; Zheng et al. 2023; Meriggi et al. 2024; Zheng et al. 2024). Therefore, it is essential to not only consider changes in temperature and ice cover in this region but also to evaluate how these changes impact invasive cyanobacterial species and the phytoplankton structure.\u003c/p\u003e \u003cp\u003eFreshwater ecosystems such as lakes, rivers, and ponds have larger biodiversity per surface area than marine and terrestrial ecosystems (Dudgeon et al. 2006) and they have an operating role that impacts human societies positively, which are nutrient and water cycling (Wetzel 2001). However, non-indigenous species strongly modify these ecosystems by introducing different taxonomic groups (Strayer 2010; Simberloff et al. 2013). Even though some well-studied invasive species such as \u003cem\u003eDaphnia lumholtzii\u003c/em\u003e do not have a great negative impact on the environment, most of the aquatic invasive species have already harmed the ecosystems and humans in various ways (Havel et al. 2005a; Havel et al. 2005b). This is why understanding the species\u0026rsquo; invasion progress and reproduction strategies is crucial (Havel et al. 2015).\u003c/p\u003e \u003cp\u003ePotentially harmful blooms caused by Cyanobacteria are extensive in freshwater ecosystems globally and are enforced by climate change and anthropological elements (Huisman et al. 2018). Among tropical and subtropical invasive species noted in temperate Europe, \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e, \u003cem\u003eRaphidiopsis mediterranea\u003c/em\u003e, \u003cem\u003eChrysosporum bergii\u003c/em\u003e, and \u003cem\u003eSphaerospermopsis aphanizomenoides\u003c/em\u003e are considered a growing threat (St\u0026uuml;ken et al. 2006). \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e being the most important, which is already known as a highly invasive species in Western Poland, is a freshwater, planktonic, filamentous, potentially toxic, and nitrogen-fixing Cyanobacteria (Antunes et al. 2015). In addition, the presence and the formed blooms of this Cyanobacteria have swiftly increased in tropical and subtropical lakes and reservoirs globally (Haande et al. 2008; Yang et al. 2017; Sidelev et al. 2020). Cylindrospermopsins (CYNs) can be produced by \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e, which poses health risks to both humans and other organisms, although no European strains have been found to produce this toxin (Rzymski and Poniedzialek 2014; Sidelev et al. 2020). Polymethoxy-1-alkenes (PMAs) are another compound with potential toxicity to organisms in freshwater bodies (Rzymski and Poniedzialek 2014). Similar to cylindrospermopsin (CYNs), PMAs may exhibit geographical differences, with Australian strains of \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e capable of producing them, in contrast to strains found in Europe (Jaja-Chimedza et al. 2015). Some South American strains of this species are reported to be able to produce saxitoxins (STX) that are hazardous (Ferr\u0026atilde;o-Filho and Silva 2020).\u003c/p\u003e \u003cp\u003eThe aims of this study carried out in twenty-four lakes that are going through major changes due to climate change in ice cover duration and water temperature in the Mazurian and Suwałki Lakelands of Poland which are the post-glacial ones as well as in one lake in Central Poland, in Warsaw, are i) to observe the occurrence of potentially toxic, invasive cyanobacterial species in geographical gradient from the central towards North-eastern Poland, ii) reveal the composition and distribution of different classes of phytoplankton assemblages in studied lakes, and to iii) describe their associations with numerous environmental parameters. The chosen geographical gradient is important to compare the cyanobacterial invasion based on temperature values as it is claimed to be one of the most important influencing variables.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSampling region and period\u003c/h2\u003e \u003cp\u003eThe following lakes have been chosen and examined to determine the phytoplankton communities and the occurrence of invasive cyanobacterial species: Suskie (1), Piłag (2), Szczęśliwickie (3), Probarskie (4), Zjadły (5), Majcz Wielki (6), Inulec (7), Głebokie (8), Mikołajskie (9), Sztynorckie (10), Mamry (11), Brzozolasek (12), Niegocin (13), Śniardwy (14), Żabinki (15), Rekąty (16), Przerośl (17), Hańcza (18), Pobondzie (19), Długie Wigierskie (20), Leszczewek (21), Wigry (22), Dowcień (23), Zelwa (24), and Hołny (25) (Fig.\u0026nbsp;1). Among these water bodies, only Szczęśliwickie (Warsaw, Central Poland) is not part of the Mazurian or Suwałki Lakelands (post-glacial lakes) which are located in Northeastern Poland. This artificial lake situated in Central Poland was inspected due to its hypereutrophic character and potential for comparison with the north-eastern lakes. However, even though lakes were evaluated based on geographical gradient, it must be noted that the climate in Central Poland is milder than in Northeastern Poland. Structural information about the lakes is available in Table\u0026nbsp;1.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePeriod of collecting the samples and analysis of biotic and abiotic variables\u003c/h3\u003e\n\u003cp\u003eTo reveal the associations between phytoplankton structures and environmental variables, water and phytoplankton samples from the Mazurian and Suwałki Lakelands were collected between 13\u0026ndash;17 August 2023 and Szczęśliwickie on 28 August 2023. The key environmental factors were selected as water temperature (\u0026deg;C), Secchi depth (cm), conductivity (\u0026micro;S/cm), dissolved oxygen (mg/L, %), pH, and nutrients such as non-purgeable organic carbon (NPOC, mg/L), total nitrogen (TN, mg/L), total phosphorus (TP, mg/L), ammonium (N-NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, mg/L), nitrate (N-NO\u003csub\u003e3-\u003c/sub\u003e, mg/L), phosphate (P-PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e, mg/L), and sulfate (S-SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, mg/L). Apart from nutrient analyses, all parameters were checked in the field. Secchi depth was measured with a Secchi disk while the rest of the environmental factors were with a YSI 556 multiprobe. Dissolved oxygen (DO) values and water temperature values were measured at different depths (0\u0026ndash;30 cm to 9 m) depending on the lake. NPOC and TN values were detected with the combustion method by using the Multi N/C 3100 apparatus (Wakley and Black 1934) while TP values were found by nitric acid digestion method in temperature up to 230\u0026deg;C followed by measurements using continuous flow analyzer SAN\u0026thinsp;+\u0026thinsp;+\u0026thinsp;Skalar (MEWAM 1981). The values of remaining nutrients (N-NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, N-NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, P-PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e, and S-SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e) were detected with the spectrophotometric method by using a continuous flow analyzer SAN\u0026thinsp;+\u0026thinsp;+\u0026thinsp;Skalar (Gray et al. 2006).\u003c/p\u003e \u003cp\u003eFor the collection of phytoplankton samples, water from three different places in the studied lake was obtained with a water sampler. After mixing collected water in a bucket a one-liter subsample was collected in plastic containers for every lake. Fixation of the samples was accomplished by Lugol\u0026rsquo;s solution with an addition of 38% formaldehyde to the final concentration of 1.5%. All measurements and sample collections were done in most of the lakes in the middle point of the lakes, except Lakes Zjadły and Probarskie in which the samples were collected from the jetties protruding into the lakes. The samples were kept at +\u0026thinsp;5\u0026deg;C in a dark place immediately after sampling.\u003c/p\u003e\n\u003ch3\u003eIdentification of phytoplankton species\u003c/h3\u003e\n\u003cp\u003ePhytoplankton samples were identified according to Pliński and Kom\u0026aacute;rek (2007), Kom\u0026aacute;rek and Anagnostidis (2007), Pliński and Hind\u0026aacute;k (2010), Pliński and Owsianny (2011), Kom\u0026aacute;rek (2013), and Pliński and Witkowski (2013) with Uterm\u0026ouml;hl method using inverted light microscope (Uterm\u0026ouml;hl 1958). The biomass of each species was determined by volumetric analysis of cells using the geometric approach and expressed as wet weight (Wetzel and Likens 2000).\u003c/p\u003e\n\u003ch3\u003eStatistical analysis of the biotic and abiotic parameters\u003c/h3\u003e\n\u003cp\u003eAll of the statistical analyses were performed in R (v4.4.1) (R Core Team, 2024) using the \u0026ldquo;vegan\u0026rdquo; package (VCEP et al. 2022). In every statistical analysis, the water temperature and dissolved oxygen values are the values measured within the top 0\u0026ndash;30 cm of the surface. Before the analysis of the environmental variables, data was standardized using the function \u0026ldquo;decostand\u0026rdquo; to avoid false grouping due to different units of measurement of each factor. Pearson correlation analysis was performed to remove collinear environmental factors. For values below the measurement range, it was assumed the lowest range limit was the measured value for calculation purposes. We have also performed Hellinger transformation to species data because of the high fraction (\u0026gt;\u0026thinsp;85%) of zero values due to the absence of certain species. Transformed data was used for RDA analysis combining species and environmental factors data sets. Species richness and the Shannon diversity index were calculated to reveal the diversity of the phytoplankton in lakes (Shannon 1948). Pielou\u0026rsquo;s evenness index was applied to have more critical remarks about the distribution of taxa of the phytoplankton in the lakes (Pielou 1964). Euclidean distance analysis (ED) was used in determining the similarity of lakes in terms of abiotic variables (Clarke and Warwick 2001). Frequency analysis was performed to understand the percentage of the presence of the phytoplankton species in the lakes, regardless of their abundance. The phytoplankton species were divided into five different groups according to this analysis based on their presence in the lakes, defined as follows: Rare (1\u0026ndash;20%), Uncommon (21\u0026ndash;40%), Common (41\u0026ndash;60%), Very Common (61\u0026ndash;80%) and Abundant (81\u0026ndash;100%) (Kocataş 1996). Two lakes which are Probarskie and Zjadły were not included in ED due to incomplete environmental data.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eEnvironmental variables\u003c/h2\u003e \u003cp\u003eMeasurements of abiotic parameters found at twenty-five lakes in Mazurian and Suwałki Lakelands are given in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The important points are highlighted below.\u003c/p\u003e \u003cp\u003eValues for water temperature and dissolved oxygen have been measured from various ranges of depth depending on the characteristics of the lake. The values for temperature gradually decreased with the depth as was expected in every lake and the thermocline of stratified lakes was found at around 5 m depth. However, this distinction was not as clear with the values of DO. The water temperature at the surface (0\u0026ndash;50 cm) in the studied lake varied between 21.4\u0026deg;C (Śniardwy) and 27.0\u0026deg;C (Piłag). Meanwhile, at the same depth, DO was varied between 15.17 mg/L (Rekąty) and 7.02 mg/L (Zjadły). The thermocline for Inulec occurred at 7 m, Głebokie at 6 m, Żabinki at 5 m, Przerośl 6 m, Pobondzie at 5 m, Długie Wigierskie at 6 m, Wigry at 7 m, and Hołny 4 m. On the other hand, DO values significantly lowered at 1 m for Piłag, at 4 m for Inulec, at 6 m for Głebokie, at 2 m for Sztynorckie, at 4 m for Żabinki, at 2 m for Rekąty, at 6 m for Przerośl, at 3 m for Hańcza, at 5 m for Pobondzie, at 7 m for Długie Wigierskie, at 3 m for Leszczewek, at 6 m for Wigry, at 4 m for Dowcień, at 6 m for Zelwa, and 4 m for Hołny.\u003c/p\u003e \u003cp\u003eThe measurements in twenty-three lakes revealed that the maximum value of SD was in Lake Hańcza (710 cm). There was a wide difference between this value and the second-highest value (410 cm) which was observed in two lakes: Wigry and Majcz Wielki. The lowest values were noted in Sztynorckie with 60 cm, followed by Suskie (70 cm) and Szczęśliwickie (75 cm). Because samples from Lake Zjadły and Probarskie were collected from a pier protruding to the lake, we were not able to measure the Secchi depth as it exceeded the depth at the bottom sediments under the pier by 1.5 and 2 m respectively.\u003c/p\u003e \u003cp\u003eThe highest conductivity value was found in Szczęśliwickie (593 \u0026micro;S/cm) followed by Leszczewek (501 \u0026micro;S/cm). The lowest value was observed in Probarskie with 168 \u0026micro;S/cm. Except for Lake Zjadły, the studied lakes were slightly basic. The highest pH values were observed in five lakes, respectively: Probarskie (8.58), Majcz Wielki (8.55), Szczęśliwickie (8.54), Głebokie (8.53), and Niegocin (8.50). The lowest value was observed in Zjadły (6.84).\u003c/p\u003e \u003cp\u003eThe highest TN value was found in Piłag with 2.75 mg/L while the lowest was in Zelwa. For TP the most enriched lake was Sztynorckie (0.55 mg/L) but for fourteen lakes the values were lower than 0.025 mg/L although in Szczęśliwickie the lowest identified TP value was 0.03 mg/L. When it comes to N-NH₄⁺ the maximum value was found in Rekąty (0.09 mg/L) and the minimum detectable value in Piłag (0.07 mg/L), but in all other lakes the values were lower than 0.05 mg/L which was the threshold value for the chosen method. In the case of N-NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, the highest was found in Długie Wigierskie (0.13 mg/L). For P-PO₄\u0026sup3;-, in all lakes, values were found to be lower than 0.025 mg/L. Lastly, the maximum S-SO₄\u0026sup2;- value was observed in Suskie (22.20 mg/L) while the lowest was in Inulec (2.40 mg/L).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePhytoplankton communities\u003c/h3\u003e\n\u003cp\u003eIn this study conducted in the Mazurian and Suwałki Lakelands, 325 phytoplankton species were identified altogether. The most abundant class was Cyanophyceae with 170 taxa (52.3% of all taxa), 34 of which were identified to genus level. The numbers of the species found in the classes Bacillariophyceae (69 taxa, 19 of which were identified down to genus level) (21.2% of all taxa) and Chlorophyceae (68 taxa, 22 of which were identified down to genus level) (20.9% of all taxa) were close to each other. In addition, there were respectively 13 (4.0% of all taxa) (4 of which were identified down to genus level), 3 (0.9% of all taxa), and 2 (0.6% of all taxa) taxa were obtained in the classes of Dinophyceae, Cryptophyceae, and Chrysopyceae (1 of which was identified down to genus level).\u003c/p\u003e \u003cp\u003eOn a lake basis, the highest number of taxa were identified in Rekąty with 66 taxa, and 41 of them belonged to Cyanophyceae. This was followed by Pobondzie (59 taxa), and Niegocin (59 taxa). The lowest numbers of taxa were observed in Długie Wigierskie (34 taxa), Leszczewek (35 taxa), and Wigry (36 taxa). Additionally, there was no lake found without representatives of Cyanophyceae, Chlorophyceae, and Bacillariophyceae. The lowest number of Chlorophyceae members were found in Majcz Wielki and Głebokie with 2 taxa while for Bacillarophyceae the minimum number of taxa was observed in Suskie, Probarskie, Głebokie, Sztynorckie, Rekąty, Pobondzie, Długie Wigierskie, and Leszczewek with 3 taxa.\u003c/p\u003e \u003cp\u003eIn the class Cyanophyceae, the maximum number of species belonged to the genera \u003cem\u003eDolichospermum\u003c/em\u003e (13 taxa), \u003cem\u003eAphanocapsa\u003c/em\u003e (11 taxa), and \u003cem\u003eMicrocystis\u003c/em\u003e (10 taxa). In the class of Chlorophyceae, \u003cem\u003eCosmarium\u003c/em\u003e (6 taxa) and \u003cem\u003eStaurastrum\u003c/em\u003e (5 taxa) were the genera with the highest number of species while in Bacillariophyceae these genera were \u003cem\u003eNavicula\u003c/em\u003e (9 taxa) and \u003cem\u003eCymbella\u003c/em\u003e (6 taxa). In addition, the genus \u003cem\u003eCeratium\u003c/em\u003e (5 taxa) was obtained to have the highest number of species in the class Dinophyceae.\u003c/p\u003e \u003cp\u003eAccording to performed analyses, the presence of \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e was recorded in five lakes: Szczęśliwickie, Mikołajskie, Rekąty, Sztynorckie, and Pobondzie. Additionally, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e was found in three lakes: Rekąty, Żabinki, and Pobondzie, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e only in Pobondzie while \u003cem\u003eR\u003c/em\u003e. \u003cem\u003emediterranea\u003c/em\u003e in two lakes: Mikołajskie and Śniardwy.\u003c/p\u003e \u003cp\u003eThe phytoplankton community of Mazurian Lakes varied a lot. There were 49 species identified in Suskie which is the lake with the highest total biomass. Chlorophyceae accounted for 46.0% of the total phytoplankton biomass. \u003cem\u003eTrichodesmium lacustre\u003c/em\u003e and \u003cem\u003eDesmodesmus opoliensis\u003c/em\u003e were the species reported only from here. In Lake Piłag, the species richness was low, only 38 species were identified. Chlorophyceae was the dominating class with a 51.1% percentage of the biomass. It was followed by Cyanophycae (28.7%) and other classes were nearly evenly distributed compared to other lakes. \u003cem\u003ePseudopediastrum boryanum\u003c/em\u003e and \u003cem\u003eDolichospermum circinale\u003c/em\u003e found to have dominant species. \u003cem\u003eTetraedron\u003c/em\u003e sp., \u003cem\u003eUlnaria\u003c/em\u003e sp., and \u003cem\u003eUlnaria ulna\u003c/em\u003e were found only in Piłag. Szczęśliwickie is a lake studied in the sense of hydrobiology, but no phytoplankton study published from there yet. In our study, this lake also had quite a low species richness with only 37 identified species. Chlorophyceae accounted for 45.8% of the total biomass while Cyanophyceae had 40.7%. However, the significance of this lake is the occurrence of \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e which appeared in low numbers (only one individual). There were also two taxa: \u003cem\u003eGeitlerinema\u003c/em\u003e sp. and \u003cem\u003eNodularia\u003c/em\u003e sp. identified up to the genus level only in this lake. Throughout almost all summer period, the surface of Lake Szczęśliwickie was covered with gelatinous clumps of \u003cem\u003eAphanocapsa\u003c/em\u003e. During the phytoplankton identification \u003cem\u003eA\u003c/em\u003e. \u003cem\u003eincerta\u003c/em\u003e was the only species found here belonging to this genus. Probarskie and Zjadły are geographically close lakes with unrevealed phytoplankton community structure. According to our study, 41.3% of the biomass of Probarskie was formed by Chlorophyceae while Zjadły was dominated by Dinophycae by 33.7%. In addition, the species richness in Probarskie (56 species) was higher than in Zjadły (41 species). \u003cem\u003ePediastrum biradiatum\u003c/em\u003e in Probarskie and \u003cem\u003eCeratium hirundinella\u003c/em\u003e in Zjadły were the most abundant species. \u003cem\u003eJaaginema\u003c/em\u003e sp., \u003cem\u003eOscillatoria limosa\u003c/em\u003e, \u003cem\u003ePediastrum\u003c/em\u003e sp., and \u003cem\u003eTetrastrum elegans\u003c/em\u003e were identified only in Probarskie while \u003cem\u003eLeptolyngbya thermobia\u003c/em\u003e, \u003cem\u003eOscillatoria\u003c/em\u003e sp., \u003cem\u003eRadiocystis fernandoi\u003c/em\u003e, and \u003cem\u003eGomphonema minutum\u003c/em\u003e were in Zjadły. Majcz Wielki had low species with only 40 identified species. Cyanophyceae had the biggest share in biomass with 27.4% but \u003cem\u003eCeratium hirundinella\u003c/em\u003e was found to be the species with the most biomass. \u003cem\u003eAnagnostidinema ionicum\u003c/em\u003e, \u003cem\u003eEpithemia\u003c/em\u003e sp., \u003cem\u003eNitzschia inconspicua\u003c/em\u003e, and \u003cem\u003eSynedra\u003c/em\u003e sp. were encountered only in this lake. In Inulec, there were only 42 species identified, and Cyanophyceae was the dominating class with 40.3% of the biomass. However, on the species level, \u003cem\u003eCosmarium joshuae\u003c/em\u003e and \u003cem\u003eCeratium hirundinella\u003c/em\u003e were the ones with the highest biomass, respectively. \u003cem\u003eAphanocapsa rivularis\u003c/em\u003e, \u003cem\u003eSpirulina subtilissima\u003c/em\u003e, \u003cem\u003eAnkistrodesmus arcuatus\u003c/em\u003e, \u003cem\u003eStaurastrum manfeldtii\u003c/em\u003e, and \u003cem\u003eTetraedron trigonum\u003c/em\u003e were the species found only in Inulec. In Głebokie, Chlorophyceae had the biggest share in total biomass (50.4%) and \u003cem\u003ePseudopediastrum boryanum\u003c/em\u003e contributed the most to it. However, species richness here was low with only 39 identified species. \u003cem\u003eDolichospermum minisporum\u003c/em\u003e, \u003cem\u003eNostoc commune\u003c/em\u003e, \u003cem\u003eNostoc paludosum\u003c/em\u003e, \u003cem\u003eTrichodesmium\u003c/em\u003e sp., and \u003cem\u003eCocconeis pediculus\u003c/em\u003e were found only here. Compared to the other lakes, Lake Mikołajskie had a relatively high biomass of the Dinophyceae (27.8%) but the biomass of Chlorophyceae was the most (42.1%). There were 56 species identified from this lake. \u003cem\u003eGlaucospira laxissima\u003c/em\u003e, \u003cem\u003eLeptolyngbya carnea\u003c/em\u003e, \u003cem\u003ePseudanabaena galeata\u003c/em\u003e, \u003cem\u003eSpirulina baltica\u003c/em\u003e, \u003cem\u003eTetrastrum\u003c/em\u003e sp., \u003cem\u003eAulacoseira\u003c/em\u003e sp., and \u003cem\u003eCymbella tumida\u003c/em\u003e were identified only in Mikołajskie. Also, the \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e was reported from this lake and its number (2) was higher than in Szczęśliwickie. Lake Sztynorckie had relatively high species richness with 47 identified species. Cyanophyceae had the biggest share in biomass with a 70.8% contribution. Additionally, \u003cem\u003eMicrocystis aeruginosa\u003c/em\u003e and \u003cem\u003eAnagnostidinema amphibium\u003c/em\u003e were the most dominant cyanobacterial species in this lake. Most importantly, the \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e occurring in Lake Sztynorckie reached the highest biomass in the whole study. \u003cem\u003eCyanobium\u003c/em\u003e sp., \u003cem\u003eGomphosphaeria aponina\u003c/em\u003e, \u003cem\u003eJaaginema quadripunctulatum\u003c/em\u003e, \u003cem\u003eLeptolyngbya angusta\u003c/em\u003e, \u003cem\u003eMerismopedia elegans\u003c/em\u003e, and \u003cem\u003eFragilaria perminuta\u003c/em\u003e were reported only from this lake. Species richness in Mamry was quite high with 49 identified species. Chlorophyceae and Cyanophyceae were co-dominating phytoplankton classes in this lake. Compared to other lakes Dinophyceae also had a large contribution to the total biomass with 14.9%. There were many species identified only from Mamry: \u003cem\u003eAphanocapsa nubila\u003c/em\u003e, \u003cem\u003eAphanothece floccosa\u003c/em\u003e, \u003cem\u003eMicrocystis firma\u003c/em\u003e, \u003cem\u003ePlanktolyngbya undulata\u003c/em\u003e, \u003cem\u003ePseudanabaena thermalis\u003c/em\u003e, \u003cem\u003eRomeria gracilis\u003c/em\u003e, \u003cem\u003eRomeria leopoliensis\u003c/em\u003e, \u003cem\u003eTrichocoleus\u003c/em\u003e sp., \u003cem\u003eGymnodinium fuscum\u003c/em\u003e, \u003cem\u003eMicrospora abbreviata\u003c/em\u003e, \u003cem\u003eAmphora copulata\u003c/em\u003e, \u003cem\u003eCymbella neocistula\u003c/em\u003e, \u003cem\u003eDiploneis elliptica\u003c/em\u003e, \u003cem\u003eEpithemia turgida\u003c/em\u003e, and \u003cem\u003eNitzschia amphibia\u003c/em\u003e. There was no information found about the phytoplankton community of Brzozolasek. In our study, 43 species were identified from this lake and the biomass of Cyanophyceae was dominating by 52.9% which was followed by Dinophyceae by 29.0%. The contribution to the total biomass of the Chlorophyceae (6.2%) was the second lowest in this lake in the entire study. \u003cem\u003eAnabaena elegans\u003c/em\u003e, \u003cem\u003eAnabaena ellipsoidea\u003c/em\u003e, \u003cem\u003eLimnolyngbya circumcreta\u003c/em\u003e, \u003cem\u003eMicrocystis natans\u003c/em\u003e, \u003cem\u003eSynechocystis\u003c/em\u003e sp., \u003cem\u003eAmphora ovalis\u003c/em\u003e, \u003cem\u003eEncyonema ventricosum\u003c/em\u003e, and \u003cem\u003ePlanothidium frequentissimum\u003c/em\u003e were reported only from Brzozolasek. Lake Niegocin had very high species richness with 59 identified species. Chlorophyceae had the biggest share in the total biomass with a 62.8% contribution. \u003cem\u003ePediastrum duplex\u003c/em\u003e and \u003cem\u003eCosmarium reniforme\u003c/em\u003e were the species with the highest biomass, respectively. \u003cem\u003eDolichospermum fuscum\u003c/em\u003e, \u003cem\u003eGomphosphaeria\u003c/em\u003e sp., \u003cem\u003eKomvophoron schmidlei\u003c/em\u003e, \u003cem\u003eNodularia spumigena\u003c/em\u003e, \u003cem\u003ePlanktolyngbya crassa\u003c/em\u003e, \u003cem\u003eSpirulina meneghiniana\u003c/em\u003e, \u003cem\u003eNavigeia decussis\u003c/em\u003e, \u003cem\u003eOdontidium mesodon\u003c/em\u003e, and \u003cem\u003eStephanodiscus\u003c/em\u003e sp. were described only from Niegocin. In Lake Śniardwy, the largest lake in Poland species richness was found to be high with 53 identified species. 64.5% of the total phytoplankton biomass in this lake was contributed by Chlorophyceae. \u003cem\u003ePseudopediastrum boryanum\u003c/em\u003e was the species with the highest biomass. \u003cem\u003eLeptolyngbya boryana\u003c/em\u003e, \u003cem\u003eChlamydomonas ehrenbergii\u003c/em\u003e, \u003cem\u003eChlamydomonas\u003c/em\u003e sp., and \u003cem\u003eSurirella brebissonii\u003c/em\u003e were the species reported only from here. In Lake Żabinki, 45 species were identified including the invasive \u003cem\u003eChrysosporum bergii.\u003c/em\u003e 62.3% of the total phytoplankton structure was formed by Cyanophyeae, which is the second-highest percentage of Cyanophyceae in a single lake. It has been followed by Dinophyceae (15.8%). Total biomass was found to be 5.5 mg/L and the biggest contributor to this was \u003cem\u003eCeratium hirundinella\u003c/em\u003e and \u003cem\u003eLimnothrix redekei\u003c/em\u003e. \u003cem\u003ePseudanabaena articulata\u003c/em\u003e, \u003cem\u003eSpirulina major\u003c/em\u003e, \u003cem\u003eSynechocystis septentrionalis\u003c/em\u003e, \u003cem\u003eChlamydomonas reinhardtii\u003c/em\u003e, \u003cem\u003ePinnularia\u003c/em\u003e sp., and \u003cem\u003eSurirella librile\u003c/em\u003e were found only here. Lake Rekąty was characterized by the highest species richness with 66 identified species including invasive \u003cem\u003eChrysosporum bergii\u003c/em\u003e and \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e. 48.3% of the phytoplankton structure was formed by Cyanophyceae. Many cyanobacterial species that occurred only in this lake such as \u003cem\u003eAnabaena sedovii\u003c/em\u003e, \u003cem\u003eAnabaenopsis cunningtonii\u003c/em\u003e, \u003cem\u003eAnabaenopsis knipowitschii\u003c/em\u003e, \u003cem\u003eDolichospermum sigmoideum\u003c/em\u003e, \u003cem\u003eMicrocoleus autumnalis\u003c/em\u003e, \u003cem\u003eMicrocystis panniformis\u003c/em\u003e, \u003cem\u003eRhabdogloea linearis\u003c/em\u003e. In addition, other phytoplankton classes were represented by species occurring only in this lake, such as \u003cem\u003eGonyaulax apiculata\u003c/em\u003e, and \u003cem\u003eOocystis lacustris\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eIn Suwałki Lakeland there were also big differences in the composition and structure of the phytoplankton community. In Lake Przerośl, species richness was found to be high with 53 species and the class Cyanophyceae formed the structure by 45.9% biomass. On the other hand, the phytoplankton class Cryptophyceae had one of the lowest biomasses (0.2%). \u003cem\u003eAnabaena echinospora\u003c/em\u003e, Anathece \u003cem\u003eclathrata\u003c/em\u003e, \u003cem\u003eMicrocystis botrys\u003c/em\u003e, \u003cem\u003eOscillatoria tenuis\u003c/em\u003e, \u003cem\u003ePeridinium willei\u003c/em\u003e, \u003cem\u003eGonatozygon monotaenium\u003c/em\u003e, \u003cem\u003eTeilingia\u003c/em\u003e sp., \u003cem\u003eEunotia\u003c/em\u003e sp., and \u003cem\u003eGyrosigma kuetzingii\u003c/em\u003e were identified only from Przerośl. There were merely 39 species identified in the deepest lake in Poland, Hańcza which means the species richness was quite low here. 35.7% of the total biomass was formed by Cyanophyceae while 30.2% by Dinophyceae making the two classes\u0026rsquo; subdominants in this lake. It is also worth mentioning that with 7.9% the share of the Chlorophyceae was one of the lowest here in the whole study. \u003cem\u003eSnowella\u003c/em\u003e sp., \u003cem\u003eDiploneis separanda\u003c/em\u003e, \u003cem\u003eHantzschia\u003c/em\u003e sp., and \u003cem\u003ePantocsekiella ocellata\u003c/em\u003e were identified only from here. Lake Pobondzie was one of the most important lakes in this study as all three aimed-to-find cyanobacterial invasive species (\u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e, and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e) were found here even though they had very low biomasses. Unfortunately, no available phytoplankton data was found but, in this study, Cyanophyceae was dominating (40.8%) class followed by Chlorophyceae (29.8%). Species richness in Pobondzie was the second-highest in the whole study with 59 taxa. There were quite a lot of species reported only from Pobondzie: \u003cem\u003eAnathece\u003c/em\u003e sp., \u003cem\u003eDolichospermum viguieri\u003c/em\u003e, \u003cem\u003eNostoc passerinianum\u003c/em\u003e, \u003cem\u003eNostoc undulatum\u003c/em\u003e, \u003cem\u003eSphaerospermopsis aphanizomenoides\u003c/em\u003e, \u003cem\u003eSphaerospermopsis\u003c/em\u003e sp., \u003cem\u003eSynechocystis sallensis\u003c/em\u003e, \u003cem\u003ePeridiniopsis polonicum\u003c/em\u003e, \u003cem\u003eCosmarium granatum\u003c/em\u003e, and \u003cem\u003eWillea apiculata\u003c/em\u003e. Długie Wigierskie had one of the lowest species richness in this study with 34 taxa. The phytoplankton structure in this lake was dominated by Dinophyceae with 51.5% and it was the highest percentage of biomass for Dinophyceae in the entire study. \u003cem\u003eCeratium cornutum\u003c/em\u003e and \u003cem\u003eCeratium hirundinella\u003c/em\u003e were the main representatives of the phytoplankton class Dinophyceae. The total biomass was 1.00 mg/L, which was one of the lowest in the whole study. There were only two species from Bacillariophyceae encountered only from this lake which are \u003cem\u003eDiatoma\u003c/em\u003e sp. and \u003cem\u003eEunotia bilunaris\u003c/em\u003e. There were only 35 species identified from Lake Leszczewek. The biggest share of the total biomass was formed by Chrysophyceae with 34.7%. \u003cem\u003eLeptolyngbya ectocarpi\u003c/em\u003e, \u003cem\u003eSynechococcus\u003c/em\u003e sp., \u003cem\u003eKoliella longiseta\u003c/em\u003e, and \u003cem\u003eNeidium\u003c/em\u003e sp. were reported only from Leszczewek. Lake Wigry, the largest lake in Suwałki Lakeland and the third-largest lake in Poland had relatively low species richness (36 taxa), Cyanophyceae was the dominating phytoplankton class accounting for 39.0% of total phytoplankton biomass followed by Dinophyceae with 23.2%. Wigry was one of the lakes where no Cryptophyceae were found during biomass calculation. Biomass of Chrysophyceae was found to be 16.1% and it was the second highest in the entire study. There were two taxa (\u003cem\u003eGloeocapsa\u003c/em\u003e sp. and \u003cem\u003ePlaconeis\u003c/em\u003e sp.) identified down to genus level in Wigry which are found only in this lake. In Lake Dowcień, there was no Dinophyceae representative were encountered during the biomass calculation. The highest part of the biomass was formed by Chlorophyceae with 39.2% and it has been followed by Cyanophyceae with 37.1%. On the other hand, species richness was average (46 taxa). \u003cem\u003eCosmarium turpinii\u003c/em\u003e, \u003cem\u003eTreubaria\u003c/em\u003e sp., and \u003cem\u003eUlothrix tenerrima\u003c/em\u003e, \u003cem\u003eCymbella lange\u003c/em\u003e-\u003cem\u003ebertalotii\u003c/em\u003e, and \u003cem\u003eNavicula capitatoradiata\u003c/em\u003e were found only here. The phytoplankton community structure of Lake Zelwa was strongly formed by Cyanophyceae with 45.2% and the rest of the phytoplankton classes were relatively evenly distributed except Cryptophyceae (2.2% and Chrysophyceae (5.6%). Species richness here was also average (45 taxa). \u003cem\u003eDolichospermum danicum\u003c/em\u003e, \u003cem\u003eMicrocystis\u003c/em\u003e sp., \u003cem\u003eRhabdoderma\u003c/em\u003e sp., \u003cem\u003eDesmodesmus denticulatus\u003c/em\u003e, \u003cem\u003eAsterionella formosa\u003c/em\u003e, \u003cem\u003eEunotia rhomboidea\u003c/em\u003e, and \u003cem\u003eGomphonema micropus\u003c/em\u003e were present only in Zelwa. Lake Hołny, located the most to the east of the studied lakes, was dominated by Chlorophyceae with 42.8% of the biomass. \u003cem\u003eCaloneis budensis\u003c/em\u003e was encountered only here. The biomass of Cyanophycea (22.7%) and Dinophyceae (22.7%) were very close to each other. Species richness was relatively high with 50 taxa. \u003cem\u003eBorzia trilocularis\u003c/em\u003e, \u003cem\u003eChroococcus cumulatus\u003c/em\u003e, \u003cem\u003eDolichospermum mucosum\u003c/em\u003e, \u003cem\u003eEucapsis aphanocapsoides\u003c/em\u003e, \u003cem\u003eBotryococcus\u003c/em\u003e sp., \u003cem\u003eHariotina reticulata\u003c/em\u003e, \u003cem\u003eCaloneis budensis\u003c/em\u003e, and \u003cem\u003eNitzschia dissipata\u003c/em\u003e were described only from Hołny.\u003c/p\u003e\n\u003ch3\u003eStatistical Evaluation of Data\u003c/h3\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eBiomass rates of the phytoplankton communities\u003c/h2\u003e \u003cp\u003eThe mean value of total biomass in all lakes was calculated as 6.7 mg/L. The highest biomass was found in Lake Suskie with 56.2 mg/L followed by Sztynorckie (23.8 mg/L) and Szczęśliwickie (11.6 mg/L). The lowest biomass was found in Brzozolasek (0.8 mg/L) followed by Hańcza, Majcz Wielki, and Zjadły in which the total phytoplankton biomass was 0.9 mg/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Considering the phytoplankton classes, Cyanophyceae had the highest mean value for the biomass with 2.8 mg/L (42.3%) followed by Chlorophyceae at 2.5 mg/L (37.8%) and Dinophyceae at 0.8 mg/L (11.5%). Cryptophyceae (0.2 mg/L, 3.6%) and Bacillariophyceae (0.2 mg/L, 3.5%) had quite close values to each other while Chrysophyceae was 0.1 mg/L (1.4%) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Evaluating the lakes among each other, all of the biomass values of the other phytoplankton classes were found to be the highest in Suskie; except for Chrysophyceae in Leszczewek. However, this was because of the high biomass in the Suskie. When the lakes are evaluated on their own, the highest biomass rate of Cyanophyceae was in Sztynorckie (70.8%), Chlorophyceae in Śniardwy (64.5%), Bacillarophyceae in Hańcza (17.3%), Dinophyceae in Długie Wigierskie (51.5%), Cryptophyceae in Majcz Wielki (9.1%), and Chrysophyceae in Leszczewek (34.7%). \u003cem\u003eMonactinus simplex\u003c/em\u003e was the species with the highest biomass (23.5 mg/L) and it made 37.2% of the whole Chlorophyceae (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e). On the other hand, \u003cem\u003eAnagnostidinema amphibium\u003c/em\u003e was found to have the highest biomass (13.7 mg/L) in Cyanophyceae. The biomass values of the invasive species \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e (0.39 mg/L), \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e (0.09 mg/L), and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e (0.02 mg/L) were quite low in the entire study. In addition, the highest biomass of \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e was found in Sztynorckie (0.26 mg/L). In total, 11 lakes were dominated by Cyanophyceae, 10 by Chlorophyceae, two by Dinophyceae, and only one by Chrysophyceae.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eSpecies richness, Shannon diversity index, and Pielou\u0026rsquo;s evenness\u003c/h2\u003e \u003cp\u003eTo reveal the diversity of phytoplankton community structure, species richness, and the Shannon diversity index were employed based on the presence and biomass of the identified species in all lakes. Considering every lake, it was determined that the Shannon diversity index varied between 1.79 (Mikołajskie) and 2.84 (Rekąty) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Species richness, which reflects the number of identified species in lakes regardless of their biomass, showed the highest richness in Rekąty (66 taxa) and the lowest in Długie Wigierskie (34 taxa). Pielou\u0026rsquo;s evenness was also applied to reveal how evenly the species are distributed and to verify diversity. Accordingly, the highest evenness was found in Leszczewek (0.92) and the lowest in Niegocin (0.57).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eEuclidean distance analysis\u003c/h2\u003e \u003cp\u003eClustering analysis was used to determine the similarities of the freshwater bodies investigated in Northeastern Poland. Using Euclidean distance analysis (ED) the similarity between the lakes in terms of ecological variables was identified. Accordingly, Piłag and Hańcza (ED\u0026thinsp;=\u0026thinsp;8.51) were found to have the lowest similarity. On the other hand, Przerośl and Hołny (ED\u0026thinsp;=\u0026thinsp;1.11) were found to have the highest similarity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEuclidean distance analysis also revealed the closeness among Rekąty, Szczęśliwickie, Leszczewek, Sztynorckie, Suskie, and Piłag which formed a cluster separated from all other lakes. The second large cluster was divided into a small cluster grouping Lakes Hańcza and Długie Wigierskie and the other to which the rest of the lakes were assigned. The smaller groups with higher similarity can also be distinguished here. Therefore, Pobondzie, Dowcień, Przerośl, Hołny, Wigry, Mamry, Zelwa, Brzozolasek, Inulec, and Żabinki formed one cluster while Majcz Wielki, Głebokie, Niegocin, Mikołajskie, and Śniardwy the second which are oligotrophic and oligo-mesotrophic lakes with similar nutrient content. The last two clusters were among Brzozolasek, Inulec, and Żabinki and Majcz Wielki, Głebokie, Niegocin, Mikołajskie, and Śniardwy. All of these lakes are located in Mazurian Lakeland (ML) and they have similar main abiotic variables such as temperature, conductivity, pH, and dissolved oxygen. Brzozolasek was an interesting lake in this cluster, even though geographically it is located in the same area, the nutrient content and other abiotic variables of this lake were different than the others. It also had very low phytoplankton biomass.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eFrequency analysis\u003c/h2\u003e \u003cp\u003eThe most frequent species defined was \u003cem\u003eAphanizomenon gracile\u003c/em\u003e, which was not encountered only in Lake Piłag. \u003cem\u003eA\u003c/em\u003e. \u003cem\u003egracile\u003c/em\u003e was followed by \u003cem\u003eLimnothrix redekei\u003c/em\u003e and \u003cem\u003ePlanktolyngbya limnetica\u003c/em\u003e which were noted in 22 lakes. Although this analysis is not related to abundance, all of the frequently found species had relatively high biomass. 269 of 325 species were described as belonging to \"Rarely Found Species\", 29 to \"Seldomly Found Species\", 12 to \"Commonly Found Species\", 9 to \"Frequently Found Species\", and six to \"Continuously Found Species\". Moreover, all three (\u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii, C\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e, and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e) of the invasive cyanobacterial species in Poland also belong to \"Rarely Found Species\" (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Additionally, frequency analysis showed only six species that could be classified as \"Continuously Found Species\" which were \u003cem\u003eAphanizomenon gracile\u003c/em\u003e, \u003cem\u003eAnagnostidinema amphibium\u003c/em\u003e, \u003cem\u003eLimnothrix redekei\u003c/em\u003e, \u003cem\u003ePlanktolyngbya limnetica\u003c/em\u003e, \u003cem\u003eCryptomonas sp\u003c/em\u003e. and \u003cem\u003eRhodomonas\u003c/em\u003e sp. as they have been encountered in more than 20 lakes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eRedundancy analysis (RDA)\u003c/h2\u003e \u003cp\u003eAccording to the RDA results, environmental variables included in the analysis explain 37.63% of the variation in algae composition across lakes (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e). It was observed that water transparency was negatively correlated with pH. DO, TP, TN, and pH were placed together in the same quarter, opposite to transparency. In addition, it was revealed that Chlorophyceae had a positive correlation with pH and TN while they had a negative correlation with transparency, Cyanophyceae positively correlated with DO, whereas Chrysophyceae negatively correlated with DO. Bacillariophyceae, Cryptophyceae, and Dinophyceae did not have any strong relationship with environmental parameters. However, Bacillariophyceae exhibited a slight positive correlation with transparency and a negative with TN, TP, and pH (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) while Cryptophyceae showed a slightly positive with TP and TN, whereas Dinophyceae negative relationship with electrical conductivity (EC) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThroughout the whole sampling period, the phytoplankton community structure in Mazurian and Suwałki Lakelands showed a notable difference. The phytoplankton communities in twenty-five lakes were dominated by Chlorophyceae and Cyanophyceae representatives except Zjadły (Dinophyceae), Długie Wigierskie (Dinophyceae), and Leszczewek (Chrysophyceae). Mazurian and Suwałki Lakelands can be considered as well-studied areas. Therefore, spatial and temporal changes in the phytoplankton community structures will be discussed. Moreover, some lakes that have never been studied before in terms of phytoplankton and their community structure will be revealed.\u003c/p\u003e \u003cp\u003eAccording to the study performed in Suskie (Lossow et al. 2004), authors reported that this lake has been dominated by Cyanophyceae and the contribution of other phytoplankton classes was quite low except in November. In our study, there was no strict domination of a single class. Lossow et al. (2004) also reported \u003cem\u003ePlanktothrix agardhii\u003c/em\u003e (formerly known as \u003cem\u003eOscillatoria agardhii\u003c/em\u003e) and \u003cem\u003eLimnothrix redekei\u003c/em\u003e (formerly known as \u003cem\u003eOscillatoria redekei\u003c/em\u003e) were quite abundant in the class of Cyanophyceae. In support of this, \u003cem\u003eP\u003c/em\u003e. \u003cem\u003eagardhii\u003c/em\u003e and \u003cem\u003eL\u003c/em\u003e. \u003cem\u003eredekei\u003c/em\u003e were both encountered in this lake in our study. However, only \u003cem\u003eP\u003c/em\u003e. \u003cem\u003eagardhii\u003c/em\u003e had a biomass worth mentioning. \u003cem\u003eTrichodesmium lacustre\u003c/em\u003e and \u003cem\u003eDesmodesmus opoliensis\u003c/em\u003e were found only in this lake.\u003c/p\u003e \u003cp\u003eEven though there is no study about the whole phytoplankton community of Lake Majcz Wielki, this mesotrophic lake in Mazurian Lakeland has been studied in terms of various communities of phytoplankton (Gliwicz et al. 1981; Hillbricht-Ilkowska et al. 1984), picophytoplankton (Jasser 1997; Jasser 2002) zooplankton, and zoobenthos (Kołodziejczyk and Lewandowski 2009). The lake was one of 24 lakes included in a study of plankton seasonal changes summarized in the PEG model (Sommer et al. 1985). Gliwicz et al. (1981) stated that \u003cem\u003eDinobryon\u003c/em\u003e had a higher biomass share in this lake. Similarly, Hillbricht-Ilkowska et al. (1984) also reported that Majcz Wielki was dominated by \u003cem\u003eDinobryon\u003c/em\u003e. In support of this, our study revealed also that although \u003cem\u003eDinobryon divergens\u003c/em\u003e was not dominating in Majcz Wielki, it was the second most abundant species after \u003cem\u003eCeratium hirundinella\u003c/em\u003e. In addition, it was the third lake that Chrysophyceae reached this much of high biomass (13.0%) in the entire study.\u003c/p\u003e \u003cp\u003ePasztaleniec et al. (2010) reported that Cyanophyceae with dominant \u003cem\u003eMicrocystis\u003c/em\u003e sp., \u003cem\u003eWoronichiniana naegeliana\u003c/em\u003e, and \u003cem\u003eAphanizomenon issatschenkoi\u003c/em\u003e) had the largest biomass in Lake Głebokie in the whole year while in May the phytoplankton was dominated by Chlorophyceae (\u003cem\u003ePandorina morum\u003c/em\u003e, \u003cem\u003eStaurastrum cuspidatum\u003c/em\u003e, \u003cem\u003eEutetramorus planctonicus\u003c/em\u003e, and \u003cem\u003eCoelastrum microporum\u003c/em\u003e). In our study, this lake was highly dominated by Chlorophyceae. However, none of the mentioned species were encountered in this lake in August 2023. Pasztaleniec et al. (2010) also stated that in July, the lake was dominated by \u003cem\u003eCeratium hirundinella\u003c/em\u003e, which is when we also performed sampling, and in our study \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ehirundinella\u003c/em\u003e and \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ecornutum\u003c/em\u003e were found in this period as well. Even though they were not dominating, their biomass was considerably high.\u003c/p\u003e \u003cp\u003eLake Mikołajskie is another lake that has been very frequently analyzed in terms of various organisms and it was another Polish lake included in the PEG model of seasonal plankton changes (Sommer et al. 1985). Spodniewska (1976) studying phytoplankton in Mikołajskie in the seventies stated that Dinophyceae was the most dominant phytoplankton class in the summer season, and they formed 90.0% of algal biomass. In the same study, \u003cem\u003eCeratium hirundinella\u003c/em\u003e was found to be the most abundant species. In a study almost 40 years later (Ochocka and Pasztaleniec 2016) Cyanophyceae had the biggest share of phytoplankton biomass in Mikołajskie both in 2012 and 2013 when the study was conducted. However, Dinophyeae was the second most abundant phytoplankton class in 2012. In our study, the biomass of the Dinophyceae was also very high, but the Chlorophyceae was the most dominant phytoplankton class. Contrary to the earlier studies Cyanophyceae was the third class of phytoplankton with a contribution of only about 25% of total biomass. In addition, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ehirundinella\u003c/em\u003e was the second most abundant species in this lake.\u003c/p\u003e \u003cp\u003eNapi\u0026oacute;rkowska-Krzebietke et al. (2023) studying Lake Sztynorckie reported that \u003cem\u003eLimnothrix redekei\u003c/em\u003e, \u003cem\u003ePseudanabaena limnetica\u003c/em\u003e, \u003cem\u003ePlanktolyngbya limnetica\u003c/em\u003e were the most abundant species during their sampling in summer while \u003cem\u003eAphanizomenon gracile\u003c/em\u003e, \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e, and \u003cem\u003ePlanktothrix agardhii\u003c/em\u003e were occurring with relatively low biomass. They also stated that Cyanophyceae was the most abundant phytoplankton class during their summertime sampling both in June and August of 2021. In the present study, Cyanophyceae also had the biggest share in the total biomass, and it was the highest percentage in the entire study. Moreover, all of the species mentioned were found in our study as well as invasive \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e with low biomass.\u003c/p\u003e \u003cp\u003eNapi\u0026oacute;rkowska-Krzebietke and Hutorowicz (2005) analyzing phytoplankton in Lake Mamry stated that Bacillarophyceae and Chrysophyceae had the highest diversity in this between 1986\u0026ndash;2001. In our study, Cyanophyceae was the most diverse phytoplankton class in this lake, even though the lake was found to have relatively low diversity when compared with other surveyed lakes. It was also reported between 1986\u0026ndash;1989 that Bacillariophyceae, Cryptophyceae, and Dinophyceae were the dominant phytoplankton classes (Napi\u0026oacute;rkowska-Krzebietke and Hutorowicz 2005) and another study (P\u0026oacute;łtoracka 1963) stated the dominance of Bacillariophyceae as well. It was also mentioned that the genus \u003cem\u003eDinobryon\u003c/em\u003e was abundant during the summer (Napi\u0026oacute;rkowska-Krzebietke and Hutorowicz 2005). In our study, Chlorophyceae and Cyanophyceae shared the total biomass almost equally and it has been followed by Dinophyceae. The genus \u003cem\u003eDinobryon\u003c/em\u003e was found in this lake with relatively high biomass compared to others. Bukowska et al. (2017) reported that Cyanophyceae accounted for 91.0% of the total biomass in August 2011. In our study, Chlorophyceae had a slightly bigger share (32.3%) in Mamry while Chlorophyceae had (31.8%).\u003c/p\u003e \u003cp\u003eIn a study of Lake Niegocin, high levels of total phytoplankton biomass (8.20 mg/L) were recorded up to 1994 and this amount is quite similar to the biomass we found in this study (8.80 mg/L) (Napi\u0026oacute;rkowska-Krzebietke and Hutorowicz 2006). In 2000, Dinophyceae, Cyanophycae, and Cryptophyceae were reported as the three co-dominant classes (Napi\u0026oacute;rkowska-Krzebietke and Hutorowicz 2006). Meanwhile, in our study, this lake was dominated by Chlorophyceae. In several studies, (Napi\u0026oacute;rkowska-Krzebietke and Hutorowicz 2006; Bukowska et al. 2017) mentioned that in 1991, this lake was dominated by \u003cem\u003ePlanktothrix agardhii\u003c/em\u003e. In the present study, this species was reported from this lake, but it did not have significant biomass.\u003c/p\u003e \u003cp\u003eAccording to a study by Napi\u0026oacute;rkowska-Krzebietke et al. (2020), it was stated in Śniardwy which is the largest lake in Poland, 70.0% of the phytoplankton biomass was formed by Bacillariophyceae in spring and summer. However, in the present study, the dominating phytoplankton class was Chlorophyceae. Moreover, this percentage was the highest one covered by Chlorophyceae in this survey.\u003c/p\u003e \u003cp\u003eAccording to several studies (Haider et al. 2003; Zagajewski et al. 2009; Ballot et al. 2010), \u003cem\u003ePseudanabaena limnetica\u003c/em\u003e, \u003cem\u003eAn\u003c/em\u003eabaenopsis sp., and \u003cem\u003eAnabaenopsis elenkini\u003c/em\u003e were found in Rekąty. In our study, \u003cem\u003eA\u003c/em\u003e. \u003cem\u003eelenkinii\u003c/em\u003e was found in this lake with high biomass. On the other hand, \u003cem\u003eP\u003c/em\u003e. \u003cem\u003elimnetica\u003c/em\u003e which was one of the most frequent species was not encountered here, even though this lake had the highest species richness. In addition, \u003cem\u003eAnabaenopsis\u003c/em\u003e sp. was not reported from this lake either. Moreover, in another study, \u003cem\u003eAphanizomenon flos-aquae\u003c/em\u003e, \u003cem\u003eChroococcus minimus\u003c/em\u003e, \u003cem\u003eChroococcus turgidus\u003c/em\u003e, \u003cem\u003eLimnothrix redekei\u003c/em\u003e, \u003cem\u003eMicrocystis aeruginosa\u003c/em\u003e, and \u003cem\u003ePlanktolyngbya limnetica\u003c/em\u003e were reported from this lake (Jakubowska et al. 2013). They were all described in this study as well except \u003cem\u003eA\u003c/em\u003e. \u003cem\u003eflos-aquae\u003c/em\u003e and \u003cem\u003eC\u003c/em\u003e. \u003cem\u003eturgidus\u003c/em\u003e. On the other hand, Jakubowska et al. (2013) reported the occurrence of \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e from this lake.\u003c/p\u003e \u003cp\u003eHańcza is one of the most well-studied lakes and the deepest lake in Poland, but also one of the least oligotrophic lakes in the study. According to a study, in August 1973, the dominating phytoplankton classes in the lake were Dinophyceae and Cyanophyceae (Spodniewska 1978). A later study reported that in the summer of 1994, \u003cem\u003eCeratium hirundinella\u003c/em\u003e and \u003cem\u003ePeridinium\u003c/em\u003e sp. shared the highest biomass, and the Cyanophyceae contributed less (Jasser 2002). In a relatively current study (Napi\u0026oacute;rkowska-Krzebietke and Hutorowicz 2013), it was mentioned that 114 taxa were identified while in the present study, it was 39. They also claimed that the main dominating class was Bacillariophyceae representatives (\u003cem\u003eCyclotella\u003c/em\u003e sp. and \u003cem\u003eAsterionella formosa\u003c/em\u003e), which were not encountered in our study. However, the biomass of pennate \u003cem\u003eC\u003c/em\u003e. \u003cem\u003eplacentula\u003c/em\u003e was quite high. Interestingly, Napi\u0026oacute;rkowska-Krzebietke and Hutorowicz (2013) also mentioned \u003cem\u003eAphanocapsa\u003c/em\u003e and \u003cem\u003eAphanothece\u003c/em\u003e were the major phytoplankton biomass contributors in August 2006, 2007, and 2008, but in our study, these genera' were not encountered in Hańcza and \u003cem\u003eAnagnostidinema amphibium\u003c/em\u003e was the dominating Cyanophyceaen species.\u003c/p\u003e \u003cp\u003eIn a study about the genus \u003cem\u003ePediastrum\u003c/em\u003e (Lenarczyk et al. 2015), it was claimed that in Leszczewek \u003cem\u003eStauridium tetras\u003c/em\u003e (formerly known as \u003cem\u003ePediastrum tetras\u003c/em\u003e) and \u003cem\u003ePseudopediastrum boryanum\u003c/em\u003e (formerly known as \u003cem\u003ePediastrum boryanum\u003c/em\u003e) were encountered. In our study, Chlorophyceae formed a quite low percentage of biomass and the mentioned species were not found. The importance of this lake is the high percentage of biomass was formed by Chrysophyceae (\u003cem\u003eDinobryon divergens\u003c/em\u003e) which was also the maximum in the study. It has been followed by Cyanophyceae.\u003c/p\u003e \u003cp\u003eSzczęśliwickie is a highly eutrophic lake and the only lake in this study that was not part of Mazurian and Suwałki Lakelands. It had the third-highest biomass in the entire study with 11.6 mg/L of fresh biomass. This lake's phytoplankton structure was formed almost the same as Suskie which is the lake with the highest phytoplankton biomass. The phytoplankton was dominated by Chlorophyceae with a share of 45.8% and Cyanophyceae with 40.7%. It was observed that according to RDA, Szczęśliwickie had a slightly positive correlation with NPOC, and in Euclidean distance analysis (ED) it clustered with other eutrophic lakes (Rekąty, Leszczewek, Sztynorckie, Suskie, and Piłag) as an expected result. This closeness mainly came from their low Secchi depth which varied between 60\u0026ndash;150, and high nutrient concentrations. Their Secchi depth values were one of the lowest in the study and dissolved oxygen concentrations in these two lakes were quite similar. In addition, except S-SO₄\u0026sup2;-, the nutrient concentrations were very low in Hańcza and Długie Wigierskie. In addition, compared to other studied lakes, they had higher temperatures (23.2\u0026ndash;27\u0026deg;C) and pH (8.05\u0026ndash;8.54). Hańcza and Długie Wigierskie were also clustered and they are both narrow and deep lakes with lower trophic status. Lakes Probarskie and Zjadły were not included in RDA and ED, because of a lack of measured environmental parameters. These lakes that are located in Mazurian Lakeland had comparably high species richness and Zjadły was notable in the sense of having the second-highest Dinophyceae share (33.7%) in total biomass. Based on ED, Lake Inulec was closely clustered with Żabinki as they have similar nutrient content and trophic characteristics. According to RDA, Inulec had a slight positive association with both DO and TP. ED showed that Lake Brzozolasek clustered with Inulec and Żabinki. This result is interesting as both lakes mentioned had higher nutrient content than Brzozolasek. In Brzozolasek, the biomass of Chlorophyceae was very low unlike in most of the lakes.\u003c/p\u003e \u003cp\u003eIn Lake Żabinki, Chlorophyceae formed only 4% of the whole phytoplankton community structure, which was the lowest percentage in the entire study, and just as Brzozolasek, RDA revealed this lake did not exhibit any strong relationship with any abiotic influences. Lake Przerośl also did not have any strong relationship based on RDA, but a very slight positive relationship with conductivity existed. This lake had the lowest ED value which means it has the highest similarity with another lake (Hołny). They were also clustered with Lakes Dowcień and Pobondzie which are the lakes in Suwałki Lakeland with similar environmental variables.\u003c/p\u003e \u003cp\u003ePobondzie was one of the most interesting lakes in terms of invasive cyanobacterial species. All three alien species that were aimed at were found here, which are \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e, and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e. However, all of their biomass\u0026rsquo; was very low and almost unimpactful. RDA showed this lake also has a slight positive correlation with conductivity. Długie Wigierskie was interesting in terms of Dinophyceae forming more than half of the total biomass and it has a strong negative association with conductivity based on RDA. Based on RDA, Wigry with Majcz Wielki, Zelwa, and Mamry were located together in the quarter along with TR and opposite to TP, TN as four lakes were found to have very similar pH, temperature, and dissolved oxygen values. According to the results of RDA, while Dowcień had a strong positive relationship with conductivity Lake Hołny had a strong positive correlation with DO and it had the closest similarity to Przerośl on ED.\u003c/p\u003e \u003cp\u003eNumerous phytoplankton species can be suggested as eutrophic lake indicators while few of them appear to indicate oligotrophic waters (Rawson 1956). J\u0026auml;rnefelt (1952), in a comprehensive study, listed many plankters for eutrophic lakes while there were only 6 which were limited to oligotrophic waters. As suggested also by Rodhe (1948), \u003cem\u003eDinobryon divergens\u003c/em\u003e is one of these acknowledged and well-known oligotrophy indicators. In our study, this species could not be reported only from 5 lakes (Piłag, Mikołajskie, Brzozolasek, Hańcza, and Zelwa) out of twenty-five, and within these lakes, only Hańcza can be considered as oligotrophic. However, in Lake Leszczewek (mesotrophic) this species was found to have the highest biomass (0.740 mg/L) which does not correlate with the claim. It also needs to be noted that in this lake the contribution of the Chrysophyceae to total phytoplankton biomass was the most (34.7%) in the entire study. Rawson (1956) also suggested that the globally widespread species might develop ecotypes so we might have difficulty identifying them correctly. It has been also claimed that \u003cem\u003eTabellaria flocculosa\u003c/em\u003e is indicator species for oligotrophic status, \u003cem\u003eCeratium hirundinella\u003c/em\u003e, \u003cem\u003ePediastrum duplex\u003c/em\u003e, and \u003cem\u003ePseudopediastrum boryanum\u003c/em\u003e (formerly known as \u003cem\u003ePediastrum boryanum\u003c/em\u003e) for mesotrophic while \u003cem\u003eMicrocystis aeruginosa\u003c/em\u003e and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003eflos-aquae\u003c/em\u003e for eutrophic (Rawson 1956). In our study, even though these species were encountered in various water bodies, \u003cem\u003eT\u003c/em\u003e. \u003cem\u003eflocculosa\u003c/em\u003e was in Lake Mamry (0.23 mg/L) (mesotrophic). In addition, both \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ehirundinella\u003c/em\u003e (3.10 mg/L) and \u003cem\u003eP\u003c/em\u003e. \u003cem\u003eboryanum\u003c/em\u003e reached the highest biomass in Lake Mikołajskie (4.45 mg/L) while \u003cem\u003eP\u003c/em\u003e. \u003cem\u003eduplex\u003c/em\u003e in Niegocin (4.70 mg/L). Both of these lakes can be considered as eutrophic. Lastly, \u003cem\u003eM\u003c/em\u003e. \u003cem\u003eaeuruginosa\u003c/em\u003e was found to have the highest biomass respectively in Sztynorckie (4.05 mg/L) and Suskie (2.48 mg/L) which were both hypereutrophic lakes, while \u003cem\u003eM\u003c/em\u003e. \u003cem\u003eflos-aquae\u003c/em\u003e in Przerośl (0.49 mg/L) (eutrophic).\u003c/p\u003e \u003cp\u003eGeneral literature knowledge suggests genus \u003cem\u003eCyclotella\u003c/em\u003e is a common indicator for oligotrophic water bodies (Scheffler and Padis\u0026aacute;k 1997; Saros and Anderson 2015; Ossyssek et al. 2020). According to Stoermer (1978), abundant occurrence of this genus does not strongly indicate an oligotrophic, low to moderate productivity environment. In their study, this genus was found in the most excessively disturbed and polluted regions, as with the oligotrophic ones. In our study, from this genus, only \u003cem\u003eStephanocyclus meneghinianus\u003c/em\u003e (formerly known as \u003cem\u003eCyclotella meneghiniana\u003c/em\u003e) was identified from eight lakes. The trophic statuses of these lakes varied from eutrophic to oligotrophic. However, \u003cem\u003eStephanocyclus meneghinianus\u003c/em\u003e reached the maximum abundance (0.08 mg/L) in Lake Suskie which is a hypereutrophic lake in ML. \u003cem\u003eAphanizomenon flos-aquae\u003c/em\u003e was claimed as a Cyanobacteria indicating mesotrophic and eutrophic water by Kom\u0026aacute;rek and Anagnostidis (1989). In our study, this species was identified from 6 lakes (Inulec, Mikołajskie, Sztynorckie, Żabinki, Pobondize, and Dowcień) which can be classified in this spectrum.\u003c/p\u003e \u003cp\u003eThe larger phytoplankton less subject to grazing losses (Burns 1968) such as \u003cem\u003eCeratium hirundinella\u003c/em\u003e are usually a summer bloom species in eutrophic lakes. Even though cyanobacterial species receive the most attention in these productive lakes, the high increase of large Dinophyceae domination is assuredly important (Reynolds 1973; Reynolds 1973; Pollinger and Berman 1975). In the presented study, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ehirundinella\u003c/em\u003e was encountered in twenty lakes. However, the biomass of this species was the highest (3.05 mg/L) in Lake Mikołajskie which is an eutrophic water body. On the other hand, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ehirundinella\u003c/em\u003e was also claimed to be the determinant phytoplankter for mesotrophic and oligotrophic waters (Rawson 1956; Reynolds et al. 2002). Another Dinophyceae representative, \u003cem\u003ePeridinium cinctum\u003c/em\u003e was also claimed to be common for mesotrophic lake species (Reynolds et al. 2002). During our study, this species was not reported but \u003cem\u003ePeridinium bipes\u003c/em\u003e, \u003cem\u003ePeridinium willei\u003c/em\u003e, and \u003cem\u003ePeridinium\u003c/em\u003e sp. were identified in 4 lakes (Probarskie, Żabinki, Długie Wigierskie, and Dowcień). However, this genus had the highest biomass in Lake Żabinki which is a highly eutrophic lake.\u003c/p\u003e \u003cp\u003ePalmer (1969) stated that \u003cem\u003eCoelastrum\u003c/em\u003e and \u003cem\u003ePediastrum\u003c/em\u003e can be indications of eutrophic waters as they have strong resistance to organic pollution. Even though all of these genera were encountered in nearly every lake in our study, two species from \u003cem\u003eCoelastrum\u003c/em\u003e (\u003cem\u003eCoelastrum astroideum\u003c/em\u003e and \u003cem\u003eC\u003c/em\u003e. \u003cem\u003emicrosporum\u003c/em\u003e) reached their maximum biomass (1.64 mg/L) in Lake Suskie which is the most eutrophic lake in the entire study. \u003cem\u003eMonoactinus simplex\u003c/em\u003e (formerly known as \u003cem\u003ePediastrum simplex\u003c/em\u003e) was also found to have the highest biomass (18.75 mg/L) in the same lake (Palmer 1969). Lastly, \u003cem\u003eDesmodesmus communis\u003c/em\u003e (formerly known as \u003cem\u003eScenedesmus communis\u003c/em\u003e) and \u003cem\u003eTetradesmus obliquus\u003c/em\u003e (formerly known as \u003cem\u003eScenedesmus obliquus\u003c/em\u003e) from \u003cem\u003eScenedesmus\u003c/em\u003e had the highest biomass (1.35) in Lake Sztynorckie which was also a hypereutrophic. \u003cem\u003eChlamydomonas\u003c/em\u003e is also a genus claimed to be an eutrophic water indicator (Peerapornpisal et al. 1999). In our study, even though this genus was not very commonly found, 3 species (\u003cem\u003eChlamydomonas ehrenbergii\u003c/em\u003e, \u003cem\u003eChlamydomonas reinhardtii\u003c/em\u003e, and \u003cem\u003eChlamydomonas\u003c/em\u003e sp.) were identified from 2 lakes: Śniardwy (eutrophic) and Żabinki (eutrophic). Therefore, Chlorophyceae representatives showed a correct correlation with trophic status in this study.\u003c/p\u003e \u003cp\u003e \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e is one of the most interesting cyanobacterial species as it has expanded its geographical range from tropical and subtropical regions to temperate regions during the last decades (Antunes et al. 2015). Based on the comprehensive study of the occurrence of \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e in Poland (101) and Lithuania (16) in 117 lakes, Kokociński et al. (2017) revealed its presence in 25 lakes. However, even though they investigated the lakes in Northeastern Poland, 24 of the lakes in which they reported \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e were located in Western Poland while one was in Lithuania. This supports the previous findings (Kokociński and Soininen 2012) that claim \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e occurs mostly in lakes of Western Poland where they revealed the occurrence of this species in 20 lakes. In that study lakes Piłąg and Rekąty have not been investigated. In the present study, twenty-four lakes in Northeastern Poland and one in the Warsaw area were explored, and \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e was detected in five of them which are Szczęśliwickie (Warsaw, Central Poland), Mikołajskie, Sztynorckie, Rekąty (Mazurian Lakeland \u0026ndash; ML), and Pobondzie (Suwałki Lakeland - SL). In addition, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e were also found in three lakes Żabinki, Rekąty (ML), and Pobondzie (SL) while \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e only in Pobondzie.\u003c/p\u003e \u003cp\u003eThe biomass of the \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e was calculated as 0.03 mg/L in Szczęśliwickie, 0.04 mg/L in Mikołajskie, 0.26 mg/L in Sztynorckie, 0.05 mg/L in Rekąty, and 0.01 mg/L in Pobondzie which are strongly low amounts except Lake Sztynorckie. Kokociński and Soininen (2012) reported the contribution of this species varied between 0.07% (Jelonek) and 13.89% (Żabiniec) in Western Poland lakes. In addition, they found out that the \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e was not occurring in deep lakes, while it was in lakes with high TN and conductivity and large surface area. In our study, in lakes where \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e was found, Secchi depth varied between 75 (Szczęśliwickie) \u0026ndash; 130 cm (Pobondzie). Additionally, both of these lakes can be considered small-sized lakes with low mean depth.\u003c/p\u003e \u003cp\u003eIn a recent study (Napi\u0026oacute;rkowska-Krzebietke et al. 2023), \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e was reported from Sztynorckie in August 2021 and it accounted for 8.0% of the total phytoplankton community biomass. In our study, this species was encountered in the same lake and obtained there the highest biomass among the lakes where it occurred as well as the highest percentage in total phytoplankton biomass (1.1%). This suggests that Lake Sztynorckie is a lake in which the invasion of \u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e is best established, although the contribution of this species is still largely varying.\u003c/p\u003e \u003cp\u003eAdditionally, \u003cem\u003eChrysosporum bergii\u003c/em\u003e and \u003cem\u003eSphaerospermopsis aphanizomenoides\u003c/em\u003e were other tracked invasive cyanobacterial species in our study. \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e was encountered in three lakes which are Żabinki, Rekąty, and Pobondzie while \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e was found only in Pobondzie. Total biomass of both invasive species was low: 0.088 mg/L (\u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e) and 0.023 mg/L (\u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e). \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e reached its maximum biomass in Lake Żabinki which was 0.048 mg/L. Another well-known invasive species we aimed at was \u003cem\u003eRaphidiopsis mediterranea\u003c/em\u003e, found only in two lakes which are Mikołajskie and Śniardwy with low total biomass as well.\u003c/p\u003e \u003cp\u003eIn a study, \u003cem\u003eC\u003c/em\u003e. \u003cem\u003ebergii\u003c/em\u003e was reported in seven out of 19 investigated lakes in Poland, but their biomass varied between 0.03 and 0.55 mg/L (Kokociński and Soininen 2019). According to a former study in Western Poland (Kokociński et al. 2013), they did not observe this species at all or only in single localities with low biomass.\u003c/p\u003e \u003cp\u003eTo conclude, even though cyanobacterial invasion is faster in Western Poland, the findings do not support the term invasive for these species (\u003cem\u003eR\u003c/em\u003e. \u003cem\u003eraciborskii\u003c/em\u003e, \u003cem\u003eR\u003c/em\u003e. \u003cem\u003emediterranea\u003c/em\u003e, \u003cem\u003eC\u003c/em\u003e. bergi, and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eaphanizomenoides\u003c/em\u003e) in these lakes while we can name them as alien species which are at the beginning of their invasion progress. In this situation, monitoring the existence and the biomass of the mentioned species is crucial.\u003c/p\u003e \u003cp\u003eMoreover, in a study concerning alien algae in European waters, Wilk-Woźniak and Najberek (2013), identified 14 alien and three cryptogenic species. Within Cyanophyceae, \u003cem\u003eAnabaenopsis cunningtonii\u003c/em\u003e, \u003cem\u003eAnabaena minderi\u003c/em\u003e, \u003cem\u003eCuspidothrix issatschenkoi\u003c/em\u003e, \u003cem\u003eRaphidiopsis mediterranea\u003c/em\u003e; from Chlorophyceae, \u003cem\u003eCoelastrum polychordum\u003c/em\u003e and \u003cem\u003ePediastrum simplex\u003c/em\u003e; from Bacillariophyceae, \u003cem\u003eConticribra guillardii\u003c/em\u003e, \u003cem\u003eCyclostephanos delicatus\u003c/em\u003e, \u003cem\u003eDiscostella woltereckii\u003c/em\u003e, \u003cem\u003eGyrosigma fasciola\u003c/em\u003e, \u003cem\u003eSkeletonema potamos\u003c/em\u003e, \u003cem\u003eThalassiosira duostra\u003c/em\u003e; from Dinophyceae \u003cem\u003ePeridiniopsis kevei\u003c/em\u003e and \u003cem\u003ePeridinium gatunense\u003c/em\u003e were described as invasive species for European freshwater bodies. In the present study, \u003cem\u003eA\u003c/em\u003e. \u003cem\u003ecunningtonii\u003c/em\u003e (Rekąty), \u003cem\u003eR\u003c/em\u003e. \u003cem\u003emediterranea\u003c/em\u003e (Mikołajskie and Śniardwy), and \u003cem\u003eMonoactinus simplex\u003c/em\u003e (formerly known as \u003cem\u003eP\u003c/em\u003e. \u003cem\u003esimplex\u003c/em\u003e) (Suskie, Piłag, Szczęśliwickie, Inulec, Mikołajskie, Niegocin, Śniardwy, Rekąty, and Wigry) were found while no alien Bacillarophyceae and Dinophyceae species were identified.\u003c/p\u003e \u003cp\u003eIn Suskie (56.2 mg/L) and Sztynorckie (23.8), the total biomass was found to be the highest, respectively. Suskie was dominated in terms of filament numbers by \u003cem\u003eAnagnostidinema amphibium\u003c/em\u003e and \u003cem\u003eAphanizomenon gracile\u003c/em\u003e but as these filamentous cyanobacterial species have low cell biomass, the biggest contributor to the total biomass was identified as \u003cem\u003eMonoactinus simplex\u003c/em\u003e (18.8 mg/L). In addition, in Lake Sztynorckie, two Cyanobacteria contributed the most: \u003cem\u003eMicrocystis aeruginosa\u003c/em\u003e (4.0 mg/L) and \u003cem\u003eA\u003c/em\u003e. \u003cem\u003eamphibium\u003c/em\u003e (3.9 mg/L). The lowest total biomass (0.8 mg/L) was found in Brzozolasek and the largest part came from the \u003cem\u003eCeratium cornutum\u003c/em\u003e (0.2 mg/L). Considering the phytoplankton classes, Cyanophyceae (71.0 mg/L, 42.3%) and Chlorophyceae (63.4 mg/L, 37.8%) had the highest share. For Cyanophyceae, this amount came from Suskie (23.1 mg/L), Sztynorckie (16.9 mg/L), and Szczęśliwickie (4.7 mg/L) while for Chlorophyceae it was Suskie (25.8 mg/L), Niegocin (5.5 mg/L), and Szczęśliwickie (5.3 mg/L). Chrysopyceae only formed 1.4% (2.3 mg/L) of the total biomass and the biggest contributor were Leszczewek (0.7 mg/L) and Szczęśliwickie (0.3 mg/L).\u003c/p\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eThis research aimed to describe the phytoplankton community structure and reveal the occurrence of possible invasive cyanobacterial species in twenty-four lakes located in Mazurian and Suwałki Lakeland, Northeastern Poland, and one in Central Poland. Total phytoplankton biomass was found to be the highest in Suskie while considering the phytoplankton classes Cyanophyceae was the biggest contributor. 170 of them being Cyanophyceae representatives, 325 phytoplankton species were identified. The presence of \u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e was found in five lakes, \u003cem\u003eChrysosporum bergii\u003c/em\u003e in three lakes, and \u003cem\u003eSphaerospermopsis aphanizomenoides\u003c/em\u003e in just one lake. However, the low biomass of these species in all the lakes raises the question of whether they are truly invasive or simply new to the region. On the other hand, it is concerning that these cyanobacterial species, which are already established in Western Poland, are now starting to appear in Eastern Poland as well even though they do not have high biomass. This shift could be a result of a decrease in ice cover duration and an increase in water temperature caused by climate change. \u003cem\u003eAphanizomenon gracile\u003c/em\u003e was found to be the most frequent species since it has been found in twenty-four lakes while \u003cem\u003eMonoactinus simplex\u003c/em\u003e had the largest biomass as a single species. As a result, we think that it is crucial to continue the studies on invasive cyanobacterial species in Mazurian and Suwałki Lakelands as they can produce toxic compounds that can risk human health and influence native phytoplankton assemblages.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThis work was supported by the 2nd edition of Microgrants, the Comprehensive support program for the University of Warsaw's doctoral students.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eT.O.A. : Data collection, writing and editing of the manuscript, statistical analysis.R.M.C.T. : Data collection, English check of the manuscript.A.R. : Statistical analysis, data curation, critical revision of the manuscript.I.J. : Data collection, supervision, project administration, critical revision of manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe completion of my research study would not have been possible without the support and guidance of Prof. Dr. Iwona Jasser. I want to extend my sincere gratitude to Robin Michael Crucitti-Thoo and Agnieszka Rudak for their support and collaboration. In addition, we all appreciate the help and assistance of the local people of Mazurian and Suwałki Lakelands.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAntunes JT, Le\u0026atilde;o PN, Vasconcelos VM (2015) \u003cem\u003eCylindrospermopsis raciborskii\u003c/em\u003e: Review of the distribution, phylogeography, and ecophysiology of a global invasive species. Frontiers in Microbiology 6(2015): 473.\u003c/li\u003e\n \u003cli\u003eArrigo K (2005) Marine microorganisms and global nutrientcycles. Nature 437(7057): 349\u0026ndash;355.\u003c/li\u003e\n \u003cli\u003eAustin J, Colman S (2008) A century of temperature variability in Lake Superior. 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Water Research 268: 122725. \u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1.\u0026nbsp;\u003c/strong\u003eStructural information about the investigated lakes.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"605\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLakes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLatitude\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLongitude\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMean depth (m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMaximum depth (m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eArea (ha\u003csup\u003e2\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eSuskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;42\u0026apos;48.38\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e19\u0026deg;20\u0026apos;36.85\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e55.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003ePiłag\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;52\u0026apos;47.63\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e19\u0026deg;59\u0026apos;20.17\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eSzczęśliwickie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;52\u0026deg;12\u0026apos;10.25\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e20\u0026deg;57\u0026apos;30.51\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e9.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eProbarskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;49\u0026apos;43.11\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;22\u0026apos;58.02\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e163.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eZjadły\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;48\u0026apos;40.84\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;23\u0026apos;14.94\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e82.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eMajcz Wielki\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;46\u0026apos;51.31\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;27\u0026apos;29.57\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e6.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e16.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e162.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eInulec\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;48\u0026apos;24.22\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;28\u0026apos;33.56\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e178.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eGłebokie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;49\u0026apos;0.41\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;30\u0026apos;22.27\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e25.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eMikołajskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;46\u0026apos;39.41\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;35\u0026apos;57.53\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e11.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e25.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e500.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eSztynorckie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 7\u0026apos;49.76\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;40\u0026apos;38.54\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e47.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eMamry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg;10\u0026apos;27.07\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;42\u0026apos;59.97\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e9.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e43.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e2504.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eBrzozolasek\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;36\u0026apos;59.19\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;44\u0026apos;38.78\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e155.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eNiegocin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp;53\u0026deg;59\u0026apos;14.17\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;45\u0026apos;42.00\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e9.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e39.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e2600.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eŚniardwy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;46\u0026apos;57.56\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;46\u0026apos;39.02\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e23.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e11340.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eŻabinki\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 8\u0026apos;3.29\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e21\u0026deg;58\u0026apos;49.26\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e890.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eRekąty\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;53\u0026deg;55\u0026apos;4.08\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e22\u0026deg;11\u0026apos;3.34\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e53.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003ePrzerośl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg;17\u0026apos;1.32\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e22\u0026deg;35\u0026apos;52.64\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e9.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e28.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e62.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eHańcza\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg;16\u0026apos;21.74\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e22\u0026deg;49\u0026apos;22.35\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e38.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e108.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e305.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003ePobondzie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg;18\u0026apos;45.37\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e22\u0026deg;57\u0026apos;6.68\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e3.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e27.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e53.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eDługie Wigierskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 1\u0026apos;33.26\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e23\u0026deg; 1\u0026apos;41.91\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e14.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e77.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eLeszczewek\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 4\u0026apos;22.10\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e23\u0026deg; 3\u0026apos;53.44\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e3.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e21.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eWigry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 2\u0026apos;57.67\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e23\u0026deg; 6\u0026apos;15.73\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e15.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e73.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e217\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eDowcień\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 4\u0026apos;51.12\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e23\u0026deg; 7\u0026apos;36.89\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e59.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eZelwa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 1\u0026apos;28.46\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e23\u0026deg;25\u0026apos;15.89\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e12.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e81.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 110px;\"\u003e\n \u003cp\u003eHołny\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u0026nbsp;54\u0026deg; 8\u0026apos;39.66\u0026quot;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 85px;\"\u003e\n \u003cp\u003e23\u0026deg;27\u0026apos;43.15\u0026quot;E\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e15.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 66px;\"\u003e\n \u003cp\u003e158.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u0026nbsp;\u003c/strong\u003eSpecies richness, diversity, and evenness of the lakes.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"529\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLakes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSpecies richness\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 161px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eShannon diversity index\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePielou\u0026rsquo;s evenness\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eSuskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003ePiłag\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eSzczęśliwickie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eProbarskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.77\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eZjadły\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e1.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMajcz Wielki\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eInulec\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eGłebokie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e1.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMikołajskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e1.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eSztynorckie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMamry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eBrzozolasek\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e1.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eNiegocin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eŚniardwy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e1.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eŻabinki\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eRekąty\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e66\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2.84\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003ePrzerośl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eHańcza\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003ePobondzie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eDługie Wigierskie\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eLeszczewek\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.92\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eWigry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eDowcień\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eZelwa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eHołny\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e2.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Biodiversity, environmental parameters, invasive Cyanobacteria, phytoplankton structure, Raphidiopsis raciborskii","lastPublishedDoi":"10.21203/rs.3.rs-5679541/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5679541/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study conducted in Mazurian and Suwałki Lakelands (Poland), investigated the composition and distribution of phytoplankton species, currently existing invasive Cyanobacteria, and their linkages with various environmental parameters. Water and phytoplankton samples were collected from twenty-five lakes in the summer of 2023 to achieve the aims. In the study, crucial ecological influences such as pH, conductivity, dissolved oxygen, nutrient concentrations, and water temperature values were measured and their associations with phytoplankton community structure were described. In addition, the Shannon diversity index, Pielou\u0026rsquo;s evenness, Euclidean distance analysis, frequency analysis, and redundancy analysis have been applied to interpret the obtained data. In total 325 phytoplankton species were recorded, with the most abundant class being Cyanophyceae represented by 170 taxa. Although they had relatively low biomass, all of the investigated invasive cyanobacterial species (\u003cem\u003eRaphidiopsis raciborskii\u003c/em\u003e, \u003cem\u003eChrysosporum bergii\u003c/em\u003e, and \u003cem\u003eSphaerospermopsis aphanizomenoides\u003c/em\u003e) have been identified in several water bodies. The Shannon diversity index showed that the highest diversity was found in one of the most eutrophic lake (Rekąty). Euclidean distance analysis described the highest similarity between two lakes with similar trophic status in Suwałki Lakeland (Przerośl and Hołny). RDA analysis revealed the positive correlations between Chlorophyceae and pH; Cyanophyceae and dissolved oxygen concentration.\u003c/p\u003e","manuscriptTitle":"Associations of invasive cyanobacterial species and phytoplankton community structure with abiotic influences in post-glacial temperate lakes under climate change","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-23 14:36:36","doi":"10.21203/rs.3.rs-5679541/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"422e22f0-1eb9-4c70-b3d8-2dc654142606","owner":[],"postedDate":"December 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-01-10T09:38:23+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-23 14:36:36","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5679541","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5679541","identity":"rs-5679541","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}