Multiple stressor effects on the phyto- and zooplankton communities in a mining lake affected by acid mine drainage

Multiple stressor effects on the phyto- and zooplankton communities in a mining lake affected by acid mine drainage | 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 Multiple stressor effects on the phyto- and zooplankton communities in a mining lake affected by acid mine drainage Elwira Sienkiewicz, Michał Gąsiorowski, Ilona Sekudewicz, Šárka Matoušková, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6512111/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 16 Oct, 2025 Read the published version in Journal of Paleolimnology → Version 1 posted 9 You are reading this latest preprint version Abstract Before 1925, an artificial lake (TR-17) was created in a pit excavation in the area of Łuk Mużakowa (southwestern Poland). In the 19th century, this area was an active lignite mine, which means that its location was within the range of acid mine drainage. Between 1928 and 1943, the lake was transformed into a municipal bathing area with developed infrastructure. In the 1970s, a pig farm and meat processing plant were in operation. Sewage resulting from breeding and meat production was released directly into the surrounding fields. Together with surface and ground water, nutrients and toxic metals were delivered to the lake, impacting the phyto- and zooplankton communities. After the closure of the meat processing plant, the lake began to recover from both eutrophication and heavy metal pollution. During that time, other factors, such as liming and fish stocking, affected the development of phyto- and zooplankton. pit lake diatoms Cladocera pig farm eutrophication pollution Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Postmining areas are among the regions most severely affected by human activity. Changes in the morphology of the terrain, disruption of the groundwater regime, heavy metal pollution or oxidation of sulfide minerals causing acidification of waters are some of the processes that occur there (Friese et al. 1998 ; Geller et al. 1998 ; Sánchez España et al. 2008 ; Cánovas et al. 2016 ). A frequent element of the landscape of postmining areas is water reservoirs that occupy inactive pits or sinkholes after underground mining (Brugam and Lusk 1986 ; Friese 2004 ; Hamilton et al. 2015 , Sienkiewicz et al. 2023 ). These lakes are often characterized by elongated shapes, steep banks, undeveloped littoral zones, and a lack of surface inflow and outflow. In regions where sulfide- or pyrite-containing deposits (e.g., coal or lignite deposits) are present and oxidize upon contact with meteoric waters, these lakes are often characterized by acidic waters (e.g., Blodau 2006 ; Tomiyama et al. 2019 ; Acharya and Kharel 2020 ). One of the largest postmining areas in Central Europe is Łuk Mużakowa (Koźma and Migoń 2024 ). This large-scale terminal moraine consists of glacial clays and sands with layers of lignite coal embedded within it. Lignite mining has taken place here since the 19th century (Koźma 2017 ), with the most intensive extraction occurring during the interwar period. Łuk Mużakowa is divided by the valley of the Lusatian Neisse River into a western part belonging to Germany and an eastern part lying within Polish borders. In the eastern part alone, there are more than 100 postmining lakes. Some of them occupy former pottery clay pits and have been characterized by water with a pH close to neutral from the beginning (Sienkiewicz and Gąsiorowski 2018 ). Others, which formed pits and sinkholes after lignite mining, have been acidic since their formation. Some of these lakes are undergoing a neutralization process, and in the oldest reservoirs, the water now has a pH of 6.5–7 (Sienkiewicz and Gąsiorowski 2016 ; 2019 ; Pukacz et al. 2018 ). Postmining reservoirs are often repurposed in various ways. Some are used for recreational activities such as fishponds or swimming areas, whereas others serve as recipients of wastewater and solid waste. Some bacteria undergo natural processes of neutralization, eutrophication, and overgrowth (Pukacz et al. 2018 ). The organisms inhabiting these reservoirs face a variety of stressors, not only those resulting from acid mine drainage (AMD). In addition to low pH and elevated concentrations of heavy metals in the water, other significant factors include intensive nutrient inputs, frequent and substantial fluctuations in water levels, changes in catchment land use, and artificial stocking. One lake with an exceptionally rich history of human influence on its ecosystem is reservoir TR-17 (Solski et al. 1988 ; Sienkiewicz and Gąsiorowski 2016 ; 2017 ). The lake existed prior to 1925 (Fig. 1 ) and, despite acidic water, initially served as a municipal bathing area. Over time, it became affected by pollution from a nearby pig farm. Food industry facilities are typically sources of wastewater with high pollutant loads, containing various substances of different types and sizes. These include dissolved substances, colloidal particles, and suspensions composed of both organic compounds (mainly proteins and fats) and inorganic compounds such as chlorides, nitrates, phosphates, sulfates, and carbonates (Konieczny and Szymański 2007 ). In recent years, it has served as an angling fishery and is subjected to annual liming of water and artificial stocking. The goal of this study was to track the influence of pig farming and meat processing plant activities, along with the effects of lignite mining, on lake ecosystem located in AMD-affected area over the last fifty years. We hypothesized that pig farming and meat processing are associated with the emission of sewage sludge, causing additional pollution by heavy metals such as Cu, Ni, and Zn (Moral et al. 2008 ; Jensen et al. 2016 ). The study of these alterations was based on qualitative and quantitative analyses of subfossil phyto- and zooplankton and sediment geochemistry. Some diatom and cladoceran species can adapt to extensive heavy metal contamination (Pociecha et al. 2020 ) and other anthropogenic changes, such as industrial pollution, whereas others disappear with increasing pollution. Study site Lake TR-17 is located near Trzebiel (Fig. 2 ) in the central area of the Polish part of the Łuk Mużakowa region (SW Poland). Łuk Mużakowa is a unique glacitectonic structure located on the border of Poland and Germany. It is one of the largest moraines in Europe and the only such phenomenon that can be seen with the naked eye from space. It is a deeply eroded frontal formation with disturbed Miocene, Pliocene, and early Pleistocene sediments (Koźma 2011 ). The moraine is 40 km long and 3–5 km wide and originated during the Last Glacial Maximum. The lakes in this region are of anthropogenic origin and are remnants of lignite, gravel, sand, and clay exploitation. The studied lake was created as a sinkhole following the collapse of the abandoned Hoffnung lignite mine (Kupetz et al. 2004 ) after exploitation ceased in the 1920s. Between 1928 and 1943, the lake was used as a municipal bathing area (Städt Badeanstalt, Freibad Birkensee) (Fig. 1 ). In the 1970s and 1980s, there was a pig farm nearby, from which sewage was discharged into the fields immediately adjacent to the lake. Today, the lake is used as a fish pond; it is bordered on the east by farmland and otherwise surrounded by forest. It is supplied by a single inflow. The basic characteristics of the lake are listed in Table 1 . Table 1 Morphometry and water parameters of the Lake TR-17. Morphometry Maximal lenght (m) 276 Maximal width (m) 100 Area (ha) 18.5 Maximal depth (m) 10.6 Catchment area (ha) 86 Physicochemical parameters 1986, Aug* 2014-09-03 2020-06-11 2022-05-15 2024-09-03 Temperature (°C) 27.0 18.8 20.6 23.0 n.a. * data from Solski et al. ( 1988 ) Materials and methods Sampling and field work A sediment core of lake TR-17 was collected in 2014 (70 cm long) using a Kajak-type gravity corer. The amount of sediment was insufficient for all the analyses; thus, in 2020, a second core was obtained (40 cm long). Both cores were correlated with each other on the basis of radiometric measurements and elemental (C, H, N, S) analyses. The sediments were divided every 1 cm in the field and packed into plastic bags. In the laboratory, the sediments were subsampled for phyto- and zooplankton identification, dating, and elemental and geochemical analyses. Lake bathymetry was measured along two transects using a portable echo sounder (Echotest II). The physicochemical parameters (pH, oxidation‒reduction potential (ORP), electrical conductivity (EC), and dissolved oxygen (DO)) of the lake water were measured in situ via a multiparameter portable meter (Multi 3620 IDS SET G) during field trips in 2014, 2020, 2022, and 2024. Measurements of the lake tributary water were performed in 2022 and 2024. Water samples were collected using a 5 L vertical sampler during field trips in September 2020 (every metre along the entire length of the water column) and May 2022 (only from the surface layer). Each water sample was filtered through CA membrane filters (pore size: 0.45 µm), preserved with double-distilled HCl (35%), and stored in 50 mL polyethylene bottles at 4°C until analysis. Water and sediment analyses Dissolved organic carbon (DOC) in the lake water was analysed in triplicate using the combustion catalytic infrared method and a Shimadzu TOC-V CPH at the Institute of Geology, Czech Academy of Sciences in Prague (GLI CAS). Oxalic acid dihydrate was used as the basic standard solution. Potassium hydrogen phthalate (Shimadzu) dissolved in double-distilled water was used as a secondary standard to ensure measurement stability. The relative standard deviation (RSD) of the analytical results was < 5%. The contents of major elements in the water samples were analysed in triplicate using ICP‒OES (Agilent 5100) at the GLI CAS. A multielement calibration solution prepared from single-element standards (Analytika spol. s.r.o.), was used for instrument calibration. The trace element concentrations in the water samples were determined in triplicate using HR-ICP-MS (Element 2, Thermo Scientific) at the GLI CAS. A mixed calibration solution prepared from single-element standards (CPA Chem) was used for instrument calibration. An indium solution (1 ppb) was used as an internal standard for correcting instrumental drift. The certified reference material (CRM) ERM CA 615 (EC Joint Research Centre) was measured to control the quality and repeatability of the ICP‒OES and ICP-MS analyses. The RSDs of all the analytical results were < 5%. The selected samples of lake sediments were digested with double-distilled HNO 3 (65%), HCl (32%), and HF (48%) using the MARS 6 microwave digestion system (CEM Corporation, USA) at the Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research. The CRM, marine sediment (NRC-MESS-4), was digested, and four procedural blanks were prepared to validate the procedure. Next, the samples were evaporated using the XVap accessory of the microwave. The samples were subsequently diluted with double-distilled 1.5 M HNO 3 before analysis. The elemental composition of the sediment samples was measured in triplicate using ICP‒OES (iCAP 7000 Series, Thermo Scientific, USA) at the AWI, Helmholtz Centre for Polar and Marine Research. External calibrations for quantitative analysis were prepared using single-element standards (Roti®Star, CarlRoth GmbH). The CRM was analysed every four to six samples to monitor the quality and repeatability of the results. The RSD for all the measurements was < 5%. Sediment elemental analyses Elemental parameters, such as the concentrations of total organic carbon (TOC) and total nitrogen (TN), were measured with a Vario Cube elemental analyser. Five to ten milligrams were treated with 10% HCl to remove carbonates, washed with distilled water, dried, and transferred to preweighed tin capsules. The samples, excluding those used for biological analyses, were dried, ground and homogenized. The samples were combusted at a temperature of 1150°C, and the obtained gases were separated on a chromatographic column and measured with a thermal conductivity detector. The measurement uncertainties for the TOC and TN were 0.6 and 0.18%, respectively. Dating of lake sediments The radiochemical separation of 210 Po from lake sediments was conducted following a modified procedure outlined by Flynn ( 1968 ). Approximately 0.6 g of each selected sample was spiked with 208+209 Po and digested on a hot plate using HCl (35%) and HNO 3 (65%). The organic components were removed with HNO 3 (65%) and H 2 O 2 (32%) (Jia et al. 2004; Matthews et al. 2007 ). Polonium isotopes were then spontaneously deposited onto silver discs in 0.5 M HCl (Martin and Blanchard 1969 ). To prevent the deposition of competing ions, such as Fe 3+ , sodium citrate and hydroxylamine hydrochloride were added prior to deposition (Flynn 1968 ; Jia et al. 2004). The activity concentrations of the polonium isotopes were measured using an Octete alpha spectrometer (Ortec) at the Institute of Geological Sciences Polish Academy of Sciences (IGS PAS), with an average uncertainty of 1.8 Bq.kg − 1 (3.5%, n = 24). The chemical recovery for 208+209 Po ranged from 60 to 70%. The activity concentrations of 137 Cs in selected samples from the sediment core were determined using a low-background gamma spectrometer (Canberra Packard) with a BE5030 detector (FWHM = 1.07 keV at 661.7 keV for 137 Cs) at the IGS PAS. The CRM (IAEA-SL-2) was analysed to ensure the quality of the measurements. All the samples were analysed in a flat cylinder geometry for 48 to 72 h. The obtained data were processed using Genie 2000 software. All values were converted to the date of sampling (24 September 2020). The typical minimum detectable activity (MDA) for 137 Cs was 1.5 Bq kg − 1 , and the measurement uncertainty ranged from 17 to 37%. Diatom analysis The sediment samples for diatom analysis were prepared according to the standard method (Battarbee 1986 ). The samples (volume of 1 cm 3 ) were treated with 10% HCl to remove carbonates and heated with 30% H 2 O 2 until all the organic matter was oxidized, and then the samples were washed several times with distilled water. Permanent slides were mounted in Naphrax® (R.I.=1.75). The quantification analysis results were obtained between 1 cm (AD 2014) and 33 cm (AD 1970). Only in two samples (5 and 8 cm) was the frequency of diatoms too small to perform quantitative analysis. The remaining samples did not contain diatoms or only single valves of diatoms. Diatom identification was based on Krammer and Lange-Bertalot ( 1986 , 1988 , 1991a , b ) and Lange-Bertalot and Metzeltin ( 1996 ). The core was divided into diatom assemblage zones (DAZs) on the basis of the Constrained Incremental Sum of Squares Cluster Analysis (CONISS, Grim 1987) performed by rjojaPlot 1.03. The number of statistically significant zones was assessed using the broken-stick model (Juggins 2022 ). The diatom inferred pH (DI-pH) was reconstructed on the basis of the mining pH training set (Sienkiewicz and Gąsiorowski 2017 ). The values of past water pH were estimated using the weighted average with downweighted species with high pH tolerance and inverse deshrinking (RMSE WA_Inv =0.69). Cladocera analysis The Cladocera species composition was determined via a standard procedure (Korhola and Rautio 2001 ). The 1 cm 3 sediment samples were heated and stirred in 8% KOH on a hot plate for approximately 30 minutes and sieved through a 33-µm mesh screen. The sieved material was stored in 10 mL of distilled water. Temporary slides, each prepared from a 0.1 mL portion of a sample, were used for identification and to count the cladoceran remains. The slides were prepared for examination under a light microscope at magnifications of 100–400× until a minimum of 200 remains were encountered and identified following Szeroczyńska and Sarmaja-Korjonen ( 2007 ). Chydorus sphaericus is considered C. sphaericus sensu lato ( s.l. ) (Frey, 1986 ). Cladocera percentage abundances were calculated from the sum of individuals. The most abundant body part was chosen for each taxon to represent the number of individuals. Statistical analyses Hierarchical clustering with similarity index correlation was used to analyse the elemental composition of the sediment results after normalization using the PAST 4.03 program (Hammer et al. 2001 ). To determine the optimal number of clusters, the elbow method was used, which was performed in R ver. 4.0.4 using the ‘factoextra’ and ‘cluster’ packages (Kassambara 2020 ; Maechler et al. 2025 ). The species diversity was checked with Hill’s N2 parameter. Changes in element concentrations and diatom and Cladocera species composition were explored with multivariate analyses. Principal component analysis (PCA) was applied to the elemental dataset due to short gradients (0.2 SD). In contrast, owing to the long gradient in the datasets (gradient lengths of 3.6 and 3.0 SD), detrended correspondence analysis (DCA) with square-root transformed species data was used for diatoms and Cladocera. Community changes that were detected from the DCA axis 1 sample scores were further verified with analysis of similarities (ANOSIM, one-way) for their significant differences. The DCA was run with Canoco software CANOCO 4.5 (ter Braak and Šmilauer 2002), and ANOSIMs were run with the program PAST 4.03 (Hammer et al. 2001 ) via Bray‒Curtis distance measures, 10 000 permutations, and Bonferroni-corrected p values. Results In situ measurements and water sample analyses The results of the physicochemical parameter measurements, as well as the contents of dissolved oxygen (DO), dissolved organic carbon (DOC), and selected elements (F, S, Co, Ni, and Zn) in the water column of lake TR-17, are presented in Fig. 3 . The pH of the surface layer of the water column has varied significantly over time. The lowest value (pH = 5.19) was measured in September 2020, whereas the highest value (pH = 7.4) was recorded in 1986 by Solski et al. ( 1988 ). The DO content significantly increased over time compared with the measurements taken by Solski (1988), reaching more than 10 mg L -1 in the surface water (1 m depth of the water column) in the 2000s. The elemental content did not change significantly compared with the reported data, except for Co and Zn. The concentration of Fe in the surface water collected in 2020 was below the detection limit, whereas the concentrations of S, Co, Ni, and Zn were 68.3 mg L -1 , 0.7 µg L -1 , 3.9 µg L -1 , and 10.1 µg L -1 , respectively. The contents of other heavy metals, such as Cd, Cr, Cu, and Pb, were below the detection limits. The results revealed that the physicochemical parameters and the contents of DO, DOC, and selected elements changed significantly with depth throughout the water column. The greatest differences were observed at a depth of 5 m, where the pH, electrical conductivity (EC), and contents of DOC and Fe increased, whereas the oxidation‒reduction potential (ORP) and concentrations of DO, S, Ni, and Zn decreased. The pH levels of the surface water from the lake tributary, measured near its outlet in September 2020 and 2024, were 6.95 and 6.8, respectively. The concentrations of the tested elements in the surface water collected from the tributary in September 2020 were 22.8 mg L -1 for Fe, 57.6 mg L -1 for S, 0.5 µg L -1 for Ni, and 8 µg L -1 for Zn. The concentration of Co was below the detection limit. Sediment lithology and chronology The dry bulk densities, TOC and TN contents, and C:N ratios are presented in Fig. 4 . The dry bulk density of the lake sediments decreased over time, from 0.73 g cm − 3 at the bottom of the core to 0.08 g cm − 3 in the upper section. Sediment layers with relatively high bulk density values ​​were observed mostly at depths of 70, 66, 59, 43 − 40 and 28 cm within the core. The contents of TOC and TN increased in the core. Sediment layers enriched in TN were detected at depths of 9, 20, 28–34, and 48 cm within the sediment column. The C:N ratio varied significantly along the core, from 56 at the bottom to 13 at the top. Below a depth of 35 cm, the C:N ratio exhibited considerable fluctuations, which stabilized in the upper section of the core. Elevated C:N ratios were observed at depths of 65, 58, 51 − 49, 44 − 41 and 6 − 4 cm within the sediment profile. The vertical distributions of the 210 Pb and 137 Cs activity concentrations are presented in Fig. 4 . 137 Cs was irregularly distributed throughout the sediment column, with visible peaks in activity concentrations at depths of 23, 28, and 35–36 cm. Assuming that the sediment layer enriched in 137 Cs at a depth of 23 cm in the core corresponds to Chernobyl fallout, the sedimentation rate in this part of the lake was calculated to be 0.7 cm y − 1 . The observed peaks in the 137 Cs content below a depth of 23 cm may be related to nuclear tests conducted in the 1960s. Elemental composition The downcore profiles of the concentrations of selected elements in the core are shown in Fig. 5 . The contents of most studied elements varied significantly with core depth. A decrease in S content was observed upwards along the sediment profile, particularly above a depth of 26 cm in the core. A similar trend was noted for P, Co, Cu, Ni, and Zn, with their concentrations decreasing notably above a depth of 20 cm in the core. The smallest variability in the vertical distribution of content along the sediment profile was shown by Fe and Pb (coefficient of variation < 0.11). On the basis of the cluster analysis, 4 zones were identified: the individual zones included samples collected from depths of 1–16 cm in the core (Zone I), 20–26 cm (Zone II), 28–36 cm (Zone III), and greater than 38 cm (Zone IV). The samples in the upper part of the core (collected from depths of 1–4 cm) are characterized by elevated contents of Al, K, Ti, and Cr and slightly elevated contents of Co, Cu, Ni, and Zn. Significant increases in the concentrations of Al, Mn, P, Co, Ni, and Zn were observed at depths between 7 and 12 cm (with a maximum at 10 cm) in the sediment column. Significantly elevated concentrations of S, P, Co, Cu, Ni, and Zn are also evident at depths of 16–24 cm (with a maximum at 20 cm), 28 cm, and 32–36 cm in the core. Below a depth of 38 cm in the core (Zone IV), decreases in the contents of Co, Cu, Ni, Pb, Zn, S and P were observed. The mean concentrations (n = 18) of heavy metals, including Cr, Co, Cu, Ni, Pb, and Zn, were 4.8, 6.2, 19.6, 19.8, 11.2, and 121.9 mg kg − 1 , respectively. The highest contents recorded for these metals in the sediment column were 9.5 mg kg − 1 for Cr, 9.4 mg kg − 1 for Co, 53 mg kg − 1 for Cu, 33.2 mg kg − 1 for Ni, 15.2 mg kg − 1 for Pb, and 244 mg kg − 1 for Zn. An increased P content was also observed in the sediment profile, with an average of 8.3 g kg − 1 (n = 18). The first two axes of the PCA of the elemental concentration data explained 82% of the variation in the dataset (Fig. 6 ). The samples grouped along the first axis and samples from horizons 36–10 had negative score values. The samples deposited during the pig farm operation period clustered together with the vectors of N, P, Co, Cu, Zn and Ni. The youngest sediment samples had positive PC1 values related mostly to higher C:N ratios. The main factors associated with the samples scattered along the PC2 axis were the concentrations of Cr, Ti, K, and Al (positive values) and Ca, Mn and Sr (negative values). Diatom stratigraphy and Chrysophyceae cyst abundance A total of 76 diatom species belonging to 23 genera were identified. The diatom stratigraphy was divided into 3 diatom assemblage zones (DAZs 1–3) (Fig. 7 ). The ratio of chrysophycean statospores to diatoms in the sediments of TR-17 was also determined. A high ratio of diatom frustules to cysts indicates a period of nutrient enrichment (Smol 1988 ). Compared with diatoms, chrysophycean algae are more sensitive to both eutrophication and metal contamination (Chen et al. 2014 ). The number of stomatocysts in the core ranged between 0.5 and 55.5%. The highest number of stomatocysts occurred before the processing plant was in operation. This suggests that there were fewer nutrients in the lake than in the following years. In the sediment portion below a depth of 37 cm, diatoms occurred as fragmentary broken single valves that were impossible to identify at the species level. Above this layer, at a depth of 33 cm, only quantitative analysis was possible due to an insufficient number of diatom valves. The most numerous taxa were Ulnaria acus (Kütz.) Aboal and Fragilaria nanana Lange-Bertalot. Nitzschia palea (Kütz.) W. Smith, Gomphonema parvulum (Kütz.) Kützing and Lemnicola hungarica (Grun.) Round & Basson were observed in smaller numbers. DAZ 1 (33–16 cm; 1970–1992 AD) The zone is characterized by diatoms that are highly tolerant of organic pollution and acidic water, such as Eunotia exigua (Bréb. in Kütz.) Rabenhorst and Eolimna minima (Grun.) Lange-Bertalot. In the lower part of DAZ 1 around the second half of the 1960s, the highest frequency of chrysophycean cysts was observed (55.5%) in terms of the ratio of diatoms. Since the beginning of the 1970s, a rapid decrease in the number of stomatocysts has reached 0.5% at a depth of 17 cm (i.e., 1991). DAZ 2 (16–7.5 cm; 1992–2004 AD) At the beginning of the zone, the frequency of diatom dominance in the previous zone decreased. The diatoms, such as Eolimna minima and N. palea , disappeared at the end of the zone. The most frequent taxon was U. acus , which reached its maximum abundance in the core. Rapid increases in Eunotia exigua and E. nymanniana Grunow in the upper part of the zone were also noted. However, the last sample in this part of the core had an insufficient number of diatom valves for quantitative analysis. Initially, at the beginning of DAZ 2 (1992), the percentage of chrysophycean statospores increased to 15.5%. However, after a short period, diatoms dominated this zone. In the uppermost part of this period, a slight increase in chrysophycean taxa was again observed. DAZ 3a (7.5–4.5 cm; 2004–2009 AD) This subzone is characterized by the dominance of diatoms, such as Eunotia implicata Nörpel, Lange-Bertalot & Alles, Frustulia saxonica Rabenhorst and Pinnularia gibba (Ehr.) Ehrenberg, which reached the highest frequency in the core. Owing to the small number of diatom valves in the highest sample at DAZ 3a, only qualitative diatom analysis was performed. During this time, the number of stomatocysts increased above 20%. DAZ 3b (4.5–0 cm; since 2009) The lower part of the youngest sediments was dominated by diatoms occurring in more alkaline waters than those from the previous subzone. There are Discostella pseudostelligera (Hust.) Houk & Klee, Fragilaria gracili s Østrup and F. nanana Lange-Bertalot. In the upper part of the zone, a significant increase in acidophilous taxa (e.g., Eunotia spp.) and a decrease in indifferent and alkaliphilous diatoms were observed. In the youngest sediments, an increase in diatoms was observed. The frequency of Chrysophycean statospores decreased, but in the uppermost sample, it increased again to 20%. The DCA diagram of diatom species changes explained 29% of the variance in the community (Fig. 6 ). The taxa are organized along axis 1 according to their pH preferences, with lower scores for more acid-tolerant species. Reconstruction of diatom-inferred pH (DI-pH) The values of the DI-pH varied between 6.43 and 7.22 (Fig. 8 ). Until the first half of the 1990s, the curve of the water pH was relatively stable and indicated the neutral character of water. From that time to the present, the DI-pH has fluctuated to a greater or lesser extent but has generally shown a decreasing trend. The minimum value of the DI-pH (6.43) occurred in 2014. This value does not correspond to the value measured in the field, which was much lower (5.53). This discrepancy may result from large disproportions between the percentage of species dominating in the core ( Ulnaria acus (up to 80%), Lemnicola hungarica and Eolimna minima (both approximately 40%)) and those occurring in the Mining pH training set (Sienkiewicz and Gąsiorowski 2017 ) used to the reconstruction of water pH in TR-17. Both latter species occurred only in 4 and 1 lake in the Mining pH training set, respectively. This could overestimate the reconstructed values to some extent. 3.5 Cladocera stratigraphy The species diversity of Cladocera remaining in the sediments of lake TR-17 was relatively low. Only 8 taxa belonging to 3 families, Daphniidae, Bosminidae and Chydoridae, were identified. Cladocera remains were found only in the upper 21 cm of the sediment core. The Cladocera assemblage development was divided into two Cladocera assemblage zones (CAZs). Differences between zones were statistically significant (p < 0.003 in the one-way ANOSIM test). CAZ 1 (21–7 cm; 1985–2005). Only 3 Cladocera taxa were identified in this zone: Bosmina longirostris , Daphnia spp. and Chydorus sphaericus sensu lato. Only daphnia remains were present in the sample from a depth of 15 cm. The abundance of the remaining sediment was low, with 200–400 individuals per 1 cm 3 of wet sediment. CAZ 2 (7–1 cm; 2005–2014) The second zone was characterized by greater species diversity. In addition to the taxa found in CAZ 1, benthic and littoral zone-dwelling species, including Alona affinis and Alonella nana , which occur in relatively high numbers, appeared. In the youngest samples, the daphnia disappeared completely, and Bosmina longirostris developed. A detrended correspondence analysis (DCA) diagram explained 39.3% of the variation in the Cladocera assemblage (Fig. 6 ). The taxa are organized along axis1 and planktonic species are placed to the right of diagram while littoral are to the left (species scores > 0.2). Discussion Lake formation and AMD impact on the lake’s ecosystem Lake TR 17, like many other lakes in the region, originated in a depression that formed after the collapse of the corridors of an underground lignite mine (Solski et al. 1988 ). According to archival maps and historical data (Fig. 1 ), the lake existed as early as 1925 and served as a bathing area for the residents of Trzebiel. Sediment analysis indicated that at this time, the lake contained acidic water, and the low pH prevented the development of phyto- and zooplankton. The bottom section of the sediment core is characterized by relatively high bulk density and high C:N ratios (greater than 55), indicating the supply of organic matter from the lignite deposit, although lignite particles were not recognized in the macroscopic image. At a sediment depth of 65–37 cm, i.e., from 1935–1967, the C:N values were approximately 15–30, indicating that the dominant source of organic matter in the sediment was the lake catchment, with only a minor contribution from primary production. However, the influence of lignite deposits was no longer clear. This indicates the stabilization of hydrological and morphological conditions within the lake basin and the predominant influence of surface water recharge. Water chemistry prevented diatom and Cladocera development at that time. The Cladocera remains were completely absent, and diatoms were represented only by fragmented valves. Similar conditions were used in the same mining area at lake TR-33 (Sienkiewicz and Gąsiorowski 2016 ). However, TR-33 is ~ 50 years older, and the initial period of its development ended much earlier than that of lake TR-17 (i.e., the 1940s). Moreover, TR-33 was not impacted later by human activity and evolved naturally towards neutralization. Artificial input of nutrients and lake eutrophication Since the early 1970s, pig farming and meat processing operations have been established near lake TR-17 (Fig. 2 ). Manure and wastewater from the processing plant were discharged directly into the fields surrounding the lake to the east. Together with ground water and surface runoff, the sewage was transported to the lake. In the sediment profile, this process included an abrupt increase in the TN concentration, a decrease in the C:N ratio and elevated concentrations of several metals, namely, Zn, Ni, Cu, and Co (Figs. 4 , 5 , and 6 ). A similar increase in heavy metals, such as Cu, Ni, and Zn, related to the operation of pig farms has also been recorded by other researchers (Jensen et al. 2016 ; Moral et al. 2008 ). The input of nutrients into the lake caused the development of diatom flora with species that tolerate elevated concentrations of heavy metals, such as Lemnicola hungarica, Gomphonema parvulum, Eolimna minima and Nitzschia palea (Morin et al. 2012 ; Pociecha et al. 2020 ). The sewage input was also confirmed by direct measurements, e.g., high alkalinity, which was 9.2 mval L − 1 , whereas the alkalinity of other lakes in the region varied between 0.5 and 3.5 mval L − 1 (Solski et al. 1988 ). This high alkalinity was an isolated phenomenon among the lakes located in this area. Moreover, Solski et al. ( 1988 ) measured elevated concentrations of nitrates (1.94 mg L − 1 ), nitrites (0.198 mg L − 1 ), and potassium (53 mg L − 1 ) in lake water and reported that their source was sewage from meat processing plants. For comparison, the K concentration in a surface water sample (collected in 2020) was 6.7 mg L − 1 (Fig. 3 ). The input of pollution from the pig farming accelerated the changes in the lake and disturbed the processes of natural neutralization. Instead of the relatively long transitional stage of development with acidic-tolerant diatoms and Cladocera observed in the nearby lake TR-33 (Sienkiewicz and Gąsiorowski 2016 ), lake TR-17 experienced rapid neutralization of acidic water with wastewater. This change could only be survived by some diatom species, while Cladocera were completely absent until the late stage of the pollution period (i.e., 1985). Even after the closure of the pig farm, the only Cladocera that occurred in the lake were planktonic species, and in 1991, the only taxon was Daphnia spp. Recovery from eutrophication and pollution A pig farm near the lake existed until 1991. After its closure, there was a significant and rapid change in the water quality of the reservoir. The first signs of a decline in nutrients and heavy metals were observed in samples dating back to 1993. Changes in diatom flora resulted in a reduction in the frequency of pollution-tolerant taxa, and the prevalence of Ulnaria acus reached 80% in the core. This taxon is found in epilithic and epiphytic substrates in moderately alkaline, oligosaprobic, and eutrophic freshwater streams and lakes (Lange-Bertalot and Ulrich 2014 ). A clear increase in U. acus is connected to the closure of the meat processing plant and the subsequent end of sewage discharge into the lake, as Ulnaria thrives in less polluted waters. The diatoms typical for polluted waters have occurred from the beginning of meat processing plant operation, while after the factory closed, it seems that AMD (i.e., acidic environments) again had a significant impact on diatom development (Fig. 8 ). This is evidenced by the presence of acidophilous and acidobiontic diatoms, such as Eunotia denticulata (Bréb. ex Kütz.) Rabenhorst, E. nymanniana and E. exigua . The abundance of these taxa, especially E. exigua and E. nymanniana , in the following years significantly decreased as late as 2002 (the top of DAZ 2). In the first years of the recovery period (1991–2002), Cladocera were still represented only by planktonic taxa. The slow change from large to small-bodied species may have been caused by the gradual colonization of the lake by fish and selective predation on the more visible, large Cladocera. The accumulation of sediments at the beginning of the 21st century (the top of DAZ 2 and DAZ 3a) was likely connected with an episode of more acidic water delivery from AMD than that in the previous period. The highest frequency was reached by Eunotia implicata and Frustulia saxonica , which appeared twice as early as single valves in the core. In particular, E. implicata dominated this part of the core (up to 82%). The last subzone (DAZ 3b) is characterized by the dominance of Fragilaria gracilis, F. nanana , and Discostella pseudostelligera . This is a completely different kind of diatom flora than that in the previous subzone. The frequency of acidophilous taxa significantly decreased, whereas the abundance of diatoms living in meso- and eutrophic environments increased. This situation may be the result of two factors: heavy rainfall in 2010 (IMGW-PIB, 2010), which caused local flooding, and limnification of the lake. Since 2010, people have managed this lake by pouring 1 ton of lime in the autumn (personal communication) to increase the water pH. Today, this lake is used as a fish pond, and the water pH cannot be too low. These processes also caused the development of a littoral zone, which was indicated by the occurrence of littoral and plant-associated Cladocera species. In both cases, i.e., flooding and limning, changes in the diatom community were caused by the increase in water pH. The highest sediment sample (2014) is dominated by acidophilous diatoms, such as Eunotia exigua, E. nymanniana and E. bilunaris . This latter taxon is characterized by wide ecological tolerance and can live in water with increased concentrations of sulfate (Alles et al. 1991 ). The topmost sample represents a process of acidification, confirmed by direct measurement of the water pH in 2014 (Fig. 8 ). Conclusions Lake TR-17 is a postmining reservoir created at a former lignite excavation site. The C:N ratio indicates the presence of lignite lenses in the bottom sediments. Despite the presence of heavy metals and other harmful compounds associated with lignite deposits and exploitation, the lake was transformed into a municipal bathing area between 1929 and 1930, remaining in use until 1945. A pig farm and meat processing plant operated in the vicinity of the lake from the 1970s to the 1990s. Manure runoff from the farm released onto the surrounding fields, along with surface water, carried pollutants contained in the sewage into the lake, contaminating the water. Some organic and inorganic compounds contributed to an increase in the trophic level (e.g., through a rise in phosphate levels) and the concentration of heavy metals (e.g., Cu, Ni, Zn). The closure of the pig farm and the meat processing plant triggered a decrease in heavy metal concentrations. Changes in phyto- and zooplankton were also observed at this time. In the diatom community, a reduced frequency or disappearance of taxa tolerant to highly polluted waters (e.g., Lemnicola hungarica ) and the development of some diatoms inhabiting the least polluted waters (e.g., Ulnaria acus ) were observed. Cladocera fauna appeared in the lake at the end of the farming activities. Most likely, the water was too polluted earlier for cladoceran taxa to develop. The lake is located within an AMD area, and along with groundwater, it is supplied with acidic compounds. To neutralize acidic water, the lake has been limed every year since 2010. Declarations E-mail addresses [email protected] (E. Sienkiewicz), [email protected] (M. Gąsiorowski), [email protected] (I. Sekudewicz), [email protected] (I. Stimac), [email protected] (Š. Matoušková) Author Contribution Conceptualization, methodology, data curation, formal analysis, writing—original draft, supervision: E.S., M.G. Formal analysis, writing—original draft, art work: IS. Formal analysis : Š.M., I.S. Acknowledgements This work was financially supported by a grant no. 2012/07/B/ST10/04204 awarded by the Polish National Centre of Science. We thank Agata Jaskółka and Wojtek Sienkiewicz for their help during the fieldwork and the employees of the Forest Districts of Lipinki and Lubsko for permission to collect the lake sediments. We also want to thank Karolina Kaucha from the Institute of Geological Sciences, Polish Academy of Sciences, for her assistance with the laboratory work. 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Cite Share Download PDF Status: Published Journal Publication published 16 Oct, 2025 Read the published version in Journal of Paleolimnology → Version 1 posted Editorial decision: Revision requested 03 Jul, 2025 Reviews received at journal 02 Jul, 2025 Reviewers agreed at journal 09 Jun, 2025 Reviews received at journal 26 May, 2025 Reviewers agreed at journal 29 Apr, 2025 Reviewers invited by journal 29 Apr, 2025 Editor assigned by journal 25 Apr, 2025 Submission checks completed at journal 25 Apr, 2025 First submitted to journal 23 Apr, 2025 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-6512111","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":449695774,"identity":"581bed8d-cb98-4d51-818a-ebc352d12dd4","order_by":0,"name":"Elwira Sienkiewicz","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYFACxgYGhgMSDPxgDhtMtIAILZJtKFoMCNl0AKjmGLFa+PkPNz4uOGMhZ3y/x/BzRZkdgzn72QPMBXi0SM5IbDaecUPC2OwYj7HkmXPJDJY9eQnMM/BoMbjB2CbN80Eicdsx3g2SjW3MDAYHcgyYefBosT9/sP03UEv95jbezT8b2+oZDM6/wa/FgCGxjZnnhkSCARvvNqAth4H2ErBF4kZiszTPGQnDGcfyv1k2nDvOYznjjcFhfH7h7z/+8DPPsTp5/uZjyTcbyqrlzPlzDB8XVODWggHATjpMggYGSCQyk6ZlFIyCUTAKhjkAAEJ4TN83CBQjAAAAAElFTkSuQmCC","orcid":"","institution":"Polish Academy of Sciences, Research Centre at Warsaw","correspondingAuthor":true,"prefix":"","firstName":"Elwira","middleName":"","lastName":"Sienkiewicz","suffix":""},{"id":449695775,"identity":"b70312ad-cbc6-4480-b541-f6bcc3e73db5","order_by":1,"name":"Michał Gąsiorowski","email":"","orcid":"","institution":"Polish Academy of Sciences, Research Centre at Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Michał","middleName":"","lastName":"Gąsiorowski","suffix":""},{"id":449695776,"identity":"53d22c97-27ab-4468-a20c-da7ae6255214","order_by":2,"name":"Ilona Sekudewicz","email":"","orcid":"","institution":"Polish Academy of Sciences, Research Centre at Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Ilona","middleName":"","lastName":"Sekudewicz","suffix":""},{"id":449695777,"identity":"2880eb4b-b02a-44c1-ac3e-ae5f7cdc6d22","order_by":3,"name":"Šárka Matoušková","email":"","orcid":"","institution":"Czech Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Šárka","middleName":"","lastName":"Matoušková","suffix":""},{"id":449695778,"identity":"95d5ac0c-481c-4225-a092-062d1da7688c","order_by":4,"name":"Ingrid Stimac","email":"","orcid":"","institution":"Alfred Wegener Institute","correspondingAuthor":false,"prefix":"","firstName":"Ingrid","middleName":"","lastName":"Stimac","suffix":""}],"badges":[],"createdAt":"2025-04-23 11:23:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6512111/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6512111/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10933-025-00380-0","type":"published","date":"2025-10-16T15:56:59+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81947888,"identity":"2cfe84ec-05fd-4dde-ac53-1d7b6d7a9426","added_by":"auto","created_at":"2025-05-05 08:35:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":9276184,"visible":true,"origin":"","legend":"\u003cp\u003eArchival maps and photos of the studied site. A – map of Trzebiel area in 1903, B – map of Trzebiel area in 1925(Topographische Karte 1903-1925), C, D – photos of the municipal bathing area Freibad Birkensee in 1928 (https://polska-org.pl/6511860,foto.html?idEntity=563990). Red circle – location of the present lake.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/5a54ce7d948315a511fa5ea6.png"},{"id":81947890,"identity":"51387cd9-a030-4aff-b204-4eb219ef367e","added_by":"auto","created_at":"2025-05-05 08:35:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1163142,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eLocation of the study site. A – location of the lake in Central Europe, B – lake catchment, C – bathymetry, isobaths every 2 meters.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/b70a5b40bc18f3a869ccaad7.png"},{"id":81948593,"identity":"58d2b159-4d77-440b-9c42-98e763c18868","added_by":"auto","created_at":"2025-05-05 08:43:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1197333,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003ePhysicochemical parameters (pH, oxidation-reduction potential (ORP), electrical conductivity (EC)) and the concentrations of dissolved oxygen (DO), dissolved organic carbon (DOC), and selected elements (Fe, S, Co, Ni, Zn) in the water column of Lake TR-17. 1986* - data from Solski et al. (1988).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/7a26a7efa7a679b981d8edd5.png"},{"id":81947882,"identity":"3682aa87-180c-439c-a10e-fde9396008ad","added_by":"auto","created_at":"2025-05-05 08:35:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":688532,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eDry bulk density (g cm\u003c/em\u003e\u003csup\u003e\u003cem\u003e-3\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e), content of total organic carbon and total nitrogen (%), and \u003c/em\u003e\u003csup\u003e\u003cem\u003e210\u003c/em\u003e\u003c/sup\u003e\u003cem\u003ePb and \u003c/em\u003e\u003csup\u003e\u003cem\u003e137\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eCs activity concentrations (Bq kg\u003c/em\u003e\u003csup\u003e\u003cem\u003e-1\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e) in TR-17 sediment core.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/52f7e7ccdd4cc0b3632a65e0.png"},{"id":81948592,"identity":"8b5d5611-19c4-48bd-8bf7-c88ff42e8496","added_by":"auto","created_at":"2025-05-05 08:43:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":651551,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eThe content of Al, Fe, S, and P (g/kg), and Mn, Cr, Co, Cu, Ni, Pb, and Zn (mg/kg) in the sediment core measured using ICP-OES. The zones (I-IV) were distinguished based on the cluster analysis; the results of clustering are presented in the dendrogram.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/047aa8b5e4e2dd2f6ce1e634.png"},{"id":81947883,"identity":"df0f1853-8eb9-4ea3-be4d-ad6a3bf7fde9","added_by":"auto","created_at":"2025-05-05 08:35:56","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":781393,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eA - biplot diagrams of principal component analysis (PCA) for concentration of selected elements in the TR-17 Lake sediment sequence; open circles indicate sediment samples (numbers are depth in cm), blue arrows are for element scores and red arrows are interpretation for clustering of elements vectors, shadowed ellipse symbolized the period of intensive input of organic pollution to the lake; B – detrended correspondence analysis (DCA) results for diatom assemblages from the TR-17 lake, red arrow indicates increase in acidity as reconstruct from the diatom inferred pH (DI-pH), species name codes: NavicSp - Navicula sp., DiscPseu - Discostella pseudostelligera, FragNana - Fragilaria nanana, UlnrAcus - Ulnaria acus, FragCapc - Fragilaria capucina, SyndUlna - Synedra ulna, AchnMint - Achnanthidium minutissimum, GompParv - Gomphonema parvulum, TablFloc - Tabellaria flocculosa, LemnHung - Lemnicola hungarica, NitzPale - Nitzschia palea, SyndCfAc – Synedra cf. acus, EolmMinm - Eolimna mininma, EuntImpl - Eunotia implicata, FrusSaxn – Frustulia saxonica, PinnGibb - Pinnularia gibba, EuntNymn - Eunotia nymanniana, NitzPerm -Nitschia perminuta, PsamSacc - Psammothidium sacculum, EunotSp - Eunotia sp., EuntBiln - Eunotia bilunaris, EuntExig - Eunotia exigua, EuntDent - Eunotia denticulata; C – detrended correspondence analysis (DCA) results for Cladocera assemblages from the TR17 lake, green arrow indicates increasing share of littoral/benthic taxa, species name codes: DaphnSp - Daphnia sp., BosmLong - Bosmiona longirostris, ChydSpha - Chydorus sphaericus, AlonAffn - Alona affinis, AcrpHarp - Acroperus harpae, AlonGutt - Alona guttata, AlonNana - Alonella nana, CerioSp - Ceriodaphnia sp.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/cbc1eaefa31848a77a59ed41.png"},{"id":81947886,"identity":"a5429dec-6df3-4686-a3f1-0689d52eb414","added_by":"auto","created_at":"2025-05-05 08:35:56","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":718049,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eDiatom, and Cladocera stratigraphy and the ratio of diatoms to chrysophycean statospores in TR-17 sediment core.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/283acf3390680b87dda02263.png"},{"id":81949604,"identity":"bc47f9b2-1513-49f5-a6ca-76edcd83d34e","added_by":"auto","created_at":"2025-05-05 08:59:56","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":440746,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eN2 - Diatom (blue) and Cladocera (orange) species diversity expressed as Hill’s N2 values; PC1 - Detrended correspondence analysis (DCA) axis 1 scores of diatom (blue) and cladoceran (orange) assemblages; DI-pH – diatom inferred pH values based on Mining pH training set, red asterisks represent pH values measured in 1986 and 2014; the period of pig farm operation and fish stocking were also indicated.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/6a55f21ae4642378b86efe26.png"},{"id":93955898,"identity":"28d6d0dc-56cc-4a60-ac94-a2183aa3d3e3","added_by":"auto","created_at":"2025-10-20 16:05:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":15302440,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6512111/v1/982197f8-8aca-4c44-a40b-547231cdc299.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Multiple stressor effects on the phyto- and zooplankton communities in a mining lake affected by acid mine drainage","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePostmining areas are among the regions most severely affected by human activity. Changes in the morphology of the terrain, disruption of the groundwater regime, heavy metal pollution or oxidation of sulfide minerals causing acidification of waters are some of the processes that occur there (Friese et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Geller et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; S\u0026aacute;nchez Espa\u0026ntilde;a et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; C\u0026aacute;novas et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). A frequent element of the landscape of postmining areas is water reservoirs that occupy inactive pits or sinkholes after underground mining (Brugam and Lusk \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Friese \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Hamilton et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Sienkiewicz et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). These lakes are often characterized by elongated shapes, steep banks, undeveloped littoral zones, and a lack of surface inflow and outflow. In regions where sulfide- or pyrite-containing deposits (e.g., coal or lignite deposits) are present and oxidize upon contact with meteoric waters, these lakes are often characterized by acidic waters (e.g., Blodau \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Tomiyama et al. \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Acharya and Kharel \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOne of the largest postmining areas in Central Europe is Łuk Mużakowa (Koźma and Migoń \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This large-scale terminal moraine consists of glacial clays and sands with layers of lignite coal embedded within it. Lignite mining has taken place here since the 19th century (Koźma \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), with the most intensive extraction occurring during the interwar period. Łuk Mużakowa is divided by the valley of the Lusatian Neisse River into a western part belonging to Germany and an eastern part lying within Polish borders. In the eastern part alone, there are more than 100 postmining lakes. Some of them occupy former pottery clay pits and have been characterized by water with a pH close to neutral from the beginning (Sienkiewicz and Gąsiorowski \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Others, which formed pits and sinkholes after lignite mining, have been acidic since their formation. Some of these lakes are undergoing a neutralization process, and in the oldest reservoirs, the water now has a pH of 6.5\u0026ndash;7 (Sienkiewicz and Gąsiorowski \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Pukacz et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePostmining reservoirs are often repurposed in various ways. Some are used for recreational activities such as fishponds or swimming areas, whereas others serve as recipients of wastewater and solid waste. Some bacteria undergo natural processes of neutralization, eutrophication, and overgrowth (Pukacz et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The organisms inhabiting these reservoirs face a variety of stressors, not only those resulting from acid mine drainage (AMD). In addition to low pH and elevated concentrations of heavy metals in the water, other significant factors include intensive nutrient inputs, frequent and substantial fluctuations in water levels, changes in catchment land use, and artificial stocking. One lake with an exceptionally rich history of human influence on its ecosystem is reservoir TR-17 (Solski et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Sienkiewicz and Gąsiorowski \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The lake existed prior to 1925 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and, despite acidic water, initially served as a municipal bathing area. Over time, it became affected by pollution from a nearby pig farm. Food industry facilities are typically sources of wastewater with high pollutant loads, containing various substances of different types and sizes. These include dissolved substances, colloidal particles, and suspensions composed of both organic compounds (mainly proteins and fats) and inorganic compounds such as chlorides, nitrates, phosphates, sulfates, and carbonates (Konieczny and Szymański \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In recent years, it has served as an angling fishery and is subjected to annual liming of water and artificial stocking.\u003c/p\u003e \u003cp\u003eThe goal of this study was to track the influence of pig farming and meat processing plant activities, along with the effects of lignite mining, on lake ecosystem located in AMD-affected area over the last fifty years. We hypothesized that pig farming and meat processing are associated with the emission of sewage sludge, causing additional pollution by heavy metals such as Cu, Ni, and Zn (Moral et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Jensen et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The study of these alterations was based on qualitative and quantitative analyses of subfossil phyto- and zooplankton and sediment geochemistry. Some diatom and cladoceran species can adapt to extensive heavy metal contamination (Pociecha et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and other anthropogenic changes, such as industrial pollution, whereas others disappear with increasing pollution.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eStudy site\u003c/p\u003e \u003cp\u003eLake TR-17 is located near Trzebiel (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) in the central area of the Polish part of the Łuk Mużakowa region (SW Poland). Łuk Mużakowa is a unique glacitectonic structure located on the border of Poland and Germany. It is one of the largest moraines in Europe and the only such phenomenon that can be seen with the naked eye from space. It is a deeply eroded frontal formation with disturbed Miocene, Pliocene, and early Pleistocene sediments (Koźma \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The moraine is 40 km long and 3\u0026ndash;5 km wide and originated during the Last Glacial Maximum. The lakes in this region are of anthropogenic origin and are remnants of lignite, gravel, sand, and clay exploitation. The studied lake was created as a sinkhole following the collapse of the abandoned Hoffnung lignite mine (Kupetz et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2004\u003c/span\u003e) after exploitation ceased in the 1920s. Between 1928 and 1943, the lake was used as a municipal bathing area (St\u0026auml;dt Badeanstalt, Freibad Birkensee) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In the 1970s and 1980s, there was a pig farm nearby, from which sewage was discharged into the fields immediately adjacent to the lake. Today, the lake is used as a fish pond; it is bordered on the east by farmland and otherwise surrounded by forest. It is supplied by a single inflow. The basic characteristics of the lake are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMorphometry and water parameters of the Lake TR-17.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eMorphometry\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximal lenght (m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003e276\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximal width (m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArea (ha)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003e18.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximal depth (m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003e10.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCatchment area (ha)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003e86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003ePhysicochemical parameters\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1986, Aug*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2014-09-03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2020-06-11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2022-05-15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2024-09-03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTemperature (\u0026deg;C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e23.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003en.a.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e* data from Solski et al. (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1988\u003c/span\u003e)\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eSampling and field work\u003c/p\u003e \u003cp\u003eA sediment core of lake TR-17 was collected in 2014 (70 cm long) using a Kajak-type gravity corer. The amount of sediment was insufficient for all the analyses; thus, in 2020, a second core was obtained (40 cm long). Both cores were correlated with each other on the basis of radiometric measurements and elemental (C, H, N, S) analyses. The sediments were divided every 1 cm in the field and packed into plastic bags. In the laboratory, the sediments were subsampled for phyto- and zooplankton identification, dating, and elemental and geochemical analyses. Lake bathymetry was measured along two transects using a portable echo sounder (Echotest II). The physicochemical parameters (pH, oxidation‒reduction potential (ORP), electrical conductivity (EC), and dissolved oxygen (DO)) of the lake water were measured in situ via a multiparameter portable meter (Multi 3620 IDS SET G) during field trips in 2014, 2020, 2022, and 2024. Measurements of the lake tributary water were performed in 2022 and 2024. Water samples were collected using a 5 L vertical sampler during field trips in September 2020 (every metre along the entire length of the water column) and May 2022 (only from the surface layer). Each water sample was filtered through CA membrane filters (pore size: 0.45 \u0026micro;m), preserved with double-distilled HCl (35%), and stored in 50 mL polyethylene bottles at 4\u0026deg;C until analysis.\u003c/p\u003e \u003cp\u003eWater and sediment analyses\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eDissolved organic carbon (DOC) in the lake water was analysed in triplicate using the combustion catalytic infrared method and a Shimadzu TOC-V CPH at the Institute of Geology, Czech Academy of Sciences in Prague (GLI CAS). Oxalic acid dihydrate was used as the basic standard solution. Potassium hydrogen phthalate (Shimadzu) dissolved in double-distilled water was used as a secondary standard to ensure measurement stability. The relative standard deviation (RSD) of the analytical results was \u0026lt;\u0026thinsp;5%.\u003c/p\u003e\u003cp\u003eThe contents of major elements in the water samples were analysed in triplicate using ICP‒OES (Agilent 5100) at the GLI CAS. A multielement calibration solution prepared from single-element standards (Analytika spol. s.r.o.), was used for instrument calibration. The trace element concentrations in the water samples were determined in triplicate using HR-ICP-MS (Element 2, Thermo Scientific) at the GLI CAS. A mixed calibration solution prepared from single-element standards (CPA Chem) was used for instrument calibration. An indium solution (1 ppb) was used as an internal standard for correcting instrumental drift. The certified reference material (CRM) ERM CA 615 (EC Joint Research Centre) was measured to control the quality and repeatability of the ICP‒OES and ICP-MS analyses. The RSDs of all the analytical results were \u0026lt;\u0026thinsp;5%.\u003c/p\u003e\u003cp\u003eThe selected samples of lake sediments were digested with double-distilled HNO\u003csub\u003e3\u003c/sub\u003e (65%), HCl (32%), and HF (48%) using the MARS 6 microwave digestion system (CEM Corporation, USA) at the Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research. The CRM, marine sediment (NRC-MESS-4), was digested, and four procedural blanks were prepared to validate the procedure. Next, the samples were evaporated using the XVap accessory of the microwave. The samples were subsequently diluted with double-distilled 1.5 M HNO\u003csub\u003e3\u003c/sub\u003e before analysis. The elemental composition of the sediment samples was measured in triplicate using ICP‒OES (iCAP 7000 Series, Thermo Scientific, USA) at the AWI, Helmholtz Centre for Polar and Marine Research. External calibrations for quantitative analysis were prepared using single-element standards (Roti\u0026reg;Star, CarlRoth GmbH). The CRM was analysed every four to six samples to monitor the quality and repeatability of the results. The RSD for all the measurements was \u0026lt;\u0026thinsp;5%.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eSediment elemental analyses\u003c/p\u003e \u003cp\u003eElemental parameters, such as the concentrations of total organic carbon (TOC) and total nitrogen (TN), were measured with a Vario Cube elemental analyser. Five to ten milligrams were treated with 10% HCl to remove carbonates, washed with distilled water, dried, and transferred to preweighed tin capsules. The samples, excluding those used for biological analyses, were dried, ground and homogenized. The samples were combusted at a temperature of 1150\u0026deg;C, and the obtained gases were separated on a chromatographic column and measured with a thermal conductivity detector. The measurement uncertainties for the TOC and TN were 0.6 and 0.18%, respectively.\u003c/p\u003e \u003cp\u003eDating of lake sediments\u003c/p\u003e \u003cp\u003eThe radiochemical separation of \u003csup\u003e210\u003c/sup\u003ePo from lake sediments was conducted following a modified procedure outlined by Flynn (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1968\u003c/span\u003e). Approximately 0.6 g of each selected sample was spiked with \u003csup\u003e208+209\u003c/sup\u003ePo and digested on a hot plate using HCl (35%) and HNO\u003csub\u003e3\u003c/sub\u003e (65%). The organic components were removed with HNO\u003csub\u003e3\u003c/sub\u003e (65%) and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (32%) (Jia et al. 2004; Matthews et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Polonium isotopes were then spontaneously deposited onto silver discs in 0.5 M HCl (Martin and Blanchard \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1969\u003c/span\u003e). To prevent the deposition of competing ions, such as Fe\u003csup\u003e3+\u003c/sup\u003e, sodium citrate and hydroxylamine hydrochloride were added prior to deposition (Flynn \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1968\u003c/span\u003e; Jia et al. 2004). The activity concentrations of the polonium isotopes were measured using an Octete alpha spectrometer (Ortec) at the Institute of Geological Sciences Polish Academy of Sciences (IGS PAS), with an average uncertainty of 1.8 Bq.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (3.5%, n\u0026thinsp;=\u0026thinsp;24). The chemical recovery for \u003csup\u003e208+209\u003c/sup\u003ePo ranged from 60 to 70%.\u003c/p\u003e \u003cp\u003eThe activity concentrations of \u003csup\u003e137\u003c/sup\u003eCs in selected samples from the sediment core were determined using a low-background gamma spectrometer (Canberra Packard) with a BE5030 detector (FWHM\u0026thinsp;=\u0026thinsp;1.07 keV at 661.7 keV for \u003csup\u003e137\u003c/sup\u003eCs) at the IGS PAS. The CRM (IAEA-SL-2) was analysed to ensure the quality of the measurements. All the samples were analysed in a flat cylinder geometry for 48 to 72 h. The obtained data were processed using Genie 2000 software. All values were converted to the date of sampling (24 September 2020). The typical minimum detectable activity (MDA) for \u003csup\u003e137\u003c/sup\u003eCs was 1.5 Bq kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the measurement uncertainty ranged from 17 to 37%.\u003c/p\u003e \u003cp\u003eDiatom analysis\u003c/p\u003e \u003cp\u003eThe sediment samples for diatom analysis were prepared according to the standard method (Battarbee \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). The samples (volume of 1 cm\u003csup\u003e3\u003c/sup\u003e) were treated with 10% HCl to remove carbonates and heated with 30% H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e until all the organic matter was oxidized, and then the samples were washed several times with distilled water. Permanent slides were mounted in Naphrax\u0026reg; (R.I.=1.75). The quantification analysis results were obtained between 1 cm (AD 2014) and 33 cm (AD 1970). Only in two samples (5 and 8 cm) was the frequency of diatoms too small to perform quantitative analysis. The remaining samples did not contain diatoms or only single valves of diatoms. Diatom identification was based on Krammer and Lange-Bertalot (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1986\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1988\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1991a\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003eb\u003c/span\u003e) and Lange-Bertalot and Metzeltin (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). The core was divided into diatom assemblage zones (DAZs) on the basis of the Constrained Incremental Sum of Squares Cluster Analysis (CONISS, Grim 1987) performed by rjojaPlot 1.03. The number of statistically significant zones was assessed using the broken-stick model (Juggins \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe diatom inferred pH (DI-pH) was reconstructed on the basis of the mining pH training set (Sienkiewicz and Gąsiorowski \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The values of past water pH were estimated using the weighted average with downweighted species with high pH tolerance and inverse deshrinking (RMSE\u003csub\u003eWA_Inv\u003c/sub\u003e=0.69).\u003c/p\u003e \u003cp\u003eCladocera analysis\u003c/p\u003e \u003cp\u003eThe Cladocera species composition was determined via a standard procedure (Korhola and Rautio \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). The 1 cm\u003csup\u003e3\u003c/sup\u003e sediment samples were heated and stirred in 8% KOH on a hot plate for approximately 30 minutes and sieved through a 33-\u0026micro;m mesh screen. The sieved material was stored in 10 mL of distilled water. Temporary slides, each prepared from a 0.1 mL portion of a sample, were used for identification and to count the cladoceran remains. The slides were prepared for examination under a light microscope at magnifications of 100\u0026ndash;400\u0026times; until a minimum of 200 remains were encountered and identified following Szeroczyńska and Sarmaja-Korjonen (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). \u003cem\u003eChydorus sphaericus\u003c/em\u003e is considered \u003cem\u003eC. sphaericus sensu lato\u003c/em\u003e (\u003cem\u003es.l.\u003c/em\u003e) (Frey, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). Cladocera percentage abundances were calculated from the sum of individuals. The most abundant body part was chosen for each taxon to represent the number of individuals.\u003c/p\u003e \u003cp\u003eStatistical analyses\u003c/p\u003e \u003cp\u003eHierarchical clustering with similarity index correlation was used to analyse the elemental composition of the sediment results after normalization using the PAST 4.03 program (Hammer et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). To determine the optimal number of clusters, the elbow method was used, which was performed in R ver. 4.0.4 using the \u0026lsquo;factoextra\u0026rsquo; and \u0026lsquo;cluster\u0026rsquo; packages (Kassambara \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Maechler et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The species diversity was checked with Hill\u0026rsquo;s N2 parameter. Changes in element concentrations and diatom and Cladocera species composition were explored with multivariate analyses. Principal component analysis (PCA) was applied to the elemental dataset due to short gradients (0.2 SD). In contrast, owing to the long gradient in the datasets (gradient lengths of 3.6 and 3.0 SD), detrended correspondence analysis (DCA) with square-root transformed species data was used for diatoms and Cladocera. Community changes that were detected from the DCA axis 1 sample scores were further verified with analysis of similarities (ANOSIM, one-way) for their significant differences. The DCA was run with Canoco software CANOCO 4.5 (ter Braak and Šmilauer 2002), and ANOSIMs were run with the program PAST 4.03 (Hammer et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) via Bray‒Curtis distance measures, 10 000 permutations, and Bonferroni-corrected p values.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cem\u003eIn situ\u003c/em\u003e measurements and water sample analyses\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe results of the physicochemical parameter measurements, as well as the contents of dissolved oxygen (DO), dissolved organic carbon (DOC), and selected elements (F, S, Co, Ni, and Zn) in the water column of lake TR-17, are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The pH of the surface layer of the water column has varied significantly over time. The lowest value (pH\u0026thinsp;=\u0026thinsp;5.19) was measured in September 2020, whereas the highest value (pH\u0026thinsp;=\u0026thinsp;7.4) was recorded in 1986 by Solski et al. (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). The DO content significantly increased over time compared with the measurements taken by Solski (1988), reaching more than 10 mg L\u003csup\u003e-1\u003c/sup\u003e in the surface water (1 m depth of the water column) in the 2000s. The elemental content did not change significantly compared with the reported data, except for Co and Zn. The concentration of Fe in the surface water collected in 2020 was below the detection limit, whereas the concentrations of S, Co, Ni, and Zn were 68.3 mg L\u003csup\u003e-1\u003c/sup\u003e, 0.7 \u0026micro;g L\u003csup\u003e-1\u003c/sup\u003e, 3.9 \u0026micro;g L\u003csup\u003e-1\u003c/sup\u003e, and 10.1 \u0026micro;g L\u003csup\u003e-1\u003c/sup\u003e, respectively. The contents of other heavy metals, such as Cd, Cr, Cu, and Pb, were below the detection limits.\u003c/p\u003e\u003cp\u003eThe results revealed that the physicochemical parameters and the contents of DO, DOC, and selected elements changed significantly with depth throughout the water column. The greatest differences were observed at a depth of 5 m, where the pH, electrical conductivity (EC), and contents of DOC and Fe increased, whereas the oxidation‒reduction potential (ORP) and concentrations of DO, S, Ni, and Zn decreased.\u003c/p\u003e\u003cp\u003eThe pH levels of the surface water from the lake tributary, measured near its outlet in September 2020 and 2024, were 6.95 and 6.8, respectively. The concentrations of the tested elements in the surface water collected from the tributary in September 2020 were 22.8 mg L\u003csup\u003e-1\u003c/sup\u003e for Fe, 57.6 mg L\u003csup\u003e-1\u003c/sup\u003e for S, 0.5 \u0026micro;g L\u003csup\u003e-1\u003c/sup\u003e for Ni, and 8 \u0026micro;g L\u003csup\u003e-1\u003c/sup\u003e for Zn. The concentration of Co was below the detection limit.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSediment lithology and chronology\u003c/p\u003e \u003cp\u003eThe dry bulk densities, TOC and TN contents, and C:N ratios are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The dry bulk density of the lake sediments decreased over time, from 0.73 g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e at the bottom of the core to 0.08 g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e in the upper section. Sediment layers with relatively high bulk density values ​​were observed mostly at depths of 70, 66, 59, 43\u0026thinsp;\u0026minus;\u0026thinsp;40 and 28 cm within the core. The contents of TOC and TN increased in the core. Sediment layers enriched in TN were detected at depths of 9, 20, 28\u0026ndash;34, and 48 cm within the sediment column. The C:N ratio varied significantly along the core, from 56 at the bottom to 13 at the top. Below a depth of 35 cm, the C:N ratio exhibited considerable fluctuations, which stabilized in the upper section of the core. Elevated C:N ratios were observed at depths of 65, 58, 51\u0026thinsp;\u0026minus;\u0026thinsp;49, 44\u0026thinsp;\u0026minus;\u0026thinsp;41 and 6\u0026thinsp;\u0026minus;\u0026thinsp;4 cm within the sediment profile.\u003c/p\u003e \u003cp\u003eThe vertical distributions of the \u003csup\u003e210\u003c/sup\u003ePb and \u003csup\u003e137\u003c/sup\u003eCs activity concentrations are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. \u003csup\u003e137\u003c/sup\u003eCs was irregularly distributed throughout the sediment column, with visible peaks in activity concentrations at depths of 23, 28, and 35\u0026ndash;36 cm. Assuming that the sediment layer enriched in \u003csup\u003e137\u003c/sup\u003eCs at a depth of 23 cm in the core corresponds to Chernobyl fallout, the sedimentation rate in this part of the lake was calculated to be 0.7 cm y\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The observed peaks in the \u003csup\u003e137\u003c/sup\u003eCs content below a depth of 23 cm may be related to nuclear tests conducted in the 1960s.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eElemental composition\u003c/p\u003e \u003cp\u003eThe downcore profiles of the concentrations of selected elements in the core are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The contents of most studied elements varied significantly with core depth. A decrease in S content was observed upwards along the sediment profile, particularly above a depth of 26 cm in the core. A similar trend was noted for P, Co, Cu, Ni, and Zn, with their concentrations decreasing notably above a depth of 20 cm in the core. The smallest variability in the vertical distribution of content along the sediment profile was shown by Fe and Pb (coefficient of variation\u0026thinsp;\u0026lt;\u0026thinsp;0.11). On the basis of the cluster analysis, 4 zones were identified: the individual zones included samples collected from depths of 1\u0026ndash;16 cm in the core (Zone I), 20\u0026ndash;26 cm (Zone II), 28\u0026ndash;36 cm (Zone III), and greater than 38 cm (Zone IV). The samples in the upper part of the core (collected from depths of 1\u0026ndash;4 cm) are characterized by elevated contents of Al, K, Ti, and Cr and slightly elevated contents of Co, Cu, Ni, and Zn. Significant increases in the concentrations of Al, Mn, P, Co, Ni, and Zn were observed at depths between 7 and 12 cm (with a maximum at 10 cm) in the sediment column. Significantly elevated concentrations of S, P, Co, Cu, Ni, and Zn are also evident at depths of 16\u0026ndash;24 cm (with a maximum at 20 cm), 28 cm, and 32\u0026ndash;36 cm in the core. Below a depth of 38 cm in the core (Zone IV), decreases in the contents of Co, Cu, Ni, Pb, Zn, S and P were observed.\u003c/p\u003e \u003cp\u003eThe mean concentrations (n\u0026thinsp;=\u0026thinsp;18) of heavy metals, including Cr, Co, Cu, Ni, Pb, and Zn, were 4.8, 6.2, 19.6, 19.8, 11.2, and 121.9 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. The highest contents recorded for these metals in the sediment column were 9.5 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Cr, 9.4 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Co, 53 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Cu, 33.2 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Ni, 15.2 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Pb, and 244 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Zn. An increased P content was also observed in the sediment profile, with an average of 8.3 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (n\u0026thinsp;=\u0026thinsp;18).\u003c/p\u003e \u003cp\u003eThe first two axes of the PCA of the elemental concentration data explained 82% of the variation in the dataset (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The samples grouped along the first axis and samples from horizons 36\u0026ndash;10 had negative score values. The samples deposited during the pig farm operation period clustered together with the vectors of N, P, Co, Cu, Zn and Ni. The youngest sediment samples had positive PC1 values related mostly to higher C:N ratios. The main factors associated with the samples scattered along the PC2 axis were the concentrations of Cr, Ti, K, and Al (positive values) and Ca, Mn and Sr (negative values).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDiatom stratigraphy and Chrysophyceae cyst abundance\u003c/p\u003e \u003cp\u003eA total of 76 diatom species belonging to 23 genera were identified. The diatom stratigraphy was divided into 3 diatom assemblage zones (DAZs 1\u0026ndash;3) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). The ratio of chrysophycean statospores to diatoms in the sediments of TR-17 was also determined. A high ratio of diatom frustules to cysts indicates a period of nutrient enrichment (Smol \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). Compared with diatoms, chrysophycean algae are more sensitive to both eutrophication and metal contamination (Chen et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The number of stomatocysts in the core ranged between 0.5 and 55.5%. The highest number of stomatocysts occurred before the processing plant was in operation. This suggests that there were fewer nutrients in the lake than in the following years.\u003c/p\u003e \u003cp\u003eIn the sediment portion below a depth of 37 cm, diatoms occurred as fragmentary broken single valves that were impossible to identify at the species level. Above this layer, at a depth of 33 cm, only quantitative analysis was possible due to an insufficient number of diatom valves. The most numerous taxa were \u003cem\u003eUlnaria acus\u003c/em\u003e (K\u0026uuml;tz.) Aboal and \u003cem\u003eFragilaria nanana\u003c/em\u003e Lange-Bertalot. \u003cem\u003eNitzschia palea\u003c/em\u003e (K\u0026uuml;tz.) W. Smith, \u003cem\u003eGomphonema parvulum\u003c/em\u003e (K\u0026uuml;tz.) K\u0026uuml;tzing and \u003cem\u003eLemnicola hungarica\u003c/em\u003e (Grun.) Round \u0026amp; Basson were observed in smaller numbers.\u003c/p\u003e \u003cp\u003eDAZ 1 (33\u0026ndash;16 cm; 1970\u0026ndash;1992 AD)\u003c/p\u003e \u003cp\u003eThe zone is characterized by diatoms that are highly tolerant of organic pollution and acidic water, such as \u003cem\u003eEunotia exigua\u003c/em\u003e (Br\u0026eacute;b. in K\u0026uuml;tz.) Rabenhorst and \u003cem\u003eEolimna minima\u003c/em\u003e (Grun.) Lange-Bertalot. In the lower part of DAZ 1 around the second half of the 1960s, the highest frequency of chrysophycean cysts was observed (55.5%) in terms of the ratio of diatoms. Since the beginning of the 1970s, a rapid decrease in the number of stomatocysts has reached 0.5% at a depth of 17 cm (i.e., 1991).\u003c/p\u003e \u003cp\u003eDAZ 2 (16\u0026ndash;7.5 cm; 1992\u0026ndash;2004 AD)\u003c/p\u003e \u003cp\u003eAt the beginning of the zone, the frequency of diatom dominance in the previous zone decreased. The diatoms, such as \u003cem\u003eEolimna minima\u003c/em\u003e and \u003cem\u003eN. palea\u003c/em\u003e, disappeared at the end of the zone. The most frequent taxon was \u003cem\u003eU. acus\u003c/em\u003e, which reached its maximum abundance in the core. Rapid increases in \u003cem\u003eEunotia exigua\u003c/em\u003e and \u003cem\u003eE. nymanniana\u003c/em\u003e Grunow in the upper part of the zone were also noted. However, the last sample in this part of the core had an insufficient number of diatom valves for quantitative analysis. Initially, at the beginning of DAZ 2 (1992), the percentage of chrysophycean statospores increased to 15.5%. However, after a short period, diatoms dominated this zone. In the uppermost part of this period, a slight increase in chrysophycean taxa was again observed.\u003c/p\u003e \u003cp\u003eDAZ 3a (7.5\u0026ndash;4.5 cm; 2004\u0026ndash;2009 AD)\u003c/p\u003e \u003cp\u003eThis subzone is characterized by the dominance of diatoms, such as \u003cem\u003eEunotia implicata\u003c/em\u003e N\u0026ouml;rpel, Lange-Bertalot \u0026amp; Alles, \u003cem\u003eFrustulia saxonica\u003c/em\u003e Rabenhorst and \u003cem\u003ePinnularia gibba\u003c/em\u003e (Ehr.) Ehrenberg, which reached the highest frequency in the core. Owing to the small number of diatom valves in the highest sample at DAZ 3a, only qualitative diatom analysis was performed. During this time, the number of stomatocysts increased above 20%.\u003c/p\u003e \u003cp\u003eDAZ 3b (4.5\u0026ndash;0 cm; since 2009)\u003c/p\u003e \u003cp\u003eThe lower part of the youngest sediments was dominated by diatoms occurring in more alkaline waters than those from the previous subzone. There are \u003cem\u003eDiscostella pseudostelligera\u003c/em\u003e (Hust.) Houk \u0026amp; Klee, \u003cem\u003eFragilaria gracili\u003c/em\u003es \u0026Oslash;strup and \u003cem\u003eF. nanana\u003c/em\u003e Lange-Bertalot. In the upper part of the zone, a significant increase in acidophilous taxa (e.g., \u003cem\u003eEunotia\u003c/em\u003e spp.) and a decrease in indifferent and alkaliphilous diatoms were observed.\u003c/p\u003e \u003cp\u003eIn the youngest sediments, an increase in diatoms was observed. The frequency of Chrysophycean statospores decreased, but in the uppermost sample, it increased again to 20%.\u003c/p\u003e \u003cp\u003eThe DCA diagram of diatom species changes explained 29% of the variance in the community (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The taxa are organized along axis 1 according to their pH preferences, with lower scores for more acid-tolerant species.\u003c/p\u003e \u003cp\u003eReconstruction of diatom-inferred pH (DI-pH)\u003c/p\u003e \u003cp\u003eThe values of the DI-pH varied between 6.43 and 7.22 (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Until the first half of the 1990s, the curve of the water pH was relatively stable and indicated the neutral character of water. From that time to the present, the DI-pH has fluctuated to a greater or lesser extent but has generally shown a decreasing trend. The minimum value of the DI-pH (6.43) occurred in 2014. This value does not correspond to the value measured in the field, which was much lower (5.53). This discrepancy may result from large disproportions between the percentage of species dominating in the core (\u003cem\u003eUlnaria acus\u003c/em\u003e (up to 80%), \u003cem\u003eLemnicola hungarica\u003c/em\u003e and \u003cem\u003eEolimna minima\u003c/em\u003e (both approximately 40%)) and those occurring in the Mining pH training set (Sienkiewicz and Gąsiorowski \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) used to the reconstruction of water pH in TR-17. Both latter species occurred only in 4 and 1 lake in the Mining pH training set, respectively. This could overestimate the reconstructed values to some extent.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003e3.5 Cladocera stratigraphy\u003c/h3\u003e\n\u003cp\u003eThe species diversity of Cladocera remaining in the sediments of lake TR-17 was relatively low. Only 8 taxa belonging to 3 families, Daphniidae, Bosminidae and Chydoridae, were identified. Cladocera remains were found only in the upper 21 cm of the sediment core. The Cladocera assemblage development was divided into two Cladocera assemblage zones (CAZs). Differences between zones were statistically significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.003 in the one-way ANOSIM test).\u003c/p\u003e \u003cp\u003eCAZ 1 (21\u0026ndash;7 cm; 1985\u0026ndash;2005).\u003c/p\u003e \u003cp\u003eOnly 3 Cladocera taxa were identified in this zone: \u003cem\u003eBosmina longirostris\u003c/em\u003e, \u003cem\u003eDaphnia\u003c/em\u003e spp. and \u003cem\u003eChydorus sphaericus\u003c/em\u003e sensu lato. Only daphnia remains were present in the sample from a depth of 15 cm. The abundance of the remaining sediment was low, with 200\u0026ndash;400 individuals per 1 cm\u003csup\u003e3\u003c/sup\u003e of wet sediment.\u003c/p\u003e \u003cp\u003eCAZ 2 (7\u0026ndash;1 cm; 2005\u0026ndash;2014)\u003c/p\u003e \u003cp\u003eThe second zone was characterized by greater species diversity. In addition to the taxa found in CAZ 1, benthic and littoral zone-dwelling species, including \u003cem\u003eAlona affinis\u003c/em\u003e and \u003cem\u003eAlonella nana\u003c/em\u003e, which occur in relatively high numbers, appeared. In the youngest samples, the daphnia disappeared completely, and \u003cem\u003eBosmina longirostris\u003c/em\u003e developed.\u003c/p\u003e \u003cp\u003eA detrended correspondence analysis (DCA) diagram explained 39.3% of the variation in the Cladocera assemblage (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The taxa are organized along axis1 and planktonic species are placed to the right of diagram while littoral are to the left (species scores\u0026thinsp;\u0026gt;\u0026thinsp;0.2).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eLake formation and AMD impact on the lake\u0026rsquo;s ecosystem\u003c/p\u003e \u003cp\u003eLake TR 17, like many other lakes in the region, originated in a depression that formed after the collapse of the corridors of an underground lignite mine (Solski et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). According to archival maps and historical data (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the lake existed as early as 1925 and served as a bathing area for the residents of Trzebiel. Sediment analysis indicated that at this time, the lake contained acidic water, and the low pH prevented the development of phyto- and zooplankton. The bottom section of the sediment core is characterized by relatively high bulk density and high C:N ratios (greater than 55), indicating the supply of organic matter from the lignite deposit, although lignite particles were not recognized in the macroscopic image. At a sediment depth of 65\u0026ndash;37 cm, i.e., from 1935\u0026ndash;1967, the C:N values were approximately 15\u0026ndash;30, indicating that the dominant source of organic matter in the sediment was the lake catchment, with only a minor contribution from primary production. However, the influence of lignite deposits was no longer clear. This indicates the stabilization of hydrological and morphological conditions within the lake basin and the predominant influence of surface water recharge. Water chemistry prevented diatom and Cladocera development at that time. The Cladocera remains were completely absent, and diatoms were represented only by fragmented valves. Similar conditions were used in the same mining area at lake TR-33 (Sienkiewicz and Gąsiorowski \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, TR-33 is ~\u0026thinsp;50 years older, and the initial period of its development ended much earlier than that of lake TR-17 (i.e., the 1940s). Moreover, TR-33 was not impacted later by human activity and evolved naturally towards neutralization.\u003c/p\u003e \u003cp\u003eArtificial input of nutrients and lake eutrophication\u003c/p\u003e \u003cp\u003eSince the early 1970s, pig farming and meat processing operations have been established near lake TR-17 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Manure and wastewater from the processing plant were discharged directly into the fields surrounding the lake to the east. Together with ground water and surface runoff, the sewage was transported to the lake. In the sediment profile, this process included an abrupt increase in the TN concentration, a decrease in the C:N ratio and elevated concentrations of several metals, namely, Zn, Ni, Cu, and Co (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). A similar increase in heavy metals, such as Cu, Ni, and Zn, related to the operation of pig farms has also been recorded by other researchers (Jensen et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Moral et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The input of nutrients into the lake caused the development of diatom flora with species that tolerate elevated concentrations of heavy metals, such as \u003cem\u003eLemnicola hungarica, Gomphonema parvulum, Eolimna minima\u003c/em\u003e and \u003cem\u003eNitzschia palea\u003c/em\u003e (Morin et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Pociecha et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe sewage input was also confirmed by direct measurements, e.g., high alkalinity, which was 9.2 mval L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, whereas the alkalinity of other lakes in the region varied between 0.5 and 3.5 mval L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Solski et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). This high alkalinity was an isolated phenomenon among the lakes located in this area. Moreover, Solski et al. (\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1988\u003c/span\u003e) measured elevated concentrations of nitrates (1.94 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), nitrites (0.198 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and potassium (53 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in lake water and reported that their source was sewage from meat processing plants. For comparison, the K concentration in a surface water sample (collected in 2020) was 6.7 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe input of pollution from the pig farming accelerated the changes in the lake and disturbed the processes of natural neutralization. Instead of the relatively long transitional stage of development with acidic-tolerant diatoms and Cladocera observed in the nearby lake TR-33 (Sienkiewicz and Gąsiorowski \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), lake TR-17 experienced rapid neutralization of acidic water with wastewater. This change could only be survived by some diatom species, while Cladocera were completely absent until the late stage of the pollution period (i.e., 1985). Even after the closure of the pig farm, the only Cladocera that occurred in the lake were planktonic species, and in 1991, the only taxon was \u003cem\u003eDaphnia\u003c/em\u003e spp.\u003c/p\u003e \u003cp\u003eRecovery from eutrophication and pollution\u003c/p\u003e \u003cp\u003eA pig farm near the lake existed until 1991. After its closure, there was a significant and rapid change in the water quality of the reservoir. The first signs of a decline in nutrients and heavy metals were observed in samples dating back to 1993. Changes in diatom flora resulted in a reduction in the frequency of pollution-tolerant taxa, and the prevalence of \u003cem\u003eUlnaria acus\u003c/em\u003e reached 80% in the core. This taxon is found in epilithic and epiphytic substrates in moderately alkaline, oligosaprobic, and eutrophic freshwater streams and lakes (Lange-Bertalot and Ulrich \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). A clear increase in \u003cem\u003eU. acus\u003c/em\u003e is connected to the closure of the meat processing plant and the subsequent end of sewage discharge into the lake, as \u003cem\u003eUlnaria\u003c/em\u003e thrives in less polluted waters. The diatoms typical for polluted waters have occurred from the beginning of meat processing plant operation, while after the factory closed, it seems that AMD (i.e., acidic environments) again had a significant impact on diatom development (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). This is evidenced by the presence of acidophilous and acidobiontic diatoms, such as \u003cem\u003eEunotia denticulata\u003c/em\u003e (Br\u0026eacute;b. ex K\u0026uuml;tz.) Rabenhorst, \u003cem\u003eE. nymanniana\u003c/em\u003e and \u003cem\u003eE. exigua\u003c/em\u003e. The abundance of these taxa, especially \u003cem\u003eE. exigua\u003c/em\u003e and \u003cem\u003eE. nymanniana\u003c/em\u003e, in the following years significantly decreased as late as 2002 (the top of DAZ 2). In the first years of the recovery period (1991\u0026ndash;2002), Cladocera were still represented only by planktonic taxa. The slow change from large to small-bodied species may have been caused by the gradual colonization of the lake by fish and selective predation on the more visible, large Cladocera.\u003c/p\u003e \u003cp\u003eThe accumulation of sediments at the beginning of the 21st century (the top of DAZ 2 and DAZ 3a) was likely connected with an episode of more acidic water delivery from AMD than that in the previous period. The highest frequency was reached by \u003cem\u003eEunotia implicata\u003c/em\u003e and \u003cem\u003eFrustulia saxonica\u003c/em\u003e, which appeared twice as early as single valves in the core. In particular, \u003cem\u003eE. implicata\u003c/em\u003e dominated this part of the core (up to 82%). The last subzone (DAZ 3b) is characterized by the dominance of \u003cem\u003eFragilaria gracilis, F. nanana\u003c/em\u003e, and \u003cem\u003eDiscostella pseudostelligera\u003c/em\u003e. This is a completely different kind of diatom flora than that in the previous subzone. The frequency of acidophilous taxa significantly decreased, whereas the abundance of diatoms living in meso- and eutrophic environments increased. This situation may be the result of two factors: heavy rainfall in 2010 (IMGW-PIB, 2010), which caused local flooding, and limnification of the lake. Since 2010, people have managed this lake by pouring 1 ton of lime in the autumn (personal communication) to increase the water pH. Today, this lake is used as a fish pond, and the water pH cannot be too low. These processes also caused the development of a littoral zone, which was indicated by the occurrence of littoral and plant-associated Cladocera species. In both cases, i.e., flooding and limning, changes in the diatom community were caused by the increase in water pH. The highest sediment sample (2014) is dominated by acidophilous diatoms, such as \u003cem\u003eEunotia exigua, E. nymanniana\u003c/em\u003e and \u003cem\u003eE. bilunaris\u003c/em\u003e. This latter taxon is characterized by wide ecological tolerance and can live in water with increased concentrations of sulfate (Alles et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1991\u003c/span\u003e). The topmost sample represents a process of acidification, confirmed by direct measurement of the water pH in 2014 (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eLake TR-17 is a postmining reservoir created at a former lignite excavation site. The C:N ratio indicates the presence of lignite lenses in the bottom sediments. Despite the presence of heavy metals and other harmful compounds associated with lignite deposits and exploitation, the lake was transformed into a municipal bathing area between 1929 and 1930, remaining in use until 1945. A pig farm and meat processing plant operated in the vicinity of the lake from the 1970s to the 1990s. Manure runoff from the farm released onto the surrounding fields, along with surface water, carried pollutants contained in the sewage into the lake, contaminating the water. Some organic and inorganic compounds contributed to an increase in the trophic level (e.g., through a rise in phosphate levels) and the concentration of heavy metals (e.g., Cu, Ni, Zn). The closure of the pig farm and the meat processing plant triggered a decrease in heavy metal concentrations. Changes in phyto- and zooplankton were also observed at this time. In the diatom community, a reduced frequency or disappearance of taxa tolerant to highly polluted waters (e.g., \u003cem\u003eLemnicola hungarica\u003c/em\u003e) and the development of some diatoms inhabiting the least polluted waters (e.g., \u003cem\u003eUlnaria acus\u003c/em\u003e) were observed. Cladocera fauna appeared in the lake at the end of the farming activities. Most likely, the water was too polluted earlier for cladoceran taxa to develop. The lake is located within an AMD area, and along with groundwater, it is supplied with acidic compounds. To neutralize acidic water, the lake has been limed every year since 2010.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eE-mail addresses\u003c/h2\u003e \u003cp\[email protected] (E. Sienkiewicz), [email protected] (M. Gąsiorowski), [email protected] (I. Sekudewicz), [email protected] (I. Stimac), [email protected] (Š. Matouškov\u0026aacute;)\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, methodology, data curation, formal analysis, writing\u0026mdash;original draft, supervision: E.S., M.G. Formal analysis, writing\u0026mdash;original draft, art work: IS. Formal analysis : Š.M., I.S.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was financially supported by a grant no. 2012/07/B/ST10/04204 awarded by the Polish National Centre of Science. We thank Agata Jask\u0026oacute;łka and Wojtek Sienkiewicz for their help during the fieldwork and the employees of the Forest Districts of Lipinki and Lubsko for permission to collect the lake sediments. We also want to thank Karolina Kaucha from the Institute of Geological Sciences, Polish Academy of Sciences, for her assistance with the laboratory work. Elemental analyses were contributed by the ICP Facility of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany. This work was also supported by the Bekker Program of the Polish National Agency for Academic Exchange (NAWA) (BPN/BEK/2021/1/00411).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAcharya BS, Kharel G (2020) Acid mine drainage from coal mining in the United States \u0026ndash;An overview. J Hydrol 588:125061. https://doi.org/10.1016/j.jhydrol.2020.125061\u003c/li\u003e\n\u003cli\u003eAlles E, N\u0026ouml;rpel-Schempp M, Lange-Bertalot H (1991) Taxonomy and ecology of characteristic Eunotia species in headwaters with low electric conductivity. Nova Hedwigia 53:171-213\u003c/li\u003e\n\u003cli\u003eBattarbee RW (1986) Diatom analysis. In: Handbook of Holocene palaeoecology and Palaeohydrology (ed) Berglund BE, J Willey and Sons, Chichester, pp 527\u0026ndash;570\u003c/li\u003e\n\u003cli\u003eBrugam RB, Lusk M (1986) Diatom evidence for neutralization in acid surface mine lakes. 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Gustav Fischer Verlag, Stuttgart\u003c/li\u003e\n\u003cli\u003eKrammer K, Lange-Bertalot H (1991a) Suswasserflora von Mitteleuropa. Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. Gustav Fischer Verlag, Stuttgart\u003c/li\u003e\n\u003cli\u003eKrammer K, Lange-Bertalot H (1991b) Suswasserflora von Mitteleuropa. Bacillariophyceae. 4. Teil: Achnanthaceae, Kritische Erg\u0026auml;nzungen zu \u003cem\u003eNavicula \u003c/em\u003e(Lineolatae) und \u003cem\u003eGomphonema \u003c/em\u003eTeil. Gustav Fischer Verlag, Stuttgart\u003c/li\u003e\n\u003cli\u003eKupetz A, Kupetz M, Rascher J (2004) Der Muskauer Faltenbogen. Gesellschaft f\u0026uuml;r Geowissenbschaften e. V. Berlin, pp 53 \u003c/li\u003e\n\u003cli\u003eLange-Bertalot H, Metzeltin D (1996) Ecology\u0026ndash;diversity\u0026ndash;taxonomy. Indicators of oligotrophy\u0026ndash;800 taxa representative of three ecologically distinct lake types. In: Lange-Bertalot H (ed) Iconographia Diatomologica 2. Koeltz Scientific Books, Koenigstein\u003c/li\u003e\n\u003cli\u003eLange-Bertalot H, Ulrich S (2014) Contributions to the taxonomy of needle-shaped \u003cem\u003eFragilaria\u003c/em\u003e and \u003cem\u003eUlnaria\u003c/em\u003e species. Lauterbornia 78:1-73\u003c/li\u003e\n\u003cli\u003eMaechler M, Rousseeuw P, Struyf A, Hubert M, Hornik K (2025) cluster: Cluster Analysis Basics and Extensions. R package version 2.1.8.1. https://CRAN.R-project.org/package=cluster\u003c/li\u003e\n\u003cli\u003eMartin A, Blanchard RL (1969) The thermal volatilisation of caesium-137, polonium-210 and lead-210 from in vivo labelled samples. Analyst 94:441\u0026ndash;446. https://doi.org/10.1039/AN9699400441\u003c/li\u003e\n\u003cli\u003eMatthews KM, Kim CK, Martin P (2007) Determination of \u003csup\u003e210\u003c/sup\u003ePo in environmental materials: a review of analytical methodology. Appl Radiat Isot 65:267\u0026ndash;279. DOI: 10.1016/j.apradiso.2006.09.005.\u003c/li\u003e\n\u003cli\u003eMoral R, Perez-Murcia MD, Perez-Espinosa A, Moreno-Caselles J, Paredes C, Rufete B (2008) Salinity, organic content, micronutrients and heavy metals in pig slurries from South-eastern Spain. Waste Manag 28:367\u0026ndash;371. https://doi.org/10.1016/J.WASMAN.2007.01.009\u003c/li\u003e\n\u003cli\u003eMorin S, Cordonier A, Lavoie I, Arini A, Blanco S, Duong TT, Torn\u0026eacute;s E, Bonet B, Corcoll N, Faggiano L, Laviale M, P\u0026eacute;r\u0026egrave;s F, Becares E, Coste M, Feurtet-Mazel A, Fortin C, Guasch H, Sabater S (2012) Consistency in Diatom Response to Metal-Contaminated Environments. In: Guasch H, Ginebreda A, Geiszinger A (eds) Emerging and Priority Pollutants in Rivers. The Handbook of Environmental Chemistry, vol 19:117-146. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-25722-3_5\u003c/li\u003e\n\u003cli\u003ePociecha A, Wojtal AZ, Szarek-Gwiazda E, Cieplok A, Ciszewski D. Cichoń S (2020) Neo- and paleo-limnological studies on diatom and cladoceran communities of subsidence ponds affected by mine waters (S. Poland) Water 12 (6):1581\u003c/li\u003e\n\u003cli\u003ePukacz A, Oszkinis-Golon M, Frankowski M (2018) The Physico-Chemical Diversity of Pit Lakes of the Muskau Arch (Western Poland) in the Context of Their Evolution and Genesis. Limnol Rev (2018) 18:115-126\u003c/li\u003e\n\u003cli\u003eS\u0026aacute;nchez Espa\u0026ntilde;a J, Pamo EL, Pastor ES, Ercilla M. D (2008) The acidic mine pit lakes of the Iberian Pyrite Belt: An approach to their physical limnology and hydrogeochemistry. App Geochem 23(5):1260\u0026ndash;1287. https://doi.org/10.1016/j.apgeochem.2007.12.036\u003c/li\u003e\n\u003cli\u003eSienkiewicz E, Gąsiorowski M (2016) The evolution of a mining lake\u0026mdash;from acidity to natural neutralization. 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J Contam Hydrol 225:103502\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-paleolimnology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jopl","sideBox":"Learn more about [Journal of Paleolimnology](http://link.springer.com/journal/10933)","snPcode":"10933","submissionUrl":"https://submission.nature.com/new-submission/10933/3","title":"Journal of Paleolimnology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"pit lake, diatoms, Cladocera, pig farm, eutrophication, pollution","lastPublishedDoi":"10.21203/rs.3.rs-6512111/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6512111/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBefore 1925, an artificial lake (TR-17) was created in a pit excavation in the area of Łuk Mużakowa (southwestern Poland). In the 19th century, this area was an active lignite mine, which means that its location was within the range of acid mine drainage. Between 1928 and 1943, the lake was transformed into a municipal bathing area with developed infrastructure. In the 1970s, a pig farm and meat processing plant were in operation. Sewage resulting from breeding and meat production was released directly into the surrounding fields. Together with surface and ground water, nutrients and toxic metals were delivered to the lake, impacting the phyto- and zooplankton communities. After the closure of the meat processing plant, the lake began to recover from both eutrophication and heavy metal pollution. During that time, other factors, such as liming and fish stocking, affected the development of phyto- and zooplankton.\u003c/p\u003e","manuscriptTitle":"Multiple stressor effects on the phyto- and zooplankton communities in a mining lake affected by acid mine drainage","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-05 08:35:51","doi":"10.21203/rs.3.rs-6512111/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-03T10:13:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-03T03:05:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"190986828839051411925391234896011809703","date":"2025-06-09T05:17:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-26T10:49:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"143080382038313018138528911825275772587","date":"2025-04-29T12:35:28+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-29T11:42:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-25T15:19:55+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-25T15:16:20+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Paleolimnology","date":"2025-04-23T11:20:36+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-paleolimnology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jopl","sideBox":"Learn more about [Journal of Paleolimnology](http://link.springer.com/journal/10933)","snPcode":"10933","submissionUrl":"https://submission.nature.com/new-submission/10933/3","title":"Journal of Paleolimnology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1ee725c1-6792-4e92-bc18-d4ef0dd7bc3b","owner":[],"postedDate":"May 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T15:59:21+00:00","versionOfRecord":{"articleIdentity":"rs-6512111","link":"https://doi.org/10.1007/s10933-025-00380-0","journal":{"identity":"journal-of-paleolimnology","isVorOnly":false,"title":"Journal of Paleolimnology"},"publishedOn":"2025-10-16 15:56:59","publishedOnDateReadable":"October 16th, 2025"},"versionCreatedAt":"2025-05-05 08:35:51","video":"","vorDoi":"10.1007/s10933-025-00380-0","vorDoiUrl":"https://doi.org/10.1007/s10933-025-00380-0","workflowStages":[]},"version":"v1","identity":"rs-6512111","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6512111","identity":"rs-6512111","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}