Assessing shifts in diatom communities in eastern Ontario recreational lakes in relation to land-use and climate changes over the past ~150 years using a top-bottom paleolimnological approach.

Assessing shifts in diatom communities in eastern Ontario recreational lakes in relation to land-use and climate changes over the past ~150 years using a top-bottom paleolimnological approach. | 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 Assessing shifts in diatom communities in eastern Ontario recreational lakes in relation to land-use and climate changes over the past ~150 years using a top-bottom paleolimnological approach. Mubashshera Rahman, Jesse C. Vermaire This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6100349/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 08 Oct, 2025 Read the published version in Journal of Paleolimnology → Version 1 posted 9 You are reading this latest preprint version Abstract Eastern Ontario, Canada, is a lake-rich, rural region, located primarily over Precambrian Shield. These lakes are typically nutrient-limited with total phosphorus (TP) less than 20 µgL -1 , and serve as the primary tourist attraction, contributing substantially to the local economy of this region. However, in recent years, residents have become concerned about the perceived increase in nuisance algal blooms. Due to the lack of long-term water quality monitoring data little information exists on pre-impact conditions, and water quality trends of these lakes. To address this gap, a top-bottom paleolimnological approach was used to examine diatom community shifts in 35 presently nutrient-limited (TP 5–19 µgL -1 ) lakes across the Mississippi and Rideau River watersheds of eastern Ontario. Shifts in diatom taxon between bottom and top sediment layers align with climate change indicators, suggesting increasing temperatures, longer ice-off periods, and reduced wind speeds, across the region. A spatial analysis conducted to determine if present-day TP concentrations correlated with modern land-use patterns revealed that the percentage of croplands and wetlands in nearshore riparian buffer zones (300 m) was positively corelated with present-day TP concentrations of the lakes. An increasing trend in the relative abundance of mesotrophic diatoms with lower sinking rates was observed across our study lakes, which is consistent with lake response to climate warming and nutrient enrichment. This research demonstrates that both land-use and climate change have had impacts on lake ecosystems in eastern Ontario over ~ 150 years. eutrophication climate change environmental change land-use change diatoms Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Since the mid-twentieth century, many freshwater bodies in North American have experienced cultural eutrophication due to excessive phosphorus loading from adjacent watersheds as a result of anthropogenic activities (Kalff 2003 , Schindler 2008, Vermaire et al. 2017 ). Concurrently, climate change is reshaping algal communities and promoting algal blooms (Rühland et al. 2008, 2015 , Taranu et al. 2015 ). For example, increasing air and water temperatures have extended the length of the ice-free season in temperate lakes, leading to longer growing periods, expanded habitat for primary producers and creating more favorable conditions for algal growth (Vincent et al. 2013, Rühland et al. 2008, 2015 ). Temperate lakes in eastern Ontario are largely located over the undulating Precambrian Shield and are typically clear (average Secchi depth ≥ 3.5 m) and nutrient-limited with total phosphorus (TP)) lower than 20 µgL -1 (Minnes and Douglas 2013 , MVCA 2020, RVCA 2019). These lakes are often located away from urban areas, and are popular sites for tourism, fishing, cottaging, and other recreational activities (MVCA 2020, RVCA 2019). However, over the past couple of years, frequent algal blooms have been reported in many of these nutrient-limited systems, which has led to increased concerns about water quality in the region (Winter et al. 2011 , Pick et al. 2016). While it is likely that both land-use change and climate warming are promoting algal blooms in eastern Ontario, the full impacts are not yet understood. The ecological response of aquatic ecosystems to environmental stressors, such as climate change and nutrient pollution, require longer monitoring datasets than typically available in the instrumental record to be detected (Smol 2002 , Randsalu-Wendrup et al. 2016 ). In this study, a top-bottom paleolimnological approach is used to examine shifts in diatom (Bacillariophyceae, unicellular algae) communities in 35 nutrient-limited (TP < 20 µgL -1 ), shield lakes in eastern Ontario. The goal of this study is to assess diatom community assemblage changes at a regional scale from pre-impact (bottom sediments) to present-day conditions (surface sediments) in relation to present day total phosphorus, land use, and climate change to assess which factors are having the greatest influence on diatom assemblage changes in these lakes. Further, we test the relationship between modern land use patterns at different spatial scales to present-day TP concentrations to examine if land-use changes are positively related to TP concentrations, suggesting a level of cultural eutrophication in these lakes. Methodology and materials Site description and study lakes selection The eastern Ontario region extends from the eastern side of Toronto to the Ottawa River from east to west, and from Algonquin Provincial Park to Lake Ontario in the north-south direction. This area (49,000 km 2 ) consists of 14 counties and several watersheds, including the Mississippi and the Rideau River watersheds. This undulating shield region is well-drained and slopes from the west to the north-east direction. The Pre-Cambrian bedrock of this region is covered by a thin layer of acidic soil composed of Melanic Brunosolic, Humo-ferric Podzol and some Luvisols. This terrain is extensively covered by deciduous and mixed forest zones and largely covered by wetlands, lakes, and rivers. In this predominantly rural area, forests and natural grasslands prevail, while scattered croplands and urban settlements are minimal (Baldwin et al. 2000, Minnes and Douglas 2013). Thirty-five shield lakes in eastern Ontario were selected for this study, located over the Mississippi and Rideau River watersheds, spanning Lanark Highland, Frontenac, Addington Highlands, and Leeds and Grenville counties. Lakes were selected on a gradient of total phosphorus (TP) concentrations ranging from 5 µgL -1 to 19 µgL -1 , with a maximum depth of 10 m or greater (Table 1 and Figure 1). Bedrocks of this study region are mainly composed of igneous and metamorphic rich bedrock (Figure 2, B), which is mostly covered mostly by thin acidic soil layer. Land-use in this zone consists of approximately 10% settlements and built-up areas, 10% wetlands, 20% croplands, and 60% of the land is forests, natural grasslands, and water bodies (Figure 2, A). In the late seventieth to ninetieth centuries, European people moved into eastern Ontario, originally inhabited by First Nation communities including Iroquois, Anishinaabe and Algonquin people (Watson 1996). Early European settlement was mainly concentrated near the north shore of the St. Lawrence River in Kingston, Prince Edward County and some parts of the Ottawa Valley. The settlers primarily engaged in farming, milling, and lumbering. However, during the late nineteenth and early twentieth century rapid urbanization, farmland expansion, and post-war population growth collectively led to large changes in land-use across the region (Watson 1996). Climate change impacts have also been documented across the region. An analysis by the Ministry of Environment, based on 35 years of temperature data (1975–2009) for Ontario's Shield region, revealed a significant decrease in the duration of the ice-covered season with a reduction of 24 ice-covered days over the past 35 years (MOE 2013). Diatom as bioindicators Diatoms are widely recognized as robust indicators of environmental change (Stoemer and Smol 1999). Their silicious shell make them well-preserved in lake sediments and their cell walls (frustules) ornamentation, valve shape and size make them easily identifiable at species level. They are highly sensitive to light, temperature, flow velocity, nutrients, pH, salinity and other environmental factors. Diatom communities rapidly shift in response to changes in the environment (Stoemer and Smol 1999, Smol 2002). A detailed study of diatom communities in lake sediment cores can provide excellent information about the timing and magnitude of historical environmental changes. However, diatom identification is labour-intensive and time-consuming; therefore, typically, only a few sites (lakes) can be examined for detailed study within a limited time and budget. A top-bottom approach to diatom analysis where the only the top and bottom layers of a sediment core are analyzed for diatoms allows for the investigation of a larger number of lakes to better understand water quality changes at the landscape scale. It should be noted that this approach has some drawbacks, such as a lack of precise temporal resolution. However, paleolimnological studies conducted numerous lakes across North America (Smol 2002, Rühland et al. 2003) have been able to confirm that the bottom layer of full sediment cores (typically > 20 cm in length) is representative of pre-industrial conditions. In this study, we collected the full sediment cores ranging from 15 cm to 30 cm in length. Therefore, the bottom layers of the sediment cores are representative of environmental conditions before widespread land-use and climate changes occurring post-1950 and extend to pre-impact (pre-1850) conditions. Field and laboratory methods We collected lake sediments via gravity sediment cores at the deepest point in each study lake. Sediment cores ranged in length from about 15 to 30 cm and were sectioned into 1 cm intervals using a Glew extruder (1988). Approximately 0.5 g of wet sediment samples from the top and bottom layers of the core were collected in labelled vials. Ten percent hydrochloric acid (HCl) was then added to each sample to remove carbonates followed by seven rinses with deionized water. Between rinses the sample was allowed to settle overnight to ensure no diatoms were lost during the rinses. Then the sediment samples were treated with 30% hydrogen peroxide (H 2 O 2 ) and heated in a water bath at 70 °C for 8 hours to oxidize organic material. Following the water bath diatom samples underwent seven rinses with dionized water to remove hydrogen peroxide residue with samples being allowed to settle overnight between rinses. Before platting onto coverslips, a drop of 10% HCl was added to each sample promote dispersion of the diatom on the coverslip. Samples then underwent a dilution series and were platted on coverslips at four different dilution concentrations, where each dilution contained approximately 50% of the diatom concentration as the sample before. The diatom samples were then pipetted onto coverslips on slide warmers and allowed to dry overnight while covered. Once the solutions were dry the coverslips were mounted onto microscope slides using Naphrax. A minimum of 400 diatom valves were counted per interval using a Leica DMRB light microscope at 1000 times magnification in order to identify diatom to the lowest taxonomical level possible. Krammer and Lange Bertalot (1986, 1988, 1991a, 1991b) taxonomic guides used here to identify diatom species (Spaulding et al. 2021). The diatom counts were converted to relative abundance data and stratigraphic plots were produced using C2 version 1.7.7 (Juggins 2014) to show taxa with a relative abundance ≥ 5%. Common taxa were identified based on those diatoms that reached a relative abundance ≥ 2% in at least one lake across the study region. To identify significant shifts in diatom species composition from the bottom to the top layer, we employed the Wilcoxon signed-rank test, a hypothesis test designed for non-parametric data analysis using R software (R Core Team 2020). This non-parametric test is used here, for comparing paired data (diatom sp. of top and bottom layer). The ratio of chrysophyte cysts to diatom valves was also analyzed in this study. Chrysophyte algae are common in freshwater ecosystem and usually occur with diatoms. Chrysophyte algae produce morphologically distinct siliceous, microscopic cysts during the resting stage of their life cycle and preserved in sediments (Adam and Mahood 1981, Köster et al. 2005). Cysts are often restricted to specific environmental conditions making the cyst:diatom ratio a useful as indicator to detect environmental changes (Adam and Mahood 1981, Köster et al. 2005). Spatial Data A Geographical Information System (GIS) and ARC-Map (10.7) software was used to quantify land-use within the watersheds of the study lakes. Spatial data were collected from the National Hydro Network and Scholars geo-portal to specify the lakes’ locations (DMTI 2015). Lake surface area (LA) and lake catchment area (CA) of individual lakes (as sub-catchment of the watersheds), as well as the catchment area to lake area ratio (CA:LA) were calculated. To delineate study lakes’ catchment, we used the Ontario integrated hydrology- data packages, which provide raster datasets of elevation (e.g. enforced and filled Digital Elevation Model), flow direction, flow accumulation, integrated with mapped vector features such as lake locations and surface areas (OMNRF 2019). GIS watershed tools were used to determine the pour-points for each lake and based on these points, the gross catchment (whole catchment) for each lake was delineated. The immediate (local) lake catchment was then isolated from the gross catchment area. Mackavoy Lake, with a lake surface area of ~0.3 km 2 , is the smallest lake in the study region. Waterbodies having surface area ranging from 0.001 to 1 km 2 are often classified as pond rather than lakes (Richarson et al. 2022), Therefore, we classified all the waterbodies with a surface area less than 0.3 km 2 as smaller waterbodies. Por points were created for water bodies with a lake surface area ≥ 0.3 km 2 , and catchment boundaries for each individual smaller waterbody were delineated. Next, the catchments for individual small waterbodies were separated from the gross catchment area and finally we delineated the local lake catchment boundary for each lake. Riparian buffer zones of 300 m and 500 m around each lake were also delineated using spatial analysis tool in GIS. Natural riparian zones act as the interface between aquatic and terrestrial ecosystems, playing a critical role in regulating surface run-off and nutrient loading to the lake ecosystem (Wang et al. 2020). Land-use data were collected from Agriculture and Agri-Food Canada, created in 2010 (AAFC 2010). Using ARC-Map (version 10.7) software in GIS, spatial data with a pixel resolution of 30 m was analyzed in the World Geodetic System (WGS) 84 coordinate. The original land-use data comprised fifteen different classes, which were simplified into six groups for this study: Croplands, Forest and Natural Grasslands (excluding commercial grasslands in our study region), Roads and Built-Up Urban Areas, Waterbodies, Wetlands, and Other. After the reclassification, the TIF raster data was converted into (vector) shapefiles. Additionally, the slope of the lake catchment (local and gross catchment) and the riparian buffer zones (300 m, 500 m) was determined through spatial analysis of the Digital Elevation Model (DEM), obtained from Ontario integrated hydrology- data packages (OIH data). Water quality data (Epilimnetic TP) Modern water quality data for all the study lakes was collected from the Mississippi and Rideau Valley Conservation Authorities’ water-quality monitoring programs (MVCA 2015, 2018, 2020, RVCA 2019, 2020). Secchi depth, pH, chlorophyll-a (CHL-a), nitrogen (N), dissolved organic carbon (DOC), and Total Phosphorus (TP) levels were collected from the epilimnion of each lake. To better understand the physical properties of the study lakes, data about the lake surface area (LA), perimeter, shoreline, and maximum depth were also collected. Mean total phosphorus (TP) data from 2008 to 2018 was used as an indicator of each lake’s present-day trophic status. Linear Regression Models (R software) were used to test the relationship between modern TP concentrations and the percentage of different land covers at multiple spatial scales (R Core Team 2020). Climate data To understand historical climate in the study region, historical (1880-2019) climate data from the nearest weather stations were collected. Adjusted and homogenized mean annual temperature (Ottawa weather Station ID 6105976), precipitation (Ottawa weather Station ID 6105976) and wind speed data (Ottawa McDonald Cartier INTL Station ID 6106000, Muskoka Station ID 6115525, Kingston Station ID 6104146) (ECCC 2020) were obtained covering a time period between 1890-2020. A Mann-Kendall test was used to examine if the time-series data for annual temperature, precipitation and wind-speed have significantly changed over time using software R (R Core Team 2020). Results Land-use impacts Total Phosphorus (TP) concentration of a lake was moderately correlated to land use within the lake’s catchment (Fig 3). Percent croplands and wetlands within the 300 m and 500 m riparian buffer zones were positively related to TP and explained a similar amount of the variance in TP (300 m: R 2 = 0.37, p < 0.001; 500 m: R 2 = 0.32, p < 0.001). Positive relationships were also found within the gross catchment (R 2 = 0.13, p = 0.02) and local catchment (R 2 = 0.15, p = 0.01), but the R 2 values suggest a weaker model fit, explaining about 13% to 15% of the variability in TP concentrations. This implies that croplands and wetlands within 300 m to 500 m buffer zones have a more substantial influence on explaining the variability in the present-day trophic status of lakes. No significant relationships were found between catchment slope within the gross catchment, lake area (LA, m 2 ), lake depth (m), and TP (µgL -1 ) concentrations. Similarly, a negative relationship was observed between percent forest, natural grasslands, and water bodies within 300 m (R 2 = 0.24, p = 0.002) and 500 m (R 2 = 0.24, p = 0.002) riparian buffer zones with TP concentrations (Fig 4). Negative relationships were also observed across multiple spatial scales: local catchment (R 2 = 0.17, p = 0.008) and gross catchment (R 2 = 0.10, p = 0.03), where the R 2 values suggest a weaker model fit. Climate change impact The mean annual, winter and summer temperature data (homogenised), collected from1890 to 2020 at MacDonald Cartier Int. weather station (ID 6106000) in Ottawa. A linear regression model showed (Supplementary Figure 1) a positive increasing trend in mean annual, winter and summer air temperatures. A linear regression model estimates a substantial ~2 °C increase in mean annual temperature from 1890 to 2020. Increase in mean winter and summer temperature was also observed. However, the R² values for winter (0.1846) and summer (0.1233) indicate limited explanatory power in the linear model for these specific seasons. The Mann-Kendall tests indicated a significant increase in annual mean temperature (p < 0.005) and in winter (p 0.005). Mann-Kendall test indicated a significant decrease in summer wind-speed in Kingston (p < 0.005), Ottawa Macdonald Cartier Int. (p < 0.005) and Muskoka (p < 0.005) weather stations over the time (Supplementary Figure 2). A Mann-Kendall test indicated no significant change in precipitation from 1890 to 2020 (p = 0.5). Change in Diatom Composition The diatom stratigraphic plot does not clearly illustrate a distinct trend of either increasing or decreasing diatom taxa among all 35 study lakes (Figure 5). However, notable patterns appeared in the relative abundance of certain planktonic taxa across the sediment layers. The top layers exhibited a visible increase in the relative abundance of planktonic taxa. We did not observe a consistent shift to nutrient-tolerant diatom taxa across the study region. A significant rise in the abundance of elongated mesotrophic, lighter, planktonic diatom taxa, namely Fragilaria crotonensis (p = 0.001) and Asterionella fromosa (p = 0.003) (relative abundance > 2%) was evident in the modern sediment intervals compared to the pre-impact bottom sediment samples (Figure 6, A, B). A significant (p = 0.01) decreasing trend in the cyst: diatom ratio was also observed between bottom and surface sediments but appeared to be driven by a few lakes that underwent large changes in this ratio (Figure 6, C). Discussion Lakes of eastern Ontario are mostly nutrient limited (TP < 20 mgL -1 ) systems, largely due to the natural landscape. Additionally, this paleolimnological study did not find any significant shift in eutrophic diatom taxa from the bottom to the top sediment layers, suggesting that the trophic levels of these lakes have remained relatively stable over time, which is consistent with the modern trophic classification of these lakes from oligotrophic to mesotrophic. However, this study revealed a significant positive relationship between present-day land use (percent of croplands and wetlands) in near shore zone (300 m, 500 m buffer) and TP concentrations in the lake, suggesting that land-use change may have resulted in nutrient enrichment of these lakes but this nutrient enrichment has not yet been substantial enough to push these lakes into a eutrophic state. This aligns with studies indicating a correlation between land-use change and lake water quality (Carpenter et al. 2008). In general, wetlands are a sink of nutrients and impurities, helping to purify water bodies. However, in some cases, wetlands also act as a source of nutrients or may act as a transformer of nutrients to the lakes, which depends on the slope, land-use cover of the watershed, as well as position and characteristics of wetlands (Reddy et al. 2010). This depends on the wetlands' nature and land-use pattern (e.g. percentage of croplands) across the region (Emi Fergus et al. 2011). It has been documented that local wetlands are linked to increased TP levels in temperate lake ecosystems, where the percentage of croplands is lower on a regional scale (Emi Fergus et al. 2011). It has also been highlighted that land-use impacts near the lake shore have a greater effect on aquatic species compared to the entire catchment (Alahuuta et al. 2014, Zhang 2020, Shu et al. 2022). Based on the analysis of diatom species composition, a significant increasing trend in mesotrophic elongated diatom species F. crotonensis and A. formosa was observed from pre-impact to present-day sediment layers. These taxa are also commonly found in lakes with higher TP concentrations and are classified as mesotrophic taxa (Revive et al. 2002). The observed increase in mesotrophic taxa may indicate slight nutrient enrichment of the study lakes since the reference period. However, there is some ambiguity in the literature regarding the abundance of F. crotonensis and A. formosa in lake ecosystems. In certain studies, it has been observed that their abundances correlate significantly with nitrogen (N) deposition in lakes. It's important to note that many of these studies were conducted in high-altitude lakes (Saros et al. 2005, Stewart et al. 2008). The limited studies conducted in proximity to our study area, specifically the Ontario Shield lakes, have reported no correlation between nitrogen (N) concentration and the abundance of these elongated diatom species (Sivarajah et al. 2016, Rühland et al. 2015). A significant increase in mean winter temperatures has been observed in the study region, which may lead to earlier ice-off days and longer ice-free seasons. Similarly, a significant increase in mean annual temperature indicates overall warmer temperatures, which may strengthen the study lakes' thermal stratification. In addition, a significant declining trend in mean wind speed during summer has been observed in the study region, which could ultimately bolster climate warming impacts on lake ecosystems and strengthen thermal stratification of the lakes. This could lead to deeper epilimnion and a shallower thermocline in dimictic temperate lakes, which expands habitat for primary producers and enhances the stability of the lakes' water (Kalff 2003, Vincent 2009, Rühland et al. 2023). This condition is particularly favourable for the growth of lighter phytoplankton diatom taxa, in contrast to the heavy thychoplanktonic taxa (Rühland et al. 2008, 2015). Recent paleolimnological studies on deep northern lakes also revealed that due to climate change impacts in recent years, warmer temperatures, declining ice-covered periods, and reduced wind speed resulted in a shift in diatom species composition (Rühland et al. 2023). The largest consistent shift observed in diatom taxa across our study region was an increase in Aesterionella formosa (p = 0.003) and Fragilaria crotonensis (p = 0.001) . These diatoms have a high surface area to volume ratio, making them more buoyant than other diatom taxa. F. crotonensis cells join together to arrange themselves into ribbon-shaped colonies, while A. formosa are arranged into star-shaped colonies by mucilage pads. Living in colonies provides them with the advantage of remaining more buoyant in the water column (Sivarajah et al. 2018). Therefore, these taxa can thrive when lake stratification is stronger, and the thermocline is shallower. The shift in diatom taxa from pre-impact to present-day suggests the existence of coherent climate change signals across the study area. These taxa are also mesotrophic in nature and increasing their abundance indicates a rise in lakes’ nutrient levels. Therefore, the likely cause of the increase in the relative abundance of these taxa is an interaction of climate mediated changes and nutrients. A significant declining trend between the sediment's bottom to top layers in the chrysophyte cyst:diatom ratio has also been observed among the study lakes. Cryophytes cysts are more abundant in cooler and nutrient-poor conditions (Adam and Mahood 1981, Köster et al. 2005). Therefore, the declining cyst:diatom ratio trend is also consistent with warming conditions with nutrient enrichment across the study lakes. Therefore, an increasing trend in mesotrophic elongated planktonic taxa and declining cyst:diatom ratios from pre-impact to present day across the study lakes is consistent with the combined influence of climate change and a modest increase in nutrient (TP) levels across the watershed. Conclusions Our results indicate a shift to mesotrophic diatoms with lower sinking rates across the study region, which is consistent with climate warming and slight nutrient enrichment. This study also revealed that the percent croplands and wetlands combined was positively related to TP concentrations in the lake. Croplands and wetlands in nearshore riparian buffer zones (300 m) most strongly affected lake water quality compared to broader shoreline area and lake catchments. This paleolimnological investigation suggests that lakes in eastern Ontario are experiencing pressures from both land-use changes (near shore) and climate change that is affecting the algal community of these lakes. Declarations Author Contribution MR and JCV conceptualized the study. MR carried out the laborartory work and wrote the manuscript and prepared the figures with guidance and editorial comments from JCV. Acknowledgement We would like to thank Mississippi Valley and Rideau Valley Conservation Authorities for sharing their water quality data and advising on the selection of the study lakes. Special thanks also go to the GIS support team of MacOrdum Library at Carleton University. This research was funded by a NSERC Discovery Grant to JCV. References Adam, D.P., Mahood, A.D., 1981. Chrysophyte cysts as potential environmental indicators. Geological Society of America Bulletin. 92(11), 839–844. Agriculture and Agri-Food Canada (AAFC). 2010. Land Use 2010. Retrieved from: https://open.canada.ca/data/en/dataset/fa84a70f-03ad-4946-b0f 8-a3b481dd5248 Baldwin, D. J., Desloges, J. R., & Band, L. E. 2000. Physical geography of Ontario. In: Perera, A.H., Euler, D.L., & Thompson, I.D. (eds.), Ecology of a managed terrestrial landscape: patterns and processes of forest landscapes in Ontario, 12–29. Carpenter, S. R., 2008. Phosphorus control is critical to mitigating eutrophication. Proceedings of the National Academy of Sciences, 105 (32), 11039–11040 DMTI Spatial Inc., 2015. Water names point. Retrieved from: http://geo1.scholarsportal.info/#r/tab/browseTab . Accessed 20 April 2019. Emi Fergus, C., Soranno, P. A., Cheruvelil, K. S., & Bremigan, M. T., 2011. Multiscale landscape and wetland drivers of lake total phosphorus and water color. Limnology and Oceanography, 56(6), 2127–2146. Environment and Climate Change Canada (ECCC). 2020. Adjusted and homogenized Canadian climate data. Retrieved from: https://www.canada.ca/en/environment-climate-change/services/climate-change/science-research-data/climate-trends-variability/adjusted-homogenized-canadian-data.html Juggins, S. 2014. C2 version 1.7.7. Software for ecological and palaeoecological data analysis and visualisation. Newcastle upon Tyne, UK: Newcastle University. Kalff, J., 2003. Limnology: Inland Water Ecosystems. Upper Saddle River, New Jersey: Prentice Hall Krammer, K., Lange-Bertalot, H., 1986, 1988, 1991, 1991b. Bacillariophyceae. 1. Teil: Naviculaceae In: Ettl, H., Gerloff, J., Heynig, H., Mollenhauer, D., (eds.). Süsswasserflora von Mitteleuropa, Band 2/1. Stuttgart: Gustav Fischer Verlag. p. 1–876, p. 1–596, p. 1–576, p. 1–437. German. Köster, D., Pienitz, R., Wolfe, B.B., Barry, S., Foster, D.R., Dixit, S.S., 2005. Paleolimnological assessment of human-induced impacts on Walden Pond (Massachusetts, USA) using diatoms and stable isotopes. Aquatic Ecosystem Health & Management 8(2), 117–131. Ministry of the Environment (MOE), 2013. Water Quality Ontario: Report 2012. Queen’s Printer for Ontario (PIBS # 9493e). Retrieved from: https://www.ontario.ca/page/water-quality-ontario-report-2012#section-2 Minnes, S., Douglas, J.A., 2013. A Profile of Eastern Ontario. Canadian Regional Development: A Critical Review of Theory, Practice and Potentials. Mississippi Valley Conservation Authority (MVCA), 2015. State of the Lake environment report 2015-Mississippi Lake. Retrieved from: http://mvc.on.ca/wp-content/uploads/2014/01/2015-Mississippi-Lake-Report.pdf , http://mvc.on.ca/ww-state-of-the-lake-reports/ Mississippi Valley Conservation Authority (MVCA), 2018. Water quality monitoring (raw data) collected from MVCA Mississippi Valley Conservation Authority (MVCA), 2019. Watershed Boundary. Retrieved from: http://mvc.on.ca/watershed-boundary/ Mississippi Valley Conservation Authority. 2020. Reports. Mississippi Valley Conservation. Retrieved from: Authority. https://mvc.on.ca/reports/ MLA, MVCA, Watershed Canada, French Planning Service Inc., 2015. Mississippi Lake Plan. Retrieved from: https://watersheds.ca/wp-content/uploads/2015/01/20150530-mla-lake-plan.pdf Ontario Ministry of Northern Development and Mines, 2013. Mineral Deposits Inventory. http://geo.scholarsportal.info/#r/details/_uri@=3588886954 Ontario Ministry of Environment and Energy. 2023. Map: lake partner. Retrieved from: Map: Lake partner | ontario.ca Ontario GeoHub, 2019. Ontario integrated hydrology data. Retrieved from: https://data.ontario.ca/dataset/ontario-integrated-hydrology-data . Accessed 12 September 2019 Ontario GeoHub, 2019. Conservation Authority Administrative Area. Retrieved from: https://geohub.lio.gov.on.ca/datasets/6e03611af2584378893921351f75fb35_11 Ontario Ministry of Natural Resource and Forestry (OMNRF), 2019. Ontario Integrated Hydrology (OIH) data. Retrieved from: https://www.arcgis.com/home/item.html?id=dc6da 6816e2446279210668718af91c9 Pick, F. R., 2016. Blooming algae: a Canadian perspective on the rise of toxic cyanobacteria. Canadian Journal of Fisheries and Aquatic Sciences 73(7), 1149–1158. R Core Team. 2020. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. Retrieved from https://www.R-project.org/ Randsalu-Wendrup, L., Conley, D. J., Carstensen, J., & Fritz, S. C. 2016. Paleolimnological records of regime shifts in lakes in response to climate change and anthropogenic activities. Reddy, K.R., DeLaune, R. and Craft, C.B., 2010. Nutrients in Wetlands: Implications to Water Quality under Changing Climatic Conditions. Final Report Submitted to U. Environmental Protection Agency, EPA Contact No. EP-C-0001. Richardson, D. C., Holgerson, M. A., Farragher, M. J., Hoffman, K. K., King, K. B.,Alfonso, M. B., … Sweetman, J. N. 2022. A functional definition to distinguish ponds from lakes and wetlands. Scientific reports, 12(1), 10472. Rideau Valley Conservation Authority (RVCA), 2019. Catchment. Retrieved from: https://rvcagis.github.io/jkan/datasets/rvca-catchments/ Rideau Valley Conservation Authority (RVCA), 2019. Lake monitoring reports (Raw data) collected from RVCA Rideau Valley Conservation Authority (RVCA), 2020. Sub-watershed Reports. https://watersheds.rvca.ca/component/content/article/91-middle-rideau/catchments/otter-creek/128-catchment-facts . Accessed 17 January 2020 Rideau Valley Conservation Authority (RVCA), 2021. Waterbody shape file. Retrieved from: https://rvcagis.github.io/jkan/datasets/rvca-waterbodies / Rühland, K., Priesnitz, A., & Smol, J. P., 2003. Paleolimnological evidence from diatoms for recent environmental changes in 50 lakes across Canadian Arctic treeline. Arctic, Antarctic, and Alpine Research, 35(1), 110–123. Rühland, K., Paterson, A. M., & Smol, J. P., 2008. Hemispheric-scale patterns of climate‐related shifts in planktonic diatoms from North American and European lakes. Global Change Biology, 14(11), 2740–2754. Rühland, K. M., Paterson, A. M., & Smol, J. P., 2015. Lake diatom responses to warming reviewing the evidence. Journal of paleolimnology, 54(1), 1–35. Rühland, K. M., Evans, M., and Smol, J. P., 2023. Arctic warming drives striking twenty-first century ecosystem shifts in Great Slave Lake (Subarctic Canada), North America's deepest lake. Proceedings of the Royal Society B, 290(2007), 20231252. Saros, J. E., Clow, D. W., Blett, T., & Wolfe, A. P., 2011. Critical nitrogen deposition loads in high-elevation lakes of the western US inferred from paleolimnological records. Water, Air, & Soil Pollution, 216, 193–202. Schindler, D. W., Hecky, R. E., Findlay, D. L., Stainton, M. P., Parker, B. R., Paterson, M.J., Beaty, K.G., Lyng, M. & Kasian, S. E. M., 2008. Eutrophication of lakes cannot be controlled by reducing nitrogen input: results of a 37-year whole-ecosystem experiment. Proceedings of the National Academy of Sciences, 105(32), 11254–11258. Sivarajah, B., Rühland, K.M., Labaj, A.L., Paterson, A.M., Smol, J. P., 2016. Why is the relative abundance of Asterionella formosa increasing in a Boreal Shield Lake as nutrient levels decline? Journal of paleolimnology 55(4), 357–367. Sivarajah, B., Paterson, A. M., Rühland, K. M., Köster, D., Karst-Riddoch, T., & Smol, J. P., 2018. Diatom responses to 20th century shoreline development and climate warming in three embayments of Georgian Bay, Lake Huron. Journal of Great Lakes Research, 44(6),1 33 13-Sep 50 Shu, W., Wang, P., Xu, Q., Zeng, T., Ding, M., Zhang, H., Nie, M., Huang, G., 2022. Coupled effects of landscape structures and water chemistry on bacterioplankton communities at multi-spatial scales. Science of The Total Environment, Volume 811, 1 50 35 0, 1 SSN 0048–9697, https://doi.org/10.1016/j.scitotenv.2021.151350 Smol, J.P., 2002. Pollution of lakes and rivers: a paleoenvironmental perspective. USA, NY: Oxford University Press. Spaulding, S.A,, Bishop, I.W., Edlund, M.B., Lee, S., Furey, P., Jovanovska, E., Potapova, M., 2021. Diatoms of North America. Retrieved from: https://diatoms.org/ . Accessed 29 Mar 202. Statistics Canada, 2016 Cartographic Boundary Files. Retrieved from: http://geo.scholarsportal.info/#r/details/_uri@=749265755$DLI_2016_Census_CBF_Eng_Nat_pr&_add:true_nozoom:true . Accessed 29 Mar 2021 Stoermer, E., and Smol, J.P. (Ed), 1999. The Diatoms: Applications for the Environmental and Earth Sciences.UK. Cambridge University Press. Stewart, K. A., Lamoureux, S. F., & Finney, B. P., 2008. Multiple ecological and hydrological changes recorded in varved sediments from Sanagak Lake, Nunavut, Canada. Journal of Paleolimnology, 40, 217–233. Taranu, Z. E., Gregory-Eaves, I., Leavitt, P. R., Bunting, L., Buchaca, T., Catalan, J., Domaizon, I., Guilizzoni, P., Lami, A., McGowan, S. & Moorhouse, H., 2015. Acceleration of cyanobacterial dominance in north temperate‐subarctic lakes during the Anthropocene. Ecology Letters, 18(4), 375–384 Vermaire, J.C., Taranu, Z.E., MacDonald, G.K., Velghe, K., Bennett, E.M., & Gregory-Eaves, I., 2017. Extrinsic vs. Intrinsic Regimes Shifts in Shallow Lakes: Long-Term Response of Cyanobacterial Blooms to Historical Catchment Phosphorus Loading and Climate Warming. Frontiers in Ecology and Evolution 5, 146. Vincent, W.F., 2009. Effects of climate change on lakes. Pollution and Remediation pp 55–60. http://www.cen.ulaval.ca/warwickvincent/PDFfiles/229.pdf Wang, M., Duan, L., Wang, J., Peng, J., & Zheng, B., 2020. Determining the width of lake riparian buffer zones for improving water quality base on adjustment of land use structure. Ecological Engineering, 158, 106001 Watson, W.K., 1996. Rideau Canal- National Historic Site-World Heritage Site. Retrieved from: http://www.rideau-info.com/canal/history/rideau-route/watersheds.html Winter, J.G., DeSellas, A.M., Fletcher, R., Heintsch, L., Morley, A., Nakamoto, L., Utsumi, K., 2011. Algal blooms in Ontario, Canada: increases in reports since 1994. Lake and Reservoir Management 1;27(2):107–14. DOI: 10.1080/07438141.2011.557765 Zhang, J., Li, S., Jiang, C., 2020. Effects of land use on water quality in a River Basin (Daning) of the Three Gorges Reservoir Area, China: Watershed versus riparian zone, Ecological Indicators, Volume 113, 106226, ISSN 1470–160X, https://doi.org/10.1016/j.ecolind.2020.106226 . Table Table 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Tables.pdf SupplementaryFigures1.pdf Cite Share Download PDF Status: Published Journal Publication published 08 Oct, 2025 Read the published version in Journal of Paleolimnology → Version 1 posted Editorial decision: Revision requested 30 Mar, 2025 Reviews received at journal 28 Mar, 2025 Reviews received at journal 20 Mar, 2025 Reviewers agreed at journal 03 Mar, 2025 Reviewers agreed at journal 03 Mar, 2025 Reviewers invited by journal 02 Mar, 2025 Editor assigned by journal 27 Feb, 2025 Submission checks completed at journal 27 Feb, 2025 First submitted to journal 24 Feb, 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6100349","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":423021856,"identity":"9c80e696-4e82-444e-ab48-bf3016b9ae3f","order_by":0,"name":"Mubashshera Rahman","email":"data:image/png;base64,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","orcid":"","institution":"Carleton University","correspondingAuthor":true,"prefix":"","firstName":"Mubashshera","middleName":"","lastName":"Rahman","suffix":""},{"id":423021858,"identity":"6bee2d86-8352-48fb-b4fa-e890e5071150","order_by":1,"name":"Jesse C. Vermaire","email":"","orcid":"","institution":"Carleton University","correspondingAuthor":false,"prefix":"","firstName":"Jesse","middleName":"C.","lastName":"Vermaire","suffix":""}],"badges":[],"createdAt":"2025-02-25 01:08:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6100349/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6100349/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10933-025-00376-w","type":"published","date":"2025-10-08T15:57:48+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":77566607,"identity":"7fd8df19-b164-4993-a566-e03857c8f86c","added_by":"auto","created_at":"2025-03-03 07:39:13","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1288720,"visible":true,"origin":"","legend":"\u003cp\u003eA) Spatial distribution of the study lakes across the Mississippi and Rideau River watersheds of eastern Ontario region. Lake locations in (A) correspond to lakes names and numbers in (B) (DMTI 2015, Ontario GeoHub 2019, Statistics Canada 2016, MVCA 2019, RVCA 2021) B) Average Total Phosphorus (TP, µgL\u003csup\u003e-1\u003c/sup\u003e) concentrations of the study lakes (2008-2018) (MVCA 2020, RVCA 2019, 2020).\u003c/p\u003e","description":"","filename":"Figures1.png","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/5e1c864e8d3b8fb0298f4b5f.png"},{"id":77566611,"identity":"bf953364-3d46-4871-bde3-25a74766e51a","added_by":"auto","created_at":"2025-03-03 07:39:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2678439,"visible":true,"origin":"","legend":"\u003cp\u003eA) Percentage of present-day land-use across the Mississippi River \u0026amp; Rideau River watersheds of study area (AAFC 2010, Ontario Geohub 2019, MVCA 2019, RVCA 2021), B) Bedrock composition across Mississippi River \u0026amp; Rideau River watersheds of the study area (Ontario GeoHub 2019, MVCA 2019, RVCA 2021)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figures2.png","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/7c1de256d560c59df28ddcd1.png"},{"id":77566613,"identity":"0e0dfd46-ccef-4707-bee0-e091fef348f2","added_by":"auto","created_at":"2025-03-03 07:39:14","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":45289,"visible":true,"origin":"","legend":"\u003cp\u003eThe relationship between present-day Total Phosphorus (µgL\u003csup\u003e-1\u003c/sup\u003e) levels and the percentage of the croplands and wetlands in the shore areas of study lakes: A) 300 m buffer zone, B) 500 m buffer zone, C) Local catchment, D) Gross catchment\u003c/p\u003e","description":"","filename":"Figures3.png","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/cdfe3d7bec506d16710cab0b.png"},{"id":77566616,"identity":"1c2639e2-fae9-4c5e-ba8d-8e823ae2d44f","added_by":"auto","created_at":"2025-03-03 07:39:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":48725,"visible":true,"origin":"","legend":"\u003cp\u003eThe relationship between present-day Total Phosphorus (µgL\u003csup\u003e-1\u003c/sup\u003e) levels and the percentage of the forest, natural grasslands, and water bodies in the shore areas of study lakes A) 300 m buffer zone B) 500 m buffer zone, C) Local catchment, D) Gross catchment\u003c/p\u003e","description":"","filename":"Figures4.png","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/ef193f19124b2baa37b008f6.png"},{"id":77566626,"identity":"16f29160-af33-4ab9-8f7a-244e8e85adaf","added_by":"auto","created_at":"2025-03-03 07:39:15","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":262050,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphic plot shows changes in diatom species abundance (Relative abundance ≥ 5% occurrence in at least 1 sample) from bottom to the top layers of the study lakes. Negative values with lack bars indicate that the relative abundance was greater in the bottom sediments and the red bars with positive values indicate that the diatom taxa have a greater relative abundance in the top layer of the sediment. Values of 0, indicate that the diatom relative abundance in the bottom and top sediment layers was equal. The lakes are listed in ascending order of Total Phosphorus (TP) concentration from Buckshot Lake (lowest) to Mackvoy Lake (highest). An orange dash line separates the oligotrophic (TP, 4-10 µgL\u003csup\u003e-1\u003c/sup\u003e) from mesotrophic (TP, 10-20 µgL\u003csup\u003e-1\u003c/sup\u003e) lakes.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/5f77b6d6e7e52468b81f0434.png"},{"id":77567149,"identity":"4ddf3da1-e001-456a-9243-e11b70dcb8d8","added_by":"auto","created_at":"2025-03-03 07:47:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":197628,"visible":true,"origin":"","legend":"\u003cp\u003eSignificant shifts were observed in the relative abundance of A) Fragilaria crotonensis, B) Asterionella formosa, C) Cyst and Diatom ratio from the bottom to the top sediment layers. These changes were analyzed using a Wilcoxon signed-rank test (for non-parametric data). The red lines represent the 1:1 line, indicating no change in diatom taxa between the top and bottom layers. Dots above the line show higher abundance in the top layer, while dots below the line show higher abundance in the bottom layer.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/b5b81cbc2557d939d3c1e23d.png"},{"id":93419843,"identity":"b01e79b4-83e8-470e-bb21-4f3f93a9c243","added_by":"auto","created_at":"2025-10-13 16:08:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5164074,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/33202957-1da8-47b8-a327-fee829ef5052.pdf"},{"id":77566608,"identity":"11c12503-d011-4218-a075-2fc6a8361799","added_by":"auto","created_at":"2025-03-03 07:39:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":36693,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/c4d2431c34229fcf5ac703b0.pdf"},{"id":77566628,"identity":"2046e8ff-5f07-4414-b699-ee646796dee2","added_by":"auto","created_at":"2025-03-03 07:39:15","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":121237,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFigures1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6100349/v1/1426ba413a946ab71f35d825.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eAssessing shifts in diatom communities in eastern Ontario recreational lakes in relation to land-use and climate changes over the past ~150 years using a top-bottom paleolimnological approach.\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSince the mid-twentieth century, many freshwater bodies in North American have experienced cultural eutrophication due to excessive phosphorus loading from adjacent watersheds as a result of anthropogenic activities (Kalff \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e, Schindler 2008, Vermaire et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Concurrently, climate change is reshaping algal communities and promoting algal blooms (R\u0026uuml;hland et al. 2008, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Taranu et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). For example, increasing air and water temperatures have extended the length of the ice-free season in temperate lakes, leading to longer growing periods, expanded habitat for primary producers and creating more favorable conditions for algal growth (Vincent et al. 2013, R\u0026uuml;hland et al. 2008, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTemperate lakes in eastern Ontario are largely located over the undulating Precambrian Shield and are typically clear (average Secchi depth\u0026thinsp;\u0026ge;\u0026thinsp;3.5 m) and nutrient-limited with total phosphorus (TP)) lower than 20 \u0026micro;gL\u003csup\u003e-1\u003c/sup\u003e (Minnes and Douglas \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, MVCA 2020, RVCA 2019). These lakes are often located away from urban areas, and are popular sites for tourism, fishing, cottaging, and other recreational activities (MVCA 2020, RVCA 2019). However, over the past couple of years, frequent algal blooms have been reported in many of these nutrient-limited systems, which has led to increased concerns about water quality in the region (Winter et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2011\u003c/span\u003e, Pick et al. 2016). While it is likely that both land-use change and climate warming are promoting algal blooms in eastern Ontario, the full impacts are not yet understood. The ecological response of aquatic ecosystems to environmental stressors, such as climate change and nutrient pollution, require longer monitoring datasets than typically available in the instrumental record to be detected (Smol \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, Randsalu-Wendrup et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this study, a top-bottom paleolimnological approach is used to examine shifts in diatom (Bacillariophyceae, unicellular algae) communities in 35 nutrient-limited (TP\u0026thinsp;\u0026lt;\u0026thinsp;20 \u0026micro;gL\u003csup\u003e-1\u003c/sup\u003e), shield lakes in eastern Ontario. The goal of this study is to assess diatom community assemblage changes at a regional scale from pre-impact (bottom sediments) to present-day conditions (surface sediments) in relation to present day total phosphorus, land use, and climate change to assess which factors are having the greatest influence on diatom assemblage changes in these lakes. Further, we test the relationship between modern land use patterns at different spatial scales to present-day TP concentrations to examine if land-use changes are positively related to TP concentrations, suggesting a level of cultural eutrophication in these lakes.\u003c/p\u003e"},{"header":"Methodology and materials","content":"\u003ch2\u003eSite description and study lakes selection\u003c/h2\u003e\n\u003cp\u003eThe eastern Ontario region extends from the eastern side of Toronto to the Ottawa River from east to west, and from Algonquin Provincial Park to Lake Ontario in the north-south direction. This area (49,000 km\u003csup\u003e2\u003c/sup\u003e) consists of 14 counties and several watersheds, including the Mississippi and the Rideau River watersheds. This undulating shield region is well-drained and slopes from the west to the north-east direction. The Pre-Cambrian bedrock of this region is covered by a thin layer of acidic soil composed of Melanic Brunosolic, Humo-ferric Podzol and some Luvisols. This terrain is extensively covered by deciduous and mixed forest zones and largely covered by wetlands, lakes, and rivers. In this predominantly rural area, forests and natural grasslands prevail, while scattered croplands and urban settlements are minimal (Baldwin et al. 2000, Minnes and Douglas 2013).\u003c/p\u003e\n\u003cp\u003eThirty-five shield lakes in eastern Ontario were selected for this study, located over the Mississippi and Rideau River watersheds, spanning Lanark Highland, Frontenac, Addington Highlands, and Leeds and Grenville counties. Lakes were selected on a gradient of total phosphorus (TP) concentrations ranging from 5 \u0026micro;gL\u003csup\u003e-1\u003c/sup\u003e to 19 \u0026micro;gL\u003csup\u003e-1\u003c/sup\u003e, with a maximum depth of 10 m or greater (Table 1 and Figure 1). Bedrocks of this study region are mainly composed of igneous and metamorphic rich bedrock (Figure 2, B), which is mostly covered mostly by thin acidic soil layer. Land-use in this zone consists of approximately 10% settlements and built-up areas, 10% wetlands, 20% croplands, and 60% of the land is forests, natural grasslands, and water bodies (Figure 2, A).\u003c/p\u003e\n\u003cp\u003eIn the late seventieth to ninetieth centuries, European people moved into eastern Ontario, originally inhabited by First Nation communities including Iroquois, Anishinaabe and Algonquin people (Watson 1996). Early European settlement was mainly concentrated near the north shore of the St. Lawrence River in Kingston, Prince Edward County and some parts of the Ottawa Valley. The settlers primarily engaged in farming, milling, and lumbering. However, during the late nineteenth and early twentieth century rapid urbanization, farmland expansion, and post-war population growth collectively led to large changes in land-use across the region (Watson 1996).\u003c/p\u003e\n\u003cp\u003eClimate change impacts have also been documented across the region. An analysis by the Ministry of Environment, based on 35 years of temperature data (1975\u0026ndash;2009) for Ontario\u0026apos;s Shield region, revealed a significant decrease in the duration of the ice-covered season with a reduction of 24 ice-covered days over the past 35 years (MOE 2013).\u003c/p\u003e\n\u003ch2\u003eDiatom as bioindicators\u003c/h2\u003e\n\u003cp\u003eDiatoms are widely recognized as robust indicators of environmental change (Stoemer and Smol 1999). Their silicious shell make them well-preserved in lake sediments and their cell walls (frustules) ornamentation, valve shape and size make them easily identifiable at species level. They are highly sensitive to light, temperature, flow velocity, nutrients, pH, salinity and other environmental factors. Diatom communities rapidly shift in response to changes in the environment (Stoemer and Smol 1999, Smol 2002). A detailed study of diatom communities in lake sediment cores can provide excellent information about the timing and magnitude of historical environmental changes. However, diatom identification is labour-intensive and time-consuming; therefore, typically, only a few sites (lakes) can be examined for detailed study within a limited time and budget. A top-bottom approach to diatom analysis where the only the top and bottom layers of a sediment core are analyzed for diatoms allows for the investigation of a larger number of lakes to better understand water quality changes at the landscape scale. It should be noted that this approach has some drawbacks, such as a lack of precise temporal resolution. However, paleolimnological studies conducted numerous lakes across North America (Smol 2002, R\u0026uuml;hland et al. 2003) have been able to confirm that the bottom layer of full sediment cores (typically \u0026gt; 20 cm in length) is representative of pre-industrial conditions. In this study, we collected the full sediment cores ranging from 15 cm to 30 cm in length. Therefore, the bottom layers of the sediment cores are representative of environmental conditions before widespread land-use and climate changes occurring post-1950 and extend to pre-impact (pre-1850) conditions.\u003c/p\u003e\n\u003ch2\u003eField and laboratory methods\u003c/h2\u003e\n\u003cp\u003eWe collected lake sediments via gravity sediment cores at the deepest point in each study lake. Sediment cores ranged in length from about 15 to 30 cm and were sectioned into 1 cm intervals using a Glew extruder (1988). Approximately 0.5 g of wet sediment samples from the top and bottom layers of the core were collected in labelled vials. Ten percent hydrochloric acid (HCl) was then added to each sample to remove carbonates followed by seven rinses with deionized water. Between rinses the sample was allowed to settle overnight to ensure no diatoms were lost during the rinses. Then the sediment samples were treated with 30% hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) and heated in a water bath at 70 \u0026deg;C for 8 hours to oxidize organic material. Following the water bath diatom samples underwent seven rinses with dionized water to remove hydrogen peroxide residue with samples being allowed to settle overnight between rinses. Before platting onto coverslips, a drop of 10% HCl was added to each sample promote dispersion of the diatom on the coverslip. Samples then underwent a dilution series and were platted on coverslips at four different dilution concentrations, where each dilution contained approximately 50% of the diatom concentration as the sample before. The diatom samples were then pipetted onto coverslips on slide warmers and allowed to dry overnight while covered. Once the solutions were dry the coverslips were mounted onto microscope slides using Naphrax. A minimum of 400 diatom valves were counted per interval using a Leica DMRB light microscope at 1000 times magnification in order to identify diatom to the lowest taxonomical level possible. Krammer and Lange Bertalot (1986, 1988, 1991a, 1991b) taxonomic guides used here to identify diatom species (Spaulding et al. 2021).\u003c/p\u003e\n\u003cp\u003eThe diatom counts were converted to relative abundance data and stratigraphic plots were produced using C2 version 1.7.7 (Juggins 2014) to show taxa with a relative abundance \u0026ge; 5%. Common taxa were identified based on those diatoms that reached a relative abundance \u0026ge; 2% in at least one lake across the study region. To identify significant shifts in diatom species composition from the bottom to the top layer, we employed the Wilcoxon signed-rank test, a hypothesis test designed for non-parametric data analysis using R software (R Core Team 2020). This non-parametric test is used here, for comparing paired data (diatom sp. of top and bottom layer).\u003c/p\u003e\n\u003cp\u003eThe ratio of chrysophyte cysts to diatom valves was also analyzed in this study. Chrysophyte algae are common in freshwater ecosystem and usually occur with diatoms. Chrysophyte algae produce morphologically distinct siliceous, microscopic cysts during the resting stage of their life cycle and preserved in sediments (Adam and Mahood 1981, K\u0026ouml;ster et al. 2005). Cysts are often restricted to specific environmental conditions making the cyst:diatom ratio a useful as indicator to detect environmental changes (Adam and Mahood 1981, K\u0026ouml;ster et al. 2005).\u003c/p\u003e\n\u003ch2\u003eSpatial Data\u003c/h2\u003e\n\u003cp\u003eA Geographical Information System (GIS) and ARC-Map (10.7) software was used to quantify land-use within the watersheds of the study lakes. Spatial data were collected from the National Hydro Network and Scholars geo-portal to specify the lakes\u0026rsquo; locations (DMTI 2015). Lake surface area (LA) and lake catchment area (CA) of individual lakes (as sub-catchment of the watersheds), as well as the catchment area to lake area ratio (CA:LA) were calculated. To delineate study lakes\u0026rsquo; catchment, we used the Ontario integrated hydrology- data packages, which provide raster datasets of elevation (e.g. enforced and filled Digital Elevation Model), flow direction, flow accumulation, integrated with mapped vector features such as lake locations and surface areas (OMNRF 2019). GIS watershed tools were used to determine the pour-points for each lake and based on these points, the gross catchment (whole catchment) for each lake was delineated. The immediate (local) lake catchment was then isolated from the gross catchment area. Mackavoy Lake, with a lake surface area of ~0.3 km\u003csup\u003e2\u003c/sup\u003e, is the smallest lake in the study region. Waterbodies having surface area ranging from 0.001 to 1 km\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eare often classified as pond rather than lakes (Richarson et al. 2022), Therefore, we classified all the waterbodies with a surface area less than 0.3 km\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eas smaller waterbodies. Por points were created for water bodies with a lake surface area \u0026ge; 0.3 km\u003csup\u003e2\u003c/sup\u003e, and catchment boundaries for each individual smaller waterbody were delineated. Next, the catchments for individual small waterbodies were separated from the gross catchment area and finally we delineated the local lake catchment boundary for each lake. Riparian buffer zones of 300 m and 500 m around each lake were also delineated using spatial analysis tool in GIS. Natural riparian zones act as the interface between aquatic and terrestrial ecosystems, playing a critical role in regulating surface run-off and nutrient loading to the lake ecosystem (Wang et al. 2020).\u003c/p\u003e\n\u003cp\u003eLand-use data were collected from Agriculture and Agri-Food Canada, created in 2010 (AAFC 2010). Using ARC-Map (version 10.7) software in GIS, spatial data with a pixel resolution of 30 m was analyzed in the World Geodetic System (WGS) 84 coordinate. The original land-use data comprised fifteen different classes, which were simplified into six groups for this study: Croplands, Forest and Natural Grasslands (excluding commercial grasslands in our study region), Roads and Built-Up Urban Areas, Waterbodies, Wetlands, and Other. After the reclassification, the TIF raster data was converted into (vector) shapefiles. Additionally, the slope of the lake catchment (local and gross catchment) and the riparian buffer zones (300 m, 500 m) was determined through spatial analysis of the Digital Elevation Model (DEM), obtained from Ontario integrated hydrology- data packages (OIH data).\u003c/p\u003e\n\u003ch2\u003eWater quality data (Epilimnetic TP)\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eModern water quality data for all the study lakes was collected from the Mississippi and Rideau Valley Conservation Authorities\u0026rsquo; water-quality monitoring programs (MVCA 2015, 2018, 2020, RVCA 2019, 2020). Secchi depth, pH, chlorophyll-a (CHL-a), nitrogen (N), dissolved organic carbon (DOC), and Total Phosphorus (TP) levels were collected from the epilimnion of each lake. To better understand the physical properties of the study lakes, data about the lake surface area (LA), perimeter, shoreline, and maximum depth were also collected. Mean total phosphorus (TP) data from 2008 to 2018 was used as an indicator of each lake\u0026rsquo;s present-day trophic status. Linear Regression Models (R software) were used to test the relationship between modern TP concentrations and the percentage of different land covers at multiple spatial scales (R Core Team 2020).\u003c/p\u003e\n\u003ch2\u003eClimate data\u003c/h2\u003e\n\u003cp\u003eTo understand historical climate in the study region, historical (1880-2019) climate data from the nearest weather stations were collected. Adjusted and homogenized mean annual temperature (Ottawa weather Station ID 6105976), precipitation (Ottawa weather Station ID 6105976) and wind speed data (Ottawa McDonald Cartier INTL Station ID 6106000, Muskoka Station ID 6115525, Kingston Station ID 6104146) (ECCC 2020) were obtained covering a time period between 1890-2020. A Mann-Kendall test was used to examine if the time-series data for annual temperature, precipitation and wind-speed have significantly changed over time using software R (R Core Team 2020).\u003c/p\u003e"},{"header":"Results","content":"\u003ch2\u003eLand-use impacts \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eTotal Phosphorus (TP) concentration of a lake was moderately correlated to land use within the lake\u0026rsquo;s catchment (Fig 3). Percent croplands and wetlands within the 300 m and 500 m riparian buffer zones were positively related to TP and explained a similar amount of the variance in TP (300 m: R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.37, p \u0026lt; 0.001; 500 m: R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.32, p \u0026lt; 0.001). Positive relationships were also found within the gross catchment (R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.13, p = 0.02) and local catchment (R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.15, p = 0.01), but the R\u003csup\u003e2\u003c/sup\u003e values suggest a weaker model fit, explaining about 13% to 15% of the variability in TP concentrations. This implies that croplands and wetlands within 300 m to 500 m buffer zones have a more substantial influence on explaining the variability in the present-day trophic status of lakes. No significant relationships were found between catchment slope within the gross catchment, lake area (LA, m\u003csup\u003e2\u003c/sup\u003e), lake depth (m), and TP (\u0026micro;gL\u003csup\u003e-1\u003c/sup\u003e) concentrations.\u003c/p\u003e\n\u003cp\u003eSimilarly, a negative relationship was observed between percent forest, natural grasslands, and water bodies within 300 m (R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.24, p = 0.002) and 500 m (R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.24, p = 0.002) riparian buffer zones with TP concentrations (Fig 4). Negative relationships were also observed across multiple spatial scales: local catchment (R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.17, p = 0.008) and gross catchment (R\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e= 0.10, p = 0.03), where the R\u003csup\u003e2\u003c/sup\u003e values suggest a weaker model fit.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eClimate change impact\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe mean annual, winter and summer temperature data (homogenised), collected from1890 to 2020 at MacDonald Cartier Int. weather station (ID 6106000) in Ottawa. A linear regression model showed (Supplementary\u0026nbsp;Figure 1) a positive increasing trend in mean annual, winter and summer air temperatures. A linear regression model estimates a substantial ~2 \u0026deg;C increase in mean annual temperature from 1890 to 2020. Increase in mean winter and summer temperature was also observed. However, the R\u0026sup2; values for winter (0.1846) and summer (0.1233) indicate limited explanatory power in the linear model for these specific seasons. The Mann-Kendall tests indicated a significant increase in annual mean temperature (p \u0026lt; 0.005) and in winter (p \u0026lt; 0.005) over the time. However, no significant change in mean summer temperature has observed (p \u0026gt; 0.005). Mann-Kendall test indicated a significant decrease in summer wind-speed in Kingston (p \u0026lt; 0.005), Ottawa Macdonald Cartier Int. (p \u0026lt; 0.005) and Muskoka (p \u0026lt; 0.005) weather stations over the time (Supplementary Figure 2). A Mann-Kendall test indicated no significant change in precipitation from 1890 to 2020 (p = 0.5).\u003c/p\u003e\n\u003ch2\u003eChange in Diatom Composition\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe diatom stratigraphic plot does not clearly illustrate a distinct trend of either increasing or decreasing diatom taxa among all 35 study lakes (Figure 5). However, notable patterns appeared in the relative abundance of certain planktonic taxa across the sediment layers. The top layers exhibited a visible increase in the relative abundance of planktonic taxa.\u0026nbsp;We did not observe a consistent shift to nutrient-tolerant diatom taxa across the study region.\u003c/p\u003e\n\u003cp\u003eA significant rise in the abundance of elongated mesotrophic, lighter, planktonic diatom taxa, namely Fragilaria crotonensis (p = 0.001) and Asterionella fromosa (p = 0.003) (relative abundance \u0026gt; 2%) was evident in the modern sediment intervals compared to the pre-impact bottom sediment samples (Figure 6, A, B). A significant (p = 0.01) decreasing trend in the cyst: diatom ratio was also observed between bottom and surface sediments but appeared to be driven by a few lakes that underwent large changes in this ratio (Figure 6, C). \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eLakes of eastern Ontario are mostly nutrient limited (TP \u0026lt; 20\u0026nbsp;mgL\u003csup\u003e-1\u003c/sup\u003e) systems, largely due to the natural landscape. Additionally, this paleolimnological study did not find any significant shift in eutrophic diatom taxa from the bottom to the top sediment layers, suggesting that the trophic levels of these lakes have remained relatively stable over time, which is consistent with the modern trophic classification of these lakes from oligotrophic to mesotrophic. However, this study revealed a significant positive relationship between present-day land use (percent of croplands and wetlands) in near shore zone (300 m, 500 m buffer) and TP concentrations in the lake, suggesting that land-use change may have resulted in nutrient enrichment of these lakes but this nutrient enrichment has not yet been substantial enough to push these lakes into a eutrophic state. This aligns with studies indicating a correlation between land-use change and lake water quality (Carpenter et al. 2008).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn general, wetlands are a sink of nutrients and impurities, helping to purify water bodies. However, in some cases, wetlands also act as a source of nutrients or may act as a transformer of nutrients to the lakes, which depends on the slope, land-use cover of the watershed, as well as position and characteristics of wetlands (Reddy et al. 2010). This depends on the wetlands\u0026apos; nature and land-use pattern (e.g. percentage of croplands) across the region (Emi Fergus et al. 2011). It has been documented that local wetlands are linked to increased TP levels in temperate lake ecosystems, where the percentage of croplands is lower on a regional scale (Emi Fergus et al. 2011). It has also been highlighted that land-use impacts near the lake shore have a greater effect on aquatic species compared to the entire catchment (Alahuuta et al. 2014, Zhang 2020, Shu et al. 2022).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on the analysis of diatom species composition, a significant increasing trend in mesotrophic elongated diatom species \u003cem\u003eF. crotonensis\u003c/em\u003e and \u003cem\u003eA. formosa\u003c/em\u003e was observed from pre-impact to present-day sediment layers. These taxa are also commonly found in lakes with higher TP concentrations and are classified as mesotrophic taxa (Revive et al. 2002). The observed increase in mesotrophic taxa may indicate slight nutrient enrichment of the study lakes since the reference period. However, there is some ambiguity in the literature regarding the abundance of \u003cem\u003eF. crotonensis\u003c/em\u003e and \u003cem\u003eA. formosa\u003c/em\u003e in lake ecosystems. In certain studies, it has been observed that their abundances correlate significantly with nitrogen (N) deposition in lakes. It\u0026apos;s important to note that many of these studies were conducted in high-altitude lakes (Saros et al. 2005, Stewart et al. 2008). The limited studies conducted in proximity to our study area, specifically the Ontario Shield lakes, have reported no correlation between nitrogen (N) concentration and the abundance of these elongated diatom species (Sivarajah et al. 2016, R\u0026uuml;hland et al. 2015).\u003c/p\u003e\n\u003cp\u003eA significant increase in mean winter temperatures has been observed in the study region, which may lead to earlier ice-off days and longer ice-free seasons. Similarly, a significant increase in mean annual temperature indicates overall warmer temperatures, which may strengthen the study lakes\u0026apos; thermal stratification. In addition, a significant declining trend in mean wind speed during summer has been observed in the study region, which could\u0026nbsp;ultimately bolster climate warming impacts on lake ecosystems and strengthen thermal stratification of the lakes. This could lead to deeper epilimnion and a shallower thermocline in dimictic temperate lakes, which expands habitat for primary producers and enhances the stability of the lakes\u0026apos; water (Kalff 2003, Vincent 2009, R\u0026uuml;hland et al. 2023). This condition is particularly favourable for the growth of lighter phytoplankton diatom taxa, in contrast to the heavy thychoplanktonic taxa (R\u0026uuml;hland et al. 2008, 2015). Recent paleolimnological studies on deep northern lakes also revealed that due to climate change impacts in recent years, warmer temperatures, declining ice-covered periods, and reduced wind speed resulted in a shift in diatom species composition (R\u0026uuml;hland et al. 2023).\u003c/p\u003e\n\u003cp\u003eThe largest consistent shift observed in diatom taxa across our study region was an increase\u0026nbsp;in\u0026nbsp;\u003cem\u003eAesterionella formosa\u0026nbsp;\u003c/em\u003e(p = 0.003) and\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003eFragilaria crotonensis\u0026nbsp;\u003c/em\u003e(p = 0.001)\u003cem\u003e.\u003c/em\u003e These diatoms have a high surface area to volume ratio, making them more buoyant than other diatom taxa.\u0026nbsp;\u003cem\u003eF. crotonensis\u0026nbsp;\u003c/em\u003ecells join together to arrange themselves into ribbon-shaped colonies, while\u0026nbsp;\u003cem\u003eA. formosa\u003c/em\u003e are arranged into star-shaped colonies by mucilage pads. Living in colonies provides them with the advantage of remaining more buoyant in the water column (Sivarajah et al. 2018). Therefore, these taxa can thrive when lake stratification is stronger, and the thermocline is shallower. The shift in diatom taxa from pre-impact to present-day suggests the existence of coherent climate change signals across the study area. These taxa are also mesotrophic in nature and increasing their abundance indicates a rise in lakes\u0026rsquo; nutrient levels. Therefore, the likely cause of the increase in the relative abundance of these taxa is an interaction of climate mediated changes and nutrients.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA significant declining trend between the sediment\u0026apos;s bottom to top layers in the chrysophyte cyst:diatom ratio has also been observed among the study lakes. Cryophytes cysts are more abundant in cooler and nutrient-poor conditions (Adam and Mahood 1981, K\u0026ouml;ster et al. 2005). Therefore, the declining cyst:diatom ratio trend is also consistent with warming conditions with nutrient enrichment across the study lakes. Therefore, an increasing trend in mesotrophic elongated planktonic taxa and declining cyst:diatom ratios from pre-impact to present day across the study lakes is consistent with the combined influence of climate change and a modest increase in nutrient (TP) levels across the watershed.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eOur results indicate a shift to mesotrophic diatoms with lower sinking rates across the study region, which is consistent with climate warming and slight nutrient enrichment. This study also revealed that the percent croplands and wetlands combined was positively related to TP concentrations in the lake. Croplands and wetlands in nearshore riparian buffer zones (300 m) most strongly affected lake water quality compared to broader shoreline area and lake catchments. This paleolimnological investigation suggests that lakes in eastern Ontario are experiencing pressures from both land-use changes (near shore) and climate change that is affecting the algal community of these lakes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMR and JCV conceptualized the study. MR carried out the laborartory work and wrote the manuscript and prepared the figures with guidance and editorial comments from JCV.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe would like to thank Mississippi Valley and Rideau Valley Conservation Authorities for sharing their water quality data and advising on the selection of the study lakes. Special thanks also go to the GIS support team of MacOrdum Library at Carleton University. This research was funded by a NSERC Discovery Grant to JCV.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e\u003cspan\u003eAdam, D.P., Mahood, A.D., 1981. Chrysophyte cysts as potential environmental indicators. Geological Society of America Bulletin. 92(11), 839\u0026ndash;844.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eAgriculture and Agri-Food Canada (AAFC). 2010. Land Use 2010. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://open.canada.ca/data/en/dataset/fa84a70f-03ad-4946-b0f\u003c/span\u003e\u003c/span\u003e8-a3b481dd5248\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eBaldwin, D. J., Desloges, J. R., \u0026amp; Band, L. E. 2000. Physical geography of Ontario. In: Perera, A.H., Euler, D.L., \u0026amp; Thompson, I.D. (eds.), Ecology of a managed terrestrial landscape: patterns and processes of forest landscapes in Ontario, 12\u0026ndash;29.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eCarpenter, S. R., 2008. Phosphorus control is critical to mitigating eutrophication. Proceedings of the National Academy of Sciences, \u003cem\u003e105\u003c/em\u003e(32), 11039\u0026ndash;11040\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eDMTI Spatial Inc., 2015. Water names point. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://geo1.scholarsportal.info/#r/tab/browseTab\u003c/span\u003e\u003c/span\u003e. Accessed 20 April 2019.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eEmi Fergus, C., Soranno, P. A., Cheruvelil, K. S., \u0026amp; Bremigan, M. T., 2011. Multiscale landscape and wetland drivers of lake total phosphorus and water color. Limnology and Oceanography, 56(6), 2127\u0026ndash;2146.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eEnvironment and Climate Change Canada (ECCC). 2020. Adjusted and homogenized Canadian climate data. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.canada.ca/en/environment-climate-change/services/climate-change/science-research-data/climate-trends-variability/adjusted-homogenized-canadian-data.html\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eJuggins, S. 2014. C2 version 1.7.7. Software for ecological and palaeoecological data analysis and visualisation. Newcastle upon Tyne, UK: Newcastle University.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eKalff, J., 2003. Limnology: Inland Water Ecosystems. Upper Saddle River, New Jersey: Prentice Hall\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eKrammer, K., Lange-Bertalot, H., 1986, 1988, 1991, 1991b. Bacillariophyceae. 1. Teil: Naviculaceae In: Ettl, H., Gerloff, J., Heynig, H., Mollenhauer, D., (eds.). S\u0026uuml;sswasserflora von Mitteleuropa, Band 2/1. Stuttgart: Gustav Fischer Verlag. p. 1\u0026ndash;876, p. 1\u0026ndash;596, p. 1\u0026ndash;576, p. 1\u0026ndash;437. German.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eK\u0026ouml;ster, D., Pienitz, R., Wolfe, B.B., Barry, S., Foster, D.R., Dixit, S.S., 2005. Paleolimnological assessment of human-induced impacts on Walden Pond (Massachusetts, USA) using diatoms and stable isotopes. Aquatic Ecosystem Health \u0026amp; Management 8(2), 117\u0026ndash;131.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMinistry of the Environment (MOE), 2013. Water Quality Ontario: Report 2012. Queen\u0026rsquo;s Printer for Ontario (PIBS # 9493e). Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.ontario.ca/page/water-quality-ontario-report-2012#section-2\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMinnes, S., Douglas, J.A., 2013. A Profile of Eastern Ontario. Canadian Regional Development: A Critical Review of Theory, Practice and Potentials.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMississippi Valley Conservation Authority (MVCA), 2015. State of the Lake environment report 2015-Mississippi Lake. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://mvc.on.ca/wp-content/uploads/2014/01/2015-Mississippi-Lake-Report.pdf\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://mvc.on.ca/ww-state-of-the-lake-reports/\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMississippi Valley Conservation Authority (MVCA), 2018. Water quality monitoring (raw data) collected from MVCA\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMississippi Valley Conservation Authority (MVCA), 2019. Watershed Boundary. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://mvc.on.ca/watershed-boundary/\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMississippi Valley Conservation Authority. 2020. Reports. Mississippi Valley Conservation. Retrieved from: Authority. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://mvc.on.ca/reports/\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eMLA, MVCA, Watershed Canada, French Planning Service Inc., 2015. Mississippi Lake Plan. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://watersheds.ca/wp-content/uploads/2015/01/20150530-mla-lake-plan.pdf\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eOntario Ministry of Northern Development and Mines, 2013. Mineral Deposits Inventory. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://geo.scholarsportal.info/#r/details/_uri@=3588886954\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eOntario Ministry of Environment and Energy. 2023. Map: lake partner. Retrieved from: Map: Lake partner | ontario.ca\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eOntario GeoHub, 2019. Ontario integrated hydrology data. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://data.ontario.ca/dataset/ontario-integrated-hydrology-data\u003c/span\u003e\u003c/span\u003e. Accessed 12 September 2019\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eOntario GeoHub, 2019. Conservation Authority Administrative Area. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://geohub.lio.gov.on.ca/datasets/6e03611af2584378893921351f75fb35_11\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eOntario Ministry of Natural Resource and Forestry (OMNRF), 2019. Ontario Integrated Hydrology (OIH) data. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.arcgis.com/home/item.html?id=dc6da\u003c/span\u003e\u003c/span\u003e6816e2446279210668718af91c9\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003ePick, F. R., 2016. Blooming algae: a Canadian perspective on the rise of toxic cyanobacteria. Canadian Journal of Fisheries and Aquatic Sciences 73(7), 1149\u0026ndash;1158.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eR Core Team. 2020. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. Retrieved from \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.R-project.org/\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eRandsalu-Wendrup, L., Conley, D. J., Carstensen, J., \u0026amp; Fritz, S. C. 2016. Paleolimnological records of regime shifts in lakes in response to climate change and anthropogenic activities.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eReddy, K.R., DeLaune, R. and Craft, C.B., 2010. Nutrients in Wetlands: Implications to Water Quality under Changing Climatic Conditions. Final Report Submitted to U. Environmental Protection Agency, EPA Contact No. EP-C-0001.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eRichardson, D. C., Holgerson, M. A., Farragher, M. J., Hoffman, K. K., King, K. B.,Alfonso, M. B., \u0026hellip; Sweetman, J. N. 2022. A functional definition to distinguish ponds from lakes and wetlands. Scientific reports, 12(1), 10472.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eRideau Valley Conservation Authority (RVCA), 2019. Catchment. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://rvcagis.github.io/jkan/datasets/rvca-catchments/\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eRideau Valley Conservation Authority (RVCA), 2019. Lake monitoring reports (Raw data) collected from RVCA\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eRideau Valley Conservation Authority (RVCA), 2020. Sub-watershed Reports. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://watersheds.rvca.ca/component/content/article/91-middle-rideau/catchments/otter-creek/128-catchment-facts\u003c/span\u003e\u003c/span\u003e. Accessed 17 January 2020\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eRideau Valley Conservation Authority (RVCA), 2021. Waterbody shape file. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://rvcagis.github.io/jkan/datasets/rvca-waterbodies\u003c/span\u003e\u003c/span\u003e/ R\u0026uuml;hland, K., Priesnitz, A., \u0026amp; Smol, J. P., 2003. Paleolimnological evidence from diatoms for recent environmental changes in 50 lakes across Canadian Arctic treeline. Arctic, Antarctic, and Alpine Research, 35(1), 110\u0026ndash;123.\u0026nbsp;\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eR\u0026uuml;hland, K., Paterson, A. M., \u0026amp; Smol, J. P., 2008. Hemispheric-scale patterns of climate‐related shifts in planktonic diatoms from North American and European lakes. Global Change Biology, 14(11), 2740\u0026ndash;2754.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eR\u0026uuml;hland, K. M., Paterson, A. M., \u0026amp; Smol, J. P., 2015. Lake diatom responses to warming reviewing the evidence. Journal of paleolimnology, 54(1), 1\u0026ndash;35.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eR\u0026uuml;hland, K. M., Evans, M., and Smol, J. P., 2023. Arctic warming drives striking twenty-first century ecosystem shifts in Great Slave Lake (Subarctic Canada), North America\u0026apos;s deepest lake. Proceedings of the Royal Society B, 290(2007), 20231252.\u0026nbsp;\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSaros, J. E., Clow, D. W., Blett, T., \u0026amp; Wolfe, A. P., 2011. Critical nitrogen deposition loads in high-elevation lakes of the western US inferred from paleolimnological records. Water, Air, \u0026amp; Soil Pollution, 216, 193\u0026ndash;202.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSchindler, D. W., Hecky, R. E., Findlay, D. L., Stainton, M. P., Parker, B. R., Paterson, M.J., Beaty, K.G., Lyng, M. \u0026amp; Kasian, S. E. M., 2008. Eutrophication of lakes cannot be controlled by reducing nitrogen input: results of a 37-year whole-ecosystem experiment. Proceedings of the National Academy of Sciences, 105(32), 11254\u0026ndash;11258.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSivarajah, B., R\u0026uuml;hland, K.M., Labaj, A.L., Paterson, A.M., Smol, J. P., 2016. Why is the relative abundance of Asterionella formosa increasing in a Boreal Shield Lake as nutrient levels decline? Journal of paleolimnology 55(4), 357\u0026ndash;367.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSivarajah, B., Paterson, A. M., R\u0026uuml;hland, K. M., K\u0026ouml;ster, D., Karst-Riddoch, T., \u0026amp; Smol, J. P., 2018. Diatom responses to 20th century shoreline development and climate warming in three embayments of Georgian Bay, Lake Huron. Journal of Great Lakes Research, 44(6),1 33 13-Sep 50\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eShu, W., Wang, P., Xu, Q., Zeng, T., Ding, M., Zhang, H., Nie, M., Huang, G., 2022. Coupled effects of landscape structures and water chemistry on bacterioplankton communities at multi-spatial scales. Science of The Total Environment, Volume 811, 1 50 35 0, 1 SSN 0048\u0026ndash;9697, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2021.151350\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSmol, J.P., 2002. Pollution of lakes and rivers: a paleoenvironmental perspective. USA, NY: Oxford University Press.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eSpaulding, S.A,, Bishop, I.W., Edlund, M.B., Lee, S., Furey, P., Jovanovska, E., Potapova, M., 2021. Diatoms of North America. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://diatoms.org/\u003c/span\u003e\u003c/span\u003e. Accessed 29 Mar 202.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eStatistics Canada, 2016 Cartographic Boundary Files. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://geo.scholarsportal.info/#r/details/_uri@=749265755$DLI_2016_Census_CBF_Eng_Nat_pr\u0026amp;_add:true_nozoom:true\u003c/span\u003e\u003c/span\u003e. Accessed 29 Mar 2021\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eStoermer, E., and Smol, J.P. (Ed), 1999. The Diatoms: Applications for the Environmental and Earth Sciences.UK. Cambridge University Press.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eStewart, K. A., Lamoureux, S. F., \u0026amp; Finney, B. P., 2008. Multiple ecological and hydrological changes recorded in varved sediments from Sanagak Lake, Nunavut, Canada. Journal of Paleolimnology, 40, 217\u0026ndash;233.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eTaranu, Z. E., Gregory-Eaves, I., Leavitt, P. R., Bunting, L., Buchaca, T., Catalan, J., Domaizon, I., Guilizzoni, P., Lami, A., McGowan, S. \u0026amp; Moorhouse, H., 2015. Acceleration of cyanobacterial dominance in north temperate‐subarctic lakes during the Anthropocene. Ecology Letters, 18(4), 375\u0026ndash;384\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eVermaire, J.C., Taranu, Z.E., MacDonald, G.K., Velghe, K., Bennett, E.M., \u0026amp; Gregory-Eaves, I., 2017. Extrinsic vs. Intrinsic Regimes Shifts in Shallow Lakes: Long-Term Response of Cyanobacterial Blooms to Historical Catchment Phosphorus Loading and Climate Warming. Frontiers in Ecology and Evolution 5, 146.\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eVincent, W.F., 2009. Effects of climate change on lakes. Pollution and Remediation pp 55\u0026ndash;60. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.cen.ulaval.ca/warwickvincent/PDFfiles/229.pdf\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eWang, M., Duan, L., Wang, J., Peng, J., \u0026amp; Zheng, B., 2020. Determining the width of lake riparian buffer zones for improving water quality base on adjustment of land use structure. Ecological Engineering, 158, 106001\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eWatson, W.K., 1996. Rideau Canal- National Historic Site-World Heritage Site. Retrieved from: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.rideau-info.com/canal/history/rideau-route/watersheds.html\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eWinter, J.G., DeSellas, A.M., Fletcher, R., Heintsch, L., Morley, A., Nakamoto, L., Utsumi, K., 2011. Algal blooms in Ontario, Canada: increases in reports since 1994. Lake and Reservoir Management 1;27(2):107\u0026ndash;14. DOI: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/07438141.2011.557765\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\n \u003cli\u003e\u003cspan\u003eZhang, J., Li, S., Jiang, C., 2020. Effects of land use on water quality in a River Basin (Daning) of the Three Gorges Reservoir Area, China: Watershed versus riparian zone, Ecological Indicators, Volume 113, 106226, ISSN 1470\u0026ndash;160X, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecolind.2020.106226\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\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":"eutrophication, climate change, environmental change, land-use change, diatoms","lastPublishedDoi":"10.21203/rs.3.rs-6100349/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6100349/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEastern Ontario, Canada, is a lake-rich, rural region, located primarily over Precambrian Shield. These lakes are typically nutrient-limited with total phosphorus (TP) less than 20 \u0026micro;gL\u003csup\u003e-1\u003c/sup\u003e, and serve as the primary tourist attraction, contributing substantially to the local economy of this region. However, in recent years, residents have become concerned about the perceived increase in nuisance algal blooms. Due to the lack of long-term water quality monitoring data little information exists on pre-impact conditions, and water quality trends of these lakes. To address this gap, a top-bottom paleolimnological approach was used to examine diatom community shifts in 35 presently nutrient-limited (TP 5\u0026ndash;19 \u0026micro;gL\u003csup\u003e-1\u003c/sup\u003e) lakes across the Mississippi and Rideau River watersheds of eastern Ontario. Shifts in diatom taxon between bottom and top sediment layers align with climate change indicators, suggesting increasing temperatures, longer ice-off periods, and reduced wind speeds, across the region. A spatial analysis conducted to determine if present-day TP concentrations correlated with modern land-use patterns revealed that the percentage of croplands and wetlands in nearshore riparian buffer zones (300 m) was positively corelated with present-day TP concentrations of the lakes. An increasing trend in the relative abundance of mesotrophic diatoms with lower sinking rates was observed across our study lakes, which is consistent with lake response to climate warming and nutrient enrichment. This research demonstrates that both land-use and climate change have had impacts on lake ecosystems in eastern Ontario over ~\u0026thinsp;150 years.\u003c/p\u003e","manuscriptTitle":"Assessing shifts in diatom communities in eastern Ontario recreational lakes in relation to land-use and climate changes over the past ~150 years using a top-bottom paleolimnological approach.","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-03 07:39:08","doi":"10.21203/rs.3.rs-6100349/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-03-30T13:32:51+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-28T13:18:50+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-20T08:24:57+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"276241645529433043931311827426393890660","date":"2025-03-03T12:34:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"214304902560524852688605041719895172445","date":"2025-03-03T09:25:27+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-02T23:12:18+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-02-27T07:34:22+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-02-27T07:32:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Paleolimnology","date":"2025-02-25T00:53:41+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":"52c4750f-2511-4385-bfc1-ebd0757fcc08","owner":[],"postedDate":"March 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-13T16:04:24+00:00","versionOfRecord":{"articleIdentity":"rs-6100349","link":"https://doi.org/10.1007/s10933-025-00376-w","journal":{"identity":"journal-of-paleolimnology","isVorOnly":false,"title":"Journal of Paleolimnology"},"publishedOn":"2025-10-08 15:57:48","publishedOnDateReadable":"October 8th, 2025"},"versionCreatedAt":"2025-03-03 07:39:08","video":"","vorDoi":"10.1007/s10933-025-00376-w","vorDoiUrl":"https://doi.org/10.1007/s10933-025-00376-w","workflowStages":[]},"version":"v1","identity":"rs-6100349","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6100349","identity":"rs-6100349","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}