Using paleolimnology to assess long-term acidification and recovery trajectories in lakes from Killarney Provincial Park and Sudbury (Ontario, Canada)

Using paleolimnology to assess long-term acidification and recovery trajectories in lakes from Killarney Provincial Park and Sudbury (Ontario, Canada) | 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 Using paleolimnology to assess long-term acidification and recovery trajectories in lakes from Killarney Provincial Park and Sudbury (Ontario, Canada) Courtney Lanigan, Neal Michelutti, Andrew M. Paterson, Carsten Meyer-Jacob, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4462254/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 May, 2025 Read the published version in Journal of Paleolimnology → Version 1 posted 11 You are reading this latest preprint version Abstract For over a century, the copper and nickel mining centre of Sudbury in northeastern Ontario (Canada) was a major source of sulphur dioxide and other pollutants, degrading terrestrial and aquatic ecosystems in the surrounding region. In the 1970s, emissions were drastically reduced due to concerns over widespread environmental damage. Killarney Provincial Park (KPP), located ~ 60 km southwest of Sudbury, was also impacted by Sudbury emissions, but little is known about how present-day conditions relate to pre-industrial conditions, or how recovery trajectories may be influenced by recent climate change. Here, we use a multi-proxy paleolimnological approach to examine ecological change in five lakes over the past ~ 200 years in Sudbury (Baby, Tillie, and Crooked lakes) and KPP (Ruth-Roy and Johnnie lakes). The study objectives were to: (1) infer past ecological conditions from diatom assemblages, whole-lake chlorophyll- a (VRS-Chl a ) and lake-water dissolved organic carbon (DOC) concentrations; (2) explore patterns of potential ecological recovery from acidification over the past several decades; and (3) compare any changes to recent monitoring and meteorological data. Distance from smelting operations and differences in underlying bedrock geology likely contributed to differences in the magnitude of change observed in the paleolimnological indicators. In general, the acidification period was characterized by declines in circumneutral diatom taxa (i.e., Discostella spp., Achnanthidium spp., and Aulacoseira spp.), and inferred Chl a and inferred DOC, concurrent with increased relative abundances of acidophilic diatoms (i.e., Fragilariforma acidobiontica, Eunotia spp., Tabellaria flocculosa and Asterionella ralfsii ). After ~ 1970, only limited recovery in diatom assemblages was recorded, although inferred DOC and Chl a levels increased, indicating biological recovery is lagging chemical recovery and/or the ecological trajectory has been influenced by other large-scale environmental stressors. However, given the impacted nature of the study lakes, a clear climate signal in recent diatom assemblages was not as evident as often noted in pristine Boreal Shield lakes. This highlights the need for case-by-case consideration of recovery patterns in lakes, and confirms the importance of conducting long-term, multi-proxy studies to assess ecosystem recovery and ecological trajectories. Diatoms Mining pollution Boreal Shield lakes lake sediment spectroscopy chlorophyll a dissolved organic carbon Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction During construction of the trans-Canada railway in the 1870s, rich deposits of copper and nickel were found in the Sudbury basin located in northeastern Ontario (Canada). This discovery led to concentrated mining and smelting activities in the area (Winterhalder 1995 ). In 1888, open pit roasting of these ores began, which led to the opening of Nickel Co. (currently known as Vale Inco, est. 1902), the Coniston smelter (1913), and Falconbridge Limited (currently known as Xstrata Nickel, est. 1928) (Tropea et al. 2010 ). By the 1960s, the Sudbury smelters were emitting over 2.5 million tonnes of sulphur dioxide per year, making the area one of the world’s largest sources of acid-generating pollution in the world. Due to concerns over the widespread environmental damage from mining operations, emissions were reduced by ~ 90% by 1994 (Snucins and Gunn 1998 ), and even further to the present day. Particulate emissions from smelters and mining operations contaminated much of the Sudbury region and surrounding areas (Pearson et al. 2002 ). Early smelting emissions resulted in the loss of large amounts of vegetation, and severe acidification of terrestrial and aquatic environments, with soil acidity and metal concentrations highest in areas near smelters (Winterhalder 1995 ). The loss of vegetation left Sudbury soils exposed, and they became severely eroded. Atmospheric deposition of contaminants (i.e., strong acid, metals) altered water and sediment quality, and, in the case of the metals, were toxic to aquatic organisms (Fleeger et al. 2003 ). Moreover, in the 1960s, increases in cyanobacterial and algal blooms were observed in many Sudbury lakes because of high nutrient inputs linked to soil erosion from industrial activities and urbanization. Whilst all lakes and catchments within KPP and Sudbury were likely affected to some degree by acidifying emissions, there is much variation in the magnitude, timing, and extent of impacts from acidification. For example, lake acidification and metal contamination in Sudbury peaked in the 1960s, while the acidification of lakes in KPP peaked in the 1970s and 1980s. This is likely because the KPP lakes are located farther from the mining and smelting activities, and therefore received longer range atmospheric deposition of SO 2 , as opposed to being directly exposed (Keller et al. 2008 ). In addition, this variation is due, in part, to differences in natural buffering capacity, which is especially notable in lakes that were thought to be acidic prior to the onset of smelting activities [i.e., Ruth-Roy Lake (KPP) and (Sudbury)] (Belzile et al. 2004 ). Meanwhile, delayed acidification in some lakes in KPP was believed to be due to pockets of carbonate-containing rocks in the watersheds (i.e., Lumsden and Acid lakes; Hindar and Henriksen 1998 ). Given the lack of direct, long-term monitoring data for most lakes, the effects of acidification were clearly demonstrated in many Sudbury lakes using paleolimnological approaches, conducted mainly in the 1980s and early-1990s. For example, Baby Lake, which is located ~ 1 km away from the Coniston smelter in Sudbury, showed marked changes in acid sensitive algae (i.e., diatoms and chrysophytes) that were coincident with the onset of major smelting operations and acidification, as well as subsequent recovery noted especially in chrysophyte assemblages (Dixit et al. 1992 a,b). In a study of 151 lakes in the Sudbury region, Dixit et al. ( 2002 ) concluded that 77% of modern diatom species variation could be attributed to the combined effects of various measured environmental variables (such as lake catchment characteristics, lake size, elevation, pre-industrial pH, metals). Dixit et al. ( 2002 ) also applied a diatom-based pH inference model to conclude that peak acidification occurred in the ~ 1970s in KPP and ~ 1960s in Sudbury, but also that the large reductions in sulphur dioxide emissions had resulted in early signs of recovery. Collectively, these studies, conducted more than three decades ago, demonstrated the effectiveness of diatom and chrysophyte assemblages to track changes in limnological variables related to acidification (Dixit et al. 1992 a,b). Some re-assessments of acidification and recovery patterns in select Sudbury lakes, using a variety of paleolimnological indicators, have shown that biological recovery trajectories can be varied (Tropea et al. 2010 ). Although pH is still identified as the strongest spatial variable shaping diatom assemblages across Sudbury lakes (Cheng et al. 2022 ), biological assemblages in many lakes show limited recovery, and have not returned to their pre-industrial condition. Recent warming and legacy metal contamination have been cited as possible factors complicating biological recovery (Tropea et al. 2010 ; Simmatis et al. 2021 ; Cheng et al. 2023 ). Recent climate warming has impacted Sudbury-area and KPP lakes, especially over the last few decades. Snucins and Gunn ( 2000 ) used temperature profiles to examine the thermal structure of 86 relatively small (< 550 ha) lakes in KPP to show that mixing regimes were strongly influenced by water clarity and lake depth. Snucins and Gunn ( 2000 ) found that 84% of the lakes that failed to thermally stratify were shallow (depth < 5 m) and had low DOC concentrations (< 1 mg/L). This is relevant to lakes in KPP as the small lakes of the La Cloche Mountain range are some of the clearest lakes in North America. These findings suggest that DOC decreases due to a changing climate and/or acidification will have a significant effect on various physical and chemical lake characteristics. As DOC concentrations slowly return to pre-industrial levels (Meyer-Jacob et al. 2019 ), some of these thermal changes may be reversed. In addition to the impact to and recovery of lake chemistry and biological communities from industrial activities, urbanization is complicating ecological trajectories. Tropea et al. ( 2011 ) studied four Sudbury lakes (Ramsey, Nepahwin, McFarlane and Richard lakes) to investigate the impact of urbanization and showed that diatom community composition has changed drastically over the past ~ 150 years as a result of sewage effluent, excess nutrients from fertilizers, shoreline alteration, and altered hydrology. Similar distinctions among urban and non-urban lakes in the Sudbury region have also been found in cladoceran taxa, driven by differences in aqueous specific conductance and the indirect effects of nutrient enrichment (Simmatis et al. 2022 ). Urban Sudbury lakes highlight the potential for altered ecological recovery trajectories due to a combination of legacy and modern stressors. Despite the many earlier studies on the degradation and subsequent recovery of aquatic ecosystems in KPP and Sudbury, little is known about how more recent conditions (i.e., last three decades) relate to background (pre-industrial) conditions, or how biological recovery trajectories may be affected by a rapidly changing climate. To develop this long-term perspective, we selected five study lakes for multi-proxy paleolimnological analyses, including subfossil remains of algae (diatoms), inferred whole-lake chlorophyll- a (VRS-Chl a ) and lake water dissolved organic carbon (DOC) concentrations. We examine information preserved in lake sediment to obtain a long-term (past ~ 200 years) record of ecological change, including assessing how recent warming has affected recovery trajectories. The specific study objectives are to: (1) reconstruct fossil diatom assemblages, sediment Chl a and lake-water DOC concentrations over the past several decades to assess trends in recovery from acidification, and, in particular, to compare present-day with pre-industrial conditions of five lakes in KPP and Sudbury; (2) explore patterns of potential ecological recovery from acidification over the past several decades; and (3) collectively use paleolimnological, long-term monitoring and meteorological data to explore the potential drivers and trajectories of KPP and Sudbury ecosystem changes. Study region Sudbury (46.48959° N, 80.99011° W) is located near the southern margin of the Precambrian Shield in northeastern Ontario, on the margins of the Sudbury Basin, a topographic low attributable to an ancient (1.8 mya) meteor impact and subsequent deformation of the Earth’s crust. The Sudbury basin is ~ 60 km in length and ~ 27 km in width; its structural axis is aligned northeast to southwest (Dirszowsky 2020 ; Tropea 2008 ). The rugged topography of the Shield, and basin structure modified by long-term denudation and glacial activity, has resulted in the highest number of lakes contained within a city for any urban area within Canada. The Sudbury region has a humid continental climate [Climate normal (1981–2010): mean daily minimum temperature of -17.9°C in January; mean daily maximum temperature of 24.8°C in July; mean monthly maximum precipitation of 101.1 mm in September; mean monthly minimum precipitation of 51.1mm in February; total annual precipitation of 903.2 mm; average annual wind speed of 14 km/hr; and an average frost-free period of 136 days (Sudbury station A ID 71730; ECCC 2024)]. Killarney Provincial Park (46.1333° N, 81.4167° W), located ~ 60 km southwest of Sudbury (Fig. 1 ), contains over 200 lakes and ponds. These freshwater ecosystems exhibit large differences in size, elevation, water chemistry, and catchment characteristics. The majority of KPP is underlain by the Lorrain formation, which is comprised of feldspathic and kaolinitic sandstone and orthoquartzite (Hindar and Henriksen 1998 ). The folds of quartzite rock form the ancient geological formation that characterize the La Cloche Mountain range. Located in the Ontario Shield Ecozone, KPP’s mean minimum temperature is approximately − 14°C in January, with a mean maximum temperature of approximately 24°C in July. KPP’s mean monthly precipitation reaches a maximum of over 75 mm in April and October, and a minimum of approximately 35 mm in February (Belzile et al. 2004 ). Study lakes Study lakes were chosen to reflect select limnological gradients and varying levels of impacts. This work builds on previous paleolimnological work from the 1980s and 1990s in KPP and the Sudbury region. Sediment cores for diatom analyses have not been collected from these lakes in ~ 30 years, which include lakes in KPP (Ruth-Roy and Johnnie lakes) and Sudbury (Tillie, Crooked, and Baby lakes; Fig. 1 ). Ruth-Roy Lake (46.0961 ° N, 81.2467 ° W) : Located in KPP, ~ 45.2 km from the Copper Cliff smelter (Fig. 1 ; Table 1 ), Ruth-Roy Lake has a maximum depth of 18 m and surface area of 54.5 ha. Ruth-Roy Lake has undergone numerous paleolimnological assessments. Sediment cores collected between 1975 and 1980 were analyzed for diatom and chrysophyte assemblages in core ‘tops’ (surface sediments representing current conditions) and core ‘bottoms’ (generally from > 30 cm deep, representing pre-industrial conditions) (Dixit et al. 1992 c). Earlier analyses showed that Ruth-Roy was one of the most naturally acidic lakes in the region prior to smelting (inferred pH ~ 4.9; Dixit et al. 2002 ), possibly because the lake drains quartzite ridges with little to no soil. Although being naturally acidic, Dixit et al. ( 2002 ) noted that the lake acidified further (to pH ~ 4.58) due to acid precipitation. Simmatis et al. ( 2023 ) recently re-assessed long-term changes in diatoms, cladocerans, inferred whole-lake primary production, and inferred lake-water DOC in Ruth-Roy Lake. Pre-industrial assemblages confirmed that Ruth-Roy Lake was naturally acidic but began to respond to smelting emissions as early as ~ 1920, which was attributed to its naturally low buffering capacity and, therefore, high sensitivity to acidifying emissions (Simmatis et al. 2023 ). Table 1 Summary of lake characteristics and recent measured water chemistry for the five focal study lakes. Parameter Units Baby Crooked Ruth-Roy Johnnie Tillie Distance from smelter km 1 S (Coniston) 6.3 S (Copper Cliff) 45.2 SW (Copper Cliff) 46.2 S (Copper Cliff) 62.1 N (Coniston) Elevation masl 224 310 217 213 404 Surface area ha 11.9 26.3 54.5 342.3 76.7 Max. Depth m 22.5 8 18 33.6 11 Mean Depth m 9.6 3.8 4.1 7.9 4.7 DOC (2018) 1 mg/L 1.6 8.4 2.5 4.5 9.4 pH (2018) 1 pH units 7.3 6.7 5.8 6.5 5.9 SO 4 (2018) 1 mg/L 6.70 5.25 2.95 3.55 3.45 Source : 1 MECP dataset (Sudbury full water chemistry - used with permission) Johnnie Lake (46.0915 ° N, 81.2400 ° W) : Johnnie Lake, located in KPP, ~ 42.6 km from the Copper Cliff smelter (Fig. 1 ; Table 1 ), has a maximum depth of 33.6 m and surface area of 342.3 ha. Previous studies done on Johnnie Lake include zooplankton surveys, precipitation chemistry and wet deposition data collection, paleolimnological analyses, and water chemistry analysis (Szkokan-Emilson et al. 2010 ; Keller et al. 2003 ; Snucins et al. 2001 ). Keller et al. ( 2003 ) collected lake and precipitation chemistry, and wet deposition data, between 1978 and 1998 from Johnnie Lake showing the lake experienced significant declines in calcium (measured from lake water precipitate; 140 eq/L in 1980 to ~ 80 eq/L in 2001) as well as increases in alkalinity (-7 eq/L in 1980 to 11 eq/L in 2001). Keller et al. ( 2003 ) also found that DOC concentrations increased significantly between 1988 and 2001 and that lake water pH closely tracked precipitation chemistry. Meanwhile, Snucins et al. ( 2001 ) collected water samples (from 1996–1997) for chemical analyses from several KPP lakes, including Johnnie Lake, and found that lakes with catchments that are made up of more easily weathered bedrock formations acidified the least, relative to pre-industrial diatom-inferred pH, and showed the largest increases in pH between 1981 and 1999. A recent paleolimnological top-bottom comparison of cladoceran and chironomid assemblages demonstrated that subfossil invertebrate assemblages were somewhat similar between pre-1880 and post-2010 sediments (Simmatis et al. 2021 , 2022 , 2023 ). Modern invertebrate assemblages in Johnnie Lake are most similar to lakes far from the original smelters (e.g., Whitepine Lake in Lady Evelyn-Smoothwater Provincial Park; Simmatis et al. 2022 , 2023 ). Currently, Johnnie Lake is slightly acidic (pH of ~ 6.3) and slightly above its inferred pre-industrial pH level (pH of 6.1). Baby Lake (46.4612 ° N, 80.8651 ° W) : Located ~ 1 km from the Coniston smelter (Fig. 1 , Table 1 ), Baby Lake has a maximum depth of 22.5 m and a surface area of 11.9 ha. Baby Lake has been subject to multiple studies, including water chemistry analysis (i.e., metals, sulphate and lake water pH), zooplankton identification, and paleolimnological analyses (Hutchinson and Havas 1986 ; Havas et al. 1995 ; Smol et al. 1998 ; Simmatis 2021 ). Hutchinson and Havas ( 1986 ) collected water chemistry data to show that when the Coniston smelter closed (1972), lake-water sulphate concentrations decreased by 50% (from 60 mg/L in 1968 to 30 mg/L in 1983), lake-water copper concentrations decreased by 92% (from 0.78 mg/L in 1971 to 0.06 mg/L in 1984), and nickel concentrations decreased by 87% (from 3.2 mg/L in 1970 to 0.41 mg/L in 1984). Trends in lake-water metal concentrations collected by Hutchinson and Havas ( 1986 ) were reflected by trends in more recent sedimentary metal concentrations (Simmatis 2021 ). Notably, concentrations of copper, nickel, lead, and zinc have not returned to pre-industrial concentrations (Simmatis 2021 ). Havas et al. ( 1995 ) additionally sampled Baby Lake for water chemistry and zooplankton to track biological changes over decadal timescales (1970-1990s). They found the lake had much lower phytoplankton biomass and species richness than other Shield lakes of a similar pH (6.8) in 1986. Dixit et al. ( 1992 c) completed a paleolimnological analysis and showed that long-term pH, inferred from diatom assemblages, recorded dramatic acidification of Baby Lake, changing from an inferred pH of 6.5 in 1940 to 4.2 in 1975. Beginning in 1972 (following the closure of the Coniston smelter) diatoms and especially chrysophyte assemblages in Baby Lake showed significant recovery (Dixit et al. 1992 b). Despite recovery in algal indicators, cladoceran taxa showed limited recovery, especially littoral taxa (Simmatis 2021 ). Sedimentary cladoceran assemblages have indicated reduced littoral diversity and increased abundance of generalist taxa (i.e., Chydorus brevilabris and Bosmina spp.) after ~ 1925 without recovery to pre-industrial assemblage composition (Simmatis 2021 ). Further, few chironomid head capsules were found in Baby Lake, which may be related to sediment type and high inorganic content (Simmatis 2021 ). Baby Lake was amongst the most acidic of our study lakes during the period of peak emissions from Sudbury smelters and is therefore an interesting contrast to KPP lakes that are located more distant from smelter emissions. Tillie Lake (47.0425 ° N, 81.0008 ° W) : Among the study sites, Tillie Lake is located the furthest (62.1 km) from the nearest smelter (Fig. 1 , Table 1 ). It has a maximum depth of 11.0 m and a large surface area of 76.7 ha. Tillie Lake is also located at the highest elevation of any of the study lakes (404 masl), had the highest DOC value of 5.5 mg/L in 1975, and showed recent increases in total phosphorus (Keller et al. 2019 ). A recent paleolimnological top-bottom comparison of cladoceran assemblages showed some similarities between pre-1880 and post-2010 sediments (Simmatis 2021 ). Chironomid counts were inadequate for analysis and interpretation (Simmatis 2021 ). Tillie Lake is not well-researched compared to the other study lakes, and thus a thorough paleolimnological analysis was needed to place recent limnological data within a long-term context. Crooked Lake (46.4185º N, 81.0331º W) Crooked Lake is located 6.3 km from the Copper Cliff smelter (Fig. 1 , Table 1 ), has a maximum depth of 8.0 m, and a surface area 26.29 ha. Dramatic declines in acidity have been observed in severely damaged urban lakes close to the Sudbury smelters, such as Crooked Lake (Keller et al. 2019 ). Crooked Lake had the most acidic pre-industrial diatom inferred pH values (4.0) of the selected study lakes (Dixit et al. 1992 c), and one of the most acidic pH values in 1975 (4.3) (Snucins and Gunn, 1998 ). Simmatis et al. ( 2022 ) completed top-bottom analysis of cladocerans, finding that modern assemblages had higher relative abundances of generalist taxa (i.e., Chydorus brevilabris ) and reduced littoral diversity compared to pre-industrial conditions. Relative to other Sudbury and KPP lakes, Crooked Lake experienced a moderate amount of change (Simmatis et al. 2022 ). Inadequate chironomid remains were recovered to allow for further analysis or interpretation (Simmatis 2021 ). Crooked Lake is an interesting example of a naturally acidic Sudbury lake. Materials and Methods Sediment coring and sectioning In June and July 2018, the cores from all study lakes were obtained from the deepest point in each lake using a Glew gravity corer (Glew 1988 ). The exception was the Baby Lake core which was collected the previous winter. The cores were sectioned on shore into 0.5-cm intervals using a Glew extruder (Glew 1989 ). The cores were extruded until 30 cm length, except for the core from Baby Lake, which was only 19 cm long. The sediment intervals were subsequently freeze dried and stored until further analysis. Radioisotopic dating Excess 210 Pb activities on select sediment intervals were used to develop core chronologies at PEARL (Queen’s University, Kingston, ON). Samples were prepared by freeze-drying the sediments, filling gamma tubes with the sediment and then sealing it with epoxy and letting it sit for a minimum of two weeks, allowing the equilibrium between 226 Ra and 214 Bi to be reached. 210 Pb was measured with an Ortec high-purity geranium detector. Estimates of unsupported 210 Pb (total 210 Pb minus supported 210 Pb) were used to estimate sediment age, using the constant rate of supply (CRS) model (Appleby 2001 ). 210 Pb activities and chronologies for most of the lakes are published elsewhere (Ruth-Roy Lake: Simmatis et al. 2023 ; Baby, Crooked and Tillie lakes: Meyer-Jacob et al. 2024 ). 210 Pb data for Johnnie Lake are presented in Supplemental information (Supplemental Information Fig. 1 ). Diatom preparation and analysis The preparation and analysis of diatom samples followed standard techniques, as generally outlined in Battarbee et al. ( 2002 ). In summary, subsamples of dried sediment (0.01–0.02 g) were digested using a 50:50 molar ratio of concentrated sulphuric and nitric acid to remove organic content from the sediments, done over a period of two hours in a hot water bath. The diatom slurries were left to settle for ~ 24 hours, after which the supernatant was removed by aspirating and deionized water was added to each vial. This process was repeated 6–7 times until a litmus test indicated that samples were no longer acidic. Cleaned diatom suspensions were pipetted onto coverslips and mounted onto microscope slides using Naphrax, a permanent mounting medium. A Leica DMR microscope was used (1000x magnification) to identify and enumerate diatom valves. Diatoms were counted and identified to species and variety level when feasible, using primarily Krammer and Lange-Bertalot ( 1986 ; 1988 ; 1991a , b ) as taxonomic references. A minimum of 300 valves were counted per slide. Sediment Chlorophyll-a and lake-water Dissolved Organic Carbon (DOC) Visible range spectroscopy-inferred chlorophyll-a (VRS-Chl a ; which includes its isomers and main diagenetic products; Michelutti and Smol 2016 ), and visible near infrared spectroscopy-inferred DOC (VNIRS DOC) analysis, were performed for each interval of all five cores. Small amounts (less than 0.05 g) of freeze-dried sediment were sieved through a 125-µm mesh into glass scintillation vials and analyzed in a FOSS NIRSystem model 6500 rapid content analyzer, operating over the range of 400–2500 nm. Concentrations of whole-lake chlorophyll- a and lake water DOC were inferred following methods in Michelutti et al. ( 2010 ) and Meyer-Jacob et al. ( 2020 ), respectively. Trends in sedimentary Chl a and lake-water DOC for Baby, Tillie, and Crooked lakes were previously published in an assessment of long-term changes in carbon cycling and sequestration in Sudbury lakes by Meyer-Jacob et al. ( 2024 ). Climate data Adjusted and homogenized Canadian climate data were obtained from Environment and Climate Change Canada for the climate station nearest to the selected study sites. This information is made publicly available in Open Government Canada data and includes climate and weather data from the study site between the years of ~ 1950-present day. Mean annual air temperature (MAAT) data were obtained from the station “Sudbury Climate ON” (ID 71733). Biostratigraphical zonation Stratigraphically constrained cluster analysis using the total sum of squares (CONISS) was used to identify the major changes in diatom species composition. This was completed in R using the ‘rioja’ package (Oksanen et al. 2019 ), which uses a broken-stick model to determine the number of important stratigraphical zones (Bennett 1996 ). Zonation using the broken-stick test separates the total variance into components. The total variance is represented by n and is divided into n -1 markers. The length of each segment represents the variance of each zone; if variance reduction surpasses model expectations the zone is considered important (Bennett 1996 ). Given the change in sample resolution that occurred with core depths, CONISS results should be considered only a rough guide for interpreting the long-term trends in the study lakes. Results Radioisotopic dating Total 210 Pb near-surface activities ranged from 1057.9 to 3041.0 Bq/kg, and reached equilibrium with supported 210 Pb levels between ~ 11 to ~ 28 cm depths. Mean supported activities (measured as 214 Pb) ranged from 17.0 to 44.1 Bq/kg. Unsupported 210 Pb activities declined exponentially in all cores but with some irregularities indicating changes in sedimentation rates (Supplemental Information Fig. 1 ; Simmatis et al. 2023 ; Meyer-Jacob et al. 2024 ). Ruth-Roy Lake Profiles for subfossil diatoms, Chl a and DOC have been published for Ruth-Roy Lake as part of a multidisciplinary paleolimnological study focusing on subfossil invertebrates (Simmatis et al. 2023 ), but are briefly summarized here again to allow for easy comparison among all study lakes. In the Ruth-Roy Lake sediment core, a total of 23 intervals were counted including every interval from 0 cm to 5.5 cm, then every second interval from 6 cm to 12.5 cm, and then every third interval from 12.5 cm to 30 cm. In total, 38 unique diatom taxa were identified. CONISS with a broken stick test identified two important biostratigraphic zones (Fig. 2 ). Zone 1 includes intervals from 29.75 cm (pre-~1850) to 6.25 (~ 1918; Fig. 2 ) in which Tabellaria flocculosa and Aulacoseira distans were the most common diatom taxa. Other common taxa included Cymbella hebridica (5–10%), Frustulia rhomboides var. saxonica (1–10%), and Eunotia exigua (1–10%). Acidophilic taxa, including Fragilariforma acidobiontica, Eunotia intermedia , and Eunotia bilunaris , were often recorded at < 6% or were intermittently absent during this period. VNIRS-DOC was relatively stable throughout this period and high in comparison with the remainder of the sedimentary record with a median inferred value of 4.6 mg/L (Fig. 2 ). VRS-Chl a was variable (ranging from 0.042 mg/g dwt to 0.068 mg/g dwt) during this period, but remained at high levels relative to the remainder of the sedimentary record (Fig. 2 ). At 8.25 cm (~ late 1800s), VRS-Chl a and VNIRS-DOC began to decline into Zone 2. Zone 2 includes intervals from 5.25 cm (~ 1942) to 0.25 cm (~ 2017; Fig. 2 ) in which Fragilariforma acidobiontica was the dominant taxon. F. acidobiontica sharply increased from ~ 6% at 6.25 cm (~ 1918) to greater than ~ 30% at 3.25 cm (~ 1979), eventually reaching 68% at 1.25 cm (~ 2007). After 1.25 cm (~ 2007), it declined slightly to ~ 61%. Cymbella microcephala increased from trace abundances at 4.25 cm (~ 1693) to ~ 8% abundance at 1.25 cm (~ 2007) before declining to 5.5% in the surface sediments. Eunotia intermedia increased from 4% at 5.25 cm (~ 1942) to 18% at 3.25 cm (~ 1979), before declining to ~ 8% in the most recent sediments. A number of less common taxa experienced directional declines, including Aulacoseira distans (from 16% at 5.25 cm to < 3% in the most recently deposited sediments), Cymbella hebridica (from 13% at 6.25 cm to < 2% in the most recently deposited sediments), Tabellaria flocculosa (from ~ 10% at 5.25 cm to < 5% in the most recent sediments), Eunotia exigua (from ~ 7% at 6.25 cm to < 1% in the most recent sediments), Frustulia rhomboides var. saxonica (from 5% at 6.25 cm to trace abundances in the surface sediments), and Fragilaria (Staurosira) construens (from ~ 5% at 6.25 cm to trace and sporadic presence in the most recent sediments). During this period, VRS-Chl a reached its minimum value in the sedimentary record at ~ 3.75 cm (~ 1971) and increased afterwards but concentrations did not return to Zone 1 levels. Trends in VNIRS-DOC coincided with VRS-Chl a , reaching a minimum value at ~ 3.75 cm (~ 1971), and increased afterwards without returning to Zone 1 levels. Johnnie Lake Twenty-two intervals in the Johnnie Lake sediment core were counted including every interval from 0 cm to 5.5 cm, every second interval from 6 cm to 12.5 cm, and every third interval from 12.5 cm to 30 cm. In total, 18 taxa were identified. CONISS with a broken stick test identified four important biostratigraphic zones (Fig. 3 ). Zone 1 includes intervals from 26.75 cm (pre-~1850) to 13.25 cm (~ 1922; Fig. 3 ). Asterionella ralfsii was the most common diatom taxon in Zone 1, ranging from 40–50%. Other common taxa included Aulacoseira distans (5–20% relative abundance), Discostella pseudostelligera (5% relative abundance), and Discostella stelligera (15% relative abundance). Asterionella ralfsii reached a peak at 17.25 cm (~ 50% relative abundance), from its previous value of ~ 35% at 26.75 cm. VNIRS-DOC was relatively stable throughout this period and high in comparison with the remainder of the sedimentary record with a median value of 4.1 mg/L (Fig. 3 ). VRS-Chl a was also stable throughout this period and lower in comparison to the remainder of the sedimentary record (Fig. 3 ). Zone 2 includes intervals from 14.25 cm (~ 1914) to 2.25 cm (~ 2010; Fig. 3 ). Asterionella ralfsii was still the most common diatom taxon in Zone 2, ranging from ~ 1–40% in this zone. Other common taxa included Aulacoseira distans (reaching up to ~ 10% relative abundance), and Fragilariaforma acidobiontica (~ 15% relative abundance). Asterionella ralfsii decreased from ~ 40% throughout this zone to 1% at 7.25 cm (~ 1976), recovering thereafter. From 9.25 cm (~ 1957) to 7.25 cm (~ 1976), Aulacoseira alpigena and Discostella pseudostelligera increased from ~ 1–15% relative abundance. At 5.5 cm (~ 1990), Fragiliaforma acidobiontica peaked at ~ 15% relative abundance, then dropped to ~ 5% at 2.75 cm (~ 2007). VNIRS-DOC decreased throughout this period (Fig. 3 ) from 3.8 mg/L to 1.6 mg/L between 13.25 cm (~ 1922) and 6.25 cm (~ 1990). VRS-Chl a increased throughout this period (Fig. 3 ) from 0.02 mg/ g dry weight to 0.04 mg/g dry weight between 14.25 cm (~ 1914) and 2.25 cm (~ 2010). Zone 3 includes intervals from 1.75 cm (~ 2012) to 0.75 cm (~ 2016; Fig. 3 ). Asterionella ralfsii was the most common diatom taxon in Zone 3, ranging from ~ 30% to ~ 35%. Other common taxa included Aulacoseira distans (~ 10% relative abundance) and Eunotia intermedia (~ 10% relative abundance). Eunotia intermedia increased from 5% at 1.75 cm (~ 2012) to 10% at 0.75 cm (~ 2016). Fragilariforma acidobiontica peaked near 5% at 1.75 cm (~ 2012) then decreased to 0% at 0.75 cm (~ 2016). VNIRS-DOC increased throughout this period (Fig. 3 ) from 3.1 mg/L to 3.6 mg/L between 1.75 cm (~ 2012) and 0.75 cm (~ 2016). VRS-Chl a also increased slightly throughout this period (Fig. 3 ) from 0.04 mg/ g dry weight to 0.05 mg/g dry weight between 1.75 cm (~ 2012) and 0.75 cm (~ 2016). Zone 4 only includes the surface sediments (0.25 cm, ~ 2018; Fig. 3 ). Asterionella ralfsii was still the most common diatom taxa in Zone 4 but declined to ~ 20% relative abundance (Fig. 3 ). Another common taxon was Aulacoseira alpigena (~ 10% relative abundance), which doubled in relative abundance from previous zones. Aulacoseira distans , Discostella pseudostelligera , and Discostella stelligera were absent in this zone. VNIRS-DOC continued to increase in this zone (Fig. 3 ), and VRS-Chl a also increased throughout this period (Fig. 3 ) from 0.05 mg/ g dry weight to 0.058 mg/g dry weight between 0.75 cm (~ 2016) and 0.25 cm (~ 2018). Baby Lake In the Baby Lake sediment core, 18 intervals were counted including every interval from 0 cm to 5.5 cm, every second interval from 6 cm to 12.5 cm, and every third interval from 12.5 cm to 30 cm. In total, 18 taxa were identified. CONISS with a broken stick test identified four biostratigraphic zones (Fig. 4 ). Zone 1 includes intervals from 19 cm (pre-~1850) to 8.25 cm (~ 1908; Fig. 4 ) in which Discostella stelligera , Tabellaria flocculosa , Aulacoseira ralfsii and Aulacoseira distans were the most common diatom taxa, ranging from ~ 10–20% over time. Other taxa present included Eunotia tenella and Achnanthidium minutissimum . VNIRS-DOC was relatively stable throughout this period (Fig. 4 ) and high in comparison with the remainder of the sedimentary record with a median value of 5.7 mg/L. VRS-Chl a was also stable throughout this period and high in comparison to the remainder of the sedimentary record (Fig. 4 ). Zone 2 includes intervals from 8.25 cm (~ 1908) to 4.25 cm (~ 1964; Fig. 4 ). Achnanthidium minutissimum , Lindavia ocellata , Discostella stelligera , and Tabellaria flocculosa were the most common diatom taxa in Zone 2, ranging from ~ 10% to ~ 20% over time. Tabellaria flocculosa reached a peak of ~ 25% at 6.25 cm (~ 1933) from ~ 10% in Zone 1. Asterionella ralfsii reached a peak of ~ 20% at 5.25 cm (~ 1950). VNIRS-DOC decreased from 5.7 mg/L to 2.6 mg/L, between 8.25 cm (~ 1908) and 4.25 cm (~ 1964). VRS-Chl a also declined throughout this period (Fig. 4 ) from 0.045 mg/ g dry weight to 0.02 mg/g dry weight between 8.25 cm (~ 1908) and 4.25 cm (~ 1964). Zone 3 includes intervals from 4.25 cm (~ 1964) to 1.25 cm (~ 2000; Fig. 4 ). Eunotia tenella and Achnanthidium minutissimum were the most common diatom taxa in Zone 3, ranging from ~ 10–40% over time. Other common taxa included Fragilaria rhomboides var. saxonica , Lindavia ocellata , and Asterionella ralfsii . In this zone, Eunotia tenella increased, reaching a peak of ~ 40% at 2.25 cm (~ 1986), from ~ 15% at 4.25 cm (~ 1964). Achnanthidium minutissimum, Discostella stelligera , and Asterionella ralfsii showed declining relative abundances with time in Zone 3. VNIRS-DOC increased throughout this period (Fig. 4 ) from 2.6 mg/L to 4.3 mg/L between 4.25 cm (~ 1964) and 1.25 cm (~ 2000). VRS-Chl a also increased throughout this period (Fig. 4 ) from 0.02 mg/g dry weight to 0.035 mg/g dry weight between 4.25 cm (~ 1964) and 1.25 cm (~ 2000). Zone 4 includes intervals from 1.25 cm (~ 2000) to 0.25 cm (~ 2016; Fig. 4 ). Eunotia tenella, Fragilaria rhomboides var. saxonica, Achnanthidium minutissimum , and Discostella stelligera were the most common diatom taxa in Zone 3. Other common taxa included Lindavia affinis and Brachysira vitrea . Eunotia tenella declined from ~ 30% at 1.25 cm (~ 2000) to 15% at 0.25 cm (~ 2018). Lindavia affinis , Achnanthidium minutissimum and Discostella stelligera showed increases, peaking at 0.25 cm (~ 2018). VNIRS-DOC increased throughout this period (Fig. 4 ) from 4.3 mg/L to 5.0 mg/L between 1.25 cm (~ 2000) and 0.25 cm (~ 2016). VRS-Chl a also increased throughout this period (Fig. 4 ) from 0.04 mg/ g dry weight to 0.06 mg/g dry weight between 1.25 cm (~ 1960) and 0.25 cm (~ 2018). Tillie Lake In the Tillie Lake sediment core, 30 intervals were counted including roughly every second interval from the top of the core to 30 cm. In total, 34 taxa were identified. CONISS and a broken stick test identified four biostratigraphic zones (Fig. 5 ). Zone 1 includes intervals from 28.75 cm (pre-~1850) to 25.75 cm (~ 1884; Fig. 5 ) in which Aulacoseira distans, Tabellaria flocculosa (str. III), and Aulacoseira lirata were the most common diatom taxa. Other common taxa included Asterionella formosa , Cyclotella ( Lindavia) bodanica , and Discostella spp. (including Discostella stelligera and Discostella. pseudostelligera ). Tabellaria flocculosa increased from ~ 8% at 28.75 cm (pre-~1850) to ~ 18% at 25.75 cm (~ 1884). Tabellaria quadriceps increased from ~ 1% at 28.75 cm (pre-~1850) to ~ 6% at 25.75 cm (~ 1884). Discostella spp. decreased from ~ 9% at 28.75 cm (pre-~1850) to ~ 4% at 25.75 cm (~ 1884). VNIRS-DOC (Fig. 5 ) decreased throughout this period from 6.3 mg/L at 28.75 cm (pre-~1850) to 5.2 mg/L at 25.75 cm (~ 1884). VNIRS-DOC was higher here than during most of the record with a median value of 5.8 mg/L. VRS-Chl a (Fig. 5 ) was generally stable throughout this period. Zone 2 includes intervals from 24.75 cm (~ 1894) to 8.25 cm (~ 1988; Fig. 5 ). Aulacoseira distans was the most common diatom taxon in Zone 2, ranging from ~ 23% to ~ 34% over time. Other common taxa included Tabellaria flocculosa (str. III), which varied between ~ 6% and ~ 18% over time. Tabellaria flocculosa (str. III) fluctuated from ~ 10% at 16.25 cm (~ 1950) to ~ 19% at 22.75 cm (~ 1911). Other taxa included Aulacoseira lirata and Lindavia bodanica. Aulacoseira lirata fluctuated from ~ 9% at 16.25 cm (~ 1950) to ~ 16% at 22.75 (~ 1911). Aulacoseira distans remained relatively constant at ~ 30%, except at 12.25 cm (~ 1970) where it decreases to ~ 25%. VNIRS-DOC decreased slightly during this period (Fig. 5 ) reaching its minimum value of ~ 4.0 mg/L during the mid-20th century. VRS-Chl a was relatively stable throughout Zone 2 with the exception of a rapid increase towards the Zone 3 interface. Zone 3 includes intervals from 7.25 cm (~ 1994) to 4.25 cm (~ 2008; Fig. 5 ). Aulacoseira distans and Tabellaria flocculosa (str. III) were the most common diatom taxa in Zone 3. Other common taxa included Asterionella formosa , Tabellaria quadriceps , and Aulacoseira lirata . Lindavia bodanica ranged from 0–2% throughout Zone 3, in contrast to its presence of 7–10% in Zone 2. Discostella spp. (including D. stelligera and D. pseudostelligera ) were absent from 7.25 cm (~ 1994) to 4.25 cm (~ 2008). VNIRS-DOC (Fig. 5 ) was relatively stable at ~ 6.0 mg/L from 7.25 cm (~ 1994) to 4.25 cm (~ 2008). VRS-Chl a was also relatively stable throughout this period (Fig. 5 ) after showing an increasing in values relative to Zones 1 and 2. Zone 4 includes intervals from 3.25 cm (~ 2012) to 0.25 cm (~ 2018; Fig. 5 ). Most taxa were relatively stable during this period. Aulacoseira distans and Tabellaria flocculosa (str. III) were the most common diatom taxa in Zone 3. Other common taxa included Asterionella formosa , Tabellaria quadriceps , and Aulacoseira lirata . VNIRS-DOC increased slightly throughout this period (Fig. 5 ) from 5.6 mg/L to 5.8 mg/L between 3.25 cm (~ 2012) to 0.25 cm (~ 2018). VRS-Chl a showed a slight increase throughout this zone (Fig. 5 ). Crooked Lake Thirty intervals were counted in the Crooked Lake sediment core, including every second interval from 0 cm to the bottom of the core. In total, 34 taxa were identified. CONISS with a broken stick test identified four important biostratigraphic zones (Fig. 6 ). Zone 1 includes intervals from 28.75 cm to 23.25 cm (both pre-~1850; Fig. 6 ). Aulacoseira distans was the most common diatom taxon in Zone 1, remaining at ~ 40% relative abundance. Another common taxon was Tabellaria flocculosa str. III (~ 20% relative abundance). VNIRS-DOC was relatively stable throughout this period (Fig. 6 ) and high in comparison with the remainder of the sedimentary record with a median value of 7.1 mg/L. VRS-Chl a was also relatively stable throughout this period (Fig. 6 ). Zone 2 (Fig. 6 ) includes intervals from 22.75 cm (pre-~1850) to 5.25 cm (~ 1968). Aulacoseira distans, Aulacoseira lirata, Tabellaria flocculosa (str. III), and Asterionella formosa were the most common diatom taxa in Zone 2. Other common taxa included Discostella spp. (including D. stelligera and D. pseudostelligera ) and Pinnularia microstauron . Pinnularia microstauron increased from 0% at 22.75 cm (pre-~1850) to ~ 10% at 5.25 cm (~ 1968). Tabellaria flocculosa (str. III) fluctuated from ~ 20% at 22.75 cm (pre-~1850) to ~ 5% at 5.25 cm (~ 1968). Aulacoseira distans decreased in relative abundances following 12.25 (~ 1902). VNIRS-DOC decreased from 7.0 mg/L to 3.1 mg/L between 22.75 cm (pre-~1850) to 5.25 cm (~ 1968) (Fig. 6 ). VRS-Chl a increased from 0.05 mg/ g dry weight to 0.08 mg/g dry weight between 22.75 cm (pre-~1850) and 16.25 cm (~ 1866) (Fig. 6 ), and then decreased to 0.04 mg/g dry weight at 5.25 cm (~ 1968). Zone 3 includes interval 4.25 cm (~ 1980; Fig. 6 ). Fragilaria rhomboides var. cassinerva , Pinnularia microstauron , Tabellaria flocculosa (str. III), and Aulacoseira distans were the most common diatom taxa in Zone 3. At 4.25 cm (~ 1980), Fragilaria rhomboides var. saxonica , Asterionella formosa , Discostella spp. ( D. stelligera and D. pseudostelligera ), and Aulacoseira lirata decreased to 0% from values of 5–10% in Zone 2. VNIRS-DOC (Fig. 6 ) was at 2.9 mg/L at 4.25 cm (~ 1980). VRS-Chl a (Fig. 6 ) was at 0.045 mg/g dry weight at 4.25 cm (~ 1980). Zone 4 includes intervals from 3.25 cm (~ 1991) to 0.25 cm (~ 2018; Fig. 6 ). Asterionella formosa and Tabellaria flocculosa (str. III) were the most common diatom taxa in Zone 3. Other common taxa included Frustulia rhomboides var. saxonica and Discostella spp. (including D. stelligera and D. pseudostelligera ). Frustulia rhomboides var. saxonica decreased to ~ 7% at 0.25 cm (~ 2018) from ~ 13% at 2.25 cm (~ 2000). Eunotia exigua decreased to 0% at 0.25 cm (~ 2018) from ~ 5% at 2.25 cm (~ 2000). Aulacoseira distans decreased to 0% at 0.25 cm (~ 2018) from ~ 5% at 2.25 cm (~ 2000). Tabellaria flocculosa increased to 37% at 0.25 cm (~ 2018) from 17% at 2.25 cm (~ 2000). VNIRS-DOC (Fig. 6 ) increased throughout this period from 3.2 mg/L to 7.0 mg/L between 3.75 cm (~ 1985) and 0.25 cm (~ 2018). VRS-Chl a (Fig. 6 ) also increased throughout this period from 0.048 mg/g dry weight to 0.052 mg/g dry weight. Discussion How did Sudbury and Killarney Provincial Park lakes respond to acidification? Mining and smelting activities in Sudbury affected nearby lakes in various ways, most notably acidification and metal contamination. This, in turn, influenced diatom assemblage composition, lake-water DOC concentrations and whole-lake aquatic production. With the onset and peak (~ 1960 to ~ 1970) smelter emissions in Sudbury, we show that most study lakes (with the exception of naturally acidic Ruth-Roy Lake) recorded decreases in the relative abundance of small circumneutral taxa (i.e., Discostella spp., Achnanthidium minutissimum, and Aulacoseira spp.) concurrent with increases in acidophilic taxa (i.e., Fragilariforma acidobiontica, Eunotia spp., Tabellaria flocculosa and Asterionella ralfsii ) that peaked at ~ 1960 in Sudbury and at ~ 1970 in KPP. Similar changes have previously been observed in other Sudbury and KPP lakes, and in lakes in other acid-sensitive regions, with the onset of acidic emissions (Charles 1985; Charles et al. 1990; Dixit et al. 2002 ). The direction and magnitude of acidification due to smelting emissions are moderated by several factors, including distance to the nearest smelter and the underlying bedrock geology (i.e., buffering capacity). Aquatic ecosystems closest to the smelters received more acidic deposition than lakes further away (Keller et al. 2004 ). For example, the concentration of sulphate in Baby Lake (~ 1 km from Coniston smelter) was 25.3 mg/L in 1980 compared to 10.0 mg/L in Ruth-Roy Lake (~ 45 km from Sudbury) in the same year, despite their relatively similar lake volumes (1.14 x 10 6 m 3 and 2.34 x 10 6 m 3 for Baby and Ruth-Roy lakes, respectively (Keller et al. 2016 )). In our study, the smallest temporal changes in diatom assemblages, VRS-Chl a , and VNIRS-DOC were observed in the two study sites located furthest from the smelters, specifically Johnnie (~ 42 km) and Tillie lakes (~ 62 km). The diverse responses among the study lakes can also be attributed to differences in their hydrological/physical characteristics and bedrock composition. Bedrock geology influences lake buffering capacity because of differences in carbonate and silicate content. Lakes located in catchments predominantly composed of igneous bedrock with thin overlaying till are often “acid sensitive” with low buffering capacity, such as Ruth-Roy and Baby lakes. Lakes located in catchments with calcium-rich sedimentary rocks (i.e., limestone) are less acid sensitive and boast higher buffering capacities (Mallory et al. 1998). Johnnie and Tillie lakes, for example, are situated on easily weathered bedrock (Dixit et al. 2002 ) which may contribute to higher buffering capacities and therefore relatively muted diatom responses to acid deposition. In contrast, Ruth-Roy Lake, located immediately upstream of Johnnie Lake, has a Ca 2+ plus Mg 2+ lake water concentration of only 60 µeq/L, approximately half that of Johnnie Lake (110 µeq/L). The VRS-Chl a and VNIRS-DOC profiles for both Johnnie and Tillie lakes also showed a weaker response to acidification, consistent with the more efficient neutralization of acidic inputs in the relatively well-buffered catchments. Baby Lake, located only 1 km from a smelter, responded with the most striking floristic changes, especially in the acidobiontic taxon Eunotia tenella . The lake has a relatively small watershed and is situated on exposed granitic/gneissic bedrock in a steep-sided catchment (Hutchinson and Havas 1986 ). Pre-industrial diatom assemblages were composed of acidophilic taxa (i.e., Asterionella ralfsii , Tabellaria flocculosa ) and circumneutral taxa (i.e., Aulacoseira distans , Discostella stelligera ), indicating moderately acidic conditions. With the peak of smelting activities, declines in taxa such as A. distans and increased abundances of acidobiontic taxa such as Eunotia tenella , coincident with declines in VRS-Chl a and VNIRS-DOC, indicated acidification. Ruth-Roy Lake experienced striking changes despite being ~ 45 km from the nearest smelter, as discussed in detail in Simmatis et al. ( 2023 ). Ruth-Roy Lake is situated on an orthoquartzite ridge, providing poor buffering capacity and weathering ability, which contributes to naturally acidic waters (Dixit et al. 2002 ). Ruth-Roy Lake is also small (relative to other study lakes) with a surface area of 54 ha (Keller et al. 2016 ). The combination of lake size, bedrock composition and low buffering capacity makes Ruth-Roy Lake more susceptible to acidification. Diatom assemblages in Ruth-Roy Lake prior to the onset of smelting in Sudbury were already comprised of acidophilic and acidobiontic taxa (Vinebrooke et al. 2002 ) and notable changes occurred in cladoceran assemblages after the onset of smelting operations (Simmatis et al. 2023 ). Based on shifts in the diatom assemblages, Ruth-Roy Lake was likely acidic prior to the onset of smelting in Sudbury and has remained so to present day. The diatom changes in Crooked Lake were somewhat muted despite its relative proximity to a smelter (~ 6 km). Similar muted changes were evident in subfossil invertebrate assemblages from Crooked Lake, with increased prevalence of generalist taxa in modern sediments (Simmatis et al. 2022 ). Prior to ~ 1800, Crooked Lake was primarily dominated by circumneutral taxa (i.e., Aulacoseira spp. and Discostella spp.), as well as some acidophilic taxa (i.e., Asterionella formosa ). This assemblage indicates that Crooked Lake was naturally acidic, which is supported by its pre-industrial (~ 1880) diatom inferred pH (Dixit et al. 1992 c). VRS-Chl a remained relatively constant during the period of acidification, but VNIRS-DOC showed a marked decline from ~ 7 mg/L in pre-industrial times to ~ 3 mg/L in the mid-1970s. Based largely on the shifting abundance of diatoms from circumneutral to acidophilic taxa around the onset of smelting activities, Crooked Lake experienced moderate acidification, relative to its background of naturally acidic conditions in pre-industrial times. Overall, the lakes responded to acidification based on their distance from the smelters and bedrock geology. The pre-industrial state of the lakes was also an important factor influencing how each lake responded uniquely to smelting operations. Based on this relatively small sample size and the heterogeneity in geological setting of our five study sites, regional lake responses (i.e., KPP versus Sudbury) cannot be reliably inferred. However, as noted above, the timing of peak acidification differed slightly based on distance from the smelters. Trends in chemical and biological recovery following acidification Chemical Recovery Reduced smelting emissions have decreased the amount of acid and metal inputs to lakes in and around Sudbury, allowing pH to increase and lake-water metal concentrations to decrease in most lakes (Keller et al. 2019 ). All our study lakes have experienced varying degrees of chemical recovery. In terms of pH change between 1975 and 2019, Baby Lake has experienced the largest increase (+ 2.6 pH units), followed by Crooked Lake (+ 2.4 pH units), Johnnie Lake (+ 1.16 pH units), Tillie Lake (+ 0.90 pH units) and Ruth-Roy Lake (+ 0.86 pH units). The magnitude of pH recovery in Baby Lake is attributed to several factors, including reduced sulphate emissions, alkalinity generation from lake sediments, and partial liming of the watershed (Dixit et al. 1992 c). DOC has been generally shown to increase concomitantly with reduced acid deposition because of its effects on DOC solubility and mobility in soils, promoting increased terrestrial DOC supply with recovery from acidification (Monteith et al. 2007 ; Meyer-Jacob et al. 2019 , 2020 ). Based on VNIRS-DOC inferences, DOC recovery has occurred in all our study lakes. Trends in VRS-Chl a mirrored those of VNIRS-DOC in most cases. Notably, VRS-Chl a in Johnnie Lake did not distinctly decline during the smelting period, but has increased in recent sediments. Recovery of Diatom Assemblages The extent of biological recovery varied among our study lakes and did not consistently correspond to the magnitude of chemical recovery. In our study, biological recovery was commonly marked by decreases in the relative abundance of acidophilic taxa (i.e., Fragilariforma acidobiontica , Tabellaria flocculosa ), and increases in circumneutral taxa (i.e., Aulacoseira spp. and Discostella spp.). Lakes in catchments with easily weathered geology (i.e., Johnnie and Tillie lakes) experienced more biological recovery than those with small igneous catchments (i.e., Ruth-Roy and Baby lakes), despite lower absolute magnitudes of pH change between 1975 and 2019. In Johnnie Lake, recent diatom assemblages are similar to those found in pre-impact sediments, likely reflecting its higher buffering capacity and relative resistance to acidification. Similarly, recent diatom assemblages in Tillie Lake are very similar to pre-industrial assemblages, apart from a decline in the circumneutral taxon Lindavia bodanica in the recent sediments. Given that Tillie Lake was the farthest from the Sudbury emission sources, it received the lowest amount of acid deposition, and so recovery was likely more rapid. Nonetheless, the lake’s recent diatom assemblages are still very different from pre-industrial assemblages. Lakes with small igneous catchments and limited buffering capacity experienced the highest increases in pH of our study lakes, but biological recovery has not matched the pace of chemical recovery. In Baby Lake, there is little evidence of diatom biological recovery. Decreased abundance of acidophilic taxa (i.e., Tabellaria flocculosa and Asterionella ralfisii ) support that the lake has somewhat chemically recovered from acidification, but stark differences between recent and pre-industrial sedimentary diatom assemblages do not indicate biological recovery to pre-impact conditions. As detailed in Simmatis et al. ( 2023 ), Ruth-Roy Lake has shown almost no biological recovery, indicated by the dissimilarity of recent and pre-impact diatom assemblages. Notably, recent (2000–2018) decreases were recorded in dominant taxa (i.e., Tabellaria flocculosa , Aulacoseira distans ) except for Fragilariforma acidobiontica , which dominates most of Zone 2. Nonetheless, the uppermost sediments (0.25 cm to 0.75 cm) show small reductions in Fragilariforma acidobiontica , which could be indicative of some modest recovery from acidification. Given that Ruth-Roy Lake was believed to be naturally acidic, it likely has limited capacity to recover from decreased lake-water pH (Smol et al. 1998 ; Simmatis et al. 2023 ). When considering mining-related impacts on Sudbury and the surrounding area, it has been shown that, while many lakes have undergone varying degrees of chemical recovery, similar degrees of biological recovery have not always followed suit (Jeffries et al. 2003 ). Furthermore, if and when biological recovery occurs, it often lags behind chemical recovery (Snucins and Gunn 1998 ; Jeffries et al. 2003 ). It is possible that biological recovery is slower than chemical recovery in our study lakes for several reasons, including: (1) the threshold of chemical recovery that allows biological recovery has not been reached; (2) the “time-lag” response could be caused by declines of acid-sensitive species in chemically recovered sites; and (3) acidified systems in recovery are being influenced by new environmental factors (i.e., climatic changes; Monteith et al. 2005 ), and this is preventing or slowing a return to pre-industrial diatom assemblages. Collectively, these data are consistent with other recent paleolimnological studies (e.g., Simmatis et al. 2021 , 2022 ; Cheng et al. 2023 ) indicating complex recovery patterns from acidification which can be affected by lake chemistry (i.e., chemical recovery), other large-scale regional stressors (i.e., changing climate), and/or baseline lake conditions (i.e., a naturally acidic conditions). The Role of Climate Change Large-scale environmental changes, such as climate warming, can directly or indirectly influence lake ecosystems. In Sudbury, mean annual air temperature, total annual precipitation, and total annual rainfall have increased modestly since 1985 (Simmatis 2021 ), and the Sudbury and KPP regions have experienced a warming trend of 1.4°C since the 1950s (Meyer-Jacob et al. 2019 ). Limnological changes concomitant with recent warming (i.e., less ice cover, shifts in thermal stratification; see Woolway et al. 2022 ) are often associated in medium to relatively deep lakes with increases in the relative abundance of several planktonic Cyclotella (Discostella) sensu lato species along with decreases in heavily silicified Aulacoseira and/or benthic fragilarioids, although the limnological context is key (Rühland et al. 2015 ). These taxonomic shifts, driven by climate-mediated changes in ice cover and/or changes in thermal stratification, were not clearly evident in our study lakes. Initially, this may seem unexpected, given that many other similar Boreal Shield lakes in central Ontario (unaffected by industrial emissions) are tracking recent climate-related changes in their diatom assemblages. However, these changes are largely tracked in relatively pristine, wilderness lakes. As noted by Rühland et al. ( 2008 , 2015 ), other factors, such as acidification and cultural eutrophication, can override these changes. Nonetheless, accelerated climate warming over the last few decades has likely contributed to the nature and magnitude of recent diatom changes. Conclusions It is well documented that Sudbury and Killarney Provincial Park lakes were affected by Sudbury smelting activities. Distance from the smelters, bedrock geology, and the resultant pre-industrial state of these lakes collectively influenced how each lake responded to smelting operations and subsequent declines in emissions. The differences in biological recovery patterns that we record indicate that recovery needs to be considered within a multi-stressor framework, on a case-by-case basis. Biological recovery of aquatic ecosystems from the effects of Sudbury mining activities were mainly influenced by water chemistry (i.e., chemical recovery), large-scale stressors (i.e., changing climate), and baseline lake conditions (i.e., whether or not a lake was naturally acidic). Although climate change is certainly affecting lakes in the Sudbury and KPP regions, the nature of the recent diatom assemblage shifts in our study sites appear to be, not surprisingly, mainly be a response to pH-related changes, rather than more directly to climate-related changes. Overall, our study confirms that historical reconstruction of aquatic ecosystems provides important context for lake management. Multi-disciplinary studies, at different temporal scales, should provide a more integrated view of these complex systems, and provide insights into the variability that is present in recovering lakes. Declarations Acknowledgements This study is part of the Landscape Carbon Accumulation through Reductions in Emissions (L-CARE) project, and financial support was provided by the Natural Sciences and Engineering Research Council of Canada (Grant No. CRDPJ 509182-17) and the Ontario Centres of Excellence (Grant No. 41-1-6145006). Funding declaration This research was by funded by the Natural Sciences and Engineering Research Council of Canada (Grant No. CRDPJ 509182-17) and the Ontario Centres of Excellence (Grant No. 41-1-6145006). Competing interest declaration The authors declare no competing interests. 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Hindar A, Henriksen A (1998) Northern Lakes recovery study: mapping of critical loads and critical load exceedances in the Killarney Provincial Park, Ontario, Canada. Norwegian Institute for Water Research. Accessed on 8 March 2024 from https://niva.brage.unit.no/niva-xmlui/bitstream/handle/11250/209999/3889_%28mangler%20sign%29_72dpi.pdf?sequence=1&isAllowed=y . Hutchinson TC, Havas M (1986) Recovery of previously acidified lakes near Coniston, Canada following reductions in atmospheric sulphur and metal emissions. Wat Air and Soil Pollut 28: 319–333. Doi: https://doi.org/10.1007/BF00583498 Jeffries DS, Clair TA, Couture S, Dillon PJ, Dupont J, Keller W, McNicol DK, Turner MA, Vet R, Weeber R (2003) Assessing the recovery of lakes in southeastern Canada from the effects of acidic deposition. AMBIO 32: 176–182. Doi: https://doi.org/10.1579/0044-7447-32.3.176 Keller W, Heneberry J, Dixit S (2003) Decreased acid deposition and the chemical recovery of Killarney, Ontario, lakes. 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In: Ettl H, Gerloff J, Heynig H, Mollenhauer D (eds.). Süsswasserflora von Mitteleuropa, Band 2/1. Gustav Fischer Verlag, Stuttgart, New York. p. 1–876. [German]. Krammer K, Lange-Bertalot H (1988) Bacillariophyceae. 2. Teil: Bacillariaceae, Epithemiaceae, Surirellaceae. In: Ettl H, Gerloff J, Heynig H, Mollenhauer D (eds.). Süsswasserflora von Mitteleuropa, Band 2/2. Gustav Fischer Verlag, Jena. p. 1–596. [German]. Krammer K, Lange-Bertalot H (1991a) Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In: Ettl H, Gerloff J, Heynig H, Mollenhauer D (eds.). Süsswasserflora von Mitteleuropa, Band 2/3. Gustav Fischer Verlag, Stuttgart, Jena. p. 1–576. [German]. Krammer K, Lange-Bertalot H (1991b) Bacillariophyceae. 4. Teil: Achnanthaceae, Kritische Ergänzungen zu Navicula (Lineolatae) und Gomphonema, Gesamtliteraturverzeichnis Teil 1–4. In: Ettl H, Gerloff J, Heynig H, Mollenhauer D (eds.). Süsswasserflora von Mitteleuropa, 2/4. GustavFischer Verlag, Stuttgart, Jena. p. 1–437. [German]. Meyer-Jacob C, Labaj AL, Paterson AM, Edwards BA, Keller W, Cumming BF, Smol JP (2020) Re-browning of Sudbury (Ontario, Canada) lakes now approaches pre-acid deposition lake-water dissolved organic carbon levels. Sci Total Environ 725: 138347. Doi: https://doi.org/10.1016/j.scitotenv.2020.138347 Meyer-Jacob C, Michelutti N, Paterson AM, Cumming BF, Keller W, Smol JP (2019) The browning and re-browning of lakes: Divergent lake-water organic carbon trends linked to acid deposition and climate change. Sci Rep 9: 16676. Doi: https://doi.org/10.1038/s41598-019-52912-0 Meyer-Jacob C, Labaj AL, Paterson AM, Layton-Matthews D, Smol JP (2024) Impacts of acid deposition and lake browning on long-term organic carbon storage in Canadian northern forest lakes. J Paleolimnol 71: 153–173. Michelutti N, Blais JM, Cumming BF, Paterson AM, Rühland K, Wolfe AP, Smol JP (2010) Do spectrally inferred determinations of chlorophyll a reflect trends in lake trophic status? J Paleolimnol 43: 205–217. Doi: https://doi.org/10.1007/s10933-009-9325-8 Michelutti N, Smol JP (2016) Visible spectroscopy reliably tracks trends in paleo-production. J Paleolimnol 56: 253–265. Doi: https://doi.org/10.1007/s10933-016-9921-3 Monteith DT, Hildrew AG, Flower RJ, Raven PJ, Beaumont WRB, Collen P, Kreiser AM, Shilland EM, Winterbottom JH (2005) Biological responses to the chemical recovery of acidified fresh waters in the UK. Environ Pollut 137: 83–101. Doi: https://doi.org/10.1016/j.envpol.2004.12.026 Monteith DT, Stoddard JL, Evans CD, De Wit HA, Forsius M, Høgåsen T, Wilander A, Skjelkvåle BL, Jeffries DS, Vuorenmaa J, Keller W (2007) Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry. Nature 450: 537–540. Oksanen J, Blanchet FG, Friendly M, Kindt R, Legendre P, McGlinn D, Minchin PR, O’Hara RB, Simpson GL, Solymos P, Stevens MHH (2019) vegan: Community Ecology Package. R package version 2.5-6. Pearson D, Gunn J, Keller W (2002) The Past, Present and Future of Sudbury’s Lakes. In DH Rousell and KJ Jansons (Eds.), The Physical Environment of the City of Sudbury (Vol. 6, pp. 195–215). Ontario Geological Survey. Rühland K, Paterson AM, Smol JP (2008) Hemispheric-scale patterns of climate-related shifts in planktonic diatoms from North American and European lakes: planktonic diatom responses to recent warming. Glob Change Biol 14: 2740–2754. Doi: https://doi.org/10.1111/j.1365-2486.2008.01670.x Rühland KM, Paterson AM, Smol JP (2015) Lake diatom responses to warming: Reviewing the evidence. J Paleolimnol 54: 1–35. Doi: https://doi.org/10.1007/s10933-015-9837-3 Simmatis B (2021) Paleoecotoxicology of smelting-affected lakes near Sudbury (Ontario, Canada). Doctor of Philosophy dissertation. Queen’s University. Simmatis B, Paterson AM, Edwards BA, Smol JP (2021) Linking changes in sedimentary Cladocera assemblages to limnological variables in 67 Sudbury (Ontario, Canada) lakes reflecting various degrees of metal smelter impacts. Can J Fish Aquat Sci 78: 1455–1469. Simmatis B, Paterson AM, Smol JP (2022) Comparing recent and preindustrial cladoceran assemblages in 35 metal- and smelting-affected lakes near Sudbury (Ontario, Canada). J Planton Res 44: 303–315. Simmatis B, Lanigan C, Lambert B, Meyer-Jacob C, Michelutti N, Paterson AM, Smol JP (2023) Using a multi-proxy paleolimnological approach to track the effects of multiple stressors on a naturally acidic lake in Killarney Provincial Park (Ontario, Canada). Can J Fish Aquat Sci 80: 913–923. Smol JP, Cumming BF, Dixit AS, Dixit SS (1998) Tracking recovery patterns in acidified lakes: a paleolimnological perspective. Restor Ecol 6: 318–326. Snucins E, Gunn J (1998) Chemical and biological status of Killarney Park Lakes (1995–1997): A study of lakes in the early stages of recovery from acidification. Ontario Ministry of Natural Resources. Snucins E, Gunn J (2000) Interannual variation in the thermal structure of clear and colored lakes. Limnol Oceanogr 45: 1639–1646. Doi: https://doi.org/10.4319/lo.2000.45.7.1639 Snucins E, Gunn J, Keller W, Dixit SS, Hindar A, Henriksen A (2001) Effects of regional reductions in sulphur deposition on the chemical and biological recovery of lakes within killarney Park, Ontario, Canada. Environ Monit Assess 67: 179–194. Doi: https://doi.org/10.1023/A:1006434622970 Szkokan-Emilson EJ, Wesolek BE, Gunn JM, Sarrazin-Delay C, Bedore J, Chan F, Garreau D, O’Grady A, Robinson C (2010) Recovery of benthic invertebrate communities from acidification in Killarney Park lakes. Environ Monit Assess 166: 293–302. Doi: https://doi.org/10.1007/s10661-009-1002-x Tropea AE (2008) Assessing biological recovery from acidification and metal contamination in urban lakes from Sudbury, Canada: A paleolimnological approach. Master of Science thesis. Queen’s University. Tropea AE, Paterson AM, Keller W, Smol JP (2010) Sudbury sediments revisited: evaluating limnological recovery in a multiple-stressor environment. Wat. Air and Soil Pollut. 210: 317–333. Doi: https://doi.org/10.1007/s11270-009-0255-x Tropea AE, Paterson AM, Keller W, Smol JP (2011) Diatoms as indicators of long-term nutrient enrichment in metal-contaminated urban lakes from Sudbury, Ontario. Lake Reserv Manage 27: 48–60. Doi: https://doi.org/10.1080/07438141.2011.555935 Vinebrooke RD, Dixit SS, Graham MD, Gunn JM, Chen YW, Belzile N (2002) Whole-lake algal responses to a century of acidic industrial deposition on the Canadian Shield. Can J Fish Aquat Sci 59: 483–493. Winterhalder K (1995) Early History of Human Activities in the Sudbury Area and Ecological Damage to the Landscape. In J.M. Gunn (Ed.), Restoration and Recovery of an Industrial Region (pp. 17–31). Springer New York. Woolway RI, Sharma S, Smol JP (2022) Lakes in hot water: the impacts of a changing climate on aquatic ecosystems. BioScience 72: 1050–1061. Additional Declarations No competing interests reported. Supplementary Files Supplementalinformation.docx Cite Share Download PDF Status: Published Journal Publication published 14 May, 2025 Read the published version in Journal of Paleolimnology → Version 1 posted Editorial decision: Revision requested 08 Aug, 2024 Reviews received at journal 28 Jul, 2024 Reviews received at journal 24 Jul, 2024 Reviews received at journal 12 Jul, 2024 Reviewers agreed at journal 17 Jun, 2024 Reviewers agreed at journal 14 Jun, 2024 Reviewers agreed at journal 13 Jun, 2024 Reviewers invited by journal 09 Jun, 2024 Editor assigned by journal 24 May, 2024 Submission checks completed at journal 24 May, 2024 First submitted to journal 22 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4462254","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":310193948,"identity":"594ebf01-0894-48b3-bca8-4e913b8efccf","order_by":0,"name":"Courtney Lanigan","email":"","orcid":"","institution":"Queen’s University","correspondingAuthor":false,"prefix":"","firstName":"Courtney","middleName":"","lastName":"Lanigan","suffix":""},{"id":310193949,"identity":"1e77b912-304f-41b0-975f-22ae8cc2bde0","order_by":1,"name":"Neal Michelutti","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtElEQVRIiWNgGAWjYFAC9uM/PpCohSdBcgap1hhI85Ck3lzsQIKxTdlhOX7p9mcSDDV2hLVYzk48kJxz7rCx5JwzZhIMx5KJcNXthITDuW2HEzfcyGGTYGxgJkqLYbNl2+H6/TfSnwG11BOlxZiZse1wgoFEghlQy2FitOSkMfacSzeccSPH2CLh2HFitKQfY/hRZi3PPyP94Y0PNdWEtUAAG5ROIFYDQssoGAWjYBSMAmwAANQcN0FvPz6cAAAAAElFTkSuQmCC","orcid":"","institution":"Queen’s University","correspondingAuthor":true,"prefix":"","firstName":"Neal","middleName":"","lastName":"Michelutti","suffix":""},{"id":310193950,"identity":"d7e52ddd-62de-427d-8530-07b1ddb88bf8","order_by":2,"name":"Andrew M. Paterson","email":"","orcid":"","institution":"Ontario Ministry of the Environment, Conservation and Parks","correspondingAuthor":false,"prefix":"","firstName":"Andrew","middleName":"M.","lastName":"Paterson","suffix":""},{"id":310193951,"identity":"05cf7816-10d8-4b84-ba03-59bf193b933a","order_by":3,"name":"Carsten Meyer-Jacob","email":"","orcid":"","institution":"Queen’s University","correspondingAuthor":false,"prefix":"","firstName":"Carsten","middleName":"","lastName":"Meyer-Jacob","suffix":""},{"id":310193952,"identity":"de82fd0b-ad9a-4d46-a8e9-69e2f59dd13a","order_by":4,"name":"Brigitte Simmatis","email":"","orcid":"","institution":"Queen’s University","correspondingAuthor":false,"prefix":"","firstName":"Brigitte","middleName":"","lastName":"Simmatis","suffix":""},{"id":310193953,"identity":"7435dd04-1289-4590-af48-0d539667afdd","order_by":5,"name":"John P. Smol","email":"","orcid":"","institution":"Queen’s University","correspondingAuthor":false,"prefix":"","firstName":"John","middleName":"P.","lastName":"Smol","suffix":""}],"badges":[],"createdAt":"2024-05-22 16:25:58","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4462254/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4462254/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10933-025-00356-0","type":"published","date":"2025-05-14T15:57:28+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":58077429,"identity":"63f1069d-8ed4-40bc-b0ca-f570041089b7","added_by":"auto","created_at":"2024-06-10 22:33:36","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":138739,"visible":true,"origin":"","legend":"\u003cp\u003eKillarney Provincial Park (shaded green area) relative to Sudbury. Study lakes are denoted by black circles. Source: ESRI Canada, Natural Resources Canada, Land Information Ontario. Inset: Location of studies region within Ontario (Canada).\u003c/p\u003e","description":"","filename":"LaniganetalJOPLFig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/21f30e98c3fae557921f41cf.jpg"},{"id":58077424,"identity":"ecde2fac-d023-4755-850f-fd9e8c10e269","added_by":"auto","created_at":"2024-06-10 22:33:36","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":130703,"visible":true,"origin":"","legend":"\u003cp\u003eTrends in sedimentary diatom assemblages (relative abundance), visible range spectroscopically-inferred chlorophyll \u003cem\u003ea\u003c/em\u003e (VRS-Chl-\u003cem\u003ea\u003c/em\u003e), and visible near-infrared spectroscopically-inferred dissolved organic carbon (VNIRS-DOC) over time in Ruth-Roy Lake. Diatom assemblages are expressed in percent abundances relative to the total number of individuals recovered in each interval. Only taxa with a relative abundance of \u0026gt;5% in at least two sediment intervals were plotted. Taxa are ordered by weighted average from top left to bottom right. The horizontal blue line indicates CONISS breaks identified by broken stick as notable biostratigraphic zones, named in blue text between the estimated year and midpoint y-axes. \u003csup\u003e210\u003c/sup\u003ePb dates are to the left.\u003c/p\u003e","description":"","filename":"LaniganetalJOPLFig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/52c062db67c9d12a9aec91ae.jpg"},{"id":58077714,"identity":"53bd2d08-5823-46aa-81e0-95bf82d1381a","added_by":"auto","created_at":"2024-06-10 22:41:36","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":170445,"visible":true,"origin":"","legend":"\u003cp\u003eTrends in sedimentary diatom assemblages (relative abundance), visible range spectroscopically-inferred chlorophyll a (VRS-Chl-\u003cem\u003ea\u003c/em\u003e), and visible near-infrared spectroscopically-inferred dissolved organic carbon (VNIRS-DOC) over time in\u003cem\u003e \u003c/em\u003eJohnnie Lake. Diatom assemblages are expressed in percent abundances relative to the total number of individuals recovered in each interval. Only taxa with a relative abundance of \u0026gt;5% in at least two sediment intervals were plotted. Taxa are ordered by weighted average from top left to bottom right. The horizontal blue line indicates CONISS breaks identified by broken stick as notable biostratigraphic zones, named in blue text between the estimated year and midpoint y-axes.\u003csup\u003e 210\u003c/sup\u003ePb dates are to the left.\u003c/p\u003e","description":"","filename":"LaniganetalJOPLFig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/43e78fe404a8f6a153fe2224.jpg"},{"id":58077820,"identity":"2c703990-ba9f-4287-ba4c-3557482d5f60","added_by":"auto","created_at":"2024-06-10 22:49:36","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":152790,"visible":true,"origin":"","legend":"\u003cp\u003eTrends in sedimentary diatom assemblages (relative abundance), visible range spectroscopically-inferred chlorophyll a (VRS-Chl-\u003cem\u003ea\u003c/em\u003e), and visible near-infrared spectroscopically-inferred dissolved organic carbon (VNIRS-DOC) over time in\u003cem\u003e \u003c/em\u003eBaby Lake. Diatom assemblages are expressed in percent abundances relative to the total number of individuals recovered in each interval. Only taxa with a relative abundance of \u0026gt;5% in at least two sediment intervals were plotted. Taxa are ordered by weighted average from top left to bottom right. The horizontal blue line indicates CONISS breaks identified by broken stick as notable biostratigraphic zones, named in blue text between the estimated year and midpoint y-axes. \u003csup\u003e210\u003c/sup\u003ePb dates are to the left.\u003c/p\u003e","description":"","filename":"LaniganetalJOPLFig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/f2b501ad415eb5164020de0b.jpg"},{"id":58077428,"identity":"9e906f9f-8f93-40b9-b827-090b76c726d9","added_by":"auto","created_at":"2024-06-10 22:33:36","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":191932,"visible":true,"origin":"","legend":"\u003cp\u003eTrends in sedimentary diatom assemblages (relative abundance), visible range spectroscopically-inferred chlorophyll a (VRS-Chl-\u003cem\u003ea\u003c/em\u003e), and visible near-infrared spectroscopically-inferred dissolved organic carbon (VNIRS-DOC) over time in Tillie Lake. Diatom assemblages are expressed in percent abundances relative to the total number of individuals recovered in each interval. Only taxa with a relative abundance of \u0026gt;5% in at least two sediment intervals were plotted. Taxa are ordered by weighted average from top left to bottom right. The horizontal blue line indicates CONISS breaks identified by broken stick as notable biostratigraphic zones, named in blue text between the estimated year and midpoint y-axes. \u003csup\u003e210\u003c/sup\u003ePb dates are to the left.\u003c/p\u003e","description":"","filename":"LaniganetalJOPLFig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/bdc6ea7280d43c2a82783538.jpg"},{"id":58077425,"identity":"ad357146-280c-4ea9-bfb2-7f03ff18dc0d","added_by":"auto","created_at":"2024-06-10 22:33:36","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":186502,"visible":true,"origin":"","legend":"\u003cp\u003eTrends in sedimentary diatom assemblages (relative abundance), visible range spectroscopically-inferred chlorophyll a (VRS-Chl-\u003cem\u003ea\u003c/em\u003e), and visible near-infrared spectroscopically-inferred dissolved organic carbon (VNIRS-DOC) over time in\u003cem\u003e \u003c/em\u003eCrooked Lake. Diatom assemblages are expressed in percent abundances relative to the total number of individuals recovered in each interval. Only taxa with a relative abundance of \u0026gt;5% in at least two sediment intervals were plotted. Taxa are ordered by weighted average from top left to bottom right. The horizontal blue line indicates CONISS breaks identified by broken stick as notable biostratigraphic zones, named in blue text between the estimated year and midpoint y-axes. \u003csup\u003e210\u003c/sup\u003ePb dates are to the left.\u003c/p\u003e","description":"","filename":"LaniganetalJOPLFig6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/4f10dc5118d4e71903948bec.jpg"},{"id":83068008,"identity":"992104c4-f574-4bb0-a6b7-eaa30a21bfd1","added_by":"auto","created_at":"2025-05-19 16:09:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2072826,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/94ddaf52-8334-440a-b2dd-cafdb9f7130a.pdf"},{"id":58077713,"identity":"99e045e3-57d1-4f35-a98d-582fe3403d57","added_by":"auto","created_at":"2024-06-10 22:41:36","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":76696,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementalinformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4462254/v1/c4c49fd85cae16f3d9a05a69.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Using paleolimnology to assess long-term acidification and recovery trajectories in lakes from Killarney Provincial Park and Sudbury (Ontario, Canada)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eDuring construction of the trans-Canada railway in the 1870s, rich deposits of copper and nickel were found in the Sudbury basin located in northeastern Ontario (Canada). This discovery led to concentrated mining and smelting activities in the area (Winterhalder \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). In 1888, open pit roasting of these ores began, which led to the opening of Nickel Co. (currently known as Vale Inco, est. 1902), the Coniston smelter (1913), and Falconbridge Limited (currently known as Xstrata Nickel, est. 1928) (Tropea et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). By the 1960s, the Sudbury smelters were emitting over 2.5\u0026nbsp;million tonnes of sulphur dioxide per year, making the area one of the world\u0026rsquo;s largest sources of acid-generating pollution in the world. Due to concerns over the widespread environmental damage from mining operations, emissions were reduced by ~\u0026thinsp;90% by 1994 (Snucins and Gunn \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1998\u003c/span\u003e), and even further to the present day.\u003c/p\u003e \u003cp\u003eParticulate emissions from smelters and mining operations contaminated much of the Sudbury region and surrounding areas (Pearson et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Early smelting emissions resulted in the loss of large amounts of vegetation, and severe acidification of terrestrial and aquatic environments, with soil acidity and metal concentrations highest in areas near smelters (Winterhalder \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). The loss of vegetation left Sudbury soils exposed, and they became severely eroded. Atmospheric deposition of contaminants (i.e., strong acid, metals) altered water and sediment quality, and, in the case of the metals, were toxic to aquatic organisms (Fleeger et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Moreover, in the 1960s, increases in cyanobacterial and algal blooms were observed in many Sudbury lakes because of high nutrient inputs linked to soil erosion from industrial activities and urbanization.\u003c/p\u003e \u003cp\u003eWhilst all lakes and catchments within KPP and Sudbury were likely affected to some degree by acidifying emissions, there is much variation in the magnitude, timing, and extent of impacts from acidification. For example, lake acidification and metal contamination in Sudbury peaked in the 1960s, while the acidification of lakes in KPP peaked in the 1970s and 1980s. This is likely because the KPP lakes are located farther from the mining and smelting activities, and therefore received longer range atmospheric deposition of SO\u003csub\u003e2\u003c/sub\u003e, as opposed to being directly exposed (Keller et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). In addition, this variation is due, in part, to differences in natural buffering capacity, which is especially notable in lakes that were thought to be acidic prior to the onset of smelting activities [i.e., Ruth-Roy Lake (KPP) and (Sudbury)] (Belzile et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Meanwhile, delayed acidification in some lakes in KPP was believed to be due to pockets of carbonate-containing rocks in the watersheds (i.e., Lumsden and Acid lakes; Hindar and Henriksen \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1998\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGiven the lack of direct, long-term monitoring data for most lakes, the effects of acidification were clearly demonstrated in many Sudbury lakes using paleolimnological approaches, conducted mainly in the 1980s and early-1990s. For example, Baby Lake, which is located\u0026thinsp;~\u0026thinsp;1 km away from the Coniston smelter in Sudbury, showed marked changes in acid sensitive algae (i.e., diatoms and chrysophytes) that were coincident with the onset of major smelting operations and acidification, as well as subsequent recovery noted especially in chrysophyte assemblages (Dixit et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003ea,b). In a study of 151 lakes in the Sudbury region, Dixit et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) concluded that 77% of modern diatom species variation could be attributed to the combined effects of various measured environmental variables (such as lake catchment characteristics, lake size, elevation, pre-industrial pH, metals). Dixit et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) also applied a diatom-based pH inference model to conclude that peak acidification occurred in the ~\u0026thinsp;1970s in KPP and ~\u0026thinsp;1960s in Sudbury, but also that the large reductions in sulphur dioxide emissions had resulted in early signs of recovery. Collectively, these studies, conducted more than three decades ago, demonstrated the effectiveness of diatom and chrysophyte assemblages to track changes in limnological variables related to acidification (Dixit et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003ea,b).\u003c/p\u003e \u003cp\u003eSome re-assessments of acidification and recovery patterns in select Sudbury lakes, using a variety of paleolimnological indicators, have shown that biological recovery trajectories can be varied (Tropea et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Although pH is still identified as the strongest spatial variable shaping diatom assemblages across Sudbury lakes (Cheng et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), biological assemblages in many lakes show limited recovery, and have not returned to their pre-industrial condition. Recent warming and legacy metal contamination have been cited as possible factors complicating biological recovery (Tropea et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Simmatis et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Cheng et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRecent climate warming has impacted Sudbury-area and KPP lakes, especially over the last few decades. Snucins and Gunn (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) used temperature profiles to examine the thermal structure of 86 relatively small (\u0026lt;\u0026thinsp;550 ha) lakes in KPP to show that mixing regimes were strongly influenced by water clarity and lake depth. Snucins and Gunn (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) found that 84% of the lakes that failed to thermally stratify were shallow (depth\u0026thinsp;\u0026lt;\u0026thinsp;5 m) and had low DOC concentrations (\u0026lt;\u0026thinsp;1 mg/L). This is relevant to lakes in KPP as the small lakes of the La Cloche Mountain range are some of the clearest lakes in North America. These findings suggest that DOC decreases due to a changing climate and/or acidification will have a significant effect on various physical and chemical lake characteristics. As DOC concentrations slowly return to pre-industrial levels (Meyer-Jacob et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), some of these thermal changes may be reversed.\u003c/p\u003e \u003cp\u003eIn addition to the impact to and recovery of lake chemistry and biological communities from industrial activities, urbanization is complicating ecological trajectories. Tropea et al. (\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) studied four Sudbury lakes (Ramsey, Nepahwin, McFarlane and Richard lakes) to investigate the impact of urbanization and showed that diatom community composition has changed drastically over the past ~\u0026thinsp;150 years as a result of sewage effluent, excess nutrients from fertilizers, shoreline alteration, and altered hydrology. Similar distinctions among urban and non-urban lakes in the Sudbury region have also been found in cladoceran taxa, driven by differences in aqueous specific conductance and the indirect effects of nutrient enrichment (Simmatis et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Urban Sudbury lakes highlight the potential for altered ecological recovery trajectories due to a combination of legacy and modern stressors.\u003c/p\u003e \u003cp\u003eDespite the many earlier studies on the degradation and subsequent recovery of aquatic ecosystems in KPP and Sudbury, little is known about how more recent conditions (i.e., last three decades) relate to background (pre-industrial) conditions, or how biological recovery trajectories may be affected by a rapidly changing climate. To develop this long-term perspective, we selected five study lakes for multi-proxy paleolimnological analyses, including subfossil remains of algae (diatoms), inferred whole-lake chlorophyll-\u003cem\u003ea\u003c/em\u003e (VRS-Chl \u003cem\u003ea\u003c/em\u003e) and lake water dissolved organic carbon (DOC) concentrations. We examine information preserved in lake sediment to obtain a long-term (past ~\u0026thinsp;200 years) record of ecological change, including assessing how recent warming has affected recovery trajectories. The specific study objectives are to: (1) reconstruct fossil diatom assemblages, sediment Chl \u003cem\u003ea\u003c/em\u003e and lake-water DOC concentrations over the past several decades to assess trends in recovery from acidification, and, in particular, to compare present-day with pre-industrial conditions of five lakes in KPP and Sudbury; (2) explore patterns of potential ecological recovery from acidification over the past several decades; and (3) collectively use paleolimnological, long-term monitoring and meteorological data to explore the potential drivers and trajectories of KPP and Sudbury ecosystem changes.\u003c/p\u003e\n\u003ch3\u003eStudy region\u003c/h3\u003e\n\u003cp\u003eSudbury (46.48959\u0026deg; N, 80.99011\u0026deg; W) is located near the southern margin of the Precambrian Shield in northeastern Ontario, on the margins of the Sudbury Basin, a topographic low attributable to an ancient (1.8 mya) meteor impact and subsequent deformation of the Earth\u0026rsquo;s crust. The Sudbury basin is ~\u0026thinsp;60 km in length and ~\u0026thinsp;27 km in width; its structural axis is aligned northeast to southwest (Dirszowsky \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Tropea \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The rugged topography of the Shield, and basin structure modified by long-term denudation and glacial activity, has resulted in the highest number of lakes contained within a city for any urban area within Canada. The Sudbury region has a humid continental climate [Climate normal (1981\u0026ndash;2010): mean daily minimum temperature of -17.9\u0026deg;C in January; mean daily maximum temperature of 24.8\u0026deg;C in July; mean monthly maximum precipitation of 101.1 mm in September; mean monthly minimum precipitation of 51.1mm in February; total annual precipitation of 903.2 mm; average annual wind speed of 14 km/hr; and an average frost-free period of 136 days (Sudbury station A ID 71730; ECCC 2024)].\u003c/p\u003e \u003cp\u003eKillarney Provincial Park (46.1333\u0026deg; N, 81.4167\u0026deg; W), located\u0026thinsp;~\u0026thinsp;60 km southwest of Sudbury (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), contains over 200 lakes and ponds. These freshwater ecosystems exhibit large differences in size, elevation, water chemistry, and catchment characteristics. The majority of KPP is underlain by the Lorrain formation, which is comprised of feldspathic and kaolinitic sandstone and orthoquartzite (Hindar and Henriksen \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The folds of quartzite rock form the ancient geological formation that characterize the La Cloche Mountain range. Located in the Ontario Shield Ecozone, KPP\u0026rsquo;s mean minimum temperature is approximately \u0026minus;\u0026thinsp;14\u0026deg;C in January, with a mean maximum temperature of approximately 24\u0026deg;C in July. KPP\u0026rsquo;s mean monthly precipitation reaches a maximum of over 75 mm in April and October, and a minimum of approximately 35 mm in February (Belzile et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy lakes\u003c/h2\u003e \u003cp\u003eStudy lakes were chosen to reflect select limnological gradients and varying levels of impacts. This work builds on previous paleolimnological work from the 1980s and 1990s in KPP and the Sudbury region. Sediment cores for diatom analyses have not been collected from these lakes in ~\u0026thinsp;30 years, which include lakes in KPP (Ruth-Roy and Johnnie lakes) and Sudbury (Tillie, Crooked, and Baby lakes; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cb\u003eRuth-Roy Lake (46.0961\u003c/b\u003e\u0026deg; \u003cb\u003eN, 81.2467\u003c/b\u003e\u0026deg; \u003cb\u003eW)\u003c/b\u003e: Located in KPP, ~\u0026thinsp;45.2 km from the Copper Cliff smelter (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e; Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), Ruth-Roy Lake has a maximum depth of 18 m and surface area of 54.5 ha. Ruth-Roy Lake has undergone numerous paleolimnological assessments. Sediment cores collected between 1975 and 1980 were analyzed for diatom and chrysophyte assemblages in core \u0026lsquo;tops\u0026rsquo; (surface sediments representing current conditions) and core \u0026lsquo;bottoms\u0026rsquo; (generally from \u0026gt;\u0026thinsp;30 cm deep, representing pre-industrial conditions) (Dixit et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003ec). Earlier analyses showed that Ruth-Roy was one of the most naturally acidic lakes in the region prior to smelting (inferred pH\u0026thinsp;~\u0026thinsp;4.9; Dixit et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), possibly because the lake drains quartzite ridges with little to no soil. Although being naturally acidic, Dixit et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) noted that the lake acidified further (to pH\u0026thinsp;~\u0026thinsp;4.58) due to acid precipitation. Simmatis et al. (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) recently re-assessed long-term changes in diatoms, cladocerans, inferred whole-lake primary production, and inferred lake-water DOC in Ruth-Roy Lake. Pre-industrial assemblages confirmed that Ruth-Roy Lake was naturally acidic but began to respond to smelting emissions as early as ~\u0026thinsp;1920, which was attributed to its naturally low buffering capacity and, therefore, high sensitivity to acidifying emissions (Simmatis et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of lake characteristics and recent measured water chemistry for the five focal study lakes.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUnits\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBaby\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCrooked\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRuth-Roy\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eJohnnie\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTillie\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDistance from smelter\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ekm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1 S\u003c/p\u003e \u003cp\u003e(Coniston)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.3 S\u003c/p\u003e \u003cp\u003e(Copper Cliff)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45.2 SW\u003c/p\u003e \u003cp\u003e(Copper Cliff)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e46.2 S\u003c/p\u003e \u003cp\u003e(Copper Cliff)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e62.1 N\u003c/p\u003e \u003cp\u003e(Coniston)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eElevation\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emasl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e224\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e310\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e217\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e404\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSurface area\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eha\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e26.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e54.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e342.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e76.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMax. Depth\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003em\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e33.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMean Depth\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003em\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDOC (2018)\u003c/b\u003e\u003csup\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emg/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003epH (2018)\u003c/b\u003e\u003csup\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003epH units\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSO\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e \u003cb\u003e(2018)\u003c/b\u003e\u003csup\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emg/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003cem\u003eSource\u003c/em\u003e: \u003csup\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eMECP dataset (Sudbury full water chemistry - used with permission)\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eJohnnie Lake (46.0915\u003c/b\u003e\u0026deg; \u003cb\u003eN, 81.2400\u003c/b\u003e\u0026deg; \u003cb\u003eW)\u003c/b\u003e: Johnnie Lake, located in KPP, ~\u0026thinsp;42.6 km from the Copper Cliff smelter (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e; Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), has a maximum depth of 33.6 m and surface area of 342.3 ha. Previous studies done on Johnnie Lake include zooplankton surveys, precipitation chemistry and wet deposition data collection, paleolimnological analyses, and water chemistry analysis (Szkokan-Emilson et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Keller et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Snucins et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Keller et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) collected lake and precipitation chemistry, and wet deposition data, between 1978 and 1998 from Johnnie Lake showing the lake experienced significant declines in calcium (measured from lake water precipitate; 140 eq/L in 1980 to ~\u0026thinsp;80 eq/L in 2001) as well as increases in alkalinity (-7 eq/L in 1980 to 11 eq/L in 2001). Keller et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) also found that DOC concentrations increased significantly between 1988 and 2001 and that lake water pH closely tracked precipitation chemistry. Meanwhile, Snucins et al. (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) collected water samples (from 1996\u0026ndash;1997) for chemical analyses from several KPP lakes, including Johnnie Lake, and found that lakes with catchments that are made up of more easily weathered bedrock formations acidified the least, relative to pre-industrial diatom-inferred pH, and showed the largest increases in pH between 1981 and 1999. A recent paleolimnological top-bottom comparison of cladoceran and chironomid assemblages demonstrated that subfossil invertebrate assemblages were somewhat similar between pre-1880 and post-2010 sediments (Simmatis et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Modern invertebrate assemblages in Johnnie Lake are most similar to lakes far from the original smelters (e.g., Whitepine Lake in Lady Evelyn-Smoothwater Provincial Park; Simmatis et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Currently, Johnnie Lake is slightly acidic (pH of ~\u0026thinsp;6.3) and slightly above its inferred pre-industrial pH level (pH of 6.1).\u003c/p\u003e \u003cp\u003e \u003cb\u003eBaby Lake (46.4612\u003c/b\u003e\u0026deg; \u003cb\u003eN, 80.8651\u003c/b\u003e\u0026deg; \u003cb\u003eW)\u003c/b\u003e: Located\u0026thinsp;~\u0026thinsp;1 km from the Coniston smelter (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), Baby Lake has a maximum depth of 22.5 m and a surface area of 11.9 ha. Baby Lake has been subject to multiple studies, including water chemistry analysis (i.e., metals, sulphate and lake water pH), zooplankton identification, and paleolimnological analyses (Hutchinson and Havas \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Havas et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Smol et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHutchinson and Havas (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1986\u003c/span\u003e) collected water chemistry data to show that when the Coniston smelter closed (1972), lake-water sulphate concentrations decreased by 50% (from 60 mg/L in 1968 to 30 mg/L in 1983), lake-water copper concentrations decreased by 92% (from 0.78 mg/L in 1971 to 0.06 mg/L in 1984), and nickel concentrations decreased by 87% (from 3.2 mg/L in 1970 to 0.41 mg/L in 1984). Trends in lake-water metal concentrations collected by Hutchinson and Havas (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1986\u003c/span\u003e) were reflected by trends in more recent sedimentary metal concentrations (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Notably, concentrations of copper, nickel, lead, and zinc have not returned to pre-industrial concentrations (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Havas et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1995\u003c/span\u003e) additionally sampled Baby Lake for water chemistry and zooplankton to track biological changes over decadal timescales (1970-1990s). They found the lake had much lower phytoplankton biomass and species richness than other Shield lakes of a similar pH (6.8) in 1986.\u003c/p\u003e \u003cp\u003eDixit et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003ec) completed a paleolimnological analysis and showed that long-term pH, inferred from diatom assemblages, recorded dramatic acidification of Baby Lake, changing from an inferred pH of 6.5 in 1940 to 4.2 in 1975. Beginning in 1972 (following the closure of the Coniston smelter) diatoms and especially chrysophyte assemblages in Baby Lake showed significant recovery (Dixit et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003eb). Despite recovery in algal indicators, cladoceran taxa showed limited recovery, especially littoral taxa (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Sedimentary cladoceran assemblages have indicated reduced littoral diversity and increased abundance of generalist taxa (i.e., \u003cem\u003eChydorus brevilabris\u003c/em\u003e and \u003cem\u003eBosmina\u003c/em\u003e spp.) after ~\u0026thinsp;1925 without recovery to pre-industrial assemblage composition (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Further, few chironomid head capsules were found in Baby Lake, which may be related to sediment type and high inorganic content (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Baby Lake was amongst the most acidic of our study lakes during the period of peak emissions from Sudbury smelters and is therefore an interesting contrast to KPP lakes that are located more distant from smelter emissions.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTillie Lake (47.0425\u003c/b\u003e\u0026deg; \u003cb\u003eN, 81.0008\u003c/b\u003e\u0026deg; \u003cb\u003eW)\u003c/b\u003e: Among the study sites, Tillie Lake is located the furthest (62.1 km) from the nearest smelter (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). It has a maximum depth of 11.0 m and a large surface area of 76.7 ha. Tillie Lake is also located at the highest elevation of any of the study lakes (404 masl), had the highest DOC value of 5.5 mg/L in 1975, and showed recent increases in total phosphorus (Keller et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). A recent paleolimnological top-bottom comparison of cladoceran assemblages showed some similarities between pre-1880 and post-2010 sediments (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Chironomid counts were inadequate for analysis and interpretation (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Tillie Lake is not well-researched compared to the other study lakes, and thus a thorough paleolimnological analysis was needed to place recent limnological data within a long-term context.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCrooked Lake (46.4185\u0026ordm; N, 81.0331\u0026ordm; W)\u003c/strong\u003e \u003cp\u003eCrooked Lake is located 6.3 km from the Copper Cliff smelter (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), has a maximum depth of 8.0 m, and a surface area 26.29 ha. Dramatic declines in acidity have been observed in severely damaged urban lakes close to the Sudbury smelters, such as Crooked Lake (Keller et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Crooked Lake had the most acidic pre-industrial diatom inferred pH values (4.0) of the selected study lakes (Dixit et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003ec), and one of the most acidic pH values in 1975 (4.3) (Snucins and Gunn, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Simmatis et al. (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) completed top-bottom analysis of cladocerans, finding that modern assemblages had higher relative abundances of generalist taxa (i.e., \u003cem\u003eChydorus brevilabris\u003c/em\u003e) and reduced littoral diversity compared to pre-industrial conditions. Relative to other Sudbury and KPP lakes, Crooked Lake experienced a moderate amount of change (Simmatis et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Inadequate chironomid remains were recovered to allow for further analysis or interpretation (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Crooked Lake is an interesting example of a naturally acidic Sudbury lake.\u003c/p\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eSediment coring and sectioning\u003c/h2\u003e \u003cp\u003eIn June and July 2018, the cores from all study lakes were obtained from the deepest point in each lake using a Glew gravity corer (Glew \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). The exception was the Baby Lake core which was collected the previous winter. The cores were sectioned on shore into 0.5-cm intervals using a Glew extruder (Glew \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). The cores were extruded until 30 cm length, except for the core from Baby Lake, which was only 19 cm long. The sediment intervals were subsequently freeze dried and stored until further analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eRadioisotopic dating\u003c/h2\u003e \u003cp\u003eExcess \u003csup\u003e210\u003c/sup\u003ePb activities on select sediment intervals were used to develop core chronologies at PEARL (Queen\u0026rsquo;s University, Kingston, ON). Samples were prepared by freeze-drying the sediments, filling gamma tubes with the sediment and then sealing it with epoxy and letting it sit for a minimum of two weeks, allowing the equilibrium between \u003csup\u003e226\u003c/sup\u003eRa and \u003csup\u003e214\u003c/sup\u003eBi to be reached. \u003csup\u003e210\u003c/sup\u003ePb was measured with an Ortec high-purity geranium detector. Estimates of unsupported \u003csup\u003e210\u003c/sup\u003ePb (total \u003csup\u003e210\u003c/sup\u003ePb minus supported \u003csup\u003e210\u003c/sup\u003ePb) were used to estimate sediment age, using the constant rate of supply (CRS) model (Appleby \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). \u003csup\u003e210\u003c/sup\u003ePb activities and chronologies for most of the lakes are published elsewhere (Ruth-Roy Lake: Simmatis et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Baby, Crooked and Tillie lakes: Meyer-Jacob et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). \u003csup\u003e210\u003c/sup\u003ePb data for Johnnie Lake are presented in Supplemental information (Supplemental Information Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eDiatom preparation and analysis\u003c/h2\u003e \u003cp\u003eThe preparation and analysis of diatom samples followed standard techniques, as generally outlined in Battarbee et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). In summary, subsamples of dried sediment (0.01\u0026ndash;0.02 g) were digested using a 50:50 molar ratio of concentrated sulphuric and nitric acid to remove organic content from the sediments, done over a period of two hours in a hot water bath. The diatom slurries were left to settle for ~\u0026thinsp;24 hours, after which the supernatant was removed by aspirating and deionized water was added to each vial. This process was repeated 6\u0026ndash;7 times until a litmus test indicated that samples were no longer acidic. Cleaned diatom suspensions were pipetted onto coverslips and mounted onto microscope slides using Naphrax, a permanent mounting medium. A Leica DMR microscope was used (1000x magnification) to identify and enumerate diatom valves. Diatoms were counted and identified to species and variety level when feasible, using primarily Krammer and Lange-Bertalot (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1991a\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003eb\u003c/span\u003e) as taxonomic references. A minimum of 300 valves were counted per slide.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eSediment Chlorophyll-a and lake-water Dissolved Organic Carbon (DOC)\u003c/h2\u003e \u003cp\u003eVisible range spectroscopy-inferred chlorophyll-a (VRS-Chl \u003cem\u003ea\u003c/em\u003e; which includes its isomers and main diagenetic products; Michelutti and Smol \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), and visible near infrared spectroscopy-inferred DOC (VNIRS DOC) analysis, were performed for each interval of all five cores. Small amounts (less than 0.05 g) of freeze-dried sediment were sieved through a 125-\u0026micro;m mesh into glass scintillation vials and analyzed in a FOSS NIRSystem model 6500 rapid content analyzer, operating over the range of 400\u0026ndash;2500 nm. Concentrations of whole-lake chlorophyll-\u003cem\u003ea\u003c/em\u003e and lake water DOC were inferred following methods in Michelutti et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) and Meyer-Jacob et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), respectively. Trends in sedimentary Chl \u003cem\u003ea\u003c/em\u003e and lake-water DOC for Baby, Tillie, and Crooked lakes were previously published in an assessment of long-term changes in carbon cycling and sequestration in Sudbury lakes by Meyer-Jacob et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eClimate data\u003c/h2\u003e \u003cp\u003eAdjusted and homogenized Canadian climate data were obtained from Environment and Climate Change Canada for the climate station nearest to the selected study sites. This information is made publicly available in Open Government Canada data and includes climate and weather data from the study site between the years of ~\u0026thinsp;1950-present day. Mean annual air temperature (MAAT) data were obtained from the station \u0026ldquo;Sudbury Climate ON\u0026rdquo; (ID 71733).\u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003eBiostratigraphical zonation\u003c/h2\u003e \u003cp\u003eStratigraphically constrained cluster analysis using the total sum of squares (CONISS) was used to identify the major changes in diatom species composition. This was completed in R using the \u0026lsquo;rioja\u0026rsquo; package (Oksanen et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), which uses a broken-stick model to determine the number of important stratigraphical zones (Bennett \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Zonation using the broken-stick test separates the total variance into components. The total variance is represented by \u003cem\u003en\u003c/em\u003e and is divided into \u003cem\u003en\u003c/em\u003e-1 markers. The length of each segment represents the variance of each zone; if variance reduction surpasses model expectations the zone is considered important (Bennett \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Given the change in sample resolution that occurred with core depths, CONISS results should be considered only a rough guide for interpreting the long-term trends in the study lakes.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eRadioisotopic dating\u003c/h2\u003e \u003cp\u003eTotal \u003csup\u003e210\u003c/sup\u003ePb near-surface activities ranged from 1057.9 to 3041.0 Bq/kg, and reached equilibrium with supported \u003csup\u003e210\u003c/sup\u003ePb levels between ~\u0026thinsp;11 to ~\u0026thinsp;28 cm depths. Mean supported activities (measured as \u003csup\u003e214\u003c/sup\u003ePb) ranged from 17.0 to 44.1 Bq/kg. Unsupported \u003csup\u003e210\u003c/sup\u003ePb activities declined exponentially in all cores but with some irregularities indicating changes in sedimentation rates (Supplemental Information Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e; Simmatis et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Meyer-Jacob et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eRuth-Roy Lake\u003c/h2\u003e \u003cp\u003eProfiles for subfossil diatoms, Chl \u003cem\u003ea\u003c/em\u003e and DOC have been published for Ruth-Roy Lake as part of a multidisciplinary paleolimnological study focusing on subfossil invertebrates (Simmatis et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), but are briefly summarized here again to allow for easy comparison among all study lakes. In the Ruth-Roy Lake sediment core, a total of 23 intervals were counted including every interval from 0 cm to 5.5 cm, then every second interval from 6 cm to 12.5 cm, and then every third interval from 12.5 cm to 30 cm. In total, 38 unique diatom taxa were identified. CONISS with a broken stick test identified two important biostratigraphic zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eZone 1 includes intervals from 29.75 cm (pre-~1850) to 6.25 (~\u0026thinsp;1918; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) in which \u003cem\u003eTabellaria flocculosa\u003c/em\u003e and \u003cem\u003eAulacoseira distans\u003c/em\u003e were the most common diatom taxa. Other common taxa included \u003cem\u003eCymbella hebridica\u003c/em\u003e (5\u0026ndash;10%), \u003cem\u003eFrustulia rhomboides\u003c/em\u003e var. \u003cem\u003esaxonica\u003c/em\u003e (1\u0026ndash;10%), and \u003cem\u003eEunotia exigua\u003c/em\u003e (1\u0026ndash;10%). Acidophilic taxa, including \u003cem\u003eFragilariforma acidobiontica, Eunotia intermedia\u003c/em\u003e, and \u003cem\u003eEunotia bilunaris\u003c/em\u003e, were often recorded at \u0026lt;\u0026thinsp;6% or were intermittently absent during this period. VNIRS-DOC was relatively stable throughout this period and high in comparison with the remainder of the sedimentary record with a median inferred value of 4.6 mg/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). VRS-Chl \u003cem\u003ea\u003c/em\u003e was variable (ranging from 0.042 mg/g dwt to 0.068 mg/g dwt) during this period, but remained at high levels relative to the remainder of the sedimentary record (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). At 8.25 cm (~\u0026thinsp;late 1800s), VRS-Chl \u003cem\u003ea\u003c/em\u003e and VNIRS-DOC began to decline into Zone 2.\u003c/p\u003e \u003cp\u003eZone 2 includes intervals from 5.25 cm (~\u0026thinsp;1942) to 0.25 cm (~\u0026thinsp;2017; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) in which \u003cem\u003eFragilariforma acidobiontica\u003c/em\u003e was the dominant taxon. \u003cem\u003eF. acidobiontica\u003c/em\u003e sharply increased from ~\u0026thinsp;6% at 6.25 cm (~\u0026thinsp;1918) to greater than ~\u0026thinsp;30% at 3.25 cm (~\u0026thinsp;1979), eventually reaching 68% at 1.25 cm (~\u0026thinsp;2007). After 1.25 cm (~\u0026thinsp;2007), it declined slightly to ~\u0026thinsp;61%. \u003cem\u003eCymbella microcephala\u003c/em\u003e increased from trace abundances at 4.25 cm (~\u0026thinsp;1693) to ~\u0026thinsp;8% abundance at 1.25 cm (~\u0026thinsp;2007) before declining to 5.5% in the surface sediments. \u003cem\u003eEunotia intermedia\u003c/em\u003e increased from 4% at 5.25 cm (~\u0026thinsp;1942) to 18% at 3.25 cm (~\u0026thinsp;1979), before declining to ~\u0026thinsp;8% in the most recent sediments. A number of less common taxa experienced directional declines, including \u003cem\u003eAulacoseira distans\u003c/em\u003e (from 16% at 5.25 cm to \u0026lt;\u0026thinsp;3% in the most recently deposited sediments), \u003cem\u003eCymbella hebridica\u003c/em\u003e (from 13% at 6.25 cm to \u0026lt;\u0026thinsp;2% in the most recently deposited sediments), \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (from ~\u0026thinsp;10% at 5.25 cm to \u0026lt;\u0026thinsp;5% in the most recent sediments), \u003cem\u003eEunotia exigua\u003c/em\u003e (from ~\u0026thinsp;7% at 6.25 cm to \u0026lt;\u0026thinsp;1% in the most recent sediments), \u003cem\u003eFrustulia rhomboides\u003c/em\u003e var. \u003cem\u003esaxonica\u003c/em\u003e (from 5% at 6.25 cm to trace abundances in the surface sediments), and \u003cem\u003eFragilaria (Staurosira) construens\u003c/em\u003e (from ~\u0026thinsp;5% at 6.25 cm to trace and sporadic presence in the most recent sediments). During this period, VRS-Chl \u003cem\u003ea\u003c/em\u003e reached its minimum value in the sedimentary record at ~\u0026thinsp;3.75 cm (~\u0026thinsp;1971) and increased afterwards but concentrations did not return to Zone 1 levels. Trends in VNIRS-DOC coincided with VRS-Chl \u003cem\u003ea\u003c/em\u003e, reaching a minimum value at ~\u0026thinsp;3.75 cm (~\u0026thinsp;1971), and increased afterwards without returning to Zone 1 levels.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eJohnnie Lake\u003c/h2\u003e \u003cp\u003eTwenty-two intervals in the Johnnie Lake sediment core were counted including every interval from 0 cm to 5.5 cm, every second interval from 6 cm to 12.5 cm, and every third interval from 12.5 cm to 30 cm. In total, 18 taxa were identified. CONISS with a broken stick test identified four important biostratigraphic zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eZone 1 includes intervals from 26.75 cm (pre-~1850) to 13.25 cm (~\u0026thinsp;1922; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). \u003cem\u003eAsterionella ralfsii\u003c/em\u003e was the most common diatom taxon in Zone 1, ranging from 40\u0026ndash;50%. Other common taxa included \u003cem\u003eAulacoseira distans\u003c/em\u003e (5\u0026ndash;20% relative abundance), \u003cem\u003eDiscostella pseudostelligera\u003c/em\u003e (5% relative abundance), and \u003cem\u003eDiscostella stelligera\u003c/em\u003e (15% relative abundance). \u003cem\u003eAsterionella ralfsii\u003c/em\u003e reached a peak at 17.25 cm (~\u0026thinsp;50% relative abundance), from its previous value of ~\u0026thinsp;35% at 26.75 cm. VNIRS-DOC was relatively stable throughout this period and high in comparison with the remainder of the sedimentary record with a median value of 4.1 mg/L (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). VRS-Chl \u003cem\u003ea\u003c/em\u003e was also stable throughout this period and lower in comparison to the remainder of the sedimentary record (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eZone 2 includes intervals from 14.25 cm (~\u0026thinsp;1914) to 2.25 cm (~\u0026thinsp;2010; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). \u003cem\u003eAsterionella ralfsii\u003c/em\u003e was still the most common diatom taxon in Zone 2, ranging from ~\u0026thinsp;1\u0026ndash;40% in this zone. Other common taxa included \u003cem\u003eAulacoseira distans\u003c/em\u003e (reaching up to ~\u0026thinsp;10% relative abundance), and \u003cem\u003eFragilariaforma acidobiontica\u003c/em\u003e (~\u0026thinsp;15% relative abundance). \u003cem\u003eAsterionella ralfsii\u003c/em\u003e decreased from ~\u0026thinsp;40% throughout this zone to 1% at 7.25 cm (~\u0026thinsp;1976), recovering thereafter. From 9.25 cm (~\u0026thinsp;1957) to 7.25 cm (~\u0026thinsp;1976), \u003cem\u003eAulacoseira alpigena\u003c/em\u003e and \u003cem\u003eDiscostella pseudostelligera\u003c/em\u003e increased from ~\u0026thinsp;1\u0026ndash;15% relative abundance. At 5.5 cm (~\u0026thinsp;1990), \u003cem\u003eFragiliaforma acidobiontica\u003c/em\u003e peaked at ~\u0026thinsp;15% relative abundance, then dropped to ~\u0026thinsp;5% at 2.75 cm (~\u0026thinsp;2007). VNIRS-DOC decreased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) from 3.8 mg/L to 1.6 mg/L between 13.25 cm (~\u0026thinsp;1922) and 6.25 cm (~\u0026thinsp;1990). VRS-Chl \u003cem\u003ea\u003c/em\u003e increased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) from 0.02 mg/ g dry weight to 0.04 mg/g dry weight between 14.25 cm (~\u0026thinsp;1914) and 2.25 cm (~\u0026thinsp;2010).\u003c/p\u003e \u003cp\u003eZone 3 includes intervals from 1.75 cm (~\u0026thinsp;2012) to 0.75 cm (~\u0026thinsp;2016; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). \u003cem\u003eAsterionella ralfsii\u003c/em\u003e was the most common diatom taxon in Zone 3, ranging from ~\u0026thinsp;30% to ~\u0026thinsp;35%. Other common taxa included \u003cem\u003eAulacoseira distans\u003c/em\u003e (~\u0026thinsp;10% relative abundance) and \u003cem\u003eEunotia intermedia\u003c/em\u003e (~\u0026thinsp;10% relative abundance). \u003cem\u003eEunotia intermedia\u003c/em\u003e increased from 5% at 1.75 cm (~\u0026thinsp;2012) to 10% at 0.75 cm (~\u0026thinsp;2016). \u003cem\u003eFragilariforma acidobiontica\u003c/em\u003e peaked near 5% at 1.75 cm (~\u0026thinsp;2012) then decreased to 0% at 0.75 cm (~\u0026thinsp;2016). VNIRS-DOC increased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) from 3.1 mg/L to 3.6 mg/L between 1.75 cm (~\u0026thinsp;2012) and 0.75 cm (~\u0026thinsp;2016). VRS-Chl \u003cem\u003ea\u003c/em\u003e also increased slightly throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) from 0.04 mg/ g dry weight to 0.05 mg/g dry weight between 1.75 cm (~\u0026thinsp;2012) and 0.75 cm (~\u0026thinsp;2016).\u003c/p\u003e \u003cp\u003eZone 4 only includes the surface sediments (0.25 cm, ~\u0026thinsp;2018; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). \u003cem\u003eAsterionella ralfsii\u003c/em\u003e was still the most common diatom taxa in Zone 4 but declined to ~\u0026thinsp;20% relative abundance (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Another common taxon was \u003cem\u003eAulacoseira alpigena\u003c/em\u003e (~\u0026thinsp;10% relative abundance), which doubled in relative abundance from previous zones. \u003cem\u003eAulacoseira distans\u003c/em\u003e, \u003cem\u003eDiscostella pseudostelligera\u003c/em\u003e, and \u003cem\u003eDiscostella stelligera\u003c/em\u003e were absent in this zone. VNIRS-DOC continued to increase in this zone (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), and VRS-Chl \u003cem\u003ea\u003c/em\u003e also increased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) from 0.05 mg/ g dry weight to 0.058 mg/g dry weight between 0.75 cm (~\u0026thinsp;2016) and 0.25 cm (~\u0026thinsp;2018).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eBaby Lake\u003c/h2\u003e \u003cp\u003eIn the Baby Lake sediment core, 18 intervals were counted including every interval from 0 cm to 5.5 cm, every second interval from 6 cm to 12.5 cm, and every third interval from 12.5 cm to 30 cm. In total, 18 taxa were identified. CONISS with a broken stick test identified four biostratigraphic zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eZone 1 includes intervals from 19 cm (pre-~1850) to 8.25 cm (~\u0026thinsp;1908; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) in which \u003cem\u003eDiscostella stelligera\u003c/em\u003e, \u003cem\u003eTabellaria flocculosa\u003c/em\u003e, \u003cem\u003eAulacoseira ralfsii\u003c/em\u003e and \u003cem\u003eAulacoseira distans\u003c/em\u003e were the most common diatom taxa, ranging from ~\u0026thinsp;10\u0026ndash;20% over time. Other taxa present included \u003cem\u003eEunotia tenella\u003c/em\u003e and \u003cem\u003eAchnanthidium minutissimum\u003c/em\u003e. VNIRS-DOC was relatively stable throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) and high in comparison with the remainder of the sedimentary record with a median value of 5.7 mg/L. VRS-Chl \u003cem\u003ea\u003c/em\u003e was also stable throughout this period and high in comparison to the remainder of the sedimentary record (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eZone 2 includes intervals from 8.25 cm (~\u0026thinsp;1908) to 4.25 cm (~\u0026thinsp;1964; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). \u003cem\u003eAchnanthidium minutissimum\u003c/em\u003e, \u003cem\u003eLindavia ocellata\u003c/em\u003e, \u003cem\u003eDiscostella stelligera\u003c/em\u003e, and \u003cem\u003eTabellaria flocculosa\u003c/em\u003e were the most common diatom taxa in Zone 2, ranging from ~\u0026thinsp;10% to ~\u0026thinsp;20% over time. \u003cem\u003eTabellaria flocculosa\u003c/em\u003e reached a peak of ~\u0026thinsp;25% at 6.25 cm (~\u0026thinsp;1933) from ~\u0026thinsp;10% in Zone 1. \u003cem\u003eAsterionella ralfsii\u003c/em\u003e reached a peak of ~\u0026thinsp;20% at 5.25 cm (~\u0026thinsp;1950). VNIRS-DOC decreased from 5.7 mg/L to 2.6 mg/L, between 8.25 cm (~\u0026thinsp;1908) and 4.25 cm (~\u0026thinsp;1964). VRS-Chl \u003cem\u003ea\u003c/em\u003e also declined throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) from 0.045 mg/ g dry weight to 0.02 mg/g dry weight between 8.25 cm (~\u0026thinsp;1908) and 4.25 cm (~\u0026thinsp;1964).\u003c/p\u003e \u003cp\u003eZone 3 includes intervals from 4.25 cm (~\u0026thinsp;1964) to 1.25 cm (~\u0026thinsp;2000; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). \u003cem\u003eEunotia tenella\u003c/em\u003e and \u003cem\u003eAchnanthidium minutissimum\u003c/em\u003e were the most common diatom taxa in Zone 3, ranging from ~\u0026thinsp;10\u0026ndash;40% over time. Other common taxa included \u003cem\u003eFragilaria rhomboides\u003c/em\u003e var. \u003cem\u003esaxonica\u003c/em\u003e, \u003cem\u003eLindavia ocellata\u003c/em\u003e, and \u003cem\u003eAsterionella ralfsii\u003c/em\u003e. In this zone, \u003cem\u003eEunotia tenella\u003c/em\u003e increased, reaching a peak of ~\u0026thinsp;40% at 2.25 cm (~\u0026thinsp;1986), from ~\u0026thinsp;15% at 4.25 cm (~\u0026thinsp;1964). \u003cem\u003eAchnanthidium minutissimum, Discostella stelligera\u003c/em\u003e, and \u003cem\u003eAsterionella ralfsii\u003c/em\u003e showed declining relative abundances with time in Zone 3. VNIRS-DOC increased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) from 2.6 mg/L to 4.3 mg/L between 4.25 cm (~\u0026thinsp;1964) and 1.25 cm (~\u0026thinsp;2000). VRS-Chl \u003cem\u003ea\u003c/em\u003e also increased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) from 0.02 mg/g dry weight to 0.035 mg/g dry weight between 4.25 cm (~\u0026thinsp;1964) and 1.25 cm (~\u0026thinsp;2000).\u003c/p\u003e \u003cp\u003eZone 4 includes intervals from 1.25 cm (~\u0026thinsp;2000) to 0.25 cm (~\u0026thinsp;2016; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). \u003cem\u003eEunotia tenella, Fragilaria rhomboides\u003c/em\u003e var. \u003cem\u003esaxonica, Achnanthidium minutissimum\u003c/em\u003e, and \u003cem\u003eDiscostella stelligera\u003c/em\u003e were the most common diatom taxa in Zone 3. Other common taxa included \u003cem\u003eLindavia affinis\u003c/em\u003e and \u003cem\u003eBrachysira vitrea\u003c/em\u003e. \u003cem\u003eEunotia tenella\u003c/em\u003e declined from ~\u0026thinsp;30% at 1.25 cm (~\u0026thinsp;2000) to 15% at 0.25 cm (~\u0026thinsp;2018). \u003cem\u003eLindavia affinis\u003c/em\u003e, \u003cem\u003eAchnanthidium minutissimum\u003c/em\u003e and \u003cem\u003eDiscostella stelligera\u003c/em\u003e showed increases, peaking at 0.25 cm (~\u0026thinsp;2018). VNIRS-DOC increased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) from 4.3 mg/L to 5.0 mg/L between 1.25 cm (~\u0026thinsp;2000) and 0.25 cm (~\u0026thinsp;2016). VRS-Chl \u003cem\u003ea\u003c/em\u003e also increased throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) from 0.04 mg/ g dry weight to 0.06 mg/g dry weight between 1.25 cm (~\u0026thinsp;1960) and 0.25 cm (~\u0026thinsp;2018).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eTillie Lake\u003c/h2\u003e \u003cp\u003eIn the Tillie Lake sediment core, 30 intervals were counted including roughly every second interval from the top of the core to 30 cm. In total, 34 taxa were identified. CONISS and a broken stick test identified four biostratigraphic zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eZone 1 includes intervals from 28.75 cm (pre-~1850) to 25.75 cm (~\u0026thinsp;1884; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) in which \u003cem\u003eAulacoseira distans, Tabellaria flocculosa\u003c/em\u003e (str. III), and \u003cem\u003eAulacoseira lirata\u003c/em\u003e were the most common diatom taxa. Other common taxa included \u003cem\u003eAsterionella formosa\u003c/em\u003e, \u003cem\u003eCyclotella\u003c/em\u003e (\u003cem\u003eLindavia) bodanica\u003c/em\u003e, and \u003cem\u003eDiscostella\u003c/em\u003e spp. (including \u003cem\u003eDiscostella stelligera and Discostella. pseudostelligera\u003c/em\u003e). \u003cem\u003eTabellaria flocculosa\u003c/em\u003e increased from ~\u0026thinsp;8% at 28.75 cm (pre-~1850) to ~\u0026thinsp;18% at 25.75 cm (~\u0026thinsp;1884). \u003cem\u003eTabellaria quadriceps\u003c/em\u003e increased from ~\u0026thinsp;1% at 28.75 cm (pre-~1850) to ~\u0026thinsp;6% at 25.75 cm (~\u0026thinsp;1884). \u003cem\u003eDiscostella\u003c/em\u003e spp. decreased from ~\u0026thinsp;9% at 28.75 cm (pre-~1850) to ~\u0026thinsp;4% at 25.75 cm (~\u0026thinsp;1884). VNIRS-DOC (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) decreased throughout this period from 6.3 mg/L at 28.75 cm (pre-~1850) to 5.2 mg/L at 25.75 cm (~\u0026thinsp;1884). VNIRS-DOC was higher here than during most of the record with a median value of 5.8 mg/L. VRS-Chl \u003cem\u003ea\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) was generally stable throughout this period.\u003c/p\u003e \u003cp\u003eZone 2 includes intervals from 24.75 cm (~\u0026thinsp;1894) to 8.25 cm (~\u0026thinsp;1988; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). \u003cem\u003eAulacoseira distans\u003c/em\u003e was the most common diatom taxon in Zone 2, ranging from ~\u0026thinsp;23% to ~\u0026thinsp;34% over time. Other common taxa included \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (str. III), which varied between ~\u0026thinsp;6% and ~\u0026thinsp;18% over time. \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (str. III) fluctuated from ~\u0026thinsp;10% at 16.25 cm (~\u0026thinsp;1950) to ~\u0026thinsp;19% at 22.75 cm (~\u0026thinsp;1911). Other taxa included \u003cem\u003eAulacoseira lirata\u003c/em\u003e and \u003cem\u003eLindavia bodanica. Aulacoseira lirata\u003c/em\u003e fluctuated from ~\u0026thinsp;9% at 16.25 cm (~\u0026thinsp;1950) to ~\u0026thinsp;16% at 22.75 (~\u0026thinsp;1911). \u003cem\u003eAulacoseira distans\u003c/em\u003e remained relatively constant at ~\u0026thinsp;30%, except at 12.25 cm (~\u0026thinsp;1970) where it decreases to ~\u0026thinsp;25%. VNIRS-DOC decreased slightly during this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) reaching its minimum value of ~\u0026thinsp;4.0 mg/L during the mid-20th century. VRS-Chl \u003cem\u003ea\u003c/em\u003e was relatively stable throughout Zone 2 with the exception of a rapid increase towards the Zone 3 interface.\u003c/p\u003e \u003cp\u003eZone 3 includes intervals from 7.25 cm (~\u0026thinsp;1994) to 4.25 cm (~\u0026thinsp;2008; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). \u003cem\u003eAulacoseira distans\u003c/em\u003e and \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (str. III) were the most common diatom taxa in Zone 3. Other common taxa included \u003cem\u003eAsterionella formosa\u003c/em\u003e, \u003cem\u003eTabellaria quadriceps\u003c/em\u003e, and \u003cem\u003eAulacoseira lirata\u003c/em\u003e. \u003cem\u003eLindavia bodanica\u003c/em\u003e ranged from 0\u0026ndash;2% throughout Zone 3, in contrast to its presence of 7\u0026ndash;10% in Zone 2. \u003cem\u003eDiscostella\u003c/em\u003e spp. (including \u003cem\u003eD. stelligera and D. pseudostelligera\u003c/em\u003e) were absent from 7.25 cm (~\u0026thinsp;1994) to 4.25 cm (~\u0026thinsp;2008). VNIRS-DOC (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) was relatively stable at ~\u0026thinsp;6.0 mg/L from 7.25 cm (~\u0026thinsp;1994) to 4.25 cm (~\u0026thinsp;2008). VRS-Chl \u003cem\u003ea\u003c/em\u003e was also relatively stable throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) after showing an increasing in values relative to Zones 1 and 2.\u003c/p\u003e \u003cp\u003eZone 4 includes intervals from 3.25 cm (~\u0026thinsp;2012) to 0.25 cm (~\u0026thinsp;2018; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Most taxa were relatively stable during this period. \u003cem\u003eAulacoseira distans\u003c/em\u003e and \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (str. III) were the most common diatom taxa in Zone 3. Other common taxa included \u003cem\u003eAsterionella formosa\u003c/em\u003e, \u003cem\u003eTabellaria quadriceps\u003c/em\u003e, and \u003cem\u003eAulacoseira lirata\u003c/em\u003e. VNIRS-DOC increased slightly throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) from 5.6 mg/L to 5.8 mg/L between 3.25 cm (~\u0026thinsp;2012) to 0.25 cm (~\u0026thinsp;2018). VRS-Chl \u003cem\u003ea\u003c/em\u003e showed a slight increase throughout this zone (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eCrooked Lake\u003c/h2\u003e \u003cp\u003eThirty intervals were counted in the Crooked Lake sediment core, including every second interval from 0 cm to the bottom of the core. In total, 34 taxa were identified. CONISS with a broken stick test identified four important biostratigraphic zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eZone 1 includes intervals from 28.75 cm to 23.25 cm (both pre-~1850; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). \u003cem\u003eAulacoseira distans\u003c/em\u003e was the most common diatom taxon in Zone 1, remaining at ~\u0026thinsp;40% relative abundance. Another common taxon was \u003cem\u003eTabellaria flocculosa\u003c/em\u003e str. III (~\u0026thinsp;20% relative abundance). VNIRS-DOC was relatively stable throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) and high in comparison with the remainder of the sedimentary record with a median value of 7.1 mg/L. VRS-Chl \u003cem\u003ea\u003c/em\u003e was also relatively stable throughout this period (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eZone 2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) includes intervals from 22.75 cm (pre-~1850) to 5.25 cm (~\u0026thinsp;1968). \u003cem\u003eAulacoseira distans, Aulacoseira lirata, Tabellaria flocculosa\u003c/em\u003e (str. III), and \u003cem\u003eAsterionella formosa\u003c/em\u003e were the most common diatom taxa in Zone 2. Other common taxa included \u003cem\u003eDiscostella\u003c/em\u003e spp. (including \u003cem\u003eD. stelligera\u003c/em\u003e and \u003cem\u003eD. pseudostelligera\u003c/em\u003e) and \u003cem\u003ePinnularia microstauron\u003c/em\u003e. \u003cem\u003ePinnularia microstauron\u003c/em\u003e increased from 0% at 22.75 cm (pre-~1850) to ~\u0026thinsp;10% at 5.25 cm (~\u0026thinsp;1968). \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (str. III) fluctuated from ~\u0026thinsp;20% at 22.75 cm (pre-~1850) to ~\u0026thinsp;5% at 5.25 cm (~\u0026thinsp;1968). \u003cem\u003eAulacoseira distans\u003c/em\u003e decreased in relative abundances following 12.25 (~\u0026thinsp;1902). VNIRS-DOC decreased from 7.0 mg/L to 3.1 mg/L between 22.75 cm (pre-~1850) to 5.25 cm (~\u0026thinsp;1968) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). VRS-Chl \u003cem\u003ea\u003c/em\u003e increased from 0.05 mg/ g dry weight to 0.08 mg/g dry weight between 22.75 cm (pre-~1850) and 16.25 cm (~\u0026thinsp;1866) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), and then decreased to 0.04 mg/g dry weight at 5.25 cm (~\u0026thinsp;1968).\u003c/p\u003e \u003cp\u003eZone 3 includes interval 4.25 cm (~\u0026thinsp;1980; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). \u003cem\u003eFragilaria rhomboides\u003c/em\u003e var. \u003cem\u003ecassinerva\u003c/em\u003e, \u003cem\u003ePinnularia microstauron\u003c/em\u003e, \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (str. III), and \u003cem\u003eAulacoseira distans\u003c/em\u003e were the most common diatom taxa in Zone 3. At 4.25 cm (~\u0026thinsp;1980), \u003cem\u003eFragilaria rhomboides\u003c/em\u003e var. \u003cem\u003esaxonica\u003c/em\u003e, \u003cem\u003eAsterionella formosa\u003c/em\u003e, \u003cem\u003eDiscostella\u003c/em\u003e spp. (\u003cem\u003eD. stelligera\u003c/em\u003e and \u003cem\u003eD. pseudostelligera\u003c/em\u003e), and \u003cem\u003eAulacoseira lirata\u003c/em\u003e decreased to 0% from values of 5\u0026ndash;10% in Zone 2. VNIRS-DOC (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) was at 2.9 mg/L at 4.25 cm (~\u0026thinsp;1980). VRS-Chl \u003cem\u003ea\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) was at 0.045 mg/g dry weight at 4.25 cm (~\u0026thinsp;1980).\u003c/p\u003e \u003cp\u003eZone 4 includes intervals from 3.25 cm (~\u0026thinsp;1991) to 0.25 cm (~\u0026thinsp;2018; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). \u003cem\u003eAsterionella formosa\u003c/em\u003e and \u003cem\u003eTabellaria flocculosa\u003c/em\u003e (str. III) were the most common diatom taxa in Zone 3. Other common taxa included \u003cem\u003eFrustulia rhomboides\u003c/em\u003e var. \u003cem\u003esaxonica\u003c/em\u003e and \u003cem\u003eDiscostella\u003c/em\u003e spp. (including \u003cem\u003eD. stelligera\u003c/em\u003e and D. \u003cem\u003epseudostelligera\u003c/em\u003e). \u003cem\u003eFrustulia rhomboides\u003c/em\u003e var. \u003cem\u003esaxonica\u003c/em\u003e decreased to ~\u0026thinsp;7% at 0.25 cm (~\u0026thinsp;2018) from ~\u0026thinsp;13% at 2.25 cm (~\u0026thinsp;2000). \u003cem\u003eEunotia exigua\u003c/em\u003e decreased to 0% at 0.25 cm (~\u0026thinsp;2018) from ~\u0026thinsp;5% at 2.25 cm (~\u0026thinsp;2000). \u003cem\u003eAulacoseira distans\u003c/em\u003e decreased to 0% at 0.25 cm (~\u0026thinsp;2018) from ~\u0026thinsp;5% at 2.25 cm (~\u0026thinsp;2000). \u003cem\u003eTabellaria flocculosa\u003c/em\u003e increased to 37% at 0.25 cm (~\u0026thinsp;2018) from 17% at 2.25 cm (~\u0026thinsp;2000). VNIRS-DOC (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) increased throughout this period from 3.2 mg/L to 7.0 mg/L between 3.75 cm (~\u0026thinsp;1985) and 0.25 cm (~\u0026thinsp;2018). VRS-Chl \u003cem\u003ea\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) also increased throughout this period from 0.048 mg/g dry weight to 0.052 mg/g dry weight.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eHow did Sudbury and Killarney Provincial Park lakes respond to acidification?\u003c/h2\u003e \u003cp\u003eMining and smelting activities in Sudbury affected nearby lakes in various ways, most notably acidification and metal contamination. This, in turn, influenced diatom assemblage composition, lake-water DOC concentrations and whole-lake aquatic production. With the onset and peak (~\u0026thinsp;1960 to ~\u0026thinsp;1970) smelter emissions in Sudbury, we show that most study lakes (with the exception of naturally acidic Ruth-Roy Lake) recorded decreases in the relative abundance of small circumneutral taxa (i.e., \u003cem\u003eDiscostella\u003c/em\u003e spp., \u003cem\u003eAchnanthidium minutissimum, and Aulacoseira\u003c/em\u003e spp.) concurrent with increases in acidophilic taxa (i.e., \u003cem\u003eFragilariforma acidobiontica, Eunotia\u003c/em\u003e spp., \u003cem\u003eTabellaria flocculosa\u003c/em\u003e and \u003cem\u003eAsterionella ralfsii\u003c/em\u003e) that peaked at ~\u0026thinsp;1960 in Sudbury and at ~\u0026thinsp;1970 in KPP. Similar changes have previously been observed in other Sudbury and KPP lakes, and in lakes in other acid-sensitive regions, with the onset of acidic emissions (Charles 1985; Charles et al. 1990; Dixit et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe direction and magnitude of acidification due to smelting emissions are moderated by several factors, including distance to the nearest smelter and the underlying bedrock geology (i.e., buffering capacity). Aquatic ecosystems closest to the smelters received more acidic deposition than lakes further away (Keller et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). For example, the concentration of sulphate in Baby Lake (~\u0026thinsp;1 km from Coniston smelter) was 25.3 mg/L in 1980 compared to 10.0 mg/L in Ruth-Roy Lake (~\u0026thinsp;45 km from Sudbury) in the same year, despite their relatively similar lake volumes (1.14 x 10\u003csup\u003e6\u003c/sup\u003e m\u003csup\u003e3\u003c/sup\u003e and 2.34 x 10\u003csup\u003e6\u003c/sup\u003e m\u003csup\u003e3\u003c/sup\u003e for Baby and Ruth-Roy lakes, respectively (Keller et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2016\u003c/span\u003e)). In our study, the smallest temporal changes in diatom assemblages, VRS-Chl \u003cem\u003ea\u003c/em\u003e, and VNIRS-DOC were observed in the two study sites located furthest from the smelters, specifically Johnnie (~\u0026thinsp;42 km) and Tillie lakes (~\u0026thinsp;62 km).\u003c/p\u003e \u003cp\u003eThe diverse responses among the study lakes can also be attributed to differences in their hydrological/physical characteristics and bedrock composition. Bedrock geology influences lake buffering capacity because of differences in carbonate and silicate content. Lakes located in catchments predominantly composed of igneous bedrock with thin overlaying till are often \u0026ldquo;acid sensitive\u0026rdquo; with low buffering capacity, such as Ruth-Roy and Baby lakes. Lakes located in catchments with calcium-rich sedimentary rocks (i.e., limestone) are less acid sensitive and boast higher buffering capacities (Mallory et al. 1998).\u003c/p\u003e \u003cp\u003eJohnnie and Tillie lakes, for example, are situated on easily weathered bedrock (Dixit et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) which may contribute to higher buffering capacities and therefore relatively muted diatom responses to acid deposition. In contrast, Ruth-Roy Lake, located immediately upstream of Johnnie Lake, has a Ca\u003csup\u003e2+\u003c/sup\u003e plus Mg\u003csup\u003e2+\u003c/sup\u003e lake water concentration of only 60 \u0026micro;eq/L, approximately half that of Johnnie Lake (110 \u0026micro;eq/L). The VRS-Chl \u003cem\u003ea\u003c/em\u003e and VNIRS-DOC profiles for both Johnnie and Tillie lakes also showed a weaker response to acidification, consistent with the more efficient neutralization of acidic inputs in the relatively well-buffered catchments.\u003c/p\u003e \u003cp\u003eBaby Lake, located only 1 km from a smelter, responded with the most striking floristic changes, especially in the acidobiontic taxon \u003cem\u003eEunotia tenella\u003c/em\u003e. The lake has a relatively small watershed and is situated on exposed granitic/gneissic bedrock in a steep-sided catchment (Hutchinson and Havas \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). Pre-industrial diatom assemblages were composed of acidophilic taxa (i.e., \u003cem\u003eAsterionella ralfsii\u003c/em\u003e, \u003cem\u003eTabellaria flocculosa\u003c/em\u003e) and circumneutral taxa (i.e., \u003cem\u003eAulacoseira distans\u003c/em\u003e, \u003cem\u003eDiscostella stelligera\u003c/em\u003e), indicating moderately acidic conditions. With the peak of smelting activities, declines in taxa such as \u003cem\u003eA. distans\u003c/em\u003e and increased abundances of acidobiontic taxa such as \u003cem\u003eEunotia tenella\u003c/em\u003e, coincident with declines in VRS-Chl \u003cem\u003ea\u003c/em\u003e and VNIRS-DOC, indicated acidification.\u003c/p\u003e \u003cp\u003eRuth-Roy Lake experienced striking changes despite being ~\u0026thinsp;45 km from the nearest smelter, as discussed in detail in Simmatis et al. (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Ruth-Roy Lake is situated on an orthoquartzite ridge, providing poor buffering capacity and weathering ability, which contributes to naturally acidic waters (Dixit et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Ruth-Roy Lake is also small (relative to other study lakes) with a surface area of 54 ha (Keller et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The combination of lake size, bedrock composition and low buffering capacity makes Ruth-Roy Lake more susceptible to acidification. Diatom assemblages in Ruth-Roy Lake prior to the onset of smelting in Sudbury were already comprised of acidophilic and acidobiontic taxa (Vinebrooke et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) and notable changes occurred in cladoceran assemblages after the onset of smelting operations (Simmatis et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Based on shifts in the diatom assemblages, Ruth-Roy Lake was likely acidic prior to the onset of smelting in Sudbury and has remained so to present day.\u003c/p\u003e \u003cp\u003eThe diatom changes in Crooked Lake were somewhat muted despite its relative proximity to a smelter (~\u0026thinsp;6 km). Similar muted changes were evident in subfossil invertebrate assemblages from Crooked Lake, with increased prevalence of generalist taxa in modern sediments (Simmatis et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Prior to ~\u0026thinsp;1800, Crooked Lake was primarily dominated by circumneutral taxa (i.e., \u003cem\u003eAulacoseira\u003c/em\u003e spp. and \u003cem\u003eDiscostella\u003c/em\u003e spp.), as well as some acidophilic taxa (i.e., \u003cem\u003eAsterionella formosa\u003c/em\u003e). This assemblage indicates that Crooked Lake was naturally acidic, which is supported by its pre-industrial (~\u0026thinsp;1880) diatom inferred pH (Dixit et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003ec). VRS-Chl \u003cem\u003ea\u003c/em\u003e remained relatively constant during the period of acidification, but VNIRS-DOC showed a marked decline from ~\u0026thinsp;7 mg/L in pre-industrial times to ~\u0026thinsp;3 mg/L in the mid-1970s. Based largely on the shifting abundance of diatoms from circumneutral to acidophilic taxa around the onset of smelting activities, Crooked Lake experienced moderate acidification, relative to its background of naturally acidic conditions in pre-industrial times.\u003c/p\u003e \u003cp\u003eOverall, the lakes responded to acidification based on their distance from the smelters and bedrock geology. The pre-industrial state of the lakes was also an important factor influencing how each lake responded uniquely to smelting operations. Based on this relatively small sample size and the heterogeneity in geological setting of our five study sites, regional lake responses (i.e., KPP versus Sudbury) cannot be reliably inferred. However, as noted above, the timing of peak acidification differed slightly based on distance from the smelters.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eTrends in chemical and biological recovery following acidification\u003c/h2\u003e \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e \u003ch2\u003eChemical Recovery\u003c/h2\u003e \u003cp\u003eReduced smelting emissions have decreased the amount of acid and metal inputs to lakes in and around Sudbury, allowing pH to increase and lake-water metal concentrations to decrease in most lakes (Keller et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). All our study lakes have experienced varying degrees of chemical recovery. In terms of pH change between 1975 and 2019, Baby Lake has experienced the largest increase (+\u0026thinsp;2.6 pH units), followed by Crooked Lake (+\u0026thinsp;2.4 pH units), Johnnie Lake (+\u0026thinsp;1.16 pH units), Tillie Lake (+\u0026thinsp;0.90 pH units) and Ruth-Roy Lake (+\u0026thinsp;0.86 pH units). The magnitude of pH recovery in Baby Lake is attributed to several factors, including reduced sulphate emissions, alkalinity generation from lake sediments, and partial liming of the watershed (Dixit et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1992\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003eDOC has been generally shown to increase concomitantly with reduced acid deposition because of its effects on DOC solubility and mobility in soils, promoting increased terrestrial DOC supply with recovery from acidification (Monteith et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Meyer-Jacob et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Based on VNIRS-DOC inferences, DOC recovery has occurred in all our study lakes. Trends in VRS-Chl \u003cem\u003ea\u003c/em\u003e mirrored those of VNIRS-DOC in most cases. Notably, VRS-Chl \u003cem\u003ea\u003c/em\u003e in Johnnie Lake did not distinctly decline during the smelting period, but has increased in recent sediments.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eRecovery of Diatom Assemblages\u003c/h2\u003e \u003cp\u003eThe extent of biological recovery varied among our study lakes and did not consistently correspond to the magnitude of chemical recovery. In our study, biological recovery was commonly marked by decreases in the relative abundance of acidophilic taxa (i.e., \u003cem\u003eFragilariforma acidobiontica\u003c/em\u003e, \u003cem\u003eTabellaria flocculosa\u003c/em\u003e), and increases in circumneutral taxa (i.e., \u003cem\u003eAulacoseira\u003c/em\u003e spp. and \u003cem\u003eDiscostella\u003c/em\u003e spp.).\u003c/p\u003e \u003cp\u003eLakes in catchments with easily weathered geology (i.e., Johnnie and Tillie lakes) experienced more biological recovery than those with small igneous catchments (i.e., Ruth-Roy and Baby lakes), despite lower absolute magnitudes of pH change between 1975 and 2019. In Johnnie Lake, recent diatom assemblages are similar to those found in pre-impact sediments, likely reflecting its higher buffering capacity and relative resistance to acidification. Similarly, recent diatom assemblages in Tillie Lake are very similar to pre-industrial assemblages, apart from a decline in the circumneutral taxon \u003cem\u003eLindavia bodanica\u003c/em\u003e in the recent sediments. Given that Tillie Lake was the farthest from the Sudbury emission sources, it received the lowest amount of acid deposition, and so recovery was likely more rapid. Nonetheless, the lake\u0026rsquo;s recent diatom assemblages are still very different from pre-industrial assemblages.\u003c/p\u003e \u003cp\u003eLakes with small igneous catchments and limited buffering capacity experienced the highest increases in pH of our study lakes, but biological recovery has not matched the pace of chemical recovery. In Baby Lake, there is little evidence of diatom biological recovery. Decreased abundance of acidophilic taxa (i.e., \u003cem\u003eTabellaria flocculosa\u003c/em\u003e and \u003cem\u003eAsterionella ralfisii\u003c/em\u003e) support that the lake has somewhat chemically recovered from acidification, but stark differences between recent and pre-industrial sedimentary diatom assemblages do not indicate biological recovery to pre-impact conditions. As detailed in Simmatis et al. (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), Ruth-Roy Lake has shown almost no biological recovery, indicated by the dissimilarity of recent and pre-impact diatom assemblages. Notably, recent (2000\u0026ndash;2018) decreases were recorded in dominant taxa (i.e., \u003cem\u003eTabellaria flocculosa\u003c/em\u003e, \u003cem\u003eAulacoseira distans\u003c/em\u003e) except for \u003cem\u003eFragilariforma acidobiontica\u003c/em\u003e, which dominates most of Zone 2. Nonetheless, the uppermost sediments (0.25 cm to 0.75 cm) show small reductions in \u003cem\u003eFragilariforma acidobiontica\u003c/em\u003e, which could be indicative of some modest recovery from acidification. Given that Ruth-Roy Lake was believed to be naturally acidic, it likely has limited capacity to recover from decreased lake-water pH (Smol et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Simmatis et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWhen considering mining-related impacts on Sudbury and the surrounding area, it has been shown that, while many lakes have undergone varying degrees of chemical recovery, similar degrees of biological recovery have not always followed suit (Jeffries et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Furthermore, if and when biological recovery occurs, it often lags behind chemical recovery (Snucins and Gunn \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Jeffries et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). It is possible that biological recovery is slower than chemical recovery in our study lakes for several reasons, including: (1) the threshold of chemical recovery that allows biological recovery has not been reached; (2) the \u0026ldquo;time-lag\u0026rdquo; response could be caused by declines of acid-sensitive species in chemically recovered sites; and (3) acidified systems in recovery are being influenced by new environmental factors (i.e., climatic changes; Monteith et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), and this is preventing or slowing a return to pre-industrial diatom assemblages.\u003c/p\u003e \u003cp\u003eCollectively, these data are consistent with other recent paleolimnological studies (e.g., Simmatis et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Cheng et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) indicating complex recovery patterns from acidification which can be affected by lake chemistry (i.e., chemical recovery), other large-scale regional stressors (i.e., changing climate), and/or baseline lake conditions (i.e., a naturally acidic conditions).\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eThe Role of Climate Change\u003c/h2\u003e \u003cp\u003eLarge-scale environmental changes, such as climate warming, can directly or indirectly influence lake ecosystems. In Sudbury, mean annual air temperature, total annual precipitation, and total annual rainfall have increased modestly since 1985 (Simmatis \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and the Sudbury and KPP regions have experienced a warming trend of 1.4\u0026deg;C since the 1950s (Meyer-Jacob et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eLimnological changes concomitant with recent warming (i.e., less ice cover, shifts in thermal stratification; see Woolway et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) are often associated in medium to relatively deep lakes with increases in the relative abundance of several planktonic \u003cem\u003eCyclotella (Discostella) sensu lato\u003c/em\u003e species along with decreases in heavily silicified \u003cem\u003eAulacoseira\u003c/em\u003e and/or benthic fragilarioids, although the limnological context is key (R\u0026uuml;hland et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These taxonomic shifts, driven by climate-mediated changes in ice cover and/or changes in thermal stratification, were not clearly evident in our study lakes. Initially, this may seem unexpected, given that many other similar Boreal Shield lakes in central Ontario (unaffected by industrial emissions) are tracking recent climate-related changes in their diatom assemblages. However, these changes are largely tracked in relatively pristine, wilderness lakes. As noted by R\u0026uuml;hland et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2008\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), other factors, such as acidification and cultural eutrophication, can override these changes. Nonetheless, accelerated climate warming over the last few decades has likely contributed to the nature and magnitude of recent diatom changes.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIt is well documented that Sudbury and Killarney Provincial Park lakes were affected by Sudbury smelting activities. Distance from the smelters, bedrock geology, and the resultant pre-industrial state of these lakes collectively influenced how each lake responded to smelting operations and subsequent declines in emissions. The differences in biological recovery patterns that we record indicate that recovery needs to be considered within a multi-stressor framework, on a case-by-case basis.\u003c/p\u003e \u003cp\u003eBiological recovery of aquatic ecosystems from the effects of Sudbury mining activities were mainly influenced by water chemistry (i.e., chemical recovery), large-scale stressors (i.e., changing climate), and baseline lake conditions (i.e., whether or not a lake was naturally acidic). Although climate change is certainly affecting lakes in the Sudbury and KPP regions, the nature of the recent diatom assemblage shifts in our study sites appear to be, not surprisingly, mainly be a response to pH-related changes, rather than more directly to climate-related changes.\u003c/p\u003e \u003cp\u003eOverall, our study confirms that historical reconstruction of aquatic ecosystems provides important context for lake management. Multi-disciplinary studies, at different temporal scales, should provide a more integrated view of these complex systems, and provide insights into the variability that is present in recovering lakes.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study is part of the Landscape Carbon Accumulation through Reductions in Emissions (L-CARE) project, and financial support was provided by the Natural Sciences and Engineering Research Council of Canada (Grant No. CRDPJ 509182-17) and the Ontario Centres of Excellence (Grant No. 41-1-6145006).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was by funded by the Natural Sciences and Engineering Research Council of Canada (Grant No. CRDPJ 509182-17) and the Ontario Centres of Excellence (Grant No. 41-1-6145006).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interest declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAppleby PG (2001) Chronostratigraphic techniques in recent sediments. 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Springer New York.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWoolway RI, Sharma S, Smol JP (2022) Lakes in hot water: the impacts of a changing climate on aquatic ecosystems. BioScience 72: 1050\u0026ndash;1061.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-paleolimnology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jopl","sideBox":"Learn more about [Journal of Paleolimnology](http://link.springer.com/journal/10933)","snPcode":"10933","submissionUrl":"https://submission.nature.com/new-submission/10933/3","title":"Journal of Paleolimnology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Diatoms, Mining pollution, Boreal Shield lakes, lake sediment, spectroscopy, chlorophyll a, dissolved organic carbon","lastPublishedDoi":"10.21203/rs.3.rs-4462254/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4462254/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFor over a century, the copper and nickel mining centre of Sudbury in northeastern Ontario (Canada) was a major source of sulphur dioxide and other pollutants, degrading terrestrial and aquatic ecosystems in the surrounding region. In the 1970s, emissions were drastically reduced due to concerns over widespread environmental damage. Killarney Provincial Park (KPP), located ~ 60 km southwest of Sudbury, was also impacted by Sudbury emissions, but little is known about how present-day conditions relate to pre-industrial conditions, or how recovery trajectories may be influenced by recent climate change. Here, we use a multi-proxy paleolimnological approach to examine ecological change in five lakes over the past ~ 200 years in Sudbury (Baby, Tillie, and Crooked lakes) and KPP (Ruth-Roy and Johnnie lakes). The study objectives were to: (1) infer past ecological conditions from diatom assemblages, whole-lake chlorophyll-\u003cem\u003ea\u003c/em\u003e (VRS-Chl \u003cem\u003ea\u003c/em\u003e) and lake-water dissolved organic carbon (DOC) concentrations; (2) explore patterns of potential ecological recovery from acidification over the past several decades; and (3) compare any changes to recent monitoring and meteorological data. Distance from smelting operations and differences in underlying bedrock geology likely contributed to differences in the magnitude of change observed in the paleolimnological indicators. In general, the acidification period was characterized by declines in circumneutral diatom taxa (i.e., \u003cem\u003eDiscostella\u003c/em\u003e spp., \u003cem\u003eAchnanthidium\u003c/em\u003e spp., and \u003cem\u003eAulacoseira\u003c/em\u003e spp.), and inferred Chl \u003cem\u003ea\u003c/em\u003e and inferred DOC, concurrent with increased relative abundances of acidophilic diatoms (i.e., \u003cem\u003eFragilariforma acidobiontica, Eunotia\u003c/em\u003e spp., \u003cem\u003eTabellaria flocculosa\u003c/em\u003e and \u003cem\u003eAsterionella ralfsii\u003c/em\u003e). After ~ 1970, only limited recovery in diatom assemblages was recorded, although inferred DOC and Chl \u003cem\u003ea\u003c/em\u003e levels increased, indicating biological recovery is lagging chemical recovery and/or the ecological trajectory has been influenced by other large-scale environmental stressors. However, given the impacted nature of the study lakes, a clear climate signal in recent diatom assemblages was not as evident as often noted in pristine Boreal Shield lakes. This highlights the need for case-by-case consideration of recovery patterns in lakes, and confirms the importance of conducting long-term, multi-proxy studies to assess ecosystem recovery and ecological trajectories.\u003c/p\u003e","manuscriptTitle":"Using paleolimnology to assess long-term acidification and recovery trajectories in lakes from Killarney Provincial Park and Sudbury (Ontario, Canada)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-10 22:33:31","doi":"10.21203/rs.3.rs-4462254/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-09T00:56:10+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-28T10:58:31+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-24T09:30:27+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-12T19:48:06+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"42953319850878643642150502069206548058","date":"2024-06-17T04:15:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"95082324694679688881328392231278831533","date":"2024-06-14T15:59:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"55847005248604907046939536284800522649","date":"2024-06-13T16:04:58+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-09T18:35:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-24T15:12:20+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-24T15:12:19+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Paleolimnology","date":"2024-05-22T16:24:33+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":"3784a409-4cbe-41d0-aeb8-7347abd85666","owner":[],"postedDate":"June 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-05-19T16:06:06+00:00","versionOfRecord":{"articleIdentity":"rs-4462254","link":"https://doi.org/10.1007/s10933-025-00356-0","journal":{"identity":"journal-of-paleolimnology","isVorOnly":false,"title":"Journal of Paleolimnology"},"publishedOn":"2025-05-14 15:57:28","publishedOnDateReadable":"May 14th, 2025"},"versionCreatedAt":"2024-06-10 22:33:31","video":"","vorDoi":"10.1007/s10933-025-00356-0","vorDoiUrl":"https://doi.org/10.1007/s10933-025-00356-0","workflowStages":[]},"version":"v1","identity":"rs-4462254","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4462254","identity":"rs-4462254","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}