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Base metal smelting activity around Sudbury (Ontario, Canada) has persisted for over a century, emitting metals and acidifying contaminants that affected lakes downwind of smelter stacks. Although considerable research has been directed toward the paleolimnological study of diatoms and chrysophytes in the region, relatively little comparable work has been completed on invertebrates. Here, cladoceran (Branchiopoda: Cladocera) assemblages are compared using a paleolimnological “top-bottom approach”, comparing preimpact and recent assemblages. Spatiotemporal differences were likely driven by acidification-related stressors and legacy effects of metal contamination. The replacement of the Daphnia longispina complex with the Daphnia pulex complex is attributable to diminished lake-water calcium concentrations. Increased abundances of early colonist taxa demonstrate that many acidified lakes have not fully recovered. Regional stressors further complicate recovery and the interpretation of temporal changes. Finally, clustering of recent cladoceran assemblages reflects the effects of modern multiple stressors and persistent historical stressors. This study shows that acidification history partially explains differences in cladoceran assemblages, but also that multiple stressors will likely continue to influence assemblage composition and recovery in Sudbury lakes. Defining appropriate reference conditions, considering historical and modern stressors, will be important when assessing the extent and trajectory of ecosystem recovery from widespread anthropogenic impacts.

Ruth-Roy Lake (Killarney Provincial Park, Ontario, Canada) is an ultra-oligotrophic, naturally acidic waterbody. Lakes in Killarney Provincial Park were impacted by long-range transportation of contaminants from copper-nickel smelting operations in nearby Sudbury, but recent lake monitoring indicates that Ruth-Roy Lake has been less acidic than inferred pre-industrial pH conditions. We assessed the effects of pH change, reduced sulphur emissions, and drivers of reduced acidity using biological and geochemical paleolimnological techniques. Ruth-Roy Lake experienced notable biological and chemical change over the past ~150 years. All examined proxies supported that Ruth-Roy Lake was naturally acidic but further acidified as early as ca. 1920s, with the strongest acidification signal apparent in ca. 1940s. Biological recovery in diatom and cladoceran assemblages, however, is modest. We highlight the importance of understanding reference conditions to assess ecosystem recovery and climate-mediated change in clear acidic lakes located in industrial landscapes.

Peninsula Lake, Ontario, Canada, is a Precambrian Shield lake that has experienced many environmental stressors since European settlement of the watershed in the mid-1800s, including forest clearance, water-level management, sewage inputs, and land-use changes. The deterioration of water quality by the 1970s prompted mitigation efforts intended to reduce inputs of nutrients and untreated sewage to the lake. Paleolimnological analysis of a sediment core from Peninsula Lake, collected in 1995, revealed that efforts to address eutrophication had been somewhat successful, in that the lake had returned to oligotrophic status by the early 1990s. Nevertheless, there had been little to no improvement in inferred deepwater oxygen conditions. We used similar paleolimnological techniques on a core collected in 2014 to examine ecological responses to environmental stressors and remediation efforts in the intervening years, with a particular focus on changes in the amount of oxygenated habitat available to lake trout. Specifically, we inferred trends in volume-weighted hypolimnetic oxygen (VWHO), through analysis of sedimentary chironomid assemblages, to assess long-term changes in coldwater fisheries habitat. Potential drivers of VWHO were also investigated, and included diatom-inferred total phosphorus, spectrally derived trends in sedimentary chlorophyll a and its main diagenetic products, and lake-water dissolved organic carbon. The sedimentary chironomid assemblages indicate a long period of VWHO depletion, concurrent with known anthropogenic activities from the early twentieth century to the 1990s, followed by recent recovery to near pre-impact levels. The sedimentary diatom assemblages indicate nutrient enrichment throughout most of the twentieth century, which was also followed by a return to pre-impact conditions, albeit with recent indications of renewed nutrient enrichment. In contrast, strikingly different trajectories were observed in two other regional waterbodies that support lake trout, but experienced relatively little nutrient enrichment over the past ~ 150 years. Peninsula Lake appears to be recovering from nutrient enrichment and hypolimnetic oxygen depletion, but water quality improvements have nevertheless been accompanied by increased primary production, perhaps because climate warming has extended the ice-free season and stratification period. Therefore, instead of returning to pre-impact conditions, Peninsula Lake appears to be developing a novel ecological state. Any future improvements in lake trout habitat that result from nutrient abatement may be offset by rising temperatures.

The spiny water flea (Bythotrephes cederströmii), a freshwater crustacean considered to be the world’s best-studied invasive zooplankter, was first recorded in North America in the Laurentian Great Lakes during the 1980s. Its arrival is widely considered to be the result of ocean-going cargo ships that translocated contaminated ballast water from Eurasia to the Great Lakes during the 1970–1980s. The subsequent first discovery of the species in inland lakes is consistent with the hypothesis that propagules dispersed initially from established Great Lakes populations. Here we present evidence of exoskeletal remains, including mandibles, tail spines, and resting eggs, in 210Pb-dated lake sediment cores, which suggests that B. cederströmii was already resident in four inland North American lakes (two in Minnesota, USA; two in Ontario, Canada) by at least the early 1900s. Densities of exoskeletal remains were low and relatively steady from first appearance until about 1990, after which time they increased in all cores. The earliest evidence that we found was a mandible at 33-cm depth (pre-1650) in the sediments of Three Mile Lake, Ontario, Canada. These unexpected findings challenge the current paradigm of B. cederströmii invasion, renew uncertainty about the timing and sequence of its colonization of North American lakes, and potentially question our ability to detect invasive species with traditional sampling methods. We attempted to eliminate errors in the dated stratigraphies of the exoskeletal remains that might have been introduced either methodologically (e.g., core-wall smearing) or naturally (e.g., bioturbation). Nonetheless, given the very low numbers of subfossils encountered, questions remain about the possible artifactual nature of our observations and therefore we regard our results as ‘preliminary findings’ at this time.

Winter conditions, such as ice cover and snow accumulation, are changing rapidly at northern latitudes and can have important implications for lake processes. For example, snowmelt in the watershed-a defining feature of lake hydrology because it delivers a large portion of annual nutrient inputs-is becoming earlier. Consequently, earlier and a shorter duration of snowmelt are expected to affect annual phytoplankton biomass. To test this hypothesis, we developed an index of runoff timing based on the date when 50% of cumulative runoff between January 1 and May 31 had occurred. The runoff index was computed using stream discharge for inflows, outflows, or for flows from nearby streams for 41 lakes in Europe and North America. The runoff index was then compared with summer chlorophyll-a (Chl-a) concentration (a proxy for phytoplankton biomass) across 5-53 years for each lake. Earlier runoff generally corresponded to lower summer Chl-a. Furthermore, years with earlier runoff also had lower winter/spring runoff magnitude, more protracted runoff, and earlier ice-out. We examined several lake characteristics that may regulate the strength of the relationship between runoff timing and summer Chl-a concentrations; however, our tested covariates had little effect on the relationship. Date of ice-out was not clearly related to summer Chl-a concentrations. Our results indicate that ongoing changes in winter conditions may have important consequences for summer phytoplankton biomass and production. Vermont Space Grant Consortium under NASA Cooperative Agreement [NNX15AP86H]; NASA Earth and Space Science Fellowship under NASA Cooperative Agreement [80NSSC18K1394P0000]; Swedish Infrastructure for Ecosystem Science (SITES); MANTEL [H2020-MSCA-ITN-2061]; Limnoscenes (Biodiversa); Limnoscenes (Belmond Forum); Limnoscenes (German Science Foundation); RSCF project, of Ministry of Higher Education and Research [18-44-06201, FZZE-2020-0026, FZZE-2020-0023]; Foundation for support of applied ecological studies of Lake Baikal; ERDF/ESF project Biomanipulation [CZ.02.1.01/0.0/0.0/16_025/0007417]; Estonian Research Council grant [PUT PSG32]; MANTEL ITN [H2020-MSCA-ITN-2061]; Estonian Research Council grants [PRG705] Published version Vermont Space Grant Consortium under NASA Cooperative Agreement; NASA Earth and Space Science Fellowship under NASA Cooperative Agreement; Swedish Infrastructure for Ecosystem Science (SITES); MANTEL; Limnoscenes (Biodiversa); Limnoscenes (Belmond Forum); Limnoscenes (German Science Foundation); RSCF project, of Ministry of Higher Education and Research; Foundation for support of applied ecological studies of Lake Baikal; ERDF/ESF project Biomanipulation; Estonian Research Council grant(Estonian Research Council); MANTEL ITN; Estonian Research Council grants Public domain – authored by a U.S. government employee

Yao H, Paterson AM, James AL, McConnell C, Field T, Ingram R, Zhang D, Arnott SE, Higgins SN. 2020. Contrasting long-term trends of chloride levels in remote and human-disturbed lakes in south-cent...

Cyanobacterial blooms are increasing worldwide and have negative impacts on aquatic ecosystems and the services they provide to human societies. A lack of long-term environmental monitoring data, however, has prevented the development of a baseline perspective against which drivers of the increasing frequency and severity of cyanobacterial blooms can be identified. In this study, we evaluate application of spectroscopy-based models to infer historical trends in cyanobacterial abundance from lake sediment cores. Using an amendment series (n = 15) of a sediment matrix spiked with increasing amounts of mixed cyanobacterial culture from 0 to 50 parts per thousand (‰), taxonomically diagnostic carotenoids were measured using visible near-infrared reflectance spectroscopy (VNIRS) and conventional but more costly and time-consuming high-performance liquid chromatography (HPLC). A partial least squares regression model was developed to correlate amendment series VNIR spectra to ‰ of added cyanobacteria. Despite challenges in differentiating carotenoid pigments because of overlapping absorption peaks, applications of the resulting 2-component model (r2 = 0.93, RMSEP = 0.23‰) to sediment cores from four Ontario lakes yielded temporal trends that were significantly correlated with downcore HPLC measures of cyanobacterial pigments in three out of four cases. Although our method is simplistic and may be improved in the future with more complex algorithms employing derivative analysis, we present our results as a possible stepping-stone towards spectral reconstruction of cyanobacterial production. Our study provides proof-of-concept that refinement of a method applying VNIRS to detect cyanobacterial carotenoids in lake sediments has the potential to be an important, rapid and non-destructive assessment tool for research and management of cyanobacterial blooms.

Paterson AM, Koster D, Reavie ED, Whitmore TJ. 2020. Preface: paleolimnology and lake management. Lake Reserv Manage. 36:205–209. Paleolimnology uses information preserved in lake, river, and wetla...

Simmatis B, Nelligan C, Ruhland KM, Jeziorski A, Castro V, Paterson AM, Smol JP. 2020. Tracking ∼200 years of water quality in Muskrat Lake, a eutrophic lake trout lake in Ontario (Canada) with cya...

Microplastics are ubiquitous in the environment; however, few studies have examined their abundance in atmospheric deposition in pristine environments, remote from anthropogenic emission sources. In the current study, atmospheric deposition samples were collected for 13 months (February 2019-March 2020) from four precipitation chemistry monitoring stations located in Muskoka-Haliburton, south-central Ontario, Canada. Anthropogenic particles (i.e., synthetic particles but not necessarily plastic) were observed at each station with an average deposition rate of 57 particles/m

Microplastics (mp) are a growing environmental concern due to their ubiquity in terrestrial and aquatic environments. Nonetheless, there is limited knowledge on their abundance in lakes in rural areas. In this study, we surveyed 14 headwater lakes in Muskoka-Haliburton, Ontario, to assess the spatial and temporal variability of microplastics. The average microplastic concentration across the study lakes was 1.78 mp/L during May–June 2019, with limited spatial variability (coefficient of variation = 22%). Further, microplastic abundance was weakly correlated with lake area (rs: 0.469), the number of shoreline residences (rs: 0.399), and watershed area (rs: 0.350), suggesting that diffusive inputs, such as atmospheric deposition, were the dominant source of microplastics to the study lakes. In contrast, microplastics showed a distinct temporal (seasonal) variability, as the average concentration in August 2019 (0.91 mp/L) was significantly lower (p

Temperature–oxygen profiles, collected biweekly to monthly for ∼40 years, were used to calculate end-of-summer volume-weighted hypolimnetic oxygen (VWHO) concentrations in six small lakes located in south-central Ontario, Canada. Coherent decreases in thermocline depth and increases in hypolimnetic volume, mean hypolimnetic dissolved oxygen (DO) concentration, and VWHO were observed in five of the six study lakes. All lakes underwent an abrupt increase in VWHO and mean hypolimnetic DO after 2010. In four of the six study lakes, the highest hypolimnetic DO concentrations were observed in years where chlorophyll a concentrations were low, whereas at five of the six study lakes the highest hypolimnetic volumes were observed when dissolved organic carbon concentrations were relatively high. Warmer spring or winter air temperatures were associated with higher hypolimnetic DO concentrations at two sites, and longer ice-free periods were associated with smaller hypolimnetic volumes at two sites. These results suggest that the recent VWHO increases in the studied south-central Ontario lakes may be a function of multiple drivers that include changes in primary production, lake water transparency, and regional climatic factors.

Chronic myeloid leukemia (CML) results from hematopoietic stem cell transformation by the BCR-ABL kinase. Despite the success of BCR-ABL tyrosine kinase inhibitors (TKIs) in treating CML patients, leukemia stem cells (LSCs) resist elimination and persist as a major barrier to cure. Previous studies suggest that overexpression of the sirtuin 1 (SIRT1) deacetylase may contribute to LSC maintenance in CML. Here, by genetically deleting SIRT1 in transgenic CML mice, we definitively demonstrated an important role for SIRT1 in leukemia development. We identified a previously unrecognized role for SIRT1 in mediating increased mitochondrial oxidative phosphorylation in CML LSCs. We showed that mitochondrial alterations were kinase independent and that TKI treatment enhanced inhibition of CML hematopoiesis in SIRT1-deleted mice. We further showed that the SIRT1 substrate PGC-1α contributed to increased oxidative phosphorylation and TKI resistance in CML LSCs. These results reveal an important role for SIRT1 and downstream signaling mechanisms in altered mitochondrial respiration in CML LSCs.

Background and objectives Glomerular hyperfiltration has been considered to be a contributing factor to the development of diabetic kidney disease (DKD). To address this issue, we analyzed GFR follow-up data on participants with type 1 diabetes undergoing 125 I-iothalamate clearance on entry into the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications study. Design, setting, participants, & measurements This was a cohort study of DCCT participants with type 1 diabetes who underwent an 125 I-iothalamate clearance (iGFR) at DCCT baseline. Presence of hyperfiltration was defined as iGFR levels ≥140 ml/min per 1.73 m 2 , with secondary thresholds of 130 or 150 ml/min per 1.73 m 2 . Cox proportional hazards models assessed the association between the baseline hyperfiltration status and the subsequent risk of reaching an eGFR 2 . Results Of the 446 participants, 106 (24%) had hyperfiltration (iGFR levels ≥140 ml/min per 1.73 m 2 ) at baseline. Over a median follow-up of 28 (interquartile range, 23, 33) years, 53 developed an eGFR 2 . The cumulative incidence of eGFR 2 at 28 years of follow-up was 11.0% among participants with hyperfiltration at baseline, compared with 12.8% among participants with baseline GFR 2 . Hyperfiltration was not significantly associated with subsequent risk of developing an eGFR 2 in an unadjusted Cox proportional hazards model (hazard ratio, 0.83; 95% confidence interval, 0.43 to 1.62) nor in an adjusted model (hazard ratio, 0.77; 95% confidence interval, 0.38 to 1.54). Application of alternate thresholds to define hyperfiltration (130 or 150 ml/min per 1.73 m 2 ) showed similar findings. Conclusions Early hyperfiltration in patients with type 1 diabetes was not associated with a higher long-term risk of decreased GFR. Although glomerular hypertension may be a mechanism of kidney injury in DKD, higher total GFR does not appear to be a risk factor for advanced DKD.

Dickson Lake, located in Algonquin Provincial Park, Ontario, is a remote, oligotrophic lake, where cyanobacterial blooms of the genus Dolichospermum (Ralfs ex Bornet & Flahault) P. Wacklin, L. Hoffmann and J. Komarek were reported for the first time in the fall of 2014, and subsequently in the late spring of 2015. To investigate the potential environmental triggers of these bloom events, we assessed long-term trends in water quality using a multi-proxy paleolimnological approach, examining sedimentary diatoms, chironomids, cladocerans, spectrally inferred chlorophyll a, and cyanobacterial akinetes preserved in a 210Pb-dated sediment core. Assemblage changes were modest in all biological proxies. A subtle increase in the abundance of warm-water chironomid taxa (Topt > 15 °C) commences in the year ~ 2000, with further increases in the most recent years of the sediment record (~ 2013–2015). End-of-summer volume-weighted hypolimnetic oxygen concentrations (CI-VWHO), inferred from chironomid remains, reveal a decline in oxygen concentrations over the last two decades coincident with the highest levels of sedimentary chlorophyll a and cyanobacterial akinetes in the sediment record. These paleolimnological findings corroborate observed reports of the onset of cyanobacterial blooms in Dickson Lake in late 2014 and are consistent with increasingly favourable bloom-forming conditions over the past few decades that are related to warmer air temperatures, sharp declines in wind speed, and a lengthening of the ice-free season by 2 weeks since 1975. It is plausible that late ice-out and a quick onset to stratification in 2014 may have resulted in incomplete spring mixing, early onset of hypolimnetic anoxia, and increased internal nutrient loading, that, occurring during a period when climate conditions were particularly ideal for cyanobacterial proliferation, may have fueled the unprecedented algal blooms in this remote lake. Collectively, the factors causing algal blooms in remote lakes such as Dickson Lake are not yet fully understood, and it is worrisome that with continued warming the triggering conditions may become a more common feature of Algonquin Park and other minimally impacted Boreal Shield lakes in the coming years.

The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity1,2, nutrient biogeochemistry3, greenhouse gas emissions4, and the quality of drinking water5. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity6,7, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production10. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world’s oceans6,7 and could threaten essential lake ecosystem services2,3,5,11., The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity, nutrient biogeochemistry, greenhouse gas emissions, and the quality of drinking water. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production10. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world’s oceans and could threaten essential lake ecosystem services.

The spiny water flea (Bythotrephes cederströmii), a freshwater crustacean considered to be the world’s best-studied invasive zooplankter, was first recorded in North America in the Laurentian Great Lakes during the 1980s. Its arrival is widely considered to be the result of ocean-going cargo ships that translocated contaminated ballast water from Eurasia to the Great Lakes during the 1970–1980s. The subsequent first discovery of the species in inland lakes is consistent with the hypothesis that propagules dispersed initially from established Great Lakes populations. Here we present evidence of exoskeletal remains, including mandibles, tail spines, and resting eggs, in 210Pb-dated lake sediment cores, which suggests that B. cederströmii was already resident in four inland North American lakes (two in Minnesota, USA; two in Ontario, Canada) by at least the early 1900s. Densities of exoskeletal remains were low and relatively steady from first appearance until about 1990, after which time they increased in all cores. The earliest evidence that we found was a mandible at 33-cm depth (pre-1650) in the sediments of Three Mile Lake, Ontario, Canada. These unexpected findings challenge the current paradigm of B. cederströmii invasion, renew uncertainty about the timing and sequence of its colonization of North American lakes, and potentially question our ability to detect invasive species with traditional sampling methods. We attempted to eliminate errors in the dated stratigraphies of the exoskeletal remains that might have been introduced either methodologically (e.g., core-wall smearing) or naturally (e.g., bioturbation). Nonetheless, given the very low numbers of subfossils encountered, questions remain about the possible artifactual nature of our observations and therefore we regard our results as ‘preliminary findings’ at this time.

IntroductionThe ‘Developmental Origins of Health and Disease’ hypothesis suggests that a healthy trajectory of growth and development in pregnancy and early childhood is necessary for optimal health, development and lifetime well-being. The purpose of this paper is to present the protocol for a randomised controlled trial evaluating a preconception-early childhood telephone-based intervention with tailored e-health resources for women and their partners to optimise growth and development among children in Canada: a Healthy Life Trajectory Initiative (HeLTI Canada). The primary objective of HeLTI Canada is to determine whether a 4-phase ‘preconception to early childhood’ lifecourse intervention can reduce the rate of child overweight and obesity. Secondary objectives include improved child: (1) growth trajectories; (2) cardiometabolic risk factors; (3) health behaviours, including nutrition, physical activity, sedentary behaviour and sleep; and (4) development and school readiness at age 5 years.Method and analysisA randomised controlled multicentre trial will be conducted in two of Canada’s highly populous provinces—Alberta and Ontario—with 786 nulliparous (15%) and 4444 primiparous (85%) women, their partners and, when possible, the first ‘sibling child.’ The intervention is telephone-based collaborative care delivered by experienced public health nurses trained in healthy conversation skills that includes detailed risk assessments, individualised structured management plans, scheduled follow-up calls, and access to a web-based app with individualised, evidence-based resources. An ‘index child’ conceived after randomisation will be followed until age 5 years and assessed for the primary and secondary outcomes. Pregnancy, infancy (age 2 years) and parental outcomes across time will also be assessed.Ethics and disseminationThe study has received approval from Clinical Trials Ontario (CTO 1776). The findings will be published in peer-reviewed journals and disseminated to policymakers at local, national and international agencies. Findings will also be shared with study participants and their communities.Trial registration numberISRCTN13308752; Pre-results.

© The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adap- tation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statu- tory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons. org/licenses/by/4.0/. ake surfaces are warming worldwide, raising concerns about lake organism responses to thermal habitat changes. Species may cope with temperature increases by shifting their seasonality or their depth to track suitable thermal habitats, but these responses may be constrained by ecological interactions, life histories or limiting resources. Here we use 32 million temperature measurements from 139 lakes to quantify thermal habitat change (percentage of non-overlap) and assess how this change is exacerbated by potential habitat constraints. Long-term temperature change resulted in an average 6.2% non-overlap between thermal habitats in baseline (1978–1995) and recent (1996–2013) time periods, with non-overlap increasing to 19.4% on aver- age when habitats were restricted by season and depth. Tropical lakes exhibited substantially higher thermal non-overlap com- pared with lakes at other latitudes. Lakes with high thermal habitat change coincided with those having numerous endemic species, suggesting that conservation actions should consider thermal habitat change to preserve lake biodiversity. Faculty yes

The identification of genetic variation that directly impacts infection susceptibility and disease severity of COVID-19 is an important step towards risk stratification, personalized treatment plans, therapeutic and vaccine development and deployment. Given the importance of study design in infectious disease genetic epidemiology, we use simulation and draw on current estimates of exposure, infectivity and test accuracy of COVID-19 to demonstrate the feasibility of detecting host genetic factors associated with susceptibility and severity with published COVID-19 study designs. We demonstrate why studying susceptibility to SARS-CoV-2 infection could be futile at the early stages of the pandemic. Our insights can aid in the interpretation of genetic findings emerging in the literature and guide the design of future host genetic studies.

Widespread use of NaCl for road deicing has caused increased chloride concentrations in lakes near urban centers and areas of high road density. Chloride can be toxic, and water quality guidelines have been created to regulate it and protect aquatic life. However, these guidelines may not adequately protect organisms in low-nutrient, soft water lakes such as those underlain by the Precambrian Shield. We tested this hypothesis by conducting laboratory experiments on six Daphnia species using a soft water culture medium. We also examined temporal changes in cladoceran assemblages in the sediments of two small lakes on the Canadian Shield: one near a highway and the other >3 km from roads where salt is applied in the winter. Our results showed that Daphnia were sensitive to low chloride concentrations with decreased reproduction and increased mortality occurring between 5 and 40 mg Cl-/L. Analysis of cladoceran remains in lake sediments revealed changes in assemblage composition that coincided with the initial application of road salt in this region. In contrast, there were no changes detected in the remote lake. We found that 22.7% of recreational lakes in Ontario have chloride concentrations between 5 and 40 mg/L suggesting that cladoceran zooplankton in these lakes may already be experiencing negative effects of chloride.

The Hudson Bay Lowlands (HBL) region of the far north of Ontario (Canada) is expected to undergo considerable physical, chemical and biological change as a result of ongoing climatic change. Previous research in the region has shown marked limnological changes during the past ~ 20 years in relatively deep lakes that have been attributed to increased air temperatures and changes in sea ice phenology in Hudson Bay since the mid-1990s. Here, we present diatom assemblage, primary production and geochemical data from lake sediments documenting recent limnological change in two shallow sub-arctic lakes in the Sutton River region of the HBL. Both lakes recorded increased whole-lake production and diatom diversity changes that are consistent with a longer ice-free period and growing season. Changes in diatom composition at Wolfgang Lake were characterized by a response amongst benthic/periphytic taxa whereas a modest increase in planktonic diatoms was observed at Sam Lake. Geochemical changes (δ15N, C/N and %N) were temporally coherent with diatom assemblage changes, but showed different responses in the two study lakes. Thus, although the biological and geochemical changes were consistent with recent warming, differences in the nature and timing of these shifts illustrate the heterogeneous nature of shallow lakes, and suggest that local (catchment-specific) factors are important determinants of the trajectory of limnological change in these sensitive systems.

We used high-resolution diatom-based paleolimnological techniques to assess the effects of shoreline development and recent climate warming on three large embayments of Georgian Bay, Lake Huron (two impacted and one minimally impacted by shoreline development). The sedimentary diatom assemblages recorded subtle shifts at the impacted sites (North and South Bays) as a result of the establishment of permanent settlements and recreational resorts around the turn of the 20th century. No turn-of-the-century changes were observed at the reference site (Tadenac Bay). The abrupt increase in epiphytic Cocconeis placentula and benthic fragilarioid taxa during the ~1950s at the shallower impact site (South Bay) was likely due to increased habitat provided by macrophytes. The increase in relative abundances of pennate (Asterionella formosa and Fragilaria crotonensis) and/or small centric (Cyclotella ocellata, C. comensis, and C. gordonensis) planktonic diatoms across the three sites after the 1970s suggests that recent warming-mediated changes to thermal properties (and related effects) are driving biological changes in these embayments. These recent diatom compositional changes are consistent with similar trends reported across Ontario and the Laurentian Great Lakes, where warming and its effects on aquatic ecosystem processes often favor small-celled centric diatoms. Differences in the timing and nature of diatom responses to similar environmental stressors across the three embayments highlight the importance of understanding site-specific characteristics when interpreting changes in diatom assemblages in paleolimnological records from the Laurentian Great Lakes.

A top–bottom paleolimnological analysis of 30 undisturbed lakes in the Experimental Lakes Area (ELA) in northwest Ontario showed marked increases in the relative abundance of colonial scaled chrysophyte taxa in most lakes since pre-industrial times. The increase in abundance of colonial taxa was primarily driven by Synura sphagnicola in small, high-nutrient, and warm lakes. The colonial taxa Synura petersenii and Synura echinulata also increased in the deeper study lakes. Detailed analysis of sediment cores from six lakes revealed that these changes occurred in the early to mid-1900s. Based on the modern distribution of scaled chrysophytes relative to lake physicochemical data, we propose multiple processes that may be contributing to these changes, such as changes in lake thermal properties and historical changes in the flux of important particles and solutes to lakes. Additional mechanisms that may contribute to the observed changes are discussed, including trophic interactions and changes in limnetic pCO2. Because the ELA is relatively undisturbed, our findings provide important information on the drivers responsible for increases in colonial chrysophyte abundance, which have been documented in studies of lakes in central Ontario and northeast United States.

Formerly acidified lakes and watersheds can become more productive when recovering from acidity, especially when exposed to anthropogenic disturbance and increased nutrient loading. Occasional toxic cyanobacterial blooms and other signs of eutrophication have been observed for a decade in lakes located in the Sudbury, Ontario, mining area that was severely affected by acid deposition before the start of smelter emission reductions in the 1970s. Oligotrophic Long Lake and its upstream lakes have been exposed to waste water input and development impacts from the City of Greater Sudbury and likely have a legacy of nutrient enrichment in their sediment. Based on observations from other published studies, we hypothesized that P, which was previously adsorbed by metals liberated during acidification caused by the mining activities, is now being released from the sediment as internal P loading contributing to increased cyanobacteria biomass. Support for this hypothesis includes (1) lake observations of oxygen depletion and hypolimnetic anoxia and slightly elevated hypolimnetic total P concentration and (2) P, Al, and Fe fractionation of two sediment layers (0–5, 5–10 cm), showing elevated concentrations of TP and iron releasable P (BD-fraction), decreased concentrations in fractions associated with Al, and fraction ratios indicating decreased sediment adsorption capacity. The comparison with two moderately enriched lakes within 200 km distance, but never directly affected by mining operations, supports the increasing similarity of Long Lake surficial sediment adsorption capacity with that of unaffected lakes. There is cause for concern that increased eutrophication including the proliferation of cyanobacteria of formerly acidic lakes is wide-spread and occurs wherever recovery coincides with anthropogenic disturbances and physical changes related to climate change.

Lake of the Woods (LOW) is a large, morphologically and hydrologically complex lake of international importance, located in the provinces of Ontario and Manitoba and the state of Minnesota. A high-resolution sedimentary sequence retrieved near Kenora, Ontario, and spanning at least the past ~11,000 cal yr BP (calibrated years before present), was analysed for multiple environmental proxies with an emphasis on diatom assemblage composition and spectrally-inferred chlorophyll a. These biological proxies indicate that northern LOW was relatively nutrient-rich soon after its isolation from glacial Lake Agassiz ~10,000 cal yr BP. The post-glacial hydrological and environmental history of LOW was found to be controlled by both climate and isostatic rebound. During the low water phase of the mid-Holocene dry and warm period, abrupt and synchronous shifts across all proxies suggest that the northern basin had a relatively deep and well-mixed water column that experienced increases in nutrients and whole-lake algal production. This differs from recent limnological changes associated with warming since the late-1970s, where primary production increased concurrently with large shifts in diatoms indicative of increased thermal stability, but with little change in nutrients. The millennial-scale context of this study provides evidence that climate has long played an important role in algal dynamics in LOW, with implications for lake management strategies concerning recent increases in nuisance algal blooms on LOW.

The far north of Ontario, Canada, is a region that is very vulnerable to future change due to climate warming and resource extraction. Despite its vast size (~ 450,000 km2) and large numbers of lakes (> 700,000), there has been very little study of aquatic ecosystems in this remote area. To address this lack of limnological data, forty-one northern Ontario lakes spanning two physiographic regions, the Hudson Bay Lowlands and the Canadian Shield, were sampled during 2012 for crustacean zooplankton and water chemistry. These sub-Arctic lakes support diverse crustacean plankton communities with species richness similar to the richness of lakes in central and northeastern Ontario. While some of the species collected appear to be at the northern limit of their distributions, most relatively common Ontario species occurred throughout the 2012 study area. The physico-chemical characteristics showing relationships with species richness and relative abundances were variables associated with lake morphometry, ionic strength and nutrient status. There were differences in community richness and composition between Lowlands and Shield lakes; however, these differences do not seem attributable to biogeographical influences on species occurrences. Rather, the lower species richness and differences in community composition in Lowlands lakes relative to Shield lakes appear to be largely related to lake morphometry. The shallower and generally smaller Lowlands lakes provide much less habitat diversity, i.e. niche space, than the larger, deeper Shield lakes, leading to simpler communities.

Surface water browning, the result of increasing concentrations of dissolved organic matter (DOM), has been widespread in northern ecosystems in recent decades. Here, we assess a database of 426 undisturbed headwater lakes and streams in Europe and North America for evidence of trends in DOM between 1990 and 2016. We describe contrasting changes in DOM trends in Europe (decelerating) and North America (accelerating), which are consistent with organic matter solubility responses to declines in sulfate deposition. While earlier trends (1990–2004) were almost entirely related to changes in atmospheric chemistry, climatic and chemical drivers were equally important in explaining recent DOM trends (2002–2016). We estimate that riverine DOM export from northern ecosystems increased by 27% during the study period. Increased summer precipitation strengthened upward dissolved organic carbon trends while warming apparently damped browning. Our results suggest strong but changing influences of air quality and climate on the terrestrial carbon cycle, and on the magnitude of carbon export from land to water.

Anderson JP, Paterson AM, Reavie ED, Edlund MB, Ruhland, KM. 2017. An introduction to Lake of the Woods – from science to governance in an international water body. Lake Reserv Manage. 33:325–334.Lake of the Woods (LOW), a vast lake covering over 3850 km2, is a waterbody of current and historical significance that spans the borders between Minnesota and the Canadian provinces of Ontario and Manitoba. Over the past 2 decades, there has been concern for the water quality of LOW, sparked by anecdotal evidence of increased intensity and frequency of algal blooms by the public and resource managers. Minnesota's waters of LOW were declared impaired in 2008 due to exceedances of eutrophication criteria, initiating a Total Maximum Daily Load study. LOW's impairment declaration spurred several contrasting challenges and opportunities for water quality management across this diverse lake and basin. Governance challenges are emphasized by the large number of government agencies (>25) with land or water autho...

Edlund MB, Schottler SP, Reavie ED, Engstrom DR, Baratono NG, Leavitt PR, Heathcote AJ, Wilson B, Paterson AM. 2017. Historical phosphorus dynamics in Lake of the Woods (USA–Canada) — does legacy phosphorus still affect the southern basin? Lake Reserv Manage. 33:386–402. A historical phosphorus (P) budget was constructed for southern Lake of the Woods. Sediment cores from 7 bays were radioisotopically dated and analyzed for loss-on-ignition, P, Si, diatoms, and pigments. Geochemical records for cores were combined using focusing factors for whole-basin estimates of sediment, total P, and P fraction accumulation. Although historical monitoring shows that external P loads decreased since the 1950s, sediment P has continued to increase since the mid-20th century. Much sediment P is labile and may be mobile within the sediments and/or available for internal loading and resuspension. Two mass-balance models were used to explore historical P loading scenarios and in-lake dynamics, a static one-box model and a dynamic multi-box model. The one-box model predicts presettlement external loads were slightly less than modern loads. The dynamic model shows that water-column P was higher in the 1950s–1970s than today, that the lake is sensitive to external loads because P losses from burial and outflow are high, and that the lake is moving to a new steady state with respect to water-column P and size of the active sediment P pool. The active sediment pool built up in the mid-20th century has been depleted through outflow and burial, such that its legacy effects are now minimal. Comparison of historical nutrient dynamics and sediment records of algal production showed a counterintuitive increase in production after external P loads decreased, suggesting other drivers may now regulate modern limnoecology, including seasonality of P loading, shifting nutrient limitation, and climate warming.

Paterson AM, Ruhland KM, Anstey CV, Smol JP. 2017. Climate as a driver of increasing algal production in Lake of the Woods, Ontario, Canada. Lake Reserv Manag. 33:403–414.Lake of the Woods (LOW) is...

Anthropogenic stressors, such as urban development and intensification of agricultural and industrial activities, can alter physical, chemical, and biological conditions in aquatic systems. Mounting concern over cumulative effects of multiple stressors has stimulated the need to track ecological responses and quantify degradation. Periphytic diatoms have potential to serve as early indicators of ecological degradation in aquatic systems. We examined relations between periphytic diatom community composition, water chemistry, and the magnitude of anthropogenic stressors in lakes of the Muskoka River watershed. These relations were used to develop a bioassessment framework for tracking changes in biological integrity in a region undergoing growth of tourism and related urban and recreational activities. We examined nearshore periphyton and water-chemistry samples from 86 lakes to assess relations between diatom community composition, water chemistry, and measures of 9 anthropogenic stressors (e.g., %...