Warm Lake Research Articles

Seven Decades of Surface Temperature Changes in Central European Lakes: What Is Next?

Lakes are vital components of the hydrosphere, holding both environmental and economic significance. In recent times, they have undergone transformations in one of their key characteristics—water temperature. Assessing the scale and pace of these changes depends on the length and accuracy of the available data. This study focuses on the two lakes in Poland (Białe Augustowskie and Studzieniczne) with the longest continuous water temperature records, ranging from 1954 to 2023. The results reveal a relatively stable thermal regime until the late 1980s (with changes that were statistically insignificant) and a significant shift over the past three decades, during which the water temperature increased at a rate of 0.5 °C per decade. Importantly, simulations indicate further warming of the water by the end of the 21st century. Depending on the chosen climate change scenario, the warming of both lakes is expected to continue, with the Shared Socioeconomic Pathways (SSP585) scenario projecting a steady increase of 0.5 °C per decade. Given the fundamental importance of water temperature in determining factors such as water quality, these future changes present a significant challenge for water management authorities in terms of maintaining and managing these ecosystems.

Dynamics of the risk of algal blooms induced by surface water temperature in an alpine eutrophic lake under climate warming: Insights from Lake Dianchi

Climate change-induced higher water temperature is increasing the risk of algal blooms (ABs) in eutrophic water bodies. However, it is not well known how and to what extent warming affects ABs risk. In this work, with simple data input (satellite product, lake surface observation, and climate) and method structure (ensemble learning, statistical downscaling, and hierarchical clustering), a systematic lake surface water temperature (LSWT) and ABs risk evaluation system are constructed and applied in a typical eutrophic freshwater lake. The main results are as follows: 1. The warming rate of LSWT and air temperature from 2000 to 2023 reached 0.21 °C/10a and 0.30 °C/10a respectively, resulting in an extended ABs risk in the historical period. 2. The Nash–Sutcliffe efficiency between climate and LSWT reached 0.89, and LSWT showed a significant (p < 0.05) positive correlation with algal density. 3. The escalation of ABs risks mainly spread to spring and autumn in the forthcoming future, the adverse effect of high emission scenarios will evidently emerge in the mid-21st century. Policymakers and catchment managers should be cautious of lake warming and develop countermeasures in advance.

Variability of winter cooling affects intensity of phytoplankton spring blooms – how resilient is the ciliate assemblage composition to changes in food availability?

After years of partial winter mixing in Lake Zurich (Switzerland), a complete turnover of the water column reoccurred during winter/spring 2021. It was favored by a cold, windy winter and a small difference of water temperatures between the surface zone and a hypolimnion (deep water zone) that had gradually warmed during the previous years. The trend of declining phytoplankton spring blooms due to incomplete winter mixing was interrupted by mass development of algae due to the upwelling of nutrients accumulated in the hypolimnion. The effects of this singular deep mixing on the microbial food web during spring were studied in a high-frequency sampling campaign and compared with data from two years of partial winter mixing (2020 and 2022). A particular focus was put on the quantitative composition of the ciliate assemblage. Our results showed that not all organisms reacted equally to the nutrient (phosphorus) boost in the surface zone. Centric diatoms and cryptophytes profited most directly from the deep mixing, outcompeting the otherwise dominant cyanobacterium Planktothrix rubescens. Heterotrophic bacteria and their top predators, the ‘heterotrophic nanoflagellates’ trophic guild, were less affected by the nutrient supply and showed only short-lived increases of maximal biomass. The assemblage composition of ciliate morphotypes was highly resilient over the three years, presumably due to the range of acceptable food items of the predominant omnivorous species. However, numerous ciliate morphotypes showed brief mass development in 2021, and Balanion planctonicum, small Urotricha species and tintinnids were significantly more frequent than in 2020/2022. Small interception-feeding morphotypes apparently profited from the rich supply of their cryptomonad food, and tintinnid morphotypes additionally benefited from the availability of building material (e.g., centric diatom shells) for their loricae. In summary, we show that effects of lake warming in deep stratifying lakes are not as unidirectional as previously presumed, and we reveal resilience of the pelagic ciliate morphotype assemblage to lake warming related interannual variability in Lake Zurich.

Early diagenetic evolution based on petrography and stable isotope analysis in the Barra Velha Formation of the Brazilian Pre‐salt

AbstractMineralogy and texture of diagenetic phases in the Aptian Pre‐Salt Barra Velha Formation are described, quantified and compared by facies and structural setting to understand their spatial and temporal distribution, and to develop predictive concepts for their genesis. This study examined data from eight wells from one oil‐field in the Santos Basin. Calcite is the most abundant mineral and occurs with fibro‐radial texture as spherulites and shrubs and sparse microcrystalline mudstone. The δ18O values from calcite spherulites and shrubs suggest water of similar composition and temperature, but they have different δ13C values. Mudstones show lower δ18O, suggesting warmer lake water and/or lower evaporation, whereas δ13C values indicate a variable, but commonly strong influence of biogenic CO2. Dolomite with rhombohedral habit was the first to precipitate, followed by lamellar, saddle and anhedral varieties. Rhombohedral dolomites show a positive δ13C‐δ18O correlation and a similar range in values to spherulites and shrubs, suggesting similar lake water. The lamellar dolomite is related to biofilms, whereas anhedral dolomite is attributed to mixing of pore and meteoric waters. Lamellar and anhedral dolomites have similar isotopic values, precipitating after rhombohedral dolomite in slightly warmer and/or less evaporatively concentrated pore water. Saddle dolomite is related to hydrothermal fluids that percolated the formation during early diagenesis. Silica occurs as replacement of primary calcite and Mg‐clay, but also as a cement and more rarely as a depositional chert. Both dolomite and silica display a complex range of petrographic textures, many of which are facies dependent. This study focusses on the most important phases of the paragenetic sequence that took place pre‐burial and are (1) formation of Mg‐clay, calcite spherulites and shrubs, (2) partial dolomitisation of shrubs and spherulites and precipitation of rhombohedral and lamellar dolomites, (3) precipitation of saddle dolomite, matrix and carbonate dissolution and (4) anhedral dolomite and all textures of precipitated or substituted silica.

How Could Future Climate Conditions Reshape a Devastating Lake‐Effect Snow Storm?

AbstractLake‐effect snow (LES) storms, characterized by heavy convective precipitation downwind of large lakes, pose significant coastal hazards with severe socioeconomic consequences in vulnerable areas. In this study, we investigate how devastating LES storms could evolve in the future by employing a storyline approach, using the LES storm that occurred over Buffalo, New York, in November 2022 as an example. Using a Pseudo‐Global Warming method with a fully three‐dimensional two‐way coupled lake‐land‐atmosphere modeling system at a cloud‐resolving 4 km resolution, we show a 14% increase in storm precipitation under the end‐century warming. This increase in precipitation is accompanied by a transition in the precipitation form from predominantly snowfall to nearly equal parts snowfall and rainfall. Through additional simulations with isolated atmospheric and lake warming, we discerned that the warmer lake contributes to increased storm precipitation through enhanced evaporation while the warmer atmosphere contributes to the increase in the storm's rainfall, at the expense of snowfall. More importantly, this shift from snowfall to rainfall was found to nearly double the area experiencing another winter hazard, Rain‐on‐Snow. Our study provides a plausible future storyline for the Buffalo LES storm, focusing on understanding the intricate interplay between atmospheric and lake warming in shaping the future dynamics of LES storms. It emphasizes the importance of accurately capturing the changing lake‐atmosphere dynamics during LES storms under future warming.

Multivariate extremes in lakes

Extreme within-lake conditions have the potential to exert detrimental effects on lakes. Here we use satellite observations to investigate how the occurrence of multiple types of extremes, notably algal blooms, lake heatwaves, and low lake levels, have varied in 2724 lakes since the 1980s. Our study, which focuses on bloom-affected lakes, suggests that 75% of studied lakes have experienced a concurrent increase in at least two of the extremes considered (27% defined as having a notable increase), with 25% experiencing an increase in frequency of all three extremes (5% had a notable increase). The greatest increases in the frequency of these extremes were found in regions that have experienced increases in agricultural fertilizer use, lake warming, and a decline in water availability. As extremes in lakes become more common, understanding their impacts must be a primary focus of future studies and they must be carefully considered in future risk assessments.

Thermal Response of Large Seasonally Ice‐Covered Lakes Over Tibetan Plateau to Climate Change

AbstractIn this study, a process‐based lake model is used to investigate the influence of climate change on the thermodynamics of 30 large lakes over Tibetan Plateau (TP). The lake model was driven by the atmospheric forcing derived from the bias‐corrected projections of three global climate models in the twenty‐first century under three Shared Socioeconomic Pathways (SSPs). The hindcasts during 2000–2014 can reasonably capture the seasonality and magnitude of satellite retrieved lake surface temperature (LST). Future projections during 2015–2100 suggest a widespread increased LST, declined ice cover, and prolonged stratification, with the severity of changes in line with the climate driver shifts under different SSPs. Under the scenario with the highest level of anthropogenic radiative forcing (SSP5‐8.5), the end‐of‐century (2086–2100) changes of LST, ice thickness, and stratification duration averaged across all studied lakes reach 4.90°C, −0.43 m, and 65.46 days, respectively. Note that the positive ice‐albedo feedback can cause excess lake warming by accelerating ice break‐up (30.07 days earlier) and stratification onset (46.83 days earlier). By the end of this century, more frequent, multi‐seasonal thermal extremes are anticipated to push nearly half of the studied lakes into a permanent heatwave state. Together with the remarkable LST increase and winter ice loss, the lakes will mix less frequently and may shift from a dimictic to warm monomict mixing regime. Hopefully, the irreversible thermal changes can be avoided if the anthropogenic radiative forcing is controlled within the envelope outlined by the stringent climate mitigation scenario SSP1‐2.6.

Earlier ice melt increases hypolimnetic oxygen despite regional warming in small Arctic lakes

AbstractAlthough trends toward earlier ice‐out have been documented globally, the links between ice‐out timing and lake thermal and biogeochemical structure vary spatially. In high‐latitude lakes where ice‐out occurs close to peak intensity of solar radiation, these links remain unclear. Using a long‐term dataset from 13 lakes in West Greenland, we investigated how changing ice‐out and weather conditions affect lake thermal structure and oxygen concentrations. In early ice‐out years, lakes reach higher temperatures across the water column and have deeper epilimnia. Summer hypolimnia are the warmest (~ 11°C) in years when cooler air temperatures follow early ice‐out, allowing full lake turnover. Due to the higher potential for substantive spring mixing in early ice‐out years, a warmer hypolimnion is associated with higher dissolved oxygen concentrations. By affecting variability in spring mixing, the consequences of shifts in ice phenology for lakes at high latitudes differ from expectations based on temperate regions.

Increased Warming Efficiencies of Lake Heatwaves Enhance Dryland Lake Warming over China

Lake surface water temperature (LSWT) has significantly increased over China and even globally in recent decades due to climate change. However, the responses of LSWTs to climate warming in various climatic regions remain unclear due to the limited lake observations. Satellite-observed LSWT data from the Moderate Resolution Imaging Spectroradiometer (MODIS) dataset were extended using the air2water model. This research aimed to investigate summer LSWT trends across various climatic zones in China, shedding light on the complex interplay between surface air temperatures and LSWT from 1950 to 2020. The results demonstrate robust model performance, with high Nash–Sutcliffe efficiency coefficients, affirming its capability to simulate LSWT variability. Regional disparities in LSWT patterns are identified, revealing notable warming trends in dryland lakes, particularly in central Inner Mongolia. Notably, the study unveils a substantial increase in the intensity and duration of lake heatwaves, especially in semi-arid regions. Dryland lake heatwaves emerge as dominant contributors to intensified LSWT warming, showcasing stronger and longer-lasting events than humid regions. The research highlights a positive feedback loop between lake warming and heatwaves, further amplifying dryland LSWT warming. These findings underscore the vulnerability of dryland lakes to climate change and signal the potential ramifications of increased greenhouse gas concentrations.

The impact of extreme heat on lake warming in China

Global lake ecosystems are subjected to an increased occurrence of heat extremes, yet their impact on lake warming remains poorly understood. In this study, we employed a hybrid physically-based/statistical model to assess the contribution of heat extremes to variations in surface water temperature of 2260 lakes in China from 1985 to 2022. Our study indicates that heat extremes are increasing at a rate of about 2.08 days/decade and an intensity of about 0.03 °C/ day·decade in China. The warming rate of lake surface water temperature decreases from 0.16 °C/decade to 0.13 °C/decade after removing heat extremes. Heat extremes exert a considerable influence on long-term lake surface temperature changes, contributing 36.5% of the warming trends within the studied lakes. Given the important influence of heat extremes on the mean warming of lake surface waters, it is imperative that they are adequately accounted for in climate impact studies.

Climate-associated variation in the drivers of benthic macroinvertebrate species-area relationships across shallow freshwater lakes.

The island species-area relationship (ISAR) describes how species richness increases with increasing area of a given island or island-like habitat, such as freshwater lakes. While the ISAR is one of the most common phenomena observed in ecology, there is variation in both the form of the relationship and its underlying mechanisms. We compiled a global data set of benthic macroinvertebrates from 524 shallow freshwater lakes, ranging from 1 to 293,300 ha in area. We used individual-based rarefaction to determine the degree to which ISAR was influenced by mechanisms other than passive sampling (larger islands passively sample more individuals from the regional pool and, therefore, have more species than smaller islands), which would bias results away from expected relationships between rarefied species richness (and other measures that capture relative abundances) and lake area. We also examined how climate may alter the shape of the ISARs. We found that both rarefied species richness (the number of species standardized by area or number of individuals) and a measure of evenness emphasizing common species exhibit shallow slopes in relationships with lake area, suggesting that the expected ISARs in these lakes most likely result from passive sampling. While there was considerable variation among ISARs across the investigated lakes, we found an overall positive rarefied ISAR for lakes in warm (i.e. tropical/subtropical) regions (n = 195), and in contrast, an overall negative rarefied ISAR in cool (i.e. north temperate) lakes (n = 329). This suggested that mechanisms beyond passive sampling (e.g. colonization-extinction dynamics and/or heterogeneity) were more likely to operate in warm lakes. One possible reason for this difference is that the area-dependent intensity of fish predation, which can lead to flatter ISARs, is weaker in warmer relative to cooler lakes. Our study illustrates the importance of understanding both the pattern and potential processes underlying the ISARs of freshwater lakes in different climatic regions. Furthermore, it provides a baseline for understanding how further changes to the ecosystem (i.e. in lake area or climate) might influence biodiversity patterns.

Assessing climatic and spatial variables influencing zooplankton richness for space‐for‐time predictions

Abstract The macroecological drivers of freshwater diversity are accredited geographical, spatial and climatic variables, but also to productivity, ecosystem age and landscape history. Locally diversity is also influenced by the dispersal ability of species. Here we evaluated how spatial and climatic variables influence species richness and macroecological patterns in Cladocera and Copepoda. We also discuss whether a space‐for‐time approach is suitable to predict the community's response to the current rapid warming of lakes. We use the presence‐absence of pelagic and littoral microcrustaceans in 1465 Norwegian lakes with a wide range of latitudinal, longitudinal, and altitudinal gradients, as well as a wide span in lake areas, to evaluate how spatial and climatic factors influence zooplankton diversity in two major groups: Cladocera and Copepoda. Longitude and latitude per se were poor predictors of zooplankton richness, but a combination of spatial and ecological predictors gave a good spatial prediction of cladoceran and copepod richness. These two groups did, however, not differ in their spatial distribution, with a strikingly fixed proportion of copepods close to 0.3, suggesting no obvious Allee‐ effects regarding the mode of reproduction (asexual vs sexual). Since temperature alone was a poor predictor of species richness for both groups and dispersal constraints can make it very difficult to estimate a new richness equilibrium under a future climate, space‐for‐time predictions may have limited value for assessing future patterns of microcrustacean diversity. Based on a quite unique dataset in terms of the sheer number of sites, spatial gradients, and inclusion of littoral species, our study demonstrates that assessments on how changing climate will shape and modulate zooplankton communities in the future are problematic.

Divergent Temporal Trends of Mercury in Arctic Char from Paired Lakes Influenced by Climate-Related Drivers.

Climate-driven changes including rising air temperatures, enhanced permafrost degradation, and altered precipitation patterns can have profound effects on contaminants, such as mercury (Hg), in High Arctic lakes. Two physically similar lakes, East Lake and West Lake at the Cape Bounty Arctic Watershed Observatory on Melville Island, Nunavut, Canada are being affected by climate change differently. Both lakes have experienced permafrost degradation in their catchments; however, West Lake has also undergone multiple underwater Mass Movement Events (MMEs; beginning in fall 2008), leading to a sustained 50-fold increase in turbidity. This provided the unique opportunity to understand the potential impacts of permafrost degradation and other climate-related effects on Hg concentrations and body condition of landlocked Arctic char (Salvelinus alpinus), an important sentinel species across the Circum-Arctic. Our objectives were to assess temporal trends in char Hg concentrations and to determine potential mechanisms driving the trends. There was a significant decrease in Hg concentrations in East Lake char, averaging 6.5%/year and 3.8%/year for length-adjusted and age-adjusted means, respectively, from 2008 to 2019. Conversely, in West Lake there was a significant increase, averaging 7.9%/year and 8.0%/year for length-adjusted and age-adjusted mean Hg concentrations, respectively, for 2009 to 2017 (the last year with sufficient sample size). The best predictors of length-adjusted Hg concentrations in West Lake were carbon and nitrogen stable isotope ratios, indicating a shift in diet including possible dietary starvation brought on by the profound increase in lake turbidity. Our study provides an example of how increasing lake turbidity, a likely consequence of climate warming in Arctic lakes, may influence fish condition and Hg concentrations. Environ Toxicol Chem 2023;42:2712-2725. © 2023 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Freshwater diatom evidence for Southern Westerly Wind evolution since ∼18 ka in northwestern Patagonia

We report a fossil diatom record from small closed-basin Lago Lepué (43°S) to examine past changes in freshwater ecosystems and hydrologic balance in northwestern Patagonia since ∼18 ka. The record starts with abundant staurosiroids and the heavily silicified Aulacoseira granulata suggesting deep turbulent mixing during a low lake level stand between ∼18- 16.4 ka. A. distans increased shortly after ∼16.4 ka and achieved maximum abundance between ∼15.4-13.6 ka, while A. granulata disappeared at ∼15.8 ka and A. alpigena rose at ∼14.9 ka to its maximum between ∼13-12 ka. We infer turbulent, cold, and circumneutral to slightly acid lake conditions contemporaneous with a steady lake level rise that started at ∼16.4 ka and culminated between ∼13-12 ka. These trends reversed between ∼11-7.8 ka with the dominance of Discostella stelligera and staurosiroids, suggesting warmer lake conditions and shallower mixing. Subsequent changes include increases of A. distans with D. stelligera between ∼7.8-5.8 ka, dominance of the former between ∼5.8-3.3 ka, a rapid increase in A. perglabra at ∼3.3 ka, and ensuing diversification of benthic acidophilous species. We infer a rapid lake-level decline between ∼11-7.8 ka, with subsequent rising pulses at ∼7.8 ka and ∼5.8 ka, a multimillennial-scale lake acidification trend, and overall high lake levels with centennial-scale reversals between ∼6-0 ka. Coherent variations in terrestrial and aquatic ecosystem changes recorded in the same core suggest negative hydrologic balance between ∼18-16.4 ka and ∼11–7.8 ka, positive balance between ∼14.9-12 ka and ∼6–0 ka, with transitional conditions in the interim, overprinted by millennial-scale changes and enhanced variability since ∼6 ka. Covariation with paleoclimate records at regional, pan-Patagonian, and hemispheric scale suggests millennial to centennial-scale variability superimposed upon a multi-millennial pacing of Southern Westerly Wind evolution since ∼18 ka.

Lake Heatwaves and Cold‐Spells Across Qinghai‐Tibet Plateau Under Climate Change

AbstractLake heatwaves (LHWs) and cold‐spells (LCSs), similar to marine heatwaves and cold‐spells, can have long‐term impacts on lake ecosystems and are vulnerable to climate change. Here we first comparatively assess LHW and LCS changes across the Qinghai‐Tibet Plateau (QTP) using satellite surface water temperature observations in 160 lakes over 1978–2017. Our findings reveal notable differences in the mean and trends of LHW and LCS metrics. Specifically, total days and frequency of LHW have been increasing at a rate of 8.82 ± 1.25 days per decade and 0.78 ± 0.10 counts per decade, respectively. Conversely, total days and frequency of LCS have decreased at −6.52 ± 1.46 days per decade and −0.51 ± 0.01 counts per decade, respectively. However, average duration and mean intensity show no significant difference. Additionally, the average duration of ice cover across the QTP has been decreasing (−2.60 ± 0.38 days per decade) due to the delayed freezing date (1.13 ± 0.18 days per decade) and earlier thawing date (−1.28 ± 0.27 days per decade) during 1978–2017. Furthermore, the annual mean lake surface water temperatures across the QTP exhibit a warming trend (0.00 ∼ 0.47°C per decade) from 1978 to 2017, with faster warming occurring in winter (0.00 ∼ 0.98°C per decade) compared to summer (−0.17 ∼ 0.47°C per decade). Accelerated lake warming will increase the frequency and mean intensity of LHWs while decreasing the number of LCSs. These results help to understand how QTP lakes respond to extreme temperatures under climate change.

Modelling Heat Balance of a Large Lake in Central Tibetan Plateau Incorporating Satellite Observations

The thermodynamics of many lakes around the globe are shifting under a warming climate, affecting nutrients and oxygen transportation within the lake and altering lake biota. However, long-term variation in lake heat and water balance is not well known, particularly for regions like the Tibetan Plateau. This study investigates the long-term (1963–2019) variation in the heat balance of a large lake in the Tibetan Plateau (Nam Co) by combining the strengths of modeling and remote sensing. Remotely sensed lake surface water temperatures from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Along Track Scanning Radiometer Reprocessing for Climate: Lake Surface Water Temperature and Ice Cover (ARC-Lake) are used to calibrate and validate a conceptual model (air2water) and a thermodynamic model (LAKE) for the studied lake, for which in situ observation is limited. The results demonstrate that remotely sensed lake surface water temperature can serve as a valuable surrogate for in situ observations, facilitating effective calibration and validation of lake models. Compared with the MODIS-based lake surface water temperature (LSWT) for the period 2000–2019, the correlation coefficient and root mean square error (RMSE) of the LAKE model are 0.8 and 4.2 °C, respectively, while those of the air2water model are 0.9 and 2.66 °C, respectively. Based on modeling, we found that the water temperature of Nam Co increased significantly (p &lt; 0.05) during the period of 1963–2019, corresponding to a warming climate. The rate of water temperature increase is highest at the surface layer (0.41 °C/10a). This warming trend is more noticeable in June and November. From 1963 to 2019, net radiation flux increased at a rate of 0.5 W/m2/10a. The increase in net radiation is primarily responsible for the warming of the lake water, while its impact on changes in lake evaporation is comparatively minor. The approaches developed in this study demonstrate the flexibility of incorporating remote sensing observations into modeling. The results on long-term changes in heat balance could be valuable for a systematic understanding of lake warming in response to a changing climate in the Tibetan Plateau.

Temperature-mediated microbial carbon utilization in China's lakes.

Microbes play an important role in aquatic carbon cycling but we have a limited understanding of their functional responses to changes in temperature across large geographic areas. Here, we explored how microbial communities utilized different carbon substrates and the underlying ecological mechanisms along a space-for-time substitution temperature gradient of future climate change. The gradient included 47 lakes from five major lake regions in China spanning a difference of nearly 15°C in mean annual temperatures (MAT). Our results indicated that lakes from warmer regions generally had lower values of variables related to carbon concentrations and greater carbon utilization than those from colder regions. The greater utilization of carbon substrates under higher temperatures could be attributed to changes in bacterial community composition, with a greater abundance of Cyanobacteria and Actinobacteriota and less Proteobacteria in warmer lake regions. We also found that the core species in microbial networks changed with increasing temperature, from Hydrogenophaga and Rhodobacteraceae, which inhibited the utilization of amino acids and carbohydrates, to the CL500-29-marine-group, which promoted the utilization of all almost carbon substrates. Overall, our findings suggest that temperature can mediate aquatic carbon utilization by changing the interactions between bacteria and individual carbon substrates, and the discovery of core species that affect carbon utilization provides insight into potential carbon sequestration within inland water bodies under future climate warming.

Interactions between temperature and predation impact insect emergence in alpine lakes

AbstractWhile insect populations are simultaneously threatened by many local‐ and global‐scale stressors, the interacting effects of these factors remain poorly understood. These interactions between stressors, whether additive or antagonistic, may have profound effects on our assumptions about and predictions for any given system. Here we address this gap by exploring the interactive effects of introduced predators and elevated temperatures on emerging aquatic insects across alpine lakes. Using a crossed factorial field survey, we examine whether warmer temperatures either directly affect the magnitude or diversity of insect emergence, or mediate the impacts of predation via interactions with predator presence. Based on data from more than 11,000 insects collected across a two‐year period, we find a 71% reduction in insect emergence associated with an additional 3.6°C of water temperature in oligotrophic alpine lakes. While our work confirms prior findings that predator presence drives strong reductions in insect emergence, we find that the effects of predation are significantly weaker in warmer lakes (2% reduction in warmest lakes studied vs. 75% reduction in coldest). Combining our results with regional studies of predator communities to identify mechanisms suggests that the interaction effects between temperature and predator presence are likely due to changes in predator behavior across temperatures. Critically, to fully understand the multiple stressors that impact insect populations and predict their future effects, we must consider the interactions between stressors across spatial scales.

Insights on Simulating Summer Warming of the Great Lakes: Understanding the Behavior of a Newly Developed Coupled Lake‐Atmosphere Modeling System

AbstractThe Laurentian Great Lakes are the world's largest freshwater system and regulate the climate of the Great Lakes region, which has been increasingly experiencing climatic, hydrological, and ecological changes. An accurate mechanistic representation of the Great Lakes thermal structure in Regional Climate Models (RCMs) is paramount to studying the climate of this region. Currently, RCMs have primarily represented the Great Lakes through coupled one‐dimensional (1D) column lake models; this approach works well for small inland lakes but is unable to resolve the realistic hydrodynamics of the Great Lakes and leads to inaccurate representations of lake surface temperature (LST) that influence regional climate and weather patterns. This work overcomes this limitation by developing a fully two‐way coupled modeling system using the Weather Research and Forecasting model and a three‐dimensional (3D) hydrodynamic model. The coupled model system resolves the interactive physical processes between the atmosphere, lake, and surrounding watersheds; and validated against a range of observational data. The model is then used to investigate the potential impacts of lake‐atmosphere coupling on the simulated summer LST of Lake Superior. By evaluating the difference between our two‐way coupled modeling system and our observation‐driven modeling system, we find that coupled‐lake atmosphere dynamics can lead to a higher LST during June‐September through higher net surface heat flux entering the lake in June and July and a lower net surface heat flux entering the lake in August and September. The unstratified water in June distributes the entering surface heat flux throughout the water column leading to a minor LST increase, while the stratified waters of July create a conducive thermal structure for the water surface to warm rapidly under the higher incoming surface heat flux. This research provides insight into the coupled modeling system behavior, which is critical for enhancing our predictive understanding of the Great Lakes climate system.

Increased importance of cool-water fish at high latitudes emerges from individual-level responses to warming.

High latitude ecosystems are experiencing the most rapid warming on earth, expected to trigger a diverse array of ecological responses. Climate warming affects the ecophysiology of fish, and fish close to the cold end of their thermal distribution are expected to increase somatic growth from increased temperatures and a prolonged growth season, which in turn affects maturation schedules, reproduction, and survival, boosting population growth. Accordingly, fish species living in ecosystems close to their northern range edge should increase in relative abundance and importance, and possibly displace cold-water adapted species. We aim to document whether and how population-level effects of warming are mediated by individual-level responses to increased temperatures, shift community structure, and composition in high latitude ecosystems. We studied 11 cool-water adapted perch populations in communities dominated by cold-water adapted species (whitefish, burbot, and charr) to investigate changes in the relative importance of the cool-water perch during the last 30 years of rapid warming in high latitude lakes. In addition, we studied the individual-level responses to warming to clarify the potential mechanisms underlying the population effects. Our long-term series (1991-2020) reveal a marked increase in numerical importance of the cool-water fish species, perch, in ten out of eleven populations, and in most fish communities perch is now dominant. Moreover, we show that climate warming affects population-level processes via direct and indirect temperature effects on individuals. Specifically, the increase in abundance arises from increased recruitment, faster juvenile growth, and ensuing earlier maturation, all boosted by climate warming. The speed and magnitude of the response to warming in these high latitude fish communities strongly suggest that cold-water fish will be displaced by fish adapted to warmer water. Consequently, management should focus on climate adaptation limiting future introductions and invasions of cool-water fish and mitigating harvesting pressure on cold-water fish.