No abstract

Identifying significant changes across lake ecosystems is important for understanding impacts of global environmental change. Synthesizing data on lake warming trends is challenging because individual lake datasets differ in the: (1) length of the time series available for analysis and (2) frequency of data collection (e.g., daily vs. monthly observations). This study aimed to address how dataset length, frequency of data collection, and strength of temperature trends could impact both the accuracy of summer surface‐water temperature trends and their statistical significance. Using Monte Carlo simulations, we found that accuracy in trend estimates and the ability to recover statistically significant trends were both directly related to trend strength, dataset length, and sampling frequency. To consistently retrieve statistically significant trend estimates that deviated < 25% from the true values, 30‐yr datasets with high warming rates (≥ 0.75°C decade−1) were required. These findings have important implications for efforts to analyze lake temperature trends, as the characteristics of many existing datasets fall within a range where our simulations predict low accuracy in trend estimates as well as a low probability of achieving statistical significance. Longer datasets are needed to accurately estimate warming trends and evaluate drivers of lake surface‐temperature changes, highlighting the need to support existing long‐term monitoring projects occurring across the globe, and to encourage updates to remotely sensed lake temperature datasets.

Rising temperatures are leading to permafrost thaw over vast areas of the northern hemisphere. In the Canadian Arctic, permafrost degradation is causing significant changes in surface water quality due to the release of solutes that can alter conductivity, water clarity, and nutrient levels. For this study, we examined how changes in water quality associated with permafrost thaw might impact zooplankton, a group of organisms that play an important role in the food web of Arctic lakes. We conducted a biological and water quality survey of 37 lakes in the Mackenzie Delta region of Canada's Northwest Territories. We then used this data set to develop models linking variation in the abundance, diversity, and evenness of zooplankton communities to physicochemical, biological, and spatial variables. Subsequently, we used these models to predict how zooplankton communities might respond as water quality is altered by permafrost thaw. Our models explained 47%, 68%, and 69% of the variation in zooplankton abundance, diversity, and evenness, respectively. Importantly, the most parsimonious models always included variables affected by permafrost thaw, such as calcium and conductivity. Predictions based on our models suggest significant increases in zooplankton abundance (1.6-3.6 fold) and decreases in diversity (1.2-1.7 fold) and evenness (1.1-1.4 fold) in response to water quality changes associated with permafrost thaw. These changes are in line with those described for significant perturbations such as eutrophication, acidification, and the introduction of exotic species such as the spiny water flea (Bythotrephes). Given their important role in aquatic food webs, we expect these changes in zooplankton communities will have ramifications for organisms at higher (fish) and lower (phytoplankton) trophic positions in Arctic lakes.

Gravel-pit lakes are a common feature of many human-modified landscapes throughout the world. In Canada's north, they are often formed when gravel is extracted to construct dams, bridges, and highways. Past studies suggest that gravel-pit lakes differ from natural lakes in terms of their morphometry, water quality, and biological communities. In this study, we compared gravel-pit and natural lakes by sampling lakes between Inuvik and Fort McPherson in the Northwest Territories. We collected lake morphometry, water quality, and biological data (zooplankton, macroinvertebrates, and fish presence) from six gravel-pit lakes and fifteen natural lakes. In comparison to natural lakes, gravelpit lakes were four times deeper, two times clearer, and five times smaller in their surface area. In addition, important nutrients, including phosphorus and nitrogen, were significantly lower in gravelpit lakes. Despite the differences in morphometry and nutrients, pelagic zooplankton and littoral macroinvertebrate communities did not differ significantly between the two lake types. Therefore, we conclude that despite their recent formation and unnatural morphometry, gravel-pit lakes along the Dempster Highway can support invertebrate communities typical of natural lakes in the region.

Rapid environmental change occurring in northern permafrost regions may have profound implications for fish biodiversity but remains poorly understood. Climate change, increasing human development, and resultant permafrost thaw may combine to alter the quality and quantity of fish habitat including reductions in preferred thermal habitat, changes in water quality, and modified drainage patterns. Our study objective was to understand how lake fish communities residing on permafrost landscapes may be responding to climate change and land use disturbance. We investigated the drivers of freshwater fish community health in lakes of the lower Mackenzie River basin, an ice‐rich permafrost region that is experiencing substantial warming, permafrost thaw, and new major highway development. We collected lake morphometry, water quality, and fish community data from 50 lakes and derived several indicators of aquatic health including fish species richness, relative abundance, and the occurrence of three culturally important fish species. We found that water quality and lake size were significant co‐drivers of fish community health whereas relationships with summer thermal habitat, as represented by July air temperature, were relatively negligible. Dissolved organic carbon (an indicator for lake browning) emerged as a particularly important driver of fish community structure, and fish community health steeply declined when dissolved organic carbon concentrations exceeded 17–18 mg/L. We suggest potential mechanisms for these declines including light inhibition during summer and a reduced capacity for overwintering in smaller and murkier lakes that may experience faster oxygen depletion rates. Using a more expansive regional water quality database of 203 lakes, we observed potential supporting evidence that warming and new road development increased dissolved organic carbon and total phosphorus concentrations, possibly reducing fish habitat quality in this region. Together, these results highlight how fishes relying on the numerous small and shallow lakes that dominate permafrost landscapes may be vulnerable to the combined effects of rapid warming and new infrastructure.