1] Previous studies of river hydrometric records and Indigenous Knowledge holders claim that floodinduced recharge of ecologically important perched basins decreased across the Peace-Athabasca Delta after 1968 due mainly to hydroelectric regulation of Peace River flow. Natural deltaic processes and climate are acknowledged as additional, lesser contributors, but are challenging to evaluate. We use sediment records spanning ∼115 years from nine perched basins across the Athabasca Delta to test if unidirectional drying coincides with river regulation. Results show bi-directional hydrological changes since the early 1980s, not 1968, to reduced flooding in areas east of the Embarras River confluence with Cree/Mamawi creeks and increased flooding northward along the Cree/Mamawi distributary. The timing and pattern pinpoint the 1982 Embarras Breakthrough, a natural avulsion that diverted flow northward and away from the Athabasca Delta terminus, as the principal cause. The results demonstrate the need to factor natural deltaic processes into impending decisions on the delta's UNESCO World Heritage status and implementation of a federal Action Plan to mitigate widespread drying.

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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.