FRESHWATER MICROBIAL COMMUNITY DIVERSITY IN A RAPIDLY CHANGING HIGH ARCTIC WATERSHED. High Arctic freshwater microbial communities

Current models predict increases in High Arctic temperatures and precipitation that will have profound impacts on the Arctic hydrological cycle, including enhanced glacial melt and permafrost thaw. However, it remains uncertain how these changes will impact the structure of downstream resident freshwater microbial communities and ensuing microbially driven freshwater ecosystem services. Using the Lake Hazen watershed (Nunavut, Canada; 82°N, 71°W) as a sentinel system, we related microbial community composition, characterized with 16S rRNA gene sequencing, to physicochemical parameters (e.g., temperature, dissolved oxygen, nutrients, major ions) over a complete annual hydrological cycle in three freshwater compartments within the Lake Hazen watershed: 1) glacial rivers; 2) permafrost thaw streams and the waterbodies they drain into, including small lakes and wetland areas, and; 3) Lake Hazen into which the glacial rivers and thaw streams drain. Microbial communities throughout these freshwater compartments were highly interconnected and often shaped by the availability of melt-sourced chemicals (e.g., dissolved inorganic carbon and sulfate) as the melt season progressed. Within Lake Hazen itself, water column microbial profiles were generally stable over a spring and summer season, indicating that microbial communities and the potential ecosystem services they provide therein may be resilient to environmental change. This work helps establish a baseline understanding of how microbial communities and the ecosystem services they provide in Arctic watersheds might respond to future climate change. This in turn will give insight into how local and even global freshwater ecosystem services might be affected under the current climate change regime.