LAKE-GROUNDWATER-CHANNEL CONNECTIVITY AND DISCHARGE IN ARCTIC DELTAS

Lakes in arctic deltas moderate fresh river discharge to the Arctic Ocean, capturing spring floodwaters and solutes and releasing them throughout the summer and fall. These lakes are integral to biogeochemical cycling in arctic deltas, serving as hotspots for nutrient and carbon processing especially during the 24-hour solar irradiance of arctic summers. However, remote sensing studies have shown arctic lakes are shrinking over seasonal and annual time scales with potential impacts on the ability of lakes to mitigate downstream flooding and solute loads. As the Arctic warms, lake waters transfer more heat to the aquifer and thaw underlying permafrost resulting in talik formation and growth beneath arctic lakes. The decrease of arctic lake volume and surface area has been hypothesized to result from the increased lake-channel connectivity associated with this talik growth.

To test this hypothesis and develop a mechanistic understanding of the relationship between lake-channel proximity, subsequent heat transfer and talik development, and increased groundwater connectivity, we constructed numerical freeze-thaw fluid and heat flow models. Results suggest lakes closest to the channel develop far greater lake-channel connection because of positive feedback wherein development of through taliks leads to increased flow and heat transfer to the aquifer and in turn to increased permafrost thaw. Lakes further from the channel remain isolated. These findings yield insight into the controls on thermokarst lake persistence, permit insight into the evolving role of lakes for moderating the timing of floodwaters and solutes within arctic deltas and serve provide managers with information to better understand how flood timing and magnitudes may change as the Arctic warms.