Channel-Lake Connectivity in Arctic Deltas

Arctic deltas (ADs) are ecogeomorphologically complex systems that are at risk due to climate and human forcings, e.g. warming temperatures and permafrost thaw. This will have impacts on natural and human systems since ADs have stores of permafrost carbon on the order of 90 Pg carbon, which can be mobilized into the atmosphere and ocean. Arctic lakes are estimated to be the source of two-thirds of the natural methane emissions in the Arctic and increasing methane emissions are predicted due to permafrost thaw. The potential climate change impacts and incomplete process knowledge in ADs behoove further study. For instance, observational studies and numerical experiments have indicated higher permafrost thaw rates in the presence of suprapermafrost and subpermafrost aquifers due to increased heat advection from liquid water. Here, we hypothesize that delta channel networks also contribute to more rapid permafrost thaw from this same mechanism, and that this leads to increased subsurface connectivity between the channel network and lakes located close to the channel network. We test this hypothesis by analyzing the lake drainage rates in ADs as a function of their proximity to the channel network during the active season (June - August) from 2000 to 2015 in the Yukon and Colville deltas in Alaska. We used python-based RivGraph for delta channel network extraction and for channel-lake distance computation. We controlled for interannual variability in the total seasonal streamflow and associated flooding over the delta top. We find that there are faster drainage rates of surface water with smaller distances from the channel network, indicating a higher degree of subsurface connectivity near the channel network, and supporting our hypothesis. Further analysis of connectivity in the delta will help uncover dynamical processes and predict critical transition points, which can nonlinearly accelerate permafrost thaw under climate change with unexpected consequences for the hydrology, ecology, and geomorphology of ADs.