ROLES OF GROUNDWATER/SURFACE WATER EXCHANGES IN ARCTIC STREAM AND RIVER TEMPERATURE (Invited Presentation)

Many questions exist regarding potential changes in river thermal regimes and habitat loss due to a changing climate and the associated hydrologic variability. In the context of Arctic basins, heat transfer mechanisms that currently control river temperatures are just beginning to be quantified and the role of groundwater/surface water exchanges is relatively unknown. In a headwater beaded tributary that is made up of a series of pools and chutes, conductive heat exchange with underlying frozen soils and cold groundwater inflows are important in maintaining thermally stratified conditions that are prevalent under low flows. Under high flows pools become isothermal, and groundwater thermal influences become muted due to increased mixing and lower residence times. In contrast, in a nearby higher order river, the bulk lateral inflows (combined tributary and groundwater inflows) from the basin are key to accurate river temperature predictions during higher flows. Under lower flows, however, lateral inflows are limited and the influence of hillslope drainage on river temperature is significantly decreased. Regardless, temperature predictions that account for surface heat fluxes and bed conduction under low flows are poor. This has led to the refinement of channel hydraulics due to the highly dynamic nature of stream flow and investigation of additional important heat fluxes. An accurate representation of channel geometry extracted from high resolution imagery still produces relatively poor predictions due to an unexpected temperature buffering during the lowest flow conditions. By incorporating advective exchanges with the river bed, preliminary results suggest that groundwater/surface water exchanges provide the heat sink necessary to maintain the stream temperatures during lower flows. Overall, we have found the role of groundwater/surface water exchanges to be critical in maintaining current thermal regimes for both headwater and higher order Arctic watersheds. These results further emphasize the need to understand connections between possible hydrologic changes, deeper thaw within basins, water temperature, and fish habitat in a changing climate.