Thermal Evidence for Surface and Subsurface Water Contributions to Baseflow in a High Arctic River
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Changes in river temperatures are caused by thermal energy exchanges at the interface between water and the atmosphere and between water, the streambed, and subsurface water. In permafrost regions, deeper active layer formation due to a warming climate can affect ground and channel bed thermal regimes and subsurface flow pathways. The main hypothesis is that within cold region landscapes, stream inflows into rivers provide relatively warm sources of water, while subsurface sources of water such as soil water contribute relatively cold water sources which alter the thermal and isotopic composition of the river, and as such, downstream temperature measurements can identify these sources in space and time. In this study, river water temperature patterns were used as primary indicators of slope water exchanges along the West River at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut, Canada (75º N, 109º W). Water temperature data was collected through detailed longitudinal surveys along the river during the 2014 recession and baseflow periods to locate surface and subsurface lateral inflows. Limited water stable isotope sampling was also undertaken at fixed stations to determine possible mixing from different water sources. Atmospheric factors and channel snow were found to be the main contributors to thermal variance in the river during the 2014 Summer season, with tributary inflow discharge also being a strong factor. The longitudinal temperature profiles indicate clear localized downstream changes in the thermal conditions of the river at multiple locations, and are interpreted to be indicative of subsurface and surface water exchange through inputs of cooler or warmer water. River temperature increased downstream and stable isotopic composition show progressive downstream enrichment in the two study reaches during the majority of the baseflow period, which is indicative of a culmination of localized surface flow inputs along both reaches. These results demonstrate some key processes that influence the thermal regime of a High Arctic river and will contribute to a greater understanding of how surface, subsurface and other water exchanges influence stream hydrology, ecology and biogeochemistry.