Evidence of a change in water chemistry in Canada's subarctic associated with enhanced winter streamflow

Enhanced winter streamflow is a characteristic of a nival/pluvial regime that has emerged in parts of the subarctic Canadian Shield because of increasingly common late summer rains. This phenomenon is part of a widespread trend toward higher winter streamflow in watersheds across the circumpolar north. There may be implications for biogeochemical systems as streamflow regimes undergo these types of changes associated with climate warming. Streamflow and geochemical fluxes were observed over 2years with different winter flow conditions in a subarctic Canadian Shield catchment. Results show that higher wintertime loads of carbon and solutes associated with enhanced winter streamflow were in association with an expansion of contributing areas to run off over what would have existed during typical winter recession. Furthermore, the wet fall conditions that lead to enhanced winter streamflow require water tables close to the topographic surface in highly conductive organic soil layers, which is a similar to the condition during the spring melt. Fall rainfall-runoff leaves an ample volume of water in the lakes that are ubiquitous in this landscape. This water maintains winter streamflow during a time when it traditionally would have ceased. A slowing of biological activity under lake ice increases net mineralization and nitrification rates. This convergence of nitrogen cycling and winter streamflow produced a disproportionate flux of inorganic nitrogen from the study catchment. A conceptual model of how enhanced winter streamflow changes water chemistry in a lake-dominated shield landscape is proposed and may be used as a benchmark to guide hypotheses of process interactions, change in other landscapes, or across scales.