Subsurface water flow pathways in the canadian High Arctic

Abstract

In Arctic regions subsurface flow is often a dominant flow path of water, especially as the thaw depth progresses and the active layer water storage capacity increases. Subsurface flow through the active layer is important for water delivery to streams and can be potentially routed through subsurface preferential flow pathways (PFP). The majority of research on subsurface hydrological PFP has occurred in the subarctic where organic soils and discontinuous permafrost are predominant. Research on such pathways in the High Arctic where mineral soils with minimal organic layer dominate is limited. This thesis investigated the hydrological response during active layer development in a dominantly mineral soil to understand how soil subsurface and surface water interactions are conditioned by the presence and seasonal development of PFP pathways in a headwater subcatchment at the Cape Bounty Arctic Watershed Observatory, Melville Island, Nunavut. Subsurface flow and PFP were examined through cryostructure analysis from two active layer cores, and seasonal active layer development. A network of piezometers was also installed across four land cover types (high and low hummock, mesic slope, polar semi-desert, and an area with established soil pipe drainage) to evaluate hydrological function of preferential pathways. Electrical conductivity (EC) and stable water isotopes were collected from piezometers to further infer subsurface water sources. Results indicate that drainage and saturation of soil from water in the subsurface is spatially and temporally heterogeneous in High Arctic mineral soils. The timing of the activation (effective drainage) and deactivation (termination of drainage) of subsurface water pathways was similarly heterogeneous across the study site. The timing and depth of the activation of pathways demonstrates that varying cryostructure at depth triggered the emergence of substantial water at select locations. Finally stable isotopes indicate that the source of water moving through the subsurface varies spatially and temporally over short distances with seasonal progressions from rain water to snow/ground ice, and vice versa. This knowledge provides primary observations towards understanding subsurface preferential flow pathways in a High Arctic catchment and the importance of PFP on water delivery to streams in the late thaw season.