Hydrochemical and sedimentary responses of paired High Arctic watersheds to unusual climate and permafrost disturbance, Cape Bounty, Melville Island, Canada

摘要

High Arctic river responses to changing hydroclimatic and landscape processes are poorly understood. In non-glacierized basins,nsnowmelt and rainfall generate river discharge, which provides first order control over fluxes. Further factors include thenseasonality of precipitation, seasonal active layer development, and permafrost disturbance. These controls were evaluated innterms of sedimentary and biogeochemical fluxes from paired catchments at Cape Bounty, Melville Island, Nunavut during 2006–n2009. Results indicate that the source of runoff can be more important than the amount of runoff for sediment, solutes, andnorganic yields. Although the snowmelt period is typically the most important time for these yields, heavy late summernprecipitation events can create disproportionately large yields. Rainfall increases yields because it hydrologically connects areasnotherwise isolated. Inorganic solute yields from late summer rainfall are higher because the thick active layer maximizesnhydrologic interactions with mineral soils and generates high solute concentrations. Results also indicate that while thencatchments are broadly similar, subtle topographic differences result in important inter-catchment differences in runoff andnsuspended and dissolved loads. The East watershed, which had less extensive permafrost disturbance, consistently had highernconcentrations of dissolved solids. These higher dissolved fluxes cannot therefore be explained by thermokarst features, butnrather by deeper active layer development, due to a greater proportion of south-facing slopes. Although warm temperatures inn2007 led to extensive active layer disturbance in the West watershed, because the disturbances were largely hydrologicallyndisconnected, the total disturbed area was small, and inter-annual variability in discharge was high, there was no detectablenresponse in dissolved loads to disturbances. Sediment availability increased after 2007, but yields have largely returned to predisturbancenlevels. Results indicate that seasonality and frequency-magnitude characteristics of projected increases innprecipitation must be considered along with active layer changes to predict the fluvial sedimentary and biogeochemical responsento regional climate change