Transformations of runoff chemistry in the Arctic tundra, Northwest Territories, Canada

The transformation of snowmelt water chemical composition during melt, elution and runoff in an Arctic tundra basin is investigated. The chemistry of the water flowing along pathways from the surface of melting snow to the 95Ð5 ha basin outlet is related to relevant hydrological processes. In so doing, this paper offers physically based explanations for the transformation of major ion concentrations and loads of runoff water associated with snowmelt and rainfall along hydrological pathways to the stream outlet. Late-lying snowdrifts were found to influence the ion chemistry in adjacent reaches of the stream channel greatly. As the initial pulse of ion-rich melt water drained from the snowdrift and was conveyed through hillslope flowpaths, the concentrations of most ions increased, and the duration of the peak ionic pulse lengthened. Over the first 3 m of overland flow, the concentrations of all ions except for NO3 increased by one to two orders of magnitude, with the largest increase for KC, Ca2C and Mg2C. This was roughly equivalent to the concentration increase that resulted from percolation of relatively dilute water through 0Ð25 m of unsaturated soil. The NaC and Cl were the dominant ions in snowmelt water, whereas Ca2C and Mg2C dominated the hillslope runoff. On slopes below a large melting snowdrift, ion concentrations of melt water flowing in the saturated layer of the soil were very similar to the relatively dilute concentrations found in surface runoff. However, once the snowdrift ablated, ion concentrations of subsurface flow increased above parent melt-water concentrations. Three seasonally characteristic hydrochemical regimes were identified in a stream reach adjacent to late-lying snowdrifts. In the firs