Abstract
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 95Β·5 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. Lateβlying snowdrifts were found to influence the ion chemistry in adjacent reaches of the stream channel greatly. As the initial pulse of ionβrich 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 NO$_{3}^{-}$ increased by one to two orders of magnitude, with the largest increase for K^+^, Ca^2+^ and Mg^2+^. This was roughly equivalent to the concentration increase that resulted from percolation of relatively dilute water through 0Β·25 m of unsaturated soil. The Na^+^ and Cl^β^ were the dominant ions in snowmelt water, whereas Ca^2+^ and Mg^2+^ 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 meltβwater concentrations. Three seasonally characteristic hydrochemical regimes were identified in a stream reach adjacent to lateβlying snowdrifts. In the first two stages, the water chemistry in the stream channel strongly resembled the hillslope drainage water. In the third stage, inβstream geochemical processes, including the weathering/ion exchange of Ca^2+^ and Mg^2+^, were the main control of streamwater chemistry. Copyright Β© 2006 John Wiley & Sons, Ltd.