Seasonal variation of water source and geochemistry in a northwest Iceland watershed
Maki, Christina E.
Source water and flow paths of stream water draining a subarctic catchment in northwestern Iceland were investigated using a multi-tiered, high time-resolution, monitoring program during the spring and summer of 2011. Stream water isotopic and geochemical tracers identified snowmelt as a major control on source water and flow paths for streams in the 102 km2Vatnsdalsvatn catchment. A two end-member mixing model showed an increasing percent contribution of snowmelt-like water corresponding to water originating from the more northerly high-elevation regions. This shift co-occurred with increased subsurface connectivity of highland soils, as the highland snow cover receded. A conceptual model of flow generation was established from these results. Significant temporal chemical flux variations were observed in the stream water, reflective of differing environmental controls. Runoff was the dominant control for solute stream water fluxes of Na, Si, and K, whereas V and Rb were controlled primarily by snowmelt, the release of the soil matrix from snow cover, and the hydrologic connection of the highlands to the river. In contrast, dissolved Al, Ti, Pb, Zn, Mo, and Mn --all weathering products of basalt --remained immobile until a rain event on July 2, 2011 and only then were connected to the fluvial system. Dissolved Ca:Sr molar ratios in stream water further support this analysis, suggesting that reduced snow cover co-occurs with an increased flux of dissolved basalt weathering products. This research shows the conditions under which different hydro geologic sections of the watershed might be contributing materials to Lake Vatnsdalsvatn. Furthermore, the research suggests that during warmer and wetter conditions, the subsurface highland soil water flow paths are more hydrologically connected, whereas cooler, drier years may lead to more persistent snowpack and/or a persistent frost layer in the highlands, acting as a barrier to soil porewater.