Spatiotemporal dynamics of a regulated alpine river ecosystem

The contributions of glacier-melt, snowmelt, and groundwater to stream flow in alpine catchments result in characteristic discharge regimes and unique stream habitats. The year round dynamics of alpine floodplain ecosystems are however, poorly understood, in particular the effects of flow regulation on alpine stream ecosystems have not been assessed. Fieldwork was undertaken over two summer melt-seasons (2008/2009) and the intervening winter season within the Eisboden catchment, Austrian Alps. The application of a novel diurnal statistical hydrograph classification technique to analyse flow dynamics at six stream sites elucidated the varying influences of precipitation, ablation, and groundwater contributions on spatiotemporal flow dynamics. Although a clear ablation driven seasonal progression in river flow was evident, rainfall also exerted a dominant influence altering the melt-signal during both summer seasons. Water temperature time series, monitored at 23 sites across the catchment revealed year-round spatiotemporal variability in flow permanency, and high thermal heterogeneity, amongst streams. Benthic macroinvertebrate communities were found to be associated predominately with variations in stream temperature and channel stability during the summer melt-season. However, the communities of mixed water source floodplain sites were found to be highly dynamic and considerably more diverse than expected with respect to existing conceptual models of alpine streams. Macroinvertebrate community structure differed markedly during the winter; the assemblage diversified at glacial-fed and mixed sites both in terms of taxonomic and functional diversity. Anthropogenic flow regulation from the Weiβsee hydropower storage reservoir had a large impact on the discharge and thermal regimes of streams but the macroinvertebrate community was relatively resistant in flow regulation disturbances. This finding suggests alpine stream macroinvertebrates inhabiting proglacial river systems are well adapted to the harsh and dynamic physicochemical conditions. Current hydrological and ecological conceptual models of alpine stream systems are evaluated with respect to new insights from the Eisboden and future research directions suggested.