Alpine stream habitat classification: An alternative approach incorporating the role of dynamic water source contribution

We review current understanding of dynamic interactions between environmental variables and stream benthic communities within glacierized alpine catchments to provide a context for the central theme of habitat complexity within alpine streams. We present a conceptual model summarizing the important links between environmental variables, from large-scale (regional/catchment) to stream-reach/patch-scale processes, to illustrate this physical habitat complexity. Existing alpine stream classification and zonation criteria are examined, and the environmental characteristics representative of the different stream classes are identified. The theme of habitat complexity is developed to assess the applicability of traditional (principally temperature-based) alpine stream classifications. These traditional classifications do not take into account spatial and temporal variations in water source contributions to alpine streams unless associated temperature changes occur. However, different hydrological stores and pathways impart other physical and chemical influences upon stream benthic communities that are overlooked by traditional classifications. We propose a new classification system to better describe spatial and temporal variability in glacial, snowmelt, and groundwater inputs to alpine streams, based upon the mix of proportions of water contributed from each of these sources. Field data collected in the French Pyrenees are used to support this new alpine stream classification, which we propose as a tool for further research in alpine river catchments.