Hydroecological response of alpine streams to dynamic water source contributions
Hydroecological relationships in alpine catchments are poorly understood. Glacial icemelt, snowmelt and groundwater sources each produce a distinctive suite of physico-chemical stream habitat characteristics in alpine streams. These spatially and temporally dynamic habitat conditions influence stream benthic community composition. An interdisciplinary approach (hydrology-hydrochemistry-ecology) was adopted to examine hydroecological responses to dynamic alpine water source contributions, involving development and testing of a new conceptual model of alpine stream habitat classification. Fieldwork was undertaken over two summer melt seasons (2002 and 2003) within the Taillon-Gabiétous catchment, French Pyrénées. Hydrochemical separation methods demonstrated differences in meltwater and groundwater contributions to streamflow both spatially and at diurnal, seasonal and inter-annual time-scales. Suspended sediment concentration was lowest when groundwater contributions to streamflow were dominant. Water column temperatures were lowest where snow and ice meltwaters dominated streamflow. Higher Si, Ca\(^2\)\(^+\) and HCO\(_3\)\(^-\) concentrations were found in groundwater sources. Benthic macroinvertebrate communities varied markedly throughout the summer melt season. Total macroinvertebrate abundance, number of macroinvertebrate taxa, number of EPT taxa, and community stability and persistence were higher when groundwater contributions dominated streamflow. Most taxa showed positive relationships with the proportion of groundwater but Rhyacophila were absent where the proportion was >0.5. Hydroecological patterns and processes in this alpine catchment are summarized in conceptual models to present key findings, and as a template for hydroecological research in other alpine glacierized basins.