A Hydrogeomorphological framework for the ecology of alpine proglacial rivers

1. This paper presents a framework for the analysis of glacial stream ecosystems based upon the hierarchy of physical processes that operate over timescales varying from diel to millennial. Linked conceptual models propose interrelationships between climate, hydrology and fluvial geomorphology in alpine catchments. 2. These conceptual models are illustrated using data from the Taillon/Gabietous catchment, French Pyrenees. Secondary sources provide information concerning the longterm sequence of climatic and geomorphological controls on contemporary catchment processes. Detailed hydrogeomorphological field data collected over three consecutive summer melt seasons (1995-97) permit identification of marked changes in shorter-term (diel, seasonal and inter-annual) physical processes. 3. Clear differences in the response of water quality and quantity variables were observed between years as climatic conditions varied. In two of the three study years, a precipitation-driven regime was imposed upon the typical ablation-driven river discharge pattern in alpine streams. Clear changes in water quality and quantity were evident with increasing distance from the glacier: (i) discharge increased although specific discharge decreased markedly, (ii) the mean and variability in water temperature increased, and (iii) base concentrations of suspended solids decreased. 4. The physical processes incorporated in the conceptual models presented in this paper have ecological implications because they underpin a nested suite of disturbance regimes operating over timescales from diel to millennial.