This thesis investigated the zoobenthos in a stream ecosystem of a glacial flood plain (Val Roseg, Swiss Alps). The Roseg River drains a catchment area of 66.5 km2, of which 30% is covered by glaciers. Five distinct reaches characterize the Roseg River: an unstable braided proglacial reach below Tschierva glacier, a lake outlet stream below proglacial Lake Roseg, a single thread channel incised in glacial till, the main glacial flood plain with 6 distinct channel types, and a canyon-constrained reach.
Longitudinal response patterns of benthic macroinvertebrate assemblages were clearly related to environmental gradients in the main glacial channel. Furthermore, seasonal shifts in sources and pathways of water (i.e., extent of glacial influence) strongly influenced zoobenthic distributions. During periods of favorable environmental conditions (spring and late autumn/early winter) invertebrate density and taxon richness peaked. In contrast to the kryal stream, the adjacent outlet stream of proglacial Lake Roseg differed substantially in taxonomic composition. Whereas Chironomidae (i.e., > 95% Diamesa spp.) dominated the kryal stream, Ephemeroptera, Plecoptera and Trichoptera were abundant in the lake outlet. Assemblage differences were attributable to differences in temperature, substrate stability, turbidity, and flow regime.
Seasonal changes in the balance between glacial meltwater and groundwater contributions resulted in shifting patterns of connectivity and spatial heterogeneity in the main glacial flood plain and were linked to variations in ecosystem size (i.e., seasonal changes in the length of floodplain channels). The complex interplay of these factors sets the habitat templet for the community structure in each habitat type in the glacial flood plain of Val Roseg. Furthermore, spatial heterogeneity reduced the negative effects of summer high flows (e.g., high turbidity, unstable substrates) by providing numerous refugia for the biota, thus enhancing overall ecosystem stability and biodiversity.
Finally, the feeding behavior of the limnephilid caddisfly Acrophylax zerberus, a common species in glacial flood plains, was investigated. Stable isotope analyses and food preference experiments were indicative of a generalist feeding strategy by A. zerberus, suggesting that plasticity in life history traits (e.g., feeding behavior) may play an important role in sustaining aquatic insect populations in alpine glacial streams.