Invertebrate drift and physico-chemical variables in the tributaries of the Mutt, a Swiss glacial stream

Abstract

The study of the invertebrate assemblages in a small glacial catchment of the Swiss Alps (the Mutt) was designed to categorise sites in relation to their water sources and assess the contribution of small headwater tributaries to the biodiversity of such Alpine catchments. Physico-chemical characteristics and macroinvertebrate drift were monitored in seven streams during three contrasting hydrological periods in June. August and September 1997. Physico-chemical characteristics clearly differentiated kryal (glacial) and krenal (groundwater-fed) streams. The glacial waters showed a broader amplitude in environmental variation, depending on altitude, geology and season. Macroinvertebrate drift composition was significantly correlated with the environmental conditions. In kryal streams, where harsh conditions prevailed, diversity and abundance were low, while the krenal streams showed highly diversified and dense macroinvertebrate communities, favoured by physico-chemical constancy. However, the low number of taxa found at the same time in these groundwater-fed tributaries and in the main Mutt stream indicated a low contribution from these small streams to the communities of the main stream. Nevertheless, the habitat heterogeneity generated by different water origins in the tributaries favoured the coexistence of diversified macroinvertebrate communities in a rather small catchment area. Therefore these tributaries played an important part in the biodiversity of the glacial catchment.