Macroinvertebrate communities in streams in the Himalaya, Nepal

Abstract

SUMMARY Macroinvertebrates were sampled in the riffles of fifty‐eight streams from three regions of the Himalaya (Anapurna, Langtang and Everest) in Nepal. A semi‐quantitative method with identification to family level was used to describe communities on‐site. Stream physicochemistry was assessed and the community structure of macroinvertebrates was related to chemistry, physiography (substratum composition, altitude and size), geographical location and the dominant land use in each catchment (terraced agriculture, forest or scrub). Community data were analysed by ordination (DECORANA) and classification (TWINSPAN). The concentration of cations in stream water decreased significantly with altitude. Chemistry also differed between regions; sites from Anapurna had a higher pH and conductivity than those in the other two areas. Communities were dominated by aquatic insect larvae, with Ephemeroptera, in particular the Baetidae, most numerous across sites. There were, nevertheless, differences in community structure between sites, which were related closely to stream physicochemistry. Ordination scores were strongly correlated with altitude, magnesium concentration and substratum composition. Classification was also linked to altitude and chemistry, differentiating high‐altitude sites with low silica concentrations from others. Sites from the Anapurna and Everest regions, with their contrasting chemistry, were also separated. Community structure was also related to land use: streams draining catchments dominated by terraced agriculture had different communities from those in scrub or forest. This result was confounded, however, by the strong relationship between land use, altitude and chemistry; sites in terracing were at lower altitude, had higher concentrations of silica and a higher proportion of fine sediments than those in the other land‐use types. Overall, our data indicate that natural features of the relief and geology in the Himalaya create strong gradients in their invertebrate faunas, but that activities of man may have an effect on stream structure and ecology through catchment management.