| Summary: | The influence of artificial stream bottom siltation on the may fly biocenosis in the Breitenbach stream, near Schlitz, West Germany, was studied in an in situ experiment. In an artificially-silted emergence trap, numbers of Baetis vernus and Baetis rhodani fell to 16 % and 1 %, respectively of numbers in non-silted conditions. There were marked increases of specimen numbers, however, in the case of Paraleptophlebia submarginata, Centroptilum luteolum, and Habrophlebia lauta in silted conditions. There were interspecific differences in behaviour on individual sediment fractions. Overall, biomass in the silted area was only 8-50% of that in the control area.
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