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Zusammenfassung:
Substrate type and substrate distribution are major factors influencing distribution, quality, and quantity of benthos organisms. To compare the fauna on the normal heterogenous substrate of Breitenbach (Germany), a layer of fine sand was made deposit by reducing stream velocity on a study stretch. Emerging insects were collected with the greenhouse method. Species present were the same in both cases. On the sandy stretches number of specimens decreased for more than 90% in Ephemeroptera, 30% in Plecoptera, 55% in Trichoptera and about the same in Diptera. Although total numbers strongly decreased, individual species increased by 190% (Leuctra nigra ) or even 1000% (Centroptilum lutelum ), as compared to the control.
