Ökologische Bewertung von Tieflandbächen des Ladberger Mühlenbach-Systems im Norddeutschen Tiefland, basierend auf der Standorttypie der Trichopterenbiozönosen

In the last few years ecological evaluation of lowland freshwaters was controversely discussed. Due to the fact that most basic information of assessment systems derived from upland streams, the results could not be applied to the lowland situations. Additionally, it is not sufficient for an integral freshwater evaluation only to focus on the stream to show degradation in the tight coupling of running waters and their adjacent landscape. In this study we critically tested a new method, the Standorttypie-Index (STI), to assess lowland streams using caddis-fly communities.

During 1994 and 1996 we investigated the caddisfly community at 15 sampling sites of a river system in the “Westfälische Tieflandbucht” (Northrhine-Westphalia, Germany). As a result we found 72 species belonging to 16 families of the order Trichoptera. The calculation of the “Standorttypie-Index” is based on four defined ecological categories. Although the definitions were inaccurate, each species was classified into one category. In view of stream regulation and streamwidth, we calculated for all study sites the STI of the immature stages, the adults and a combined total STI.

Although there is a correlation between the “Standorttypie-Index” and the state of degradation of the study sites, the separate analysis of larval and adult communities showed that the results easily lead to misinterpretation. The STI of adults devalues the combined total STI of regulated as well as natural study sites. As a consequence, until now it is not possible to evaluate the state of degradation in the coupling of the stream and the adjacent landscape using the STI of the caddis-fly community.