A classification of semi-natural northern prealpine river stretches based on chironomid communities

Orendt Hydrobiologie WaterBioAssessment, Steinstr. 37, 04275 Leipzig, Germany.

Corresponding author: orendt@t-online.de

Abstract

Using cluster analysis, ecological profiles of the species, and the (Diamesinae + Orthocladiinae) / Chironominae ratios, prealpine rivers were classified by their chironomid communities based on 338 species: (1) summer-cold mountain rivers (Isar, Salzach, Inn/Mühldorf), (2) summer-warm moraine-stretches (Würm, Alz/moraine rupture, Amper, Altmühl), (3) the summerwarm lowland river Upper Alz (lake outlet and the stretch to Altenmarkt village), (4) the lower section of the river Inn regulated by dams, which is dominated by a littoral community. The river Upper Alz is faunistically differentiated along it’s course. Classification of river stretches is predominantly explained by rhithral and eurytope species. Potamal and littoral species had no effect on classification. The results suggest that water temperature is the most important factor of the chironomid-based river classification, which is in harmony with studies by Rossaro (1992) and Lindegaard & Brodersen (1995). Locally, other morphological parameters as reach slope and substrate may be important factors as well. However, further data are needed to clarify their role in species distribution.