Lack of oxygen and low pH as limiting factors for Gammarus in Hessian brooks and rivers

During two decades (1968–1988) the occurrence of Gammarus was studied in Hessian running waters draining some 7700 km² of the Fulda-Eder-basin and two adjacent areas. About 1530 sites were sampled, most of them in 1968, 1978, 1981/82 and 1985, which made comparisons possible, primarily with respect to space, but partly also to time. After consideration of the relief of the landscape, geological conditions, and water-quality in the neighbourhood of human settlements, lack of oxygen (due to organic pollution) and low pH (souring) can be recognized as the most important factors which influence and alter natural distribution patterns of Gammarus fossarum, G. pulex and G. roeseli. Both vanishing and recovering populations were observed in the course of twenty years.