Auswirkungen von Niedrigwasserphasen auf benthische Lebensgemeinschaften kleiner Fließgewässer im Einzugsgebiet der Salza

Manfred Frühauf
Gerd Schmidt
Andreas Bergmann
Duration: 2011-2011

Benthic communities are used as indicators for assessing the ecological quality of surface water bodies according to the EU WFD. They have specific habitat requirements and react sensitively to changes in the hydrological, hydrochemical and ecomorphological situation of the water bodies. For this purpose, various small watercourses in the upper reaches (Dippelsbach, Querne, Kriebuschbach) of the Salza catchment area are being studied, depending on the landscape and conditions of use. The Central German Dryland is characterised by average annual precipitation below 500 mm and a tense climatic water balance. This leads to high runoff dynamics with short-term event-related runoff peaks and pronounced phases of low water flow. For the small watercourses in the catchment area of the Salza, such extreme flood discharges and long low-flow phases are characteristic. After German reunification, a large number of measures (centralisation of drinking water supply and wastewater disposal, increasing land sealing) were implemented in the area, which further exacerbate this situation. This is evident, among other things, in the slight trend of falling MQ, based on the long measurement series of the gauges Stedten (Weida), Unterrißdorf (Böse Sieben) and Zappendorf (Salza). From these already known relationships, the question arises as to how the changing hydrological conditions are presented in a spatially differentiated manner and how they affect the benthic communities in the flowing waters of this water-balanced area. The aim is to exclude possible toxic loads and salt influences in order to be able to delimit the hydrological influences. This question is important not only for the study area but also for other rivers in Saxony-Anhalt that frequently have low water levels. It touches on problems of implementing the EU WFD (a “good ecological status” is to be achieved in surface waters) as well as the Habitats Directive, since the conservation status of habitats of Annex I or of populations of species of Annexes II, IV and V may be affected.