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a b s t r a c tSalinisation of running waters is a severe problem in many parts of the world. Monitoring and management of such waters require ecological methods which consider the hydrochemical effects of salinisation on the aquatic communities in order to set targets to protect habitats and biodiversity. Several bioassays have been developed for this purpose and are surveyed here. They are based on the salt sensitivity of the following groups of organisms: diatoms, ciliates and macroinvertebrates. In this paper experiences gained so far are also considered as well as practical applications originating from this research.

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On the basis of investigations of the diatom flora and the Plecoptera, Ephemeroptera and Trichoptera fauna in two mountain brooks with different chemisms the different effects of the regional factors of the water chemism and the extraregional factors, current andt.emperature, on t lie biocoenosis is discussed. The zoocoenotic division of mountain streams is affected by the extra.regiona.1 factors; the structure of the diat,om associations and the distribution of individual species of the insect fauna. are dependent on the regional effect, of the water chemisni. Thecorrelation of the halobic indices as ecological characteristics of the diatom flora with the factors of the wat.er chemisin, pH and alkalinity, and their relationship wit.1~ the distribution ofsome species of the insect fauna suggest t.hat the halobic index is a useful criterion for theecological classification of waters. Also for the judgement of the trophic conditions and thr self-prification

Under the influence of the wastewaters of the potash industry the Werra river shows considerably varying salt contents (0.47 ... 28.2 g/l C1-, annual means 4.4 ... 11.4 g/l C1-) in dependence on the hydrological situation. Between 1982 and 1988 a total of 112 taxa of diatoms were observed. Of special interest is the occurrence of Stauroneis comtricta (EERENBERG) CLEVE, which is new for the river Werra. Its spreading upstream was observed. Compared with earlier findings as well as within each annual cycle there are observed clear changes in the species present and in the colonization structures in dependence on the salt content. The close relations between the salt content and the diatom communities are truly expressed by the index of halobic organisms. Diversity indices of 1.048 ... 3.259 as well as values of 0.074 ... 0.817 for evenness verify the imbalance of the colonization, without, however, revealing a relation to the salt content, except for variations of concentration which may be too sudden. EinleitungDurch die von der Kaliinduetrie veruraachte Verealzung der mittleren und unteren Werra wurden die Konzentrations-und Ionenverhaltniese im Wasser und damit die physiologischen Voraussetzungen fur das Leben der Wasserorganismen total v e r bdert. uber die Entwicklung derversalzung in der Werra und deren Auswjrkungen a d die okologischen Bedingungen im FluDlauf besonders in den letzten drei Jahrzehnten liegen mhlreiche Veroffentlichungen vor (ALBREOHT 1954, S U~Z 1966, V. T~~MPLING;