Salt pollution of the middle and lower sections of the river Werra (Germany) and its impact on benthic macroinvertebrates

In two survey phases (2003 and 2008) organic, nutrient and salt contamination parameters have been investigated in the lower Werra in order to estimate the importance of these different kinds of pollution for the quality component of macroinvertebrates according to the European Water Framework Directive. The chemical and biological investigations have been carried out comparing a “reference” section without salt contamination with the salt contaminated section due to the potash mining industry from Vacha to Hannoversch Münden close to the mouth of the Werra. The results show that the drastic differences between the macroinvertebrate assemblages of the Werra upstream and downstream the salt contaminated sections are clearly caused by the salt load. The other kinds of chemical impacts are not responsible for the observed fundamental change within the composition of the benthic invertebrate assemblage. General degradation of stream morphology, indicated by macroinvertebrates, shows a good ecological status for the non-salt-contaminated part of the river and a bad status for the salt contaminated sites of the lower Werra.