A new method for assessing the impact of hydromorphological degradation on the macroinvertebrate fauna of five German stream types

We developed a new Multimetric Index for stream assessment, which is mainly focussed on the impact of hydromorphological degradation on the macroinvertebrate fauna. The index was developed for five German stream types, three of which are located in the lowlands of Northern Germany and two in the lower mountainous areas. For each stream type sites representing different stages of hydromorphological degradation were investigated; the macroinvertebrate fauna of each site was sampled two or three times in 2000 (83 sites and 174 samples altogether). In addition, more than 200 parameters describing the hydromorphology of the sites have been recorded. The assessment system was developed separately for each of the stream types. The development process included (1) the generation of a new index ('German Fauna Index'), (2) the selection of faunal metrics, which correlate to hydromorphological degradation and (3) the combination of the selected metrics into a Multimetric Index. To correlate faunal metrics and hydromorphological degradation, a 'Structure Index' describing the alteration of stream morphology was generated. A correlation matrix of the selected metrics and the structure index is presented. The 'German Fauna Index' is based on taxa, which predominantly occur at sites of a certain morphological degradation class. The selection process of taxa included in the new index was in a first step based on data sampled in this study and supplemented by literature data. For one stream type (mid-sized mountain streams) the process of metric selection and validation is described in detail, including a correlation matrix of the metrics and a validation of the metrics with data on additional sampling sites.