RELATIONS BETWEEN THE MICROSCALE RIVERBED MORPHOLOGY AND THE MACROZOOBENTHOS - IMPLICATIONS FOR THE ECOLOGICAL QUALITY ASSESSMENT AND THE DEFINITION OF REFERENCE CONDITIONS

摘要

European rivers have been constantly affected by anthropogenic impairments throughout the course of human history. Since 2000 the European Water Framework Directive (WFD) accelerated the process of recognizing and reclaiming rivers as valuable ecosystems, and the restoration of river stretches has become an essential tool for the improvement of watercourses in Central Europe. These restoration measures need to be complemented by in-depth scientific evaluations to ensure the cost-effectiveness of the extensive rehabilitation programme. In this study, two restored river stretches in the middle reaches of the River Lahn (Germany) were analysed in great detail between 2006 and 2008, with a special focus on the macrozoobenthos (MZB) and the small-scale riverbed morphology. The MZB is one of four quality components used for the evaluation of rivers within the WFD and despite the more than a century-long history of limnological research focused on benthic invertebrates, the central question of which morphological processes and structures have to be improved in order to reach the 'good ecological status' is still largely unanswered as detailed research of the faunistic-morphological connections on the micro scale (choriotopes) is still few and far between. Both areas - the MZB and the hydromorphology - were covered in an extensive field work programme. The riverbed was mapped using the TRiSHa method ('Typology of Riverbed Structures and Habitats') and a detailed survey of the MZB (165 samples) was carried out in accordance with the PERLODES method. Both data sets were analysed for their spatial diversity and for their interrelations. Furthermore the 'ecological status' was assessed in accordance with the WFD. This evaluation revealed gaps in the German river typology and the assessment method that should ignite a broader scientific discussion about the benefits of nationwide unified evaluation methods versus regionalized approaches.