Identification of rivers with high and good habitat quality: methodological approach and applications in Austria

The investigation of the 52 largest Austrian rivers with catchment areas > 500 km(2) (Danube River excluded) provides a national estimate of the ecolo gical status of Austria's rivers and an example of the current status of Eu ropean alpine rivers. Emphasis is placed on evaluation criteria, such as mo rphological character, instream structures, longitudinal river corridor, la teral connectivity and hydrological regime compared with original condition s. This assessment and evaluation of nearly 5000 river kilometers identifie s the remaining river stretches with high habitat quality as well as those stretches that have been altered by systematic channelisation or hydropower development. Altogether, about 80% (3900 km) of the stretches in Austria's 'larger' rivers are moderately to heavily impacted by human activity and t hus no longer correspond to their original channel form and dynamics. Impou ndment, water diversion and hydropeaking each impact the hydrology of appro ximately 20% of the above stretches. Only about 20% of all investigated riv er stretches can still be classified as having high or good habitat quality and as retaining essentially natural functions. Using natural conditions a s a reference, the most severe losses have occurred in reaches that were or iginally braided or meandering. Analysing the amount of unaltered river str etches according to biocoenotic regions, 37% (523 km) of the originally rhi thral (trout) region (1416 km) and 18% (480 km) of the originally hyporhith ral (grayling) region (2739 km) remain today in high or good habitat qualit y. Only a few intact river stretches (totaling 43 km) can be found along fo rmerly potamal river reaches (731 km). These data underline the rarity and, therefore, national importance of the remaining unspoiled aquatic habitats . The results presented here form a basis for water resource management and nature conservation strategies, as well as for restoration programs. In pa rticular, these investigations help to fulfill the requirements of the EU-W ater Framework Directive by assisting to delineate and characterise referen ce sites of different river types.