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Effects of riparian vegetation to mitigate water temperature effects on benthic invertebrates and fish shown at the rivers Lafnitz and Pinka

Melcher, A., Dossi, F., Graf, W., Pletterbauer, F., Schaufler, K., Kalny, G., Rauch, H. P., Formayer, H., Trimmel, H., Weihs, P.
Österr Wasser- und Abfallw 2016 v.68 no.7-8 pp. 308-323
aquatic habitat, biocenosis, climate, climate change, habitat preferences, heat, invertebrates, riparian vegetation, rivers, shade, species diversity, summer, trout, water temperature, Austria
This study is based on the results of the transdisciplinary research project BIO_CLIC. The aim of this study was (1) to synthesize and reflect the scientific knowledge, (2) to understand the potential of riparian vegetation on water temperature and (3) to ameliorate the impacts on the aquatic habitats of benthic invertebrates and fish at the rivers Lafnitz and Pinka. These objectives had been achieved by detailed field investigations, the assessment of abiotic environmental parameters (water temperature, riparian vegetation, shading and morphology), the comparison of effects of dynamic processes (incl. water temperature, riparian vegetation, change of river morphology) and biotic habitat use of benthic invertebrates and fish assemblages. The results provide an environmental and biological overview of potential local impacts on water temperature during heat wave periods and additionally taking into account diverse climate scenarios. Three hotspots at each river were selected to characterize specific river types with respect to river morphology, riparian vegetation, thermal regime, as well as the biocoenosis of fish and benthic invertebrates. The temperature regime influences all life stages of fish species and benthic invertebrates. They prefer different temperature regimes along a river continuum that correspond with typical species assemblages. Our evaluation of water temperatures for longitudinal biozenotic zones showed significant differences for shaded and unshaded river reaches. The river type specific mean water temperature for trout and grayling zone in summer is between 11 °C and 16 °C and for barbel and nase above 16 °C. Temperature changes of 2 °C lead to a shift of species composition preferring „warm-water“ species. River reaches with functioning riparian vegetation are able to mitigate these effects of extreme water temperature increase.Different riparian vegetation scenarios at six hot spots, representing a different water temperature patterns, explain shading effects on benthic invertebrates and fish species assemblages. We used these scenarios to develop a synthesis for river type specific management which can support a more grounded and practical grasp of future climate change impacts in theory and practice. This synthesis fills a gap from scientific assessment to practice and summarizes the results from different areas of expertise as a fact sheet with recommendations.