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Ecological degradation of a meandering river by local channelization effects: a case study in an Austrian lowland river

Graf, W., Leitner, P., Hanetseder, I., Ittner, L. D., Dossi, F., Hauer, C.
Hydrobiologia 2016 v.772 no.1 pp. 145-160
Chironomidae, Ephemeroptera, Plecoptera, Trichoptera, anthropogenic activities, aquatic organisms, biodiversity, biomass, case studies, channelization, environmental degradation, lotic systems, macroinvertebrates, microhabitats, risk, rivers, sediment traps, sediments, watersheds, Austria
Anthropogenically induced siltation has serious effects on micro-habitat diversity and thus on aquatic organisms in lotic systems. The present study deals with the impact of siltation on the macroinvertebrate community in the River Lafnitz, south-eastern Austria. Our aim was to examine various ecological parameters in a meandering river stretch. The results significantly show (1) a generally lower taxa diversity, (2) a dominance of tolerant taxa such as Chironomidae and a clear reduction of sensitive taxa such as Ephemeroptera, Plecoptera, Trichoptera (EPT-taxa) and (3) overall lower abundances and biomass in sandy fractions. The present case study highlights various processes of fine sediment sources and sinks. While in most cases, fine sediment input is locally caused by erosion of adjacent terrestrial areas, even small-scale channelization of meandering rivers leads to subsequent trapping of huge sandy fractions especially in morphologically natural river sections. This inconspicuous but steady process is a risk to biodiversity and masks serious ecological degradation. Suitable management and restoration measures for anthropogenically silted rivers are therefore strongly recommendable. In summary, the study underlines the sensitivity of meandering systems and its dependence on catchment scale degradation and questions the reversibility of human impacts.