Tuesday, May 27, 2008
234

Spatio-temporal effects of experimental floods on benthos, drift and seston below reservoirs

Tobias Buser1, Sabine Mannes1, Christopher T. Robinson1, Dave Kelly2, and Scott Larned3. (1) Department of Aquatic Ecology, Eawag, Ueberlandstrasse 133, 8600 Duebendorf, Switzerland, (2) Department of Conservation, L5, 137 Kilmore Street, PO Box 13049, Christchurch, New Zealand, (3) National Institute of Water and Atmospheric Research, P.O. Box 8602, Christchurch, New Zealand

We examined the spatio-temporal effects of experimental floods on benthos, drift, and seston in rivers below reservoirs. Studies were conducted on the Spöl River, Switzerland and Opuha River, New Zealand. The flood in the Spöl increased discharge 28X, whereas discharge in the Opuha was increased fourfold. The duration of floods ranged from 4 to 8 hours depending on location along each river. Spatially, benthos was sampled from coarse-scale habitats along the Spöl. Drift and seston were sampled during each flood at sites longitudinally placed along each river. Coarse-scale benthic habitats all showed similar high losses of macroinvertebrates and periphyton regardless of location along the river. During each flood, peaks in drift occurred sooner than peaks in seston. All invertebrate taxa showed similar drift patterns during each flood, and drift density increased downstream during each flood. Seston showed two peaks in the Spöl as bed sediments became mobilized during the flood. Drift/seston displayed typical hysteresis curves during each flood. These data suggest that coarse-scale habitats do not provide refugia during large floods. The drift and seston data further indicate that invertebrates respond sooner to changes in flow than benthic sediments and organic matter, suggesting the role of behaviour in organism response to floods.


Web Page: floods, hysteresis, seston

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