Importance of Riparian Forests in Urban Catchments Contingent on Sediment and Hydrologic Regimes |
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| Authors: | Allison H Roy Mary C Freeman Byron J Freeman Seth J Wenger William E Ensign Judith L Meyer |
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| Institution: | (1) Institute of Ecology, University of Georgia, Athens, Georgia 30602, USA;(2) US Geological Survey, Patuxent Wildlife Research Center, University of Georgia, Athens, Georgia 30602, USA;(3) Institute of Ecology and Georgia Museum of Natural History, University of Georgia, Athens, Georgia 30602, USA;(4) Institute of Ecology, University of Georgia, Athens, Georgia 30602, USA;(5) Department of Biological and Physical Sciences, Kennesaw State University, Kennesaw, Georgia 30144, USA;(6) US Environmental Protection Agency, 26 West Martin Luther King Drive, Cincinnati, OH 45268, USA |
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| Abstract: | Forested riparian corridors are thought to minimize impacts of landscape disturbance on stream ecosystems; yet, the effectiveness
of streamside forests in mitigating disturbance in urbanizing catchments is unknown. We expected that riparian forests would
provide minimal benefits for fish assemblages in streams that are highly impaired by sediment or hydrologic alteration. We
tested this hypothesis in 30 small streams along a gradient of urban disturbance (1–65% urban land cover). Species expected
to be sensitive to disturbance (i.e., fluvial specialists and “sensitive” species that respond negatively to urbanization)
were best predicted by models including percent forest cover in the riparian corridor and a principal components axis describing
sediment disturbance. Only sites with coarse bed sediment and low bed mobility (vs. sites with high amounts of fine sediment)
had increased richness and abundances of sensitive species with higher percent riparian forests, supporting our hypothesis
that response to riparian forests is contingent on the sediment regime. Abundances of Etheostoma scotti, the federally threatened Cherokee darter, were best predicted by models with single variables representing stormflow (r2 = 0.34) and sediment (r2 = 0.23) conditions. Lentic-tolerant species richness and abundance responded only to a variable representing prolonged duration
of low-flow conditions. For these species, hydrologic alteration overwhelmed any influence of riparian forests on stream biota.
These results suggest that, at a minimum, catchment management strategies must simultaneously address hydrologic, sediment,
and riparian disturbance in order to protect all aspects of fish assemblage integrity. |
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| Keywords: | Fish assemblage Urbanization Sedimentation Hydrologic alteration Riparian buffers Watershed management |
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