TA1 Developing Suspended and Bedded Sediments Criteria
256 Portland Ballroom
8:00 AM - 12:00 PM, Tuesday
() Predicting bedload and suspended sediment export in low-order Lake Superior watersheds.
Taylor, D1, Elonen, C1, Jicha, T1, Anderson, L1, 1 U.S. Environmental Protection Agency, Mid-Continent Ecology Division, Duluth, MN, USA
ABSTRACT- To evaluate the results of human activities on sediment export, it is necessary to divide natural inter-site variation from any differences caused by anthropogenic influences. The Rosgen hierarchical stream type classification system is an integrator of stream geomorphological characteristics such as bedrock geology, width to depth ratio, entrenchment, and channel slope, but the Rosgen classification system originated in the Rocky Mountain region and its applicability to the Midwest was not known. The work described here was part of a comparative watershed study evaluating the effects of hydrogeomorphic region, and instream, riparian, and watershed features on stream water quality, habitat, and biota. Rosgen stream types proved useful for partitioning natural and human-caused sources of sediment export in 48 second and third order Lake Superior tributaries. Bedload samples and suspended sediment samples were collected between 1997 and 1999. Rosgen stream types and stream power accounted for 71 per cent of the variation in bedload mass exported. Bedload increased with increasing stream bank erosion and with decreasing forest canopy over the stream and decreased in-stream woody debris. Suspended sediment export increased with greater proportions of fine sediments in the streambeds, and with increased discharge (cubic meters per second water flow), bank erosion, and watershed land uses such as agriculture, recent logging, and road/stream intersection density. Overall, bedload appears to be limited by the ability of the stream to move sediment particles, while suspended sediment export is limited by the supply of fine sediments available in the stream channel. Using this approach will facilitate the prediction of sediment export from healthy, reference reaches of each stream type, and will permit resource managers to identify stream reaches that deviate from the reference condition. These impaired reaches can then be prioritized for restoration or sediment reduction Best Management Practices. Abstract does not necessarily reflect EPA policy.
Key words: streams, sediment, Rosgen, criteria