HR: 15:45h
AN: B44B-02    [Abstracts]
TI: The Influence of Relative Sediment Supply on Riverine Habitat Heterogeneity
AU: * Yarnell, S M
EM: yarnell@geology.ucdavis.edu
AF: Geology Department University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AB: The diversity of aquatic habitats in a stream reach and associated biological response are linked to physical processes that act at various spatial and time scales within a watershed. A fundamental driver of stream geomorphology integrating multi-scale processes is the relationship between sediment supply and transport capacity. This study explored the interactions between riverine habitat heterogeneity and the geomorphic processes governing channel conditions by testing the hypothesis that maximum habitat heterogeneity occurs in stream reaches with a moderate relative local sediment supply, as measured by the supply-capacity ratio. Habitat heterogeneity was quantified with an ecologically meaningful spatial heterogeneity index from the field of landscape ecology, Shannon's Diversity Index (SHDI), and relative sediment supply was quantified using a dimensionless bedload transport rate, q*. Data from previously published studies and a new field study on tributaries to the South Yuba River in Nevada County, California were evaluated to test the hypothesis. Results showed that in alluvial reaches where flow and sediment interacted freely without obstruction, moderate q* values correlated with high SHDI values; however, in reaches where less mobile structural elements, such as large woody debris and boulders, were present, SHDI increased as the percentage of structural elements increased. The results indicate two potential mechanisms for how relative sediment supply may drive habitat diversity at the reach scale. When structural elements are not a large proportion of the reach landscape, the supply-capacity ratio dictates the range of sediment textures and geomorphic features observed such that channels with a moderate relative sediment supply exhibit high habitat heterogeneity supporting the study hypothesis. In contrast, when structural elements are relatively abundant, increased local scour and deposition creates a greater variety of geomorphic features and sorted sediment textures, thereby increasing the habitat heterogeneity observed. For both mechanisms, it is the combination of variable sediment flux and variable flow magnitude and frequency that creates the variations in sediment mobility required to maximize geomorphic diversity.
DE: 1800 HYDROLOGY
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
SC: Biogeosciences [B]
MN: 2005 Joint Assembly