HR: 1330h
AN: NB33G-07    [Abstracts]
TI: Preliminary analysis of bed and suspended sediment transport in a protected watershed, and the effect on native mussel populations
AU: * MacGregor, K
EM: macgregor@macalester.edu
AF: Macalester College Geology Department, 1600 Grand Avenue, St. Paul, MN 55105
AU: Hornbach, D
EM: hornbach@macalester.edu
AF: Macalester College Biology Department, 1600 Grand Ave., St. Paul, MN 55105
AB: Sediment budgets in river networks are notoriously difficult to construct, but can be important for quantifying short and long-term changes to fluvial environments. Adequate sediment supply is critical for in channel, bar, and near-shore ecosystems; too much or too little sediment can be a detriment to biota, including mussels and host fish. Hornbach and others (see http://www.macalester.edu/~hornbach/St.Croix/index.html) have been collecting bed sediment at various locations along the St. Croix River since 1990 in an effort to understand controls on mussel population and diversity. These data, along with suspended sediment data collected by other agencies (e.g., Triplett and others, 2003; Metropolitan Council, 2004), can be used to examine trends in sediment transport and/or sediment delivery to the river over time. We continued the collection of bed sediment in conjunction with mussel quadrat surveying in summer 2004, and initiated sampling of suspended sediment at various locations along the river. We developed rating curves (relating suspended sediment concentration and mean daily water discharge) for several locations along the St. Croix River, and compared these to historical data. In addition, we examined trends in bed sediment grain size over the last decade. Analysis suggests that while bed sediment grain size is relatively unchanged in most of the study areas, there has been a fining trend in the region below the St. Croix Falls dam. This corresponds with a decrease in the juvenile population of the winged mapleleaf mussel, a federally-endangered species found almost exclusively in this part of the St. Croix (Hornbach, 2005). Future research will address fluvial dynamics and sources of fine sediment in this region. Suspended sediment data are more limited, but suggest transport dynamics may have changed over the last half century.
DE: 0400 Biogeosciences
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1857 Reservoirs (surface)
DE: 1860 Runoff and streamflow
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly