Wednesday, November 15, 2006 - 1:25 PM

Linking Downstream Sediment Quality to Upstream Channel Erosion: the Yalobusha River Basin and Grenada Lake, MS.

Sean J. Bennett, University at Buffalo, Department of Geography, Buffalo, NY 14261-0055

In north-central Mississippi, unstable, deeply incised streams with actively calving banks can dominate total sediment loads within these watersheds.  The Yalobusha River is one such system having a long history of channelization, excessive stream channel and bank erosion, and large woody debris recruitment and accumulation.  Analysis of the sediment impounded within this receiving reservoir and the upstream tributary channel shows that: (1) the impoundment is dominated by clay-sized sediments, with sand deposition restricted to upstream channel environs; (2) the clay-rich sediment sequestered in the reservoir has relatively high concentrations of environmentally important trace elements, which appears to have caused the bioaccumulation of mercury in the lake’s catfish and bass populations and relatively high concentrations of dissolved arsenic in the pore waters below the bottom of the lake; and (3) of the channel derived sediments eroded along the Yalobusha River, about 76% remains stored upstream of the reservoir, facilitated by an accumulation of large woody debris forcing flows out of bank.  Thus excessive streambank erosion along the Yalobusha River has led to the degradation of ecologic and water quality indices within Grenada Lake and the storage of poor-quality sediments within the floodplain upstream of the reservoir.