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Suspended sediment sources and tributary effects in the lower reaches of a coastal plain stream as indicated by radionuclides, Loco Bayou, Texas
Authors:K M Yeager  P H Santschi  J D Phillips  B E Herbert
Institution:(1) The Laboratory for Oceanographic and Environmental Research, Department of Marine Sciences, Texas A&M University, 5007 Ave. U, Galveston, TX 77551, USA;(2) Department of Geography, University of Kentucky, 1457 Patterson Office Tower, Lexington, KY 40506-0027, USA;(3) Department of Geology and Geophysics, Texas A&M University, 3115 TAMU, College Station, TX 77843-3115, USA
Abstract:Characterizing the dynamics of fluvial sediment sources over space and time is often critical in identifying human impacts on fluvial systems. Upland interfluve and subsoil sources of suspended sediment at Loco Bayou, Texas, were distinguished using 226Ra/232Th, 226Ra/230Th and, 228Ra/232Th. Source contributions were apportioned at three stations during within-bank and flood flows. 137Cs and 210Pbxs (excess 210Pb) were used to determine floodplain sedimentation; suspended sediment 210Pbxs/137Cs data mirrored results of Ra/Th, showing dominance of subsoil sources during within-bank flows, changing to interfluve sources during flood. This trend corresponds spatially to influx of sediment from ephemeral tributaries, reflecting mobilization of stored interfluvial sediments during flood stage. Upper basin sedimentation was similar but markedly less at the lowermost station. These results indicate (1) modified ephemeral tributaries store sediment derived from sheet wash, discharging them during flood, and (2) southernmost Loco Bayou is episodically re-worked, resulting in significantly reduced local rates of sedimentation.
Keywords:Radionuclides  Fingerprinting  Suspended sediment  Human agency  Texas  USA
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