Radionuclides as indicators of sediment transport in agricultural watersheds that drain to Lake Erie.
An issue in evaluating the success of agricultural management practices is the speed that eroded particles make their way through the downstream waters. In this study at Old Woman Creek (OWC) and Rock Creek (RC), two largely agricultural watersheds in Ohio, the flux of sediment and radionuclides (7Be, 210Pb, and 137Cs) in thunderstorm runoff was examined to better understand transport of eroded agricultural soils. The hydrograph in an agricultural area under no-till was similar in timing, but of lesser magnitude, than the hydrograph from a similar-sized area under conventional tillage. The activities of 210Pb and 7Be are linearly correlated and are higher in suspended sediments derived from no-till subbasins than those derived from conventionally tilled subbasins. A suspended sediment plume, identified by its unique radionuclide signature, was traced through 17 km of OWC stream channel in approximately 13.4 h (0.35 m/s). The downstream exponential decrease of 7Be activities in suspended sediments 3 to 12 h after passage of the sediment plume was used to estimate transport distances of suspended sediment from 2 to 17 km, respectively. Transport distances of suspended sediments were also calculated from wave kinematics and indicate that at OWC suspended sediment transport distances were longer in streams draining areas of no-till (19-26 km) than in the streams draining areas of conventional tillage (6-15 km). Suspended sediments travel 7 to 22 km at RC. The transport distances are long relative to the lengths of the stream channel and indicate that erosion control methods implemented in the watershed should be reflected quickly in downstream waters.
Matisoff
Gerald
G
Department of Geological Sciences, Case Western Reserve University, Cleveland, OH 44106, USA. gxm4@po.cwru.edu
Bonniwell
Everett C
EC
Whiting
Peter J
PJ
D000383:Agriculture; D001608:Beryllium / Q000032:analysis*; D002588:Cesium Radioisotopes / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D019015:Geologic Sediments / Q000737:chemistry*; D006114:Great Lakes Region; D007856:Lead Radioisotopes / Q000032:analysis*; D011868:Radioisotopes / Q000032:analysis*; D012987:Soil; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000032:analysis*
D002588:Cesium Radioisotopes; D007856:Lead Radioisotopes; D011868:Radioisotopes; D012987:Soil; D014875:Water Pollutants, Radioactive; D001608:Beryllium