Sediment Redistribution in a Mixed Land Use Watershed in Central Pennsylvania.

Radioactive fallout Cesium (¹³⁷Cs) has been used to determine the rates and pattern of soil erosion at the landscape scale. The objectives of this research were to determine patterns of soil erosion and deposition in a watershed of the Ridge and Valley physiographic region of Pennsylvania, and to determine the relative contributions of stream bank erosion or field (soil surface) erosion at the watershed outlet. The study area is WE-38, a 7.2-km² subwatershed of east Mahantango creek, a tributary of the Susquehanna River and Chesapeake Bay. Soil samples were collected along 16 transects from six different land use areas. Four transects were selected each from pasture, continuous row crop, and wood. Two transects were selected each from Christmas tree and row crop / forage. Within each transect samples were collected at six locations along the hillslope (summit to toe slope) to a depth of 20 or 50 cm at increments of 10 cm. Additional sediment samples were collected from the watershed outlet, stream banks, road cuts, gullies, and undisturbed reference areas. The count for ¹³⁷Cs was determined using Gamma-ray analyses Canberra-2000 Genie-2000 Spectroscopy System. The least disturbed land use in this watershed was wood, with a ¹³⁷Cs count from 12 to 35 Bq kg^-1 in the surface soil. The ¹³⁷Cs count from the surface soil of continuous row crop, row crop / forage, and Christmas tree land uses were consistently below 10 Bq kg^-1, indicating a similar degree of soil erosion among these land uses. Pasture occupied the lowest landscape positions along stream corridors, and the ¹³⁷Cs count in the surface soils were sometimes > 20 Bq kg^-1 and sometimes < 10 Bq kg^-1, an indication of variably reworked sediment. Greater ¹³⁷Cs count lower in the soil profile were indicative of soil accumulation at lower landscape positions.