APPLICATION OF CS-137 FOR SOIL EROSION ANALYSIS IN THE WATERSHED OF THE RAPPAHANNOCK RIVER, VIRGINIA

Soil erosion in most terrains is both a result of natural geomorphic processes as well anthropogenic human landscape modifications, mostly through deforestation, agriculture and urban development. The resulting effects of erosion are plentiful, widespread and include loss of soil fertility and declines in water quality recipient water bodies. The watershed of central Virginia's Rappahannock River has gradually shifted from a largely forested to one of increasing agricultural and metropolitan development. Farms, towns, and cities, along with the high concentration of roadways which provide for them, have replaced much of the watershed's natural land cover with bare, vulnerable and often impervious surfaces, essentially “paving the way” for erosion. Recent studies have shown that the Rappahannock River delivers more sediment per square unit of watershed than any of the other tributaries of the Chesapeake Bay.

We report results of watershed erosion rates analysis using Cs-137 inventories in soil at various locations within the Rappahannock Watershed. The study highlights both the important role of geomorphologic landscape characteristic as well variation in land-use in influencing erosion rates. The watershed was divided into two main sections based on slopes, with the upper region characterized by deeply incised valleys of relatively steeper slopes, and the lower basin of gentle slopes. Soil cores were collected from forested, grassland, cropland, and grazeland sites in both sections, and analyzed for Cs-137 content. Other soil physical and chemical attributes i.e. bulk density, particle size distribution, soil pH, effective cation-exchange capacity, organic carbon content, and magnetic susceptibility were analyzed for a more comprehensive watershed erosion analysis.