SPATIAL ANALYSIS AND RADIOGENIC CHARACTERIZATION OF SEDIMENTS TO IDENTIFY POTENTIAL POLLUTANT PATHWAYS IN REMOTE SUB-WATERSHEDS OF THE RAPPAHANNOCK RIVER

This study examines the threat to sustainable use of water resources posed by soil erosion and associated off-site sedimentation in two sub-watersheds of the Rappahannock River Basin, Stafford County, Virginia. Reliable information on sediment fluxes from different land-use/land-cover in watersheds and potential contaminant pathways is critical for proper evaluation and sound management of fluvial systems. Claiborne Run (16.8 km²) and Horsepen Run (19.8 km²) are located in close proximity to each other but have different land-use and land-cover characteristics. Claiborne Run is within the city of Fredericksburg, where urban landscape/development accounts for 67% of the watershed, while only 25% remains forested, 4% grassland, and 4% farmland. Whereas, the relatively pristine Horsepen Run watershed is characterized by 63% forest cover, with only 18% urban development and 19% farmland.

To identify critical runoff-contributing areas, ²¹⁰Pb was used as a tracer to fingerprint stream bank soils and soils in various land-use/land-cover areas in the watershed. The corresponding fingerprint values were then compared with that of each stream's suspended sediments. Preliminary results in both watersheds show that the majority of sediment influxes in the streams are characterized by farmland ²¹⁰Pb signatures, thus reflecting the impact land-uses have on stability of landscapes. The Revised Universal Soil Loss Equation (RUSLE) will be used in conjunction with the Sediment Delivery Ratios (SDR) to estimate the amount of soil loss from various land plots within the watersheds. In addition, storm and normal flow suspended sediment measurements, analysis, and characterization will be compared with, and used to validate RUSLE results. Data generated from this study provides important baseline information for monitoring the impact of urbanization and current watershed development on Stafford County's fluvial systems.