APPLICATION OF LEAD - 210 TO ANALYZE SEDIMENT FLUXES AND SOIL EROSION IN THE RAPPAHANNOCK RIVER BASIN

Excessive amounts of sediments in aquatic ecosystems are known for their negative impacts including the reduction of water clarity. Sediments also act as conveyors of pollutants including trace metals and nutrients into aquatic ecosystems. The Chesapeake Bay is an impaired water body and continues to experience diminishing water quality and loss of habitat due to excess sediments and nutrient fluxes. The Rappahannock River Basin contributes the greatest amount of sediments in tons/mi² to the Bay, therefore a comprehensive approach to water and soil management that takes into account both anthropogenic pressures and geomorphic characteristic is needed to save this important water resource. To identify critical runoff and sediment contributing areas, ²¹⁰Pb was used as a tracer to fingerprint suspended sediments and soils in various land-use/land-cover areas in three sub-watersheds of the Rappahannock, the Claiborne Run, Little Falls Run, and Horsepen Run watersheds. These sub-watersheds are in close proximity to each other, possess indentical climates and relatively similar soil types, but vary in topography and land use/land cover.

The fingerprinting result shows that in Claiborne Run and Horsepen Run suspended sediment loads were characteristic of disturbed environments, 10.71 dpm/g and 10.81 dpm/g respectively. Closely matching values were found on farmland within the Claiborne Run watershed and ATV trails within the Horsepen Run watershed. In addition, 30 cm soil cores were collected from each of the land use/land cover sites in the three watersheds in order to estimate erosion rates. Preliminary findings show that farmland sites in the Horsepen Run and Little Falls Run Watersheds have a higher rate of erosion than forests and grasslands sites.