Using fallout lead-210 measurements to estimate soil erosion on cultivatedland

Naturally occurring fallout Pb-210 is strongly adsorbed by soils and sedime nts and has been widely used as a tracer to establish the chronology of dep osited sediments in various sedimentary environments, This paper reports an attempt to explore the potential for using fallout Pb-210 to estimate rate s of water-induced soil erosion on cultivated land. Soil cores were collect ed from both cultivated and undisturbed areas in a small catchment in Devon , UK, and land use practices were shown to be the primary factor controllin g the depth distribution of fallout Pb-210. Based on existing knowledge of the behavior of Pb-210 in cultivated soils, a mass balance model has been d eveloped that enables longer-term (approximate to 100 yr) rates of erosion and deposition to be estimated from values of unsupported Pb-210 inventory for individual sampling points. In order to estimate longer-term soil redis tribution rates, the mass balance model was applied to an 8.54-ha cultivate d field within the study catchment from which 167 bulk cores had been colle cted at the intersections of a 20 by 20 m grid. Soil redistribution rates w ithin the field ranged from -5.9 kg m(-2) yr(-1) (erosion) to 6.4 kg m(-2) yr(-1) (deposition), and the mean erosion rate for the eroding area was 1.9 5 kg m(-2) yr(-1). The pattern of soil redistribution within the study fiel d reflected the influence of topography on sediment mobilization and transp ort, The results obtained confirm the potential for using fallout Pb-210 me asurements to estimate rates and patterns of water-induced soil erosion on cultivated land.