Soil erosion and sedimentation indicated by caesium 137: Jackmoor Brook catchment, Devon, England

Abstract

The tracer caesium-137 was used to study the status of soil erosion and sedimentation in the Jackmoor Brook catchment, Devon, U.K. It was postulated that (1) sites at the top of a cultivated slope should be most depleted of caesium-137, (2) sites at the base of a slope should contain greater amounts of caesium-137 and have a distinctive depth profile, (3) hillslope erosion indicated by caesium-137 levels should be related to slope length and angle, and (4) caesium-137 levels should discriminate between the chief source of sediment transferred to the stream (cultivated soils) and uncultivated soils (under pasture, orchards and woodland). These hypotheses were tested in two contrasting physiographic areas of the basin. Depletion of caesium-137 levels at the top of slopes indicated soil erosion, and deeper-than-plough-depth caesium-137 profiles at the base of slopes indicated sedimentation. These characteristics were most marked in the steeper, Upper Jackmoor, portion of the catchment. Slope-length effects on soil movement were more difficult to ascertain from the caesium-137 levels, but soil sampling of contrasting land-uses showed that cultivated soils had significantly less caesium-137, probably as a result of soil erosion. In general, the hypotheses were supported and the utility of the caesium-137 technique was confirmed.