APPLICATION OF RADIOACTIVE FALLOUT CESIUM-137 FOR MEASURING SOIL-EROSION AND SEDIMENT ACCUMULATION RATES AND PATTERNS - A REVIEW

Radioactive fallout 137Cs (cesium-137) deposited across the landscape from atmospheric nuclear tests is strongly absorbed on soil particles limiting its movement by chemical and biological processes. Most 137Cs movement in the environment is by physical processes; therefor, 137Cs is a unique tracer for studying erosion and sedimentation. Cesium-137 loss from a watershed has been shown to correlate strongly with soil loss calcualted by the Universal Soil Loss Equation (USLE) or measured from small runoff plates. By measuring spatial patterns of 137Cs in vertical and horizontal planes across the landscape, rates of soil loss or deposition can be measured for different parts of a watershed. Even within landscape units, redistribution of soil can be mapped and erosion or deposition rates for different parts of individual fields measured and mapped. Sediment accumulation rates can be measured by comparing the vertical distribution of 137Cs in sediments with the temporal deposition of fallout 137Cs from the atmosphere to locate sediment horizons. Using these dated sediment horizons, sediment accumultion rates can be measured. Interpretations about the location of these dated horizons must consider particle size of the sediments, reworking of deposited sediments, diffusional movement of 137Cs, and time rates of physical process in the sedimentation process. The 137Cs technique can be used to determine sediment accumulation rates in a wide variety of depositional environments including reservoirs, lakes, wetlands, coastal areas, and floodplains. The bibliography shows that 137Cs has been used widely for studying erosion and sedimentation in many different environments around the world.