Radiocesium in Montana soils and applications for soil erosion measurement

Abstract

Radiocesium levels in soils were measured at eleven sites throughout Montana. Cesium was mostly confined to the top of the soil profile. Both lateral and vertical displacement of cesium was attributed to mechanical movement of soil particles. The areal activity of cesium was strongly correlated to annual precipitation (R^2 = 0.92). An equation is given to predict cesium activity from annual rainfall. Methods of calculating soil erosion and deposition are discussed and performed for a wind erosion study site in Pondera County and a small watershed in Teton County. The results indicate that deposition at the wind erosion study site can be quantified. Soil deposition of 70 to 1290 m^3 ha^-1 was measured on the leeward sides of a fence and tree windbreaks while an average of 450 m^3 was lost from the windward sides. An average of 740 m^3 ha^-1 was lost since 1962 from an adjacent wind eroded field. This amounts to 34.8 Mg ha^-1 yr^-1. Soil loss since about 1962 ranged from 300 to 820 m^3 ha^-1 within the upper areas of the watershed studied. A pond at the outlet of the watershed and deposition areas at the toeslope accounted for a relatively small fraction of the soil loss within the watershed. Most of the losses are likely to be from wind erosion. Length of slopes or position within the field were more related to erosion than was steepness of slopes, Estimates of erosion rates based on 137Cs ranged from 16.5 Mg ha^-1 yr^-1 at the summit of the watershed to 45.1 Mg ha^-1 yr^-1 at the midslope. Predictions by conventional methods (wind erosion equation and the Universal Soil Loss Equation) agreed rather closely with the estimates from 137Cs.