Decadal-scale soil redistribution along hillslopes in the Mojave Desert
Abstract. This study estimates the relative magnitude of decadal-scale soil redistribution (i.e., soil loss or gain) by slope wash using 137Cs inventories measured in 46 soil profiles at four study sites in the Ft. Irwin area of the Mojave Desert of California, USA. The variability in 137Cs inventories on a <5 m scale suggests that even for the same topographic position, there is large variation in runoff generation and flow continuity. Smaller average 137Cs inventories that are suggestive of higher relative erosion rates are associated with more gently sloping sites that have a lower percentage of surficial rock-fragment and vegetation coverage. Individual 137Cs inventories from all four sites are positively correlated with the percentage of rock fragments in the upper soil profile. The increase in rock-fragment cover (i.e., soil armoring) with increasing slope gradient appears to negate any potential increase in transport effectiveness with increasing slope steepness. This armoring, together with the sandy-loam soil texture characteristic of steeper slopes, hinders runoff and slope-wash erosion. Our findings are supported by soil data that suggest that these patterns are persistent for longer timescales (i.e., centuries and millennia).