Decadal-scale soil redistribution along hillslopes in the Mojave Desert

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).