Effects of Moisture and Grain Sizes on Rainsplash Transport with Implications for Desert Plant-Soil Interactions
Abstract
Soil mounds beneath desert shrubs can develop from sediment transport associated with rainsplash of soil grains around the plants. As the canopy of a plant protects the underlying soil from the raindrop impacts, sediment accumulates beneath the shrub canopy due to differential rainsplash of grains. Previous work has clarified how rainsplash transport varies with raindrop momentum and with different sizes of dry sediment, focusing on the transfer of momentum of the drops to grains during drop impacts. Details of this transfer of momentum and grain mobilization for moist sediment conditions are not well known, which is important for understanding sediment transport by rainsplash during the progression of storms. Moreover, related work suggests that relatively immobile coarse soil grains are less likely to be splashed beneath shrub canopies than are small grains, so that smaller grains are more likely to accumulate within shrub mounds. However, systematic measurements of sediment grain sizes around and beneath desert shrubs in the Cibola National Forest, New Mexico, suggest that, aside from the coarsest lag material, larger grain sizes (0.5 - 1.5 mm) are preferentially concentrated within the mound surfaces close to the shrubs. This pattern of grain-size sorting is likely associated with effects of moisture, wherein small grains tend to be ejected during drop impacts as grain clumps rather than individually due to surface tension, and thereby behave as relative coarse grains with shorter splash distances. High-speed imaging of drop impacts on sediment reveals this clumping behavior. These results may be useful in determining the dispersal of nutrients and contaminants that preferentially adhere to the smaller grain sizes. This information also extends our understanding of rainsplash transport beyond dry conditions, that is, to storm conditions where soil moisture and grain detachment rates are changing.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMEP51A0577T
- Keywords:
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- 1826 HYDROLOGY / Geomorphology: hillslope;
- 1851 HYDROLOGY / Plant ecology;
- 1862 HYDROLOGY / Sediment transport;
- 1866 HYDROLOGY / Soil moisture