Raindrop Impact: A Neglected but Potentially Major Contributor to Particle Mobilization in Soils
2010
Bielders, C. L. | Grymonprez, B.
Drop impact, a key process of particle mobilization in interrill erosion, has been largely neglected as a mobilization mechanism in the realm of colloid-facilitated transfer (CFT) research. We investigated the contribution of drop impact to the eluviation of silt and clay particles from repacked samples of 6-mm-thick, fine earth (<2 mm) or 2- to 4-mm aggregates under simulated rainfall conditions. Samples were initially moist or dry, and protected or not from drop impact. The results indicated a complex, three-way interaction between the aggregation status, initial water content, and drop impact. Drop impact was a major contributor to particle mobilization on moist samples, increasing by a factor of three to four the mobilization that was observed without drop impact. The initial status of aggregation and the initial water content of the soil interacted to govern the rate of surface seal development and surface ponding, which are believed to interfere with the particle release process. Initially dry samples were most susceptible to sealing and released fewer particles than initially moist samples. In some cases, a first-order equation to predict particle eluviation as a function of cumulative rainfall energy appeared to be a reasonable approximation, at least up to about 400 J m⁻² of cumulative rainfall kinetic energy. Current modeling efforts that do not take drop impact into account are clearly limited in their predictive capacity when applied to bare soils. Greater interactions between the CFT and interrill erosion research communities may help advance the understanding and modeling of particle release in the topsoil by drop impact.
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