Aggregate stability and erosion response to antecedent water content of a loess soil

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Soil erosion processes are affected by the erodibility of the soil and by the erosivity of the rain. The effects of rain characteristics and invariant soil properties such as texture and organic matter content on soil erosion processes are well documented. The effect of antecedent soil water content ({theta}a) on aggregate breakdown, seal formation, and subsequent soil erosion is much more disputable, however, as opposing effects have been reported. We conducted lab experiments with a rainfall simulator on a Belgian silt loam soil. The objectives were to determine the effect of {theta}a on seal formation, runoff, and soil loss and to evaluate its effect on an empirical sediment transport equation. Air-dried soil aggregates were subjected to {theta}a of 0.04 (air-dry aggregates), 0.12, and 0.19 m3 m–3. No runoff occurred on the soils with the highest {theta}a, highest total runoff values were observed for intermediate {theta}a, while intermediate amounts of total runoff were observed for the air-dry aggregates. Soil loss, however, showed a different trend: highest values were found for the lowest {theta}a, intermediate values for the intermediate {theta}a, and no soil loss for the highest {theta}a. We further observed that {theta}a had no influence on the final runoff rates and on the final infiltration rate through the soil surface. In using a water discharge and stream power equation to predict sediment transport, the intercept and exponent of the regression equations were found to be lower for {theta}a of 0.19 than 0.12 m3 m–3, indicating decreasing erodibility with increasing {theta}a. We therefore suggest including {theta}a as an additional variable to assess soil erodibility in deterministic event-based water erosion models.

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