Aggregate enrichment ratios for splash and wash transported sediment from an Oxisol

Interrill wash and splash enrichment ratios (ER) and their temporal variation are poorly documented in the literature. Laboratory rainfall simulation experiments were conducted on a clay-rich kaolinitic Oxisol from Hawaiʹi. Three-hour storm events were replicated on slopes of 5, 10, and 20° at a constant rainfall intensity, and interrill erosion was partitioned into wash and splash components. Results indicate that both processes preferentially transport aggregates <63 μm in diameter since ER-values were significantly greater than 1.0. In addition, splash preferentially transported 500–1000 μm aggregates. Average time-integrated wash ER-values were <1.0 for all aggregates >63 μm for all slopes, and these values were significantly lower than those for splash. Wash on slopes ≤10° was not energetic enough to entrain or transport splash detached granule-size aggregates, i.e., 2000–4000 μm. With a slope increase to 20° flow became competent enough to transport granule-sized aggregates but ER-values were significantly less than 1.0, and lower than those associated with splash. Splash detached all aggregate sizes, but the most easily transported fraction was <63 μm followed by 500–1000 μm. Time-trend ER plots indicated significant temporal differences between splash and wash for the same aggregate size fractions. Nonparametric correlation and scatterplots, for selected aggregate size fractions, indicated a variety of linear and non-linear monotonic relationships with interrill sediment flux. Implications of this study are that with time preferential removal of fine material will likely produce a coarser, nutrient-depleted interrill soil matrix. These chemical and physical changes have the potential of limiting soil productivity and reducing the resilience of the soil.