AGGREGATE ENRICHMENT RATIOS FOR SPLASH AND WASH TRANSPORTED SEDIMENT FROM AN OXISOL

Interrill wash and splash enrichment ratios (ER) and their temporal va riation are poorly documented in the literature. Laboratory rainfall s imulation experiments were conducted on a clay-rich kaolinitic Oxisol from Hawai'i. Three-hour storm events were replicated on slopes of 5, 10, and 20 degrees at a constant rainfall intensity, and interrill ero sion was partitioned into wash and splash components. Results indicate that both processes preferentially transport aggregates < 63 mu m in diameter since ER-values were significantly greater than 1.0. In addit ion, splash preferentially transported 500-1000 mu m aggregates. Avera ge time-integrated wash ER-values were < 1.0 for all aggregates > 63 m u m for all slopes, and these values were significantly lower than tho se for splash. Wash on slopes less than or equal to 10 degrees was not energetic enough to entrain or transport splash detached granule-size aggregates, i.e., 2000-4000 mu m. With a slope increase to 20 degrees flow became competent enough to transport granule-sized aggregates bu t ER-values were significantly less than 1.0, and lower than those ass ociated with splash. Splash detached all aggregate sizes, but the most easily transported fraction was < 63 mu m followed by 500-1000 mu m T ime-trend ER plots indicated significant temporal differences between splash and wash for the same aggregate size fractions. Nonparametric c orrelation and scatterplots, for selected aggregate size fractions, in dicated a variety of linear and non-linear monotonic relationships wit h interrill sediment flux. Implications of this study are that with ti me 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.