Influence of rainfall energy flux density and antecedent soil moisture content on splash transport and aggregate enrichment ratios for a Hawaiian Oxisol

Erosion process information from aggregated tropical soils is under-represented in the literature. Thus, an Oxisol was used in laboratory rainfall simulation experiments to examine the importance of antecedent moisture content (AMC) and rainfall energy flux density (EFD) on splash. Ten splash experiments were conducted at EFD-values ranging from 0.064 to 0.53 W m⁻² for 1 h dry and 1 h wet runs. Results indicated that AMC had no significant influence on total splash flux or splash flux per aggregate size fraction. However, splash increased linearly with EFD. The Oxisol exhibited a very high resistance to splash detachment (whole-soil basis), and the 2000–4000 μm aggregate size fraction was the most resistant to splash detachment. There was no significant difference for total splash flux between dry AMC-low EFD and wet AMC-low EFD events; or between dry AMC-high EFD and wet AMC-high EFD events. However, time trends differed significantly, and these reflected the influence of variable water content on near-surface soil strength, panicle shielding and availability of material. Splash enrichment ratios (ER) for all AMC and EFD data indicated that the 425–2000 μm aggregates were preferentially transported (i.e., ER significantly > 1.0). Aggregates of 250–500 μm were splashed in similar proportion to their content in the original soil, and aggregates < 250 μm and > 2000 μm were significantly depleted in splashed material (i.e., ER < 1.0). The reasons for depletion include either increased cohesion with fine grained aggregates or the inability of simulated rainfall to transport the most massive aggregates. Our data show that splash is a time-dependent process influenced primarily by rainfall energy flux and to a lesser extent by interactions with antecedent soil moisture status. Data of this type are essential for incorporation into state-of-the-art erosion prediction models if they are to be truly universal.