Soil-grain transport and dispersal by rainsplash, with implications for plant-soil interactions in deserts

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This project involves describing soil transport by rainsplash. By taking into account the intermittency of soil-grain motions activated by raindrops, the formulation indicates that gradients in raindrop intensity can be as important as surface slope in effecting transport. The formulation provides a practical framework for describing transport, dispersal and sequestration of soil-borne pathogens and nutrients by rainsplash. Building on recent success in clarifying the physics of the grain splash process, the project combines theoretical, experimental and field-based work to: (i) pursue a deeper understanding of soil-grain transport and dispersal by rainsplash; and (ii) illustrate how storage and release of sediments beneath desert shrubs in relation to rainsplash represents the behavior of a ?capacitor? that contributes to setting the rate of desert land-surface evolution. Experiments involve high-speed imaging of sediment grain transport during drop impacts, and measurements of transport and dispersal under controlled rainfall conditions. Field work involves measurements of soil features beneath and surrounding desert shrubs in the western U.S., aimed at clarifying relationships among the characteristic length scales of vegetation canopies and soil mounds in relation to grain splash.In addition to contributing to a clearer understanding of rainsplash transport as an important geomorphic process, the project will connect the physical details of rainsplash with studies focused on transport, dispersal and sequestration of contaminants, nutrients and pathogens in agricultural and desert settings, and on the ecology of desert vegetation, wherein desert plants are viewed as ?resource islands.? Graduate students supported during this project will gain a foundation in fluid mechanics and transport phenomena relevant to Earth-surface systems as well as other geoscience and engineering fields. Undergraduate students will be substantively involved, leading to senior thesis projects. The project will generate compelling images and videos of rainsplash that visually clarify this process. These will be readily accessible to the science community and public via educational web pages.This award will be supported by the NSF's program in Geomorphology and Land-Use Dynamics (EAR/GLD).