It has been recognized that dynamics of water and the associated materials such as sediment and nutrients are important to conserve ecosystem existing in a watershed. Among others, excess soil and nutrients transports toward the coastal zones and deposition on corals are one of the major environmental problems in Okinawa, Japan, in which agricultural area is the major source of sediment yield. In this study, we focused on a soil erosion reduction measure by using biological ground cover by algae and fungi, called Biological Soil Crust, BSC. As the results of erosion experiments, interrill and rill erosion rate increased with increasing rainfall intensity and flow shear stress acting on the soil particles under the bare ground condition. These erosion rates decreased under the ground covered condition with BSC. Significantly, rill erosion did not occur while the soil is covered with BSC. The reduction effect of BSC was sustained even though the surface cover was detached by rain drops. Soil erodibities were identified from measured erosion rates, and the parameters of soil erodibilities were input into the Water Erosion Prediction Project, WEPP model. Simulation results of WEPP model revealed that the sediment yield under the ground covered condition with BSC decreased by around 90% of that under the bare ground condition.
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