黄土高原退耕还林草工程实施后，生物结皮广泛发育，显著影响坡面水土流失过程，改变了坡面水土流失格局。明确生物结皮坡面水土流失规律，量化评价生物结皮对坡面水土流失的影响，是退耕还林草工程水土保持效益评估的关键科学问题和国家需求。项目从生物结皮对坡面土壤抗蚀性和渗透性的影响入手，通过降雨试验、数理统计、数值模拟方法，研究多因素综合作用下，不同组成、盖度、分布的生物结皮对坡面降雨入渗、土壤抗蚀性、产汇流及土壤流失过程的影响，确定坡面水-土流失过程分离（水流土留）及耦合（水土同步流失）条件及阈值。进而借助示踪法，研究生物结皮对坡面土壤侵蚀-搬运-沉积过程的影响，从生物结皮增强土壤抗蚀性和影响侵蚀动力两方面，揭示生物结皮对坡面侵蚀产沙的影响机理，明确生物结皮坡面水土流失规律。基于已有模型，修正建立考虑生物结皮因子的坡面水土流失预报模型，为区域水土流失评价及恢复生态系统的管理提供科学依据。

Biological soil crusts were developed widely since the implementation of the“Grain for Green”project on the Loess Plateau, which significantly affected the slope soil erosion process and altered the pattern of soil and water losses on the slope. It is a key scientific problem and national demand to evaluate the soil and water loss regularity of biological soil crusts and quantify the impact of biological soil crusts on the slope soil and water losses. The project started with the effect of biological soil crusts on soil erosion resistance and permeability of soils on slopes. Through rainfall experiments, mathematical statistics, and numerical simulation methods, the effects of biological soil crusts on soil infiltration and soil erosion resistance, convergence process and soil loss process were studied on the slope under the combined effects of multiple factors. The separation of water-soil loss processes (water loss and soil retention) and coupling (both water and soil loss) were determined. Based on the above research, a rare earth element (REE) tracer method was used to study the mechanism of soil erosion-transport-sedimentation on the biocrusted slope during the simultaneous loss of water and soil, revealing the water-soil loss pattern on biocrusted soil, and revealing the law of water-soil loss on biological soil slopes. Based on the quantitative relationship between soil and water loss and biological soil crust factors on the slope, and based on the existed model, a runoff model and soil loss model considering the biological soil crust factors were established. The results will provide a scientific basis for the evaluation of regional soil erosion and restoration of ecosystem management.