基于RUSLE模型的黄土高原草地植被覆盖因子研究

Vegetation and its community structure is one of the key factors that affected soil erosion. Vegetation canopy, litter, biological soil crusts, plant root characteristics, soil surface roughness and soil moisture changed greatly for the implement of the “Grain-for-Green” project, which significantly affected the soil erosion and hence influenced the C factor (cover-management factor). This project, therefore, is planning to discuss the characteristic and variation of the vegetation restoration on vegetation canopy, litter, biological soil crusts, plant root system and soil moisture via runoff plot observation, artificial rainfall simulation, and modeling. The influences of cover-management subfactors of canopy cover, litter cover and incorporated with soil, biological soil crusts cover and composition, plant root type and structure, and soil moisture content on soil loss and their quantitative expression will be revealed. Also, the rational and simple cover-management factor equation on thee grassland (CG) will be developed based on the theoretical framework of RUSLE (Revised Universal Soil Loss Equation) model, and the predicting precision of CG equation will be evaluated based on the differences between simulated and measured CG values. Besides, the application range of the CG equation will be defined. The results will be helpful for developing applicable soil erosion prediction model in the Loess Plateau, evaluating their soil and water conservation benefits of “Grain-for-Green” project, and analyzing the evolution of regional erosion environment.

植被及其群落结构是影响土壤侵蚀的关键因素之一，退耕还林（草）工程的大面积实施，植被冠层、枯落物、生物结皮、根系、地表糙度及土壤水分等发生了显著变化，势必会对土壤侵蚀产生显著影响，进而影响C因子的估算。本项目以黄土高原不同演替阶段典型退耕草地为研究对象，采用野外径流小区观测、人工模拟降雨、模型模拟等技术与方法，系统研究典型草地植被冠层、枯落物、生物结皮、根系系统、土壤水分特征及其变化规律；明确冠层覆盖、枯落物覆盖及混入土壤、结皮盖度及组成、根系结构及类型、土壤含水量等植被覆盖次因子对土壤侵蚀的影响，量化各次因子特征参数与土壤流失比率间的相互关系；基于RUSLE模型的理论框架，构建合理的草地植被覆盖因子（CG）方程，验证并修正方程参数，界定方程的适用范围。为建立适合于黄土高原的土壤侵蚀预报模型、评估退耕还林（草）工程的水土保持效益、分析区域侵蚀环境演变规律提供理论基础和技术支撑。

植被群落特征可显著影响土壤侵蚀过程。本项目以黄土高原植被恢复过程中典型退耕草地为研究对象，通过植被特征调查、人工模拟降雨和野外径流小区观测等手段与方法，系统研究了冠层、枯落物、生物结皮、根系系统等植被覆盖次因子变化特征及其对坡面产流产沙过程的影响，量化了植被覆盖次因子（CG）与土壤流失比率的相互关系，构建并验证了草地植被覆盖因子方程。结果表明：（1）典型草地植被盖度（15.0~82.0%）、株高（19.5~75.9cm）、地上生物量（180.3~369.5g/m2）、枯落物蓄积量（69.4~199.9g/m2）、生物结皮盖度（11.6~94.8%）、根系生物量（2.2~5.4kg/m3）存在显著季节变化。总体而言，植被群落特征在生长旺期呈增加趋势。相较于观测初期，白羊样地上述植被特征根参数增加了1.1~5.7倍，铁杆蒿样地增加了1.2~3.8倍；（2）除土壤粘结力外，容重（1.1~1.2g/m3）、总孔隙度（55.0～62.5%）、饱和导水率（0.1～0.3cm/min）虽存在一定变化，但差异并不显著。土壤粘结力总体呈增加趋势，相较于监测初期，白羊草样地和铁杆蒿样地土壤粘结力分别减小了8.8%和增加了1.1倍，白羊草样地土壤粘结力均值略高（1.4%）；（3）白羊草和铁杆蒿样地植被特征诸如植被盖度、枯落物地表蓄积量、土壤中枯落物混入量、生物结皮盖度、根系生物量均可显著减少土壤侵蚀（2.8～93.9%）。随着上述指标的增加，土壤流失比率呈幂函数降低（R2≥0.58，p<0.05）。土壤含水量可增加土壤侵蚀（8.9～86.1倍），但与土壤流失比率无显著函数关系；（4）基于392场人工模拟降雨，筛选了影响土壤流失比率（SLR）的有效植被因素：植被盖度（C_Plant）、枯落物蓄积量（B_Litter）、生物结皮盖度（C_BSCs）和根系生物量（B_Root），构建了基于植被群落特征的植被覆盖次因方程；（5）基于29场有效自然降雨观测的径流泥沙、植被特征和降雨特征，验证、修正了草地植被覆盖因子（CG）方程（SLR=101.819C_Plant-0.323B_Litter-0.041C_BSCs-0.691 B_Root-3.533；R2=0.73，NSE=0.85）。该方程对于计算黄土高原典型草地植被覆盖次因子具有较好的适用性。本研究结果建立适合于黄土高原的土壤