黄土高原小流域植被格局对侵蚀产沙影响的定量表征与耦合关系

Optimizing the layout of vegetation patterns is one important ways to control erosion, to reduce sediment and to improve the environment quality under the circumstance of the scarcity of available water and soil resources. However, the effects of vegetation patterns on erosion and sediment yield in watershed still remain unclear, and hence far from to provide technical support on ecological construction. This is probably caused by the following two reasons: the first, proper indexes which can comprehensively reflect the influences of vegetation patterns on sediment yield were lacking; the second, the intuitive response relationship between vegetation patterns and sediment yield has not been established. Under this background, taking small typical watersheds on the Loess Plateau as an example, this study is aimed to establish the coupling relationship of vegetation patterns and sediment yield. Firstly, some typical and stochastic vegetation distribution scenes will be designed by virtue of the GIS spatial analyst technology, and the sediment yield in these scenes and different rainfall scenarios, will be calculated based on the distributed physical model. Secondly, the coupling effects of vegetation patterns and landforms on downslope erosion and upslope sediment transportation will be analyzed comprehensively. During this process, the explanation capabilities and relationships of existing vegetation patterns indexes on watershed-scale vegetation distribution, hydraulic connectivity and erosion and sediment yield will be compared and then the index considering the coupling effects of vegetation patterns and landforms on erosion and sediment yield will be proposed. Finally, after examining the relationship of the proposed index and erosion and sediment yield under different rainfall and vegetation patterns, a statistic model which can describe the coupling effects of vegetation patterns and erosion and sediment yield under the changing rainfall and vegetation cover will be established on the annual time scale and the special scale of small watershed. The results will be very valuable and useful for the optimization of vegetation patterns of soil and conservation practices and for the impact evaluation of erosion control and sediment reduction.

当前水土资源日益稀缺，优化植被布局将成为生态脆弱区未来阻蚀减沙、改善环境的重要途径。但限于缺乏良好反映侵蚀产沙影响的格局表征指数、尚未建立侵蚀产沙对植被格局直观响应关系等问题，植被格局的流域侵蚀产沙影响仍不明确，远不能满足生态建设科技需求。.项目选择黄土高原典型小流域（吕二沟/12km2，罗玉沟/73km2），借助GIS空间分析设计多种典型和随机植被分布情景，基于分布式物理模型获得其在不同降雨下的侵蚀产沙；以综合考虑植被与地形对下坡侵蚀和上坡输沙的耦合影响为主线，比较现有格局指数对流域植被分布、水文联通和侵蚀产沙的解释能力与相关程度，提出考虑植被-地形叠置格局对侵蚀产沙影响的表征指数，探析其在不同降雨和覆盖条件下与侵蚀产沙协同关系变化，构建针对年际尺度、考虑降雨和植被变化的小流域植被格局与侵蚀产沙耦合关系统计模型。.研究结果将在流域水土保持植被布局优化及阻蚀减沙效应评价中具有重要应用价值。

围绕研究目标，在主要开展上述有关研究的基础上，主要取得了4方面重要认识，有关结果可为流域和区域尺度水土保持林草植被的合理规模确定及其功能与格局优化提供理论依据和科学方法，在土壤侵蚀防治、流域水沙调控和区域生态修复等领域和实践中具有重要现实意义与良好应用前景。①原创了一种考虑植被和地形耦合影响的分布式坡长因子算法，能有有效反映植被与地形对下坡侵蚀产沙过程的综合影响，从而提升基于土壤流失方程模型的流域和区域侵蚀产输预报精度。②创新了一种流域泥沙连通性指数改进算法，并据此提出了分离植被对流域侵蚀产沙本地-异地影响贡献的量化方法，可高效定量评价流域尺度不同植被格局的水沙调控能力，揭示植被格局对流域侵蚀产沙的影响机制。③分析了黄土高塬沟壑区中尺度流域的水沙变化归因，并率先探索了土地利用/覆被格局对黄土高原区域尺度的泥沙产输能力影响，量化了对黄河泥沙减少的潜在贡献。④综合分析了区域植被恢复的水-碳耦合效应与机制，辨识确定了区域植被水分利用效率（WUE）的气候与植被变化响应及其临界阈值，可为以区域以水定绿和节水高效水土保持植被恢复提供科学依据。