黄土丘陵区坡面植被盖度及其配置格局的水蚀效应模拟

黄土高原因土壤侵蚀严重被视为生态脆弱地带,探讨植被盖度及其所处坡位对土壤侵蚀的响应,对坡面侵蚀产沙的预测和调控具有重要意义。基于WEPP模型情景模拟,分析了分布广泛、耐旱性强的长芒草和典型恢复灌木植被柠条在不同雨强(0.5、1.0、1.5 mm/min)、不同植被盖度(20%、40%、60%、80%)和不同坡位(坡上、坡中、坡下)条件下的土壤侵蚀变化情况,运用双因素方差分析和相关贡献指数阐明坡面侵蚀产沙特征对坡位和植被盖度交互作用的响应,并提出植被配置的优化模式。结果表明:(1)提高植被有效覆盖度是减小土壤侵蚀的重要举措,且当植被分布在下坡位时坡面土壤侵蚀最少;(2)植被盖度可以有效减少产沙量。小雨强时,柠条和长芒草随盖度增加对泥沙的拦截率分别从38%增加到90%,64%增加到96%;中、大雨强时,植被盖度小于20%或者大于80%时,长芒草坡面产沙量大于柠条坡面。盖度为40%—60%时,长芒草坡面产沙量小于柠条坡面;(3)双因素方差分析表明:坡位和植被盖度对坡面侵蚀产沙量有极显著的影响(P0.001);当植被是长芒草时,坡位和植被盖度交互作用对坡面侵蚀产沙有显著影响(P0.01),植被是柠条时,坡位和植被盖度交互作用对坡面侵蚀产沙作用不显著;(4)通过模拟柠条和长芒草不同配置情景得出:长芒草分布在坡面下部产沙量较小,且当柠条和长芒草配比为1∶2时产沙量最小。

Simulation of the effect of slope vegetation cover and allocation pattern on water erosion in the loess hilly region

Owing to severe erosion, ecosystems in the Loess Plateau in China are regarded as the most fragile habitats globally. Therefore, it is fundamental to explore the response of water erosion dynamics to vegetation cover and slope allocation, aiming at the accurate prediction and control of sediment yield. In the present study, the WEPP(Water Erosion Prediction Project) model was used to simulate the rainfall-erosion process at a hillslope scale, and the changing processes of soil erosion under different rainfall intensities (0.5, 1.0, 1.5 mm/min), vegetation canopy cover (20%, 40%, 60%, 80%), and slope position (upper, middle, lower) were analyzed. The responses of sediment yield to the interaction effects of vegetation canopy cover and slope positions were revealed by a double factor variance analysis and relative contribution index. The results showed that an increase of vegetation canopy cover reduced soil loss and sediment yield significantly, and the least soil loss occurred when the vegetation was distributed in the lower slope conditions. At a low (0.5 mm/min) rainfall intensity, with increased vegetation canopy cover, the interception rate of sediment of Caragana and Stipa bungeana increased from 38% to 90% and 64% to 96%, respectively. At medium (1.0 mm/min) and high rainfall (1.5 mm/min) intensities, when the vegetation canopy cover was < 20% or > 80%, the sediment yield of the S. bungeana slope was greater than that of the Caragana slope. However, when the vegetation canopy cover was between 40% to 60%, the sediment yield of the S. bungeana slope was less than that of the Caragana slope. Meanwhile, a double factor variance analysis showed that slope position and vegetation cover exhibited a significant effect on sediment yield on slopes (P < 0.001). Specifically, the interaction between the slope position and S. bungeana vegetation cover showed a significant effect on sediment yield (P < 0.01), but when the vegetation changed to Caragana, the interaction between slope position and vegetation cover became insignificant on sediment yield. Moreover, when S. bungeana was allocated on the down slope, or when the allocation of Caragana and S. bungeana was 1:2, both captured the least sediment yield.