黄土丘陵沟壑区坡沟系统产流产沙对源-汇-路径格局的响应

坡沟系统是流域水土流失与治理的基本单元，掌握其产流产沙规律是有效解决水土流失区生态环境恢复重建的核心问题之一。该研究利用无人机遥感与地理信息系统技术对流域的土地利用进行识别，再确定5个不同坡沟系统（2个无人为干扰的退耕植被恢复+自然植被坡沟系统SG1和SG2、2个人为扰动的退耕植被恢复+自然植被坡沟系统SG3和SG4、以及1个果园+坡耕地的坡沟系统SG5）内泥沙源、汇及其输移路径分布特征，并在量化指标的基础上，结合2016—2022年坊塌小流域5个坡沟系统的降雨和产流产沙的监测数据，研究了不同坡沟系统的产流产沙特征及其对源-汇-路径格局的响应。结果表明：次降雨条件下，SG1和SG2的产沙模数显著低于其他坡沟系统（P<0.05），且SG3径流深和产沙模数均较大；SG2的年平均径流深显著低于SG5（P<0.05）。坡沟系统径流深分别与总坡沟系统、沟间地、沟谷地的泥沙源和汇最大斑块面积比显著正相关（P<0.05），且与沟间地泥沙源、汇指数的相关系数均要大于沟谷地，径流深与总坡沟系统路径的分岔比、沟间地与沟谷地的路径比降均呈现出显著负相关（P<0.05）；产沙模数与各源汇指数之间均无显著的相关性，但与路径数量密度、长度密度、沟间地的路径分岔比呈显著正相关（P<0.05）；径流深和产沙模数均与路径复杂度呈显著负相关。可见，降低源/汇比例大小，适当增加泥沙输移路径的复杂度和输移距离，可有效减少坡沟系统的水土流失。研究可为坡沟系统土壤侵蚀防控以及流域生态保护和修复提供科学支撑。

Responses of runoff and sediment yield to the source-sink-path pattern in slope-gully system in the hill and gully Loess Plateau region, China

A slope-gully system is one of the basic units in the soil/water loss and governance in watersheds. Among them, the runoff and sediment can greatly contribute to the restoration and reconstruction of the ecological environment in soil erosion areas. The runoff and sediment yield can also depend mainly on the pattern of sediment sources, sinks, and transport paths in the slope-gully system. But it is still lacking in this field. In this study, unmanned aerial vehicles (UAV) remote sensing and geographic information systems were used to determine the distribution and quantitative indicators of sediment source-pathway-sinks in different slope-gully systems. The monitoring data of rainfall and runoff was combined with the sediment yield of five slope-gully systems in the Fangta small watershed from 2016 to 2022, including two with no human disturbance (SG1 and SG2) and two with grazing disturbances (SG3 and SG4) of slope-gully systems with restored vegetation and natural vegetation, one slope-gully system with orchard and sloping cultivated land (SG5). A systematic investigation was made to clarify the properties of runoff depth and sediment yield in five slope and gully systems, together with their responses to sediment source-pathway-sink patterns. The results show that the sediment yield modulus in SG1 and SG2 was significantly lower than that of the rest (P<0.05), and the maximum runoff depth and sediment yield were found in SG3 under rainfall events. The average annual runoff depth of SG1 and SG2 was significantly lower than that of SG5 (P<0.05), and the average annual yield was significantly lower than that of the rest (P<0.05). The runoff depth was significantly positively correlated with the maximum patch index both of the sediment source and sink area in the slope-gully system, valley land, and gully land (P<0.05), respectively. In addition, the degree of correlation between the sediment source and sink index and the depth of runoff in the valley were greater than those in the gully land. The runoff depth also showed a significant negative correlation (P<0.05) with the path number density and the bifurcation ratio in the total slope-gully system, and the path gradient both in the valley and the gully land. There was no significant correlation between the sediment yield modulus and each index of source and sink, but there was a significant positive correlation (P<0.05) between the path length density and the path bifurcation ratio in the valley land. In addition, the increasing path complexity also significantly reduced the runoff depth and sediment yield modulus. In short, the appropriately increasing complexity and transport distance of sediment transport paths can be expected to effectively reduce the soil and water loss in slope-gully systems. This finding can provide scientific support for the prevention and control of soil erosion in the slope and gully systems, the ecological protection, and the restoration of watersheds.