大规模果园开发对南方红壤丘陵区水土流失的影响及其机理研究

The problem of soil erosion in red soil regions of southern China is serious and has long been a priority and hotspot issue for research. As the main drinking water source of Hong Kong and Pearl River Delta, the problems of ecological environment of head waters of Dongjiang River have drawn the most attention. In recent years, the problem of soil and water loss under forest with "Far look green, near the water and soil loss" was serious due to development of fruit industry. The land use/land cover changes accompanying with single hierarchy, missing of undergrowth and less coverage or no coverage under the surface. Analyzing the mechanism of production of soil and water loss and quantifying the contribution rate of orchard development to soil and water loss was the key to control soil erosion in head waters of Dongjiang River. The Dongjiang River head source was selected as the study area. The runoff plot test with different inter-cropping pattern for orchards were scattered to obtain the parameters of palnt and properties. Also, the slope-length auto modified module was used to establish the sediments yield model for hilly area with red soils based on SWAT model. Based on the results of runoff plot test and land use scenarios simulation, the runoff and sediments yield were calculated with SWAT model. At last, orchard development model with good effect on Soil and water conservation were selected to achieve the purpose for reducing sediment yield but not runoff yield. The study provided a scientific base for water and soil conservation in Dongjiang River source area and hilly area with red soils of southern China.

南方红壤丘陵区是我国主要的水土流失治理区，东江源作为香港和珠三角饮用水源地，其生态环境问题广受关注。近年来东江源规模化果园开发，造成树种单一、林下灌草层缺失，导致“远看青山在，近看水土流”的林下流问题突出。探究林下流的产生机理，定量评估大规模果园开发对产生林下流的作用大小是治理水土流失的关键。本研究拟以东江源为研究区，布设果园不同套种模式的径流小区，通过样区试验获取大规模果园开发这一典型红壤丘陵区土地利用方式下的植被属性、土壤理化性质等参数，探索林下流的产生机理；引入坡长自动修正模块，结合径流小区实验获取的植被/土壤等属性值，调整模块参数，建立适合研究区的SWAT模型；依据果园径流小区试验结果，设计SWAT模型模拟情景，计算不同情景下的径流和产沙量，探索具有良好水土保持效果的果园开发模式，达到既能减少泥沙产出又能保证水源地径流量的效果，为治理东江源乃至南方红壤丘陵区的水土流失提供决策依据。

近30年来赣南红壤丘陵区受大规模果园开发活动影响，水土流失严重，威胁区域生态环境安全，尤其是饮用水源地河流水生态安全。项目围绕东江源流域柑橘等果树大面积种植及水土保持措施不当引发的土壤侵蚀问题及机理的关键科学问题，从径流小区实验到流域等不同尺度，采用野外监测与室内分析数据、模型模拟等方法，揭示赣南红壤丘陵区大规模果园开发背景下水土流失发生过程及机理，辨识其时空分布特征和驱动因素，并评估不同治理模式的水土保持效益，筛选适宜的土地管理措施。主要研究结果如下：（1）相同雨强条件下，径流小区产流产沙开始时间及速率受土壤前期含水量的影响，连续降水及合适雨强易发生土壤侵蚀；植株大小及林下植被覆盖度也是影响坡面产流产沙的重要因子；（2）东江源寻乌水流域降水与径流在1980-1992年呈下降趋势，2009-2016年呈现增长趋势，泥沙在2009-2016年呈增长趋势；定南水流失降水与径流与寻乌水变化趋势类似，径流在1998年突变，降水突变不明显；水沙值集中在3-9月，与降水变化基本一致，最大值出现在5月或6月；（3）东江源寻乌水流域1990-2015年间果园增长42.8%，林地减少36.83%，下垫面变化剧烈。SWAT模型适合流域水沙模拟，并对流域缺失水沙数据进行插补，1990-2000年产流产沙率分别为3.0%和5.28%，2001-2015年分别为-0.41%和-0.95，与果园开发初期植株较小及林下植被覆盖较少有关。随着果树生长及水保措施完善，水土流失减轻；（4）考虑成本及经济效益，果树不同生长阶段应采取不同的水保措施。果树种植初期易发生水土流失，应采取“反式梯田+梯面梯壁植草” 方式，成熟果林可使用“普通梯田+梯壁植草”方式。本研究有助于对红壤丘陵区水土流失过程及机理的认识，为源区水生态环境建设与管理提供科学依据。