紫色土坡地泥岩裂隙潜流中的胶体迁移

Field-scale study of colloid transport in fracture flow from a sloping farmland of purple soil

为探求自然胶体迁移进入地下水的潜力,建立原位坡地径流观测场,研究了2013年夏季3场不同雨型降雨事件下,紫色土坡地（1 500 m2）泥岩裂隙潜流中自然胶体的迁移规律。结果表明：裂隙潜流中胶体对降雨的响应时间为30~90 min,比潜流对降雨的响应更迅速,且取决于坡地雨前干旱情况及降雨强度;胶体浓度峰早于潜流流量峰,峰值浓度相对背景浓度可增加1~2个数量级,最大雨强及雨型决定潜流流量和胶体浓度峰型。气液界面是胶体初始迁移响应的主要驱动因素,雨水混合土壤前期水对土壤介孔和大孔内壁胶体的剪切、裹携是胶体释放、分散与迁移的主要机制。因此,胶体辅助运移可能成为紫色土地区吸附性较强的污染物（如磷、疏水性农药等）的重要迁移方式。

To evaluate natural colloid transport potentials into groundwater, via fracture flow, a field-scale study was undertaken on a large sloping farmland plot （ 1 500 m2） in central Sichuan in the summer of 2013. Results indicated that colloid response times varied between 30--90 rain; this depending mainly on the preceding soil moisture content and the intensity of rainfall. Colloid flushing occurred prior to peak fracture flow; with colloid concentration peaks ap- pearing earlier than maximum discharge peaks. Peak colloid concentrations were 1--2 orders of magnitude larger than background colloid concentrations. Maximum rainfall intensity and patterns of rainfall dominated fracture flow and colloid concentration. Processes at the air-water interface are suggested to be the main driving factor controlling colloid release and transport during initial responses to rainfall. At these times, the flushing of colloids from soil mesopores and macropores surfaces, driven by the mixing of event rainwater and pre-event mobile soil water, is suggested to be the major mechanism of colloid mobilization and subsequent transport. It is submitted that colloid-facilitated transport could be a very important pathway for the migration of contaminants, particularly those that show large adsorption affinities to soil particles （e.g. phosphorus and hydrophobie pesticides） , in the vast purple soil region of Sichuan.