Soil colloids mobilized from a sloping farmland during the flow process can act as a carrier of agricultural chemicals. On a purple soil sloping farmland (1500 m2) in Sichuan Basin, fracture flow water sources were identified using the 18O tracing technique, and the dynamics of colloid transport were explored for two rain events on August 29th and September 10th , 2014. The results showed that, in response to the rain events, both hydrograph and colloid concentrations of fracture flow showed a pattern of early rapid rising to a peak followed by slow decrease with a long tail. Rainwater′s contribution to flow increased at the early stage of fracture flow, while pre-event mobile soil water appeared to be the main water source of fracture flow at peak flow discharge and the receding stage. Colloid concentration in the fracture flow varied from 0. 60 to 6. 85 mg∕L, with average concentrations of 1. 58 and 2. 31 mg∕L, respectively, during the two events. Ultrasonic dispersion treatment of the water samples resulted in an average increase of colloid concentration of 1. 15 and 0. 81 times for the two rain events, indicating a high degree of the aggregation of mobilized colloids. For small rain events of long duration, fracture flow chemistry (e.g. ρ(DOC), ρ(Mg2+) and EC ) dominated colloid transport dynamics;however, for the heavy storms, fracture flow rate also had a strong influence on colloid transport ( R2 > 0. 5 ) . In addition, soil water movement pattern ( laterally or downward) affected the discharge of colloid from the sloping farmland. The combined use of fracture flow hydrograph′s response to soil water potential dynamics, 18 O and conservative flow tracers is an effective way to reveal the in-depth mechanisms of fracture flow generation and colloid transport, and to support the quantification of colloid-facilitated transport of agricultural chemicals (e.g., phosphorus and pesticides).%土壤胶体是坡耕地农化物质迁移的主要载体.借助18 O(氧同位素)示踪技术,探索了2014年8月29日和9月10日两场降雨下大型紫色土坡耕地(1500 m2)裂隙潜流产流的水源来源及过程特征,并耦合了胶体颗粒释放与迁移机理的研究.结果表明,裂隙潜流及胶体迁移的水文过程线均总体呈快速上升和长拖尾的特征.随裂隙潜流产流开始,雨水对潜流的贡献逐渐增大,并在流量快速上升段支配裂隙潜流产流,而潜流流量峰值前及退水阶段,土壤前期可动水是潜流的主要产流来源.两场降雨下裂隙潜流中胶体颗粒浓度介于0.60~6.85 mg∕L之间,平均值分别为1.58和2.31 mg∕L,水浴超声后胶体颗粒浓度平均值分别为原样的2.15和1.81倍.胶体颗粒迁移速率比产流速率快(>30 min),表明胶体辅助坡地农化物质迁移的潜力较大.对于长历时小降雨事件,潜流中胶体的迁移动态受潜流水化学因素〔如ρ(DOC)、ρ(Mg2+)和EC(电导率)〕支配,而强降雨事件下,潜流中胶体颗粒浓度还与潜流流量呈极显著负相关(R2>0.5).此外,坡地内部产流方式(横向及垂向)对裂隙潜流中胶体颗粒的迁移通量有重要影响.研究显示,裂隙潜流产流过程线结合土水势、18 O及水化学指标的动态变化,能够全面揭示裂隙潜流产流的阶段特征以及胶体颗粒释放与迁移的机理,对于进一步研究胶体对磷、有机农药等憎水性农化物的辅助运移特征有重要意义.
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