Water Movement Mechanism and Colloid Transport Dynamic from Sloping Farmland of Purple Soil

ZHANG Wei; LYU Yujuan; TANG Xiangyu

doi:10.13522/j.cnki.ggps.2017.0231

Abstract：Soil water potential is the direct indicator of soil water energy and flow direction. Flow generation is greatly affected by the movementof soil water. Colloids usually act as the carrier for agro-chemicals (e.g. nutri-ents and pesticides).[Objective]Explore the water movement and colloid transport characteristics of purple soil in slopory farmland.[Method]Dynamics of soil water, flow generation and colloid transport in a sloping farm-land of purple soil were studied by the in-situ monitoring of soil water content and water potential as well as the subsurface fracture flow.[Result]Purple soil easily got saturated following single heavy storm or consecutive rainfall events with the saturated water content more than 0.45 m3/m3. Rainfall events of high intensities favored the generation of downward piston flow. While the infiltration of the mixture of rainwater and soil water from the upper slope toward to the middle and lower slope following consecutive rainfall events facilitated the supply of deep soil water content, resulting the delayed response of soil water content and water potential. The daily frac-ture flow discharge varied between 0.11 L/min to 36.56 L/min with an intense time variation (Cv=1.72). Daily col-loid concentration in the fracture flow varied between 0.20 mg/L to 15.41 mg/L and it was significantly positively correlated to flow discharge (R=0.73).[Conclusion]Soil water potential shows a more sensitive response to the water movement in the purple soil as compared with soil water content. The combination of these two factors would better reveal the mechanism of water movement. Hydraulic shearing and scouring plays the dominant role in colloid release and transport in the subsurface, and dry-wet cycling would favor the dispersion and generation of soil colloids.