Soil moisture response to rainfall in forestland and vegetable plot in Taihu Lake Basin, China

Abstract

Soil moisture and its spatial pattern are important for understanding various hydrological, pedological, ecological and agricultural processes. In this study, data of rainfall and soil moisture contents at different depths (10 cm, 20 cm, 40 cm and 60 cm) in forestland and vegetable plot in the Taihu Lake Basin, China were monitored and analyzed for characteristics of soil moisture variation and its response to several typical rainfall events. The following results were observed. First, great temporal variation of soil moisture was observed in the surface layer than in deeper layer in vegetable plot. In contrast, in forestland, soil moisture had similar variation pattern at different depths. Second, initial soil moisture was an important factor influencing the vertical movement of soil water during rainfall events. In vegetable plot, simultaneous response of soil moisture to rainfall was observed at 10- and 20-cm depths due to fast infiltration when initial soil was relatively dry. However, traditional downward response order occurred when initial soil was relatively wet. Third, critical soil horizon interface was an active zone of soil water accumulation and lateral movement. A less permeable W-B soil horizon interface (40-cm depth) in vegetable plot can create perched water table above it and elevate the soil water content at the corresponding depth. Fourth, the land cover was an effective control factor of soil moisture during small and moderate rainfall events. In the forestland, moderate and small rainfall events had tiny influences on soil moisture due to canopy and surface O horizon interception. Fifth, preferential flow and lateral subsurface interflow were important paths of soil water movement. During large and long duration rainfall events, lateral subsurface flow and preferential flow through surface crack or soil pipe occurred, which recharged the deep soil. However, in more concentrated large storm, surface crack or soil pipe connected by soil macropores was the main contributor to the occurrence of preferential flow. Findings of this study provide a theoretical foundation for sustainable water and fertilizer management and land use planning in the Taihu Lake Basin.