Hillslope soil moisture temporal stability under two contrasting land use types during different time periods

Abstract

Knowledge of soil moisture temporal stability and its controlling factors is important for hydrological and environmental management decisions. This study analyzed the influences of soil and terrain on soil moisture temporal stability (relative difference of soil moisture—δ and standard deviation of δ − Sδ) on two contrasting land use hillslopes [tea garden (TG) and bamboo forest (BF)] in the hilly area of Taihu Lake Basin, China. Soil moisture temporal stabilities were considered at two depths (0.1 and 0.3 m) and during eight different periods (entire, dry, wet, rain, spring, summer, fall and winter periods). Results showed that for each land use and soil depth, values of δ in summer were largely deviated from those during the entire period, while values of Sδ after rain storms were strongly deviated from those during the entire period. Correlation coefficients between soil/terrain and δ were generally greater on the BF hillslope (ranged from 0.35 to 0.70) than on the TG hillslope (ranged from 0.30 to 0.55). This suggested that soil moisture distribution was more spatially organized on the BF hillslope than on the TG hillslope. This can be attributed to that the management practices disturbed and mixed the soils on the TG hillslope, which made the soil moisture more randomly distributed. The controls on Sδ substantially varied with season, soil depth and land use. On the TG hillslope, soil/terrain had weak correlations with Sδ, while on the BF hillslope, rock fragment, slope and elevation had decent correlation with Sδ. This varied controlling factors of Sδ on different hillslopes, period and soil depth suggested that spatial distributions of Sδ were influenced by the occurrence of subsurface preferential flow. Findings of this study suggested that soil moisture temporal stability and its controlling factors were land use type and time period dependent.