Spatio-Temporal Dynamics of Soil Moisture in Different Vegetation Types in Semiarid Area of the Loess Plateau

摘要

Implementation of Six Forest Protection Programs has undoubtedly played a positive role to improve ecology and environment as well as erosion control. But meanwhile, the negative influences of large-scale forest programs on water resources also attracted more attention by both researches and relevant governors, especially for arid and semi-arid area of the Loess Plateau, where the water shortage is a key limited factor for human being and ecological demands. This study focuses on the spatial and temporal distribution of soil moisture in different vegetation covers. The typical study area is in the Caijiachuan watershed. The soil moisture was detected from surface to 2 m in the soil profile (every 20 cm soil as one layer), with a Time-Domain Reflector (TDR) in ll different sites from 2004 to 2008. Combined with rainfall data in the study area, this paper analyzed the spatial and temporal variability of soil moisture in different vegetations in the research area. The main results are as follows: (l) The dynamic change of soil moisture during the growing season mostly depended on rainfall and its distribution. eSDeciallv for soil moisture in shallow soil layers, and the change of soil moisture lagged gradually from top to deeper layers in the profile. The dynamic change of soil moisture was seasonal, and could be classified into two stages: consumption and accumulation. (2) Water consumption increased with an increase in forest density for the same tree species. (3) The variance coefficients of soil moisture decreased with increase m soil depth, based on two indicators: coefficient of variation and standard deviation. Variation of soil moisture in the soil profile was divided, and the reasonability and accuracy of divided results were proved through research on tree roots distribution. In a normal rainfall year in the Loess Plateau, if rainfall had no unusual distribution or was not affected by abnormal rainfall in the previous year, the precipitation and rainfall distribution affected the depth and intensity of soil moisture infiltration; there was more precipitation, soil moisture infiltration and active layer of soil moisture were deeper, and the variation degree of soil moisture of deep-root vegetation was wider than that for shallow-root vegetation.