Soil Water Content Variations and Hydrological Relations of a Typical Land Use Pattern in an Arid Inland River Basin of Northwest China

Abstract:

A good understanding of the interrelations of a typical land use pattern was essential for ecosystem management and water resources distribution in arid inland river basin. This study was conducted to compare the soil water content and explore the hydrological relation of a cropland-treebelt-desert system at the oasis-desert ecotone in the middle of China’s Heihe River Basin. Volumetric soil water content, the relationship between treebelt water use characteristics and groundwater, and plant root distribution were measured. The results showed that the mean volumetric soil water content in the 0-200 cm layer was greater in the cropland (8.88%) than that in the treebelt (5.78%) and desert (4.37%) as a result of frequent irrigation events. However, the cropland had noticeably lower mean volumetric soil water content below 200 cm depth (14.27%), compared to treebelt (18.07%) and desert (17.30%) with deeper roots to suck up groundwater. Groundwater table had negative impact on tree transpiration. The contribution of groundwater to tree transpiration was estimated to be 35.1% and 19.0% in 2012 and 2013, respectively. The great precipitation in 2013 weakened the dependence of tree transpiration on groundwater. The hydrological relation between treebelt and cropland in the upper soil layer was mainly occurred by treebelt root water uptake from cropland. The biomass of fine treebelt root extended into the cropland decreased logarithmically with the distance from the cropland-treebelt interface, which resulted in the smaller volumetric soil water content in the cropland with more proximity to the treebelt. Meanwhile, the threshold distance of cropland irrigation influencing the tree transpiration was about 8 m. The hydrological relation in the lower soil layer among cropland-treebelt-desert was caused by groundwater recharge, as cropland irrigation raised up the groundwater level to replenish the deep soil layer. The percolation in the cropland was an important water source for the growth of treebelt and desert plants.