Characteristics of soil water movement in a grass slope in a karst peak-cluster region, China

摘要

Soil water is very important in hilly areas with thin soil layers and deep groundwater tables, such as the karst peak-cluster region of Southwest China. An investigation into soil water movement can provide insights into management of shallow water resources and soil nutrients, as well as prevention of groundwater pollution. In this study, O-18 and H-2 tracers were used to trace soil water movement in planar soil mass type microhabitats in the middle part of a steep hillslope covered by grasses in a karst peak-cluster region of China. From May 2008 to July 2009, samples of precipitation and two types of soil water, which had different integrated degrees of mobility and were of different depth intervals or depths, were collected. The hydrogeochemical characteristics were compared between precipitation and soil water, and these data were applied in convolution-based lumped parameter models. Our results indicated that vertical piston flow, rather than lateral flow along the soil-bedrock interface, played an important role in soil water percolation at least in the upper soil layer approximately 7cm over the permeable bedrock. The mixing effect and preferential flow might also play a role in soil water percolation. In general, the evaporation effect on soil water was weak except for the uppermost 10cm soil matrix water during winter. The lower limits of mean transit time of soil matrix flow passing through 5, 15, 25, 35, and 41.5cm depths were 4.81, 7.70, 16.19, 21.85, and 27.44days, respectively. Our study demonstrated the crucial functions of the soil reservoir in regulating the water cycle and could provide guidance on conservation of soil water and hydrological studies. The applied method was proved to be a suitable approach for investigating soil water movement on a monthly scale.