Variations of soil water isotopes and effective contribution times of precipitation and throughfall to alpine soil water, in Wolong Nature Reserve, China

Abstract

Alpine shrubs and soils in catchments of the headwaters of the Yangtze River in west China are very important for reducing flooding and sustaining base flow during the summer. However, the contributions of precipitation, throughfall, and interflow to soil water and their effective contribution times in alpine shrub soil are not fully understood. In this study, we investigated a time series of stable isotopes in soil water, precipitation, canopy throughfall, interflow, litter, and humus water in a hillslope area. In addition, the spatial variation of water isotopes in soil profile in the Wolong Valley, located in the upper watershed of the Yangtze River, Sichuan, China, was considered. We found that (1) precipitation and throughfall significantly affected water isotopes in litter, humus, and shallow soil (0cm to 50cm deep) by affecting preferential flows. (2) Rainwater from a small precipitation event (about 4.0mm d−1) also penetrated soil to depths of 40cm to 50cm. (3) Interflow could comprise as much as 96% of water in soil columns during non-rainy days, but the proportion would decrease quickly after the precipitation amount reached more than 3mm d−1. (4) Mean effective contribution times of recharge in soil (0cm to 50cm deep) occurred 3 to 5days despite the occurrence of large precipitation events (15.0mm and 18.9mm). Therefore, preferential flows composed of precipitation/throughfall and interflow were dominant in hillslope hydrology in the southeast edge of Tibet, which caused runoff to increase during the rainy season.