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

• Precipitation/throughfall changed water isotopes in litter, humus, and shallow soil.
• Mean effective contribution times of recharge in soil occurred 3 to 5 days.
• Preferential flow and interflow were dominant in hillslope during the rainy season.

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 (0 cm to 50 cm deep) by affecting preferential flows. (2) Rainwater from a small precipitation event (about 4.0 mm d− 1) also penetrated soil to depths of 40 cm to 50 cm. (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 3 mm d− 1. (4) Mean effective contribution times of recharge in soil (0 cm to 50 cm deep) occurred 3 to 5 days despite the occurrence of large precipitation events (15.0 mm and 18.9 mm). 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.