Effects of rainfall on soil moisture and water movement in a subalpine dark coniferous forest in southwestern China Qing Xu, 1 Shirong Liu, 1 * Xianchong Wan, 2 Chunqian Jiang, 3 Xianfang Song 4 and Jingxin Wang 5 1 Laboratory of Forest Ecology and Environment of State Forestry Administration, Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Beijing, China 2 Institute of New Forest Technology, Chinese Academy of Forestry, Beijing, China 3 Institute of Forestry Research, Chinese Academy of Forestry, Beijing, China 4 Institute of Geographic Science and Natural Resources Research, Chinese Academy of Science, Beijing, China 5 Division of Forestry and Natural Resources, West Virginia University, Morgantown, WV, USA Abstract: Water content and movement in soil profile and hydrogen isotope composition (dD) of soil water, rainwater, and groundwater were examined in a subalpine dark coniferous forest in the Wolong National Nature Reserve in Sichuan, China, following rainfall events in 2003–2004. Light rainfall increased water content in the litter and at soil depth of 0–80cm, but the increased soil water was lost in several days. Heavy rainfall increased soil water content up to 85% at depths of 0–40 cm. Following the light rainfall in early spring, the dD of water from the litter, humus, illuvial, and material layers decreased first and then gradually reached the pre-rainfall level. In summer, light rainfall reached the litter humus, and illuvial layer, but did not hit the material layer. Heavy rainfall affected dD of water in all layers. The dD of soil interflow slightly fluctuated with rainfall events. The dD of shallow groundwater did not differ significantly among all rainfall events. Light rainfall altered the shape of dD profile curve of water in the upper layer of soil, whereas heavy rainfall greatly affected the shape of dD profile curve of water in all soil layers. Following the heavy rainfall, preferential flow initially occurred through macropores, decayed plant roots, and rocks at different depths of soil profile. With continuing rainfall, the litter and surface soil were nearly saturated or fully saturated, and infiltration became homogeneous and plug-like. Forest soil water, particularly in deeper soil profile, was slightly affected by rainfall and, thus, can be a source of water supply for regional needs, particularly during dry seasons. Copyright © 2011 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article. KEY WORDS hydrogen isotopic composition; soil water movement; precipitation; subalpine coniferous forest; Wolong Nature Reserve Received 8 September 2010; Accepted 27 October 2011 INTRODUCTION Water movement in unsaturated soils is an inhomogeneous, nonlinear process (Gehrels et al., 1998; Song et al., 2009) and is influenced by climatic and environmental factors, such as precipitation, evaporation, vegetation, and soil properties (Hsieh et al., 1998; Reynolds et al., 2000; Dawson et al., 2002; Lee et al., 2007). In a forest ecosystem, the distribution of soil water is controlled by precipitation and evaporation and is related to air temperature and humidity (Löffler, 2007). Vegetation can serve as a shield intercepting rainfall and may cause desiccation because of evapotranspir- ation in forest ecosystems. The effect of vegetation on soil water movement strongly depends on vegetation type and density (Gehrels et al., 1998). Soil physical properties have a profound influence on soil water movement. The heteroge- neity of soil texture and porosity makes the processes of unsaturated flow in soils complicated, causes changes in the state and content of soil water during flow, and is thus difficult to describe quantitatively (Hillel, 1998). Precipitation intensity and frequency play an important role in determining soil water movement in terms of infiltration and percolation processes (Lee et al., 2007). Thus, the magnitude, timing, and translocation of precipitation are critical factors influencing the movement and availability of soil water and ecosystem dynamics (Stephenson, 1990; Ferrio et al., 2005). The infiltration and percolation of rainfall can be changed with soil heterogeneity, texture, porosity, and water content (Beven and Germann, 1982; Kung, 1990; Fravolini et al., 2005). For example, at high water content, the downward water movement often is dominated by the flow in soil macropores, whereas at low water content, the flow is maintained in soil micropores (Bengtsson et al., 1987). In rooted zones and below the rooted zones, infiltrating water from rainfall can flow preferentially along highly permeable pathways because of heterogeneous distribu- tion of roots and rocks in forest soils (Gehrels et al., 1998). Considering the interactions among precipitation, vegetation, and soil properties could help understand hydrological processes in forest ecosystems. Stable hydrogen isotope compositions (dD) of soil water are influenced by atmospheric fractionation and water sources such as rainfall, surface runoff, and upward movement of groundwater (Dansgaard, 1964; Zimmerman *Correspondence to: Shirong Liu, Laboratory of Forest Ecology and Environment of State Forestry Administration, Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Beijing 100091, China. E-mail: liusr@caf.ac.cn HYDROLOGICAL PROCESSES Hydrol. Process. (2011) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/hyp.8400 Copyright © 2011 John Wiley & Sons, Ltd.