Effects of rainfall on soil moisture and water movement in a subalpine dark coniferous forest in southwestern China

Abstract

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 0-80 cm, 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.

Impacts of forest changes on hydrology: a case study of large watersheds in the upper reaches of Minjiang River watershed in China

“…Their results clearly showed that light rainfall (5-15 mm) events only temporally altered the shape of δD profile curve of soil water, and their impacts on the upper soil depth were quickly depleted through evaporation and plant uptake. In contrast, heavy rainfall events (about 30 mm) greatly affected the shape of δD profile curve of soil water in all layers (Xu et al, 2011a). Surprisingly, groundwater in shallow aquifers was not significantly altered at this heavy rainfall intensity.…”

“…Using the isotopic method, Xu et al (2011a) analyzed the responses of δD to different rainfall intensities in different soil layers (litter, humus, illuvial, mineral soil and shallow aquifer) in a subalpine, dark coniferous forest in the Wolong Natural Nature Reserve of the study watershed. They found that different soil layers had different responses (change rates and lengths of residence time) to rainfall intensities and subsequent evapotranspiration, with quick responses in top layers and slow responses in deep layers.…”

Reliability of meteorological drought indices for predicting soil moisture droughts

“…At 20 the 75 th percentile all drought index values below zero were taken as drought events. Together with the pF 5 and pF 30 thresholds, this defines the segments a, b and c used in equation (3) and (4) and illustrated in Appendix B. However the FR and the FAR will be same when we use same threshold of both drought index and soil water pressure (in this study 75 th percentile), because the a and c values in equation (3) and (4) will be same.…”

“…We also evaluated the correlations between pF 5 and pF 30 and 5 SPI i-1 and RDI i-1 in case the three month averages defined in equation (1) and (2) more strongly influence the next month's minimum soil water pressure.…”

“…For each site the threshold that determines a soil moisture drought event was selected by the percentile of all simulated pF 5 and pF 30 that minimizes the FR and FAR (Fig. 3).…”