Stable Isotopes Reveal the Effect of Canopy and Litter Layer Interception on Water Recharge in a Subtropical Manmade Forest of Southwest China

Abstract

In areas completely covered by vegetation, the rainwater that passes through the canopy layer and litter layer is the source supplying surface runoff and seeping into the soil layer. To reveal the influence mechanisms of the canopy and litter layer on water supply in forest areas, this study conducted event-scale water sampling and hydrogen and oxygen isotopic comparison for the rainfall, canopy throughfall and litter layer throughfall in a manmade forest. The results show that canopy interception will lead to a more concentrated distribution and lower isotopic variability. The d-excess and the intercept and slope of the δD-δ18O regression line of the canopy throughfall are slightly higher than those of rainfall, reflecting that the evaporation fractionation caused by canopy interception is weak, and the selection process may play a leading role. Compared with the canopy throughfall, the distribution of the δ18O, δD and d-excess in the litter layer throughfall is more dispersed, and the slope and intercept of the δD-δ18O regression line are higher, indicating the strong influence of non-equilibrium fractionation on the water input caused by litter layer interception. The isotopic differences between the litter layer throughfall and canopy throughfall indicate that the water components of small-scale precipitation events (precipitation amount lower than 5 mm) and the early stage of large-scale precipitation events (precipitation amount higher than 25 mm) may be dissipated by litter layer interception, while that of the latter stage of large-size events is slightly affected. The findings of this study will be helpful to deeply understand the mechanisms of the water cycle in the forest ecosystem under the background of climate change and provide insights for the sustainable utilization of water resources.