Examining the role of throughfall and stemflow on epikarst water recharges using deuterium excess data

Determination of the vegetation effect on epikarst water recharges on permeable bedrock is important for the effective management of groundwater resources in forested area. However, little information is available on the effect of fine-scale throughfall and stemflow on epikarst water sources in karst regions. In this study, the oxygen (δ 18 O) and hydrogen (δD) isotopic compositions of throughfall, stemflow, and borehole water in forested area (TO) and shrubed area (CA) were determined. In this study, the mean daily volume of throughfall (45.89 ± 26.22 mm) was far higher than that of stemflow (0.74 ± 0.51 mm). Using a mass-balance equation, throughfall contribution to groundwater recharge and stemflow contribution to groundwater recharge in TO sample plot were 49 and 51%, respectively. While in CA sample plot, throughfall contribution to groundwater and stemflow contribution to groundwater was 43.7 and 56.3%, respectively. Compared with throughfall, stemflow was only a small part of the storm input; however, it composed of the similar recharge proportion to epikarst water. Stemflow drainage from trees rapidly concentrates large volumes of water by preferential flow which bypass root–rock interface, while throughfall produced scattered point-source inputs to epikarst zone by piston flow. Throughfall and stemflow recharge to epikarst zone in vegetation area was not statistically correlated with rainfall, throughfall volumes, stemflow volumes, and groundwater depth, which was related with the structure and conduit connectivity of karst water-bearing medium. The results provided useful suggestions on groundwater exploitation and utilization in karst areas.