Geochemical responses of cave drip water to vegetation restoration

摘要

The transmission of stable isotopes and elements/ions from the outside to the inside of a cave and their incorporation into drip water can involve numerous biogeochemical processes. To understand how the original signals of stable isotopes and elements/ions are modified by these processes, integrated studies of the interactions between vegetation, soil, epikarst, and caves are required. We conducted a multi-year monitoring study of the vegetation biomass, tree breast-height diameter, PCO_2 in soil air and cave air, δ~(13)C in soil air, stable oxygen isotope in rainwater and drip water, and stable carbon isotope and elements/ions concentrations in drip water in Shawan Cave system, southwest China. The main results were as follows: (1) The evaporation effect weakened and the transpiration effect strengthened outsides the cave as vegetation improved, thus leading to a year-byyear increasing trend in the δ~(18)O value of drip water. This indicates that changes in vegetation may have been another potential factor influencing the interannual variation of the δ~(18)O value of drip water. (2) The CO_2 concentration and δ~(13)C value in soil air increased and decreased, respectively, with vegetation restoration,which caused the interannual variation in the dissolved inorganic carbon isotope (δ~(13)C_(DIC)) value of drip water during the autumn and winter to exhibit a year-by-year decreasing trend. (3) The variations in the elements/ions concentrations of drip water were affected by vegetation uptake, vegetation transpiration, and water-rock interactions. It is inferred that the interannual variation in the elements/ions concentrations of drip water responded to vegetation restoration. (4) A conceptual model demonstrated that the three response modes of drip water δ~(18)O value, δ~(13)C_(DIC) value, and elements/ions to variations in vegetation. Overall, this study highlights the responses of the interannual changes in δ~(13)C_(DIC), δ~(18)O, and elements/ions of dri