Effect of extreme precipitation events on the hydrochemistry index and stable isotope compositions of drip water in a subtropical cave, Guangxi, SW China

To study the effects of extreme precipitation events on drip water in Liangfeng Cave, hydrochemistry and stable isotope compositions of drip water and pool water samples, as well as contemporaneous precipitation samples were measured. Results show that cave temperature had marked diurnal variations, with similar trends to atmospheric temperature on season timescales. However, the amplitude of cave temperature variation was less than atmospheric temperature, related to "buffering effects" inside the cave. Drip water and pool water ionic concentrations of Ca2+, , and specific conductivity increased after extreme precipitation events, while values of delta D, delta O-18 and delta C-13(DIC) in drip water and pool water became more negative. However, samples from sites LF-9 and LF9-1 showed a longer delay to these effects, related to their longer flow paths. The delta D and delta O-18 composition of precipitation mainly controlled the isotope values in drip water, because this mainly depends on water vapor source. However, the delta C-13(DIC) of drip water and pool water negative excursions were likely caused by massive amounts of soil CO2 dissolved by percolating precipitation. Thus, hydrochemistry and stable isotope signals in cave drip and pool water appear to mainly reflect precipitation information during extreme precipitation events. Although at different drip sites (e.g., LF-9 and LF9-1), variable hydro-geochemical processes produce different timing and duration to changes in hydrochemistry and stable isotope signals.