Influence of vegetation change on drip water dynamics and geochemical proxies in a shallow karst cave system

Cave drip water is a fundamental carrier of climatic and environmental information, and its geochemical signatures are widely employed in speleothem-based paleoclimate reconstructions. While are well established, the role of rainfall intensity and vegetation-driven infiltration dynamics in shaping these signals remains insufficiently constrained. To address this, we carried out seven years of monitoring in Shawan Cave, a shallow karst cave system in Southwest China, integrating rainfall observations, continuous drip rate measurements at 30-minute resolution, and stable isotopes and elements/Ca data from drip water. Our results showed that drip water was present in both the dry and wet seasons from 2017 to 2019, whereas it was intermittently interrupted from 2020 to 2023 drip water, with more observed during the wet season and less during the dry season. This may be attributed to the deeper root systems of vegetation, which alter soil moisture and the amount of rainfall required to penetrate the soil and generate infiltration into the karst cave system, thereby changing the water reservoirs feed drip water over time. We propose that vegetation recovery, by influencing evaporation, can modulate drip water flow paths and thereby drive the enrichment of drip water δ18O. Intriguingly, although drip water δ18O during 2017–2018 did not fully reflect changes in rainfall δ18O, during 2022–2023 it appeared to inherit the δ18O signal of heavy rainfall. This indicates that drip water δ18O has gradually evolved from reflecting annual or multi-year rainfall amounts to primarily recording the heavy rainfall of the summer monsoon. These observations demonstrate that drip water signals are not simply a direct record of rainfall but are mediated by subsurface hydrological processes. We propose that the combined effects of reservoir-feeding drip water and flow path change over time are critical in governing the transmission of rainfall signals into cave environments. Recognizing the influence of vegetation change and reservoir evolution refines the interpretation of speleothem proxies, enabling more reliable reconstructions of monsoon variability at sub-annual to interannual timescales.