Spectroscopic Indices Reveal Spatiotemporal Variations of Dissolved Organic Matter in Subtropical Karst Cave Drip Water

The migration and transformation of dissolved organic matter (DOM) in highly heterogeneous and permeable karst aquifers are of great significance to the regional carbon cycle but are rarely explored, especially in response to extreme climate events. In this study, we utilized spectroscopic indices to investigate variations in DOM concentration, composition, and origin in Mahuang Cave, Southwest China, from August 2020 to October 2022. The findings indicate that meteorological conditions, hydrological pathways, and in–situ metabolism primarily control DOM dynamics in karst cave drip water. However, due to the complex cave fractures and stratigraphy, the DOM composition at the four monitoring sites—classified into slow and fast seepage—showed different responses to meteorological events. Therefore, surface reworking must be fully considered when assessing the environmental information recorded by cave sediments.