Revealing drivers for the dynamic changes of dissolved organic matter in karst cave water through optical properties

Study Region Mahuang Cave is located in Suiyang County, Zunyi City, Guizhou Province, Southwest China. It is a first-level branch cave of Shuanghe Cave(the longest dolomite cave worldwide). Study Focus This study aims to investigate the composition, sources, and transport processes of dissolved organic matter (DOM) in cave water and to analyze its coupling relationship with dissolved inorganic carbon (DIC). Using EEM-PARAFAC and redundancy analysis, we identified environmental drivers regulating DOM dynamics across different hydrological types. New Hydrological Insights for the Region During the wet season, exogenic humic-like components dominated (53%), In contrast, during the dry season, endogenic protein-like substances increased to 60%. Spatially, DOM was characterized by a high proportion of tyrosine-based compounds (51%-63%). Key findings include that in fast seepage flow, shaft flow and underground river, DOM dynamics were primarily driven by meteorological factors (temperature and precipitation), In slow-flowing systems, they were mainly regulated by hydrochemical parameters (DIC,Ca 2 + +Mg 2+ , p CO 2 ). These findings indicate that karst cave aquifer hydrological pathways acted as biochemical filters, where climate and water-rock interactions jointly regulate the transformation between organic and inorganic carbon forms through microbial metabolisms. This has a potential regulatory effect on regional carbon source and sink patterns, a role that has often been underestimated. Therefore, this study can provide a more nuanced understanding of carbon cycling in subtropical karst aquifers.