Dynamic variation of dissolved organic carbon in karst cave waters in a subtropical climatic regime

As a very important and active component of organic carbon, the role of dissolved organic carbon (DOC) in a karst dynamic system is worthy of in-depth investigation. Here, we investigated the parameters that affect DOC in the cave waters of Mahuang Cave (wild cave) and Dafeng Cave (show cave) in southwest China during a monitoring period spanning August 2020 to August 2021. Such analysis was conducted by continuously monitoring several environmental indices, including air temperature, precipitation, water temperature, DOC, dissolved inorganic carbon (DIC), pH, pCO(2), electrical conductivity (EC), and anions and cations. Our results revealed that high levels of DOC in cave water appeared after a short dry period in late Autumn 2020 and May 2021. The variation of DOC concentration was mainly controlled by meteorological conditions and was strongly associated with water-rock-air interactions during the monitoring period. However, no significant connection was observed between variations in DOC concentration and caves. We conclude that DOC in cave water could be used as a paleoclimate proxy and that its relevance with karst carbon sink is considerable.