Organic and inorganic carbon stocks and the drivers of their remobilisation in an abandoned Mediterranean saltpan

Marine saltpans are anthropogenically modified coastal wetlands used for salt extraction. Their shared characteristics with natural saline wetlands confer significant potential for carbon sequestration. However, the abandonment of saltpans may lead to positive CO 2 fluxes from their bare sediments. To date, no studies have quantified positive dark CO 2 fluxes from abandoned saltpan sediments or identified the environmental drivers of these fluxes. In this study, we analysed organic and inorganic sedimentary carbon stocks in an abandoned saltpan and measured CO 2 fluxes from drained sediments, examining their relations with environmental variables. Organic and inorganic carbon stocks were comparable to those in natural saline wetlands, with the inorganic fraction representing 17–62% of the total carbon stock in the sediment top 35 cm. Positive dark CO 2 fluxes were higher than those reported in natural saline wetlands; the main drivers exerting a positive effect on dark CO 2 fluxes were temperature and organic carbon content. In contrast, inorganic carbon content in sediments had a negative effect on the dark CO 2 fluxes. Our results indicate that, although the Marchamalo saltpan holds substantial carbon stocks, there were intense positive dark CO 2 fluxes during the cessation period. Furthermore, they suggest that inorganic carbon may play a critical role in the carbon cycle of hypersaline wetlands and highlight the need to manage abandoned saltpans appropriately to prevent high rates of CO 2 fluxes that may further intensify climate change effects. The rehabilitation and management of these systems may promote carbon sequestration, although further research is needed to infer their carbon dynamics.