High stability of carbonate weathering relevant carbon sink under biological pump effect in inland waters: Insights from Shawan Karst Experimental Site, Southwest China

Abstract

The dissolved inorganic carbon (DIC) produced by carbonate weathering may be lost by degassing or be biologically fixed as it transports from inland water to the ocean. Knowledge of DIC stability under these two processes in surface water systems is crucial for evaluating the role of carbonate weathering in the global carbon cycle. Here, we evaluated the net ecosystem productivity of aquatic ecosystems (NEPs), water‒air CO2 exchange fluxes (FCO2), and Carbon budgets (Carbonbudget=(TOCoutput+0.5DICoutput)−(TOCinput+0.5DICinput)) in five simulated spring-pond systems controlled by carbonate weathering and different land uses. Using these parameters and the unique structure of our simulation site, the stability of the carbonate weathering-driven carbon sink (DIC) in surface water was discussed. The results showed that the NEP and FCO2 of the study site presented significant negative relationships and were mainly controlled by aquatic ecosystem metabolisms than abiotic processes. Most aquatic ecosystems in our study site were autotrophic (NEP>0) due to the strong biological carbon pump effect (BCP) induced by carbonate weathering. Moreover, the DIC input enhanced the FCO2 in the warm season. The intensive BCP enhanced both CO2 release and atmospheric CO2 invasion. Moreover, we found that the stability of DIC was positively related to DIC input, which can be influenced by BCP and human land use. After considering the net changes in Carbon budget through the groundwater-surface water systems, a high average carbon stabilization rate (CSR) of approximately 103.7% of carbonate weathering carbon sink was found in our study site. This indicated that BCP could retain most of the DIC that was driven by carbonate weathering. Therefore, due to the high stability of the carbonate weathering carbon sink under the BCP, we stress that it should be considered a significant carbon sink in the global carbon cycle.