The mariculture has been proposed as a crucial approach to achieve carbon neutrality and the sediment beneath is regarded as a carbon sink in recent studies. However, previous studies predominantly focused on carbon deposition processes and failed to constrain the carbon remineralization in the sediment, likely overestimating carbon burial fluxes. In this study, we chose a typical mariculture zone, Sansha Bay of Fujian Province, to study the carbon behavior across the sediment-water interface, and utilized isotopic approaches to quantify the benthic efflux of dissolved carbon and burial flux of particulate carbon. Using the 224Ra-228Th disequilibrium method, we calculated the fluxes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). The results indicated the inner bay station had higher sediment effluxes of dissolved carbon than the outer bay station, with DIC flux of 621.88 ± 242.75 and 142.62 ± 51.60 mmol m⁻² d⁻¹, respectively, and DOC flux of 68.12 ± 26.59 and 19.71 ± 7.13 mmol m⁻² d⁻¹, respectively. Based on a sedimentation rate of 2 mm y-1 derived from sediment excess 210Pb, the average burial flux of organic carbon was calculated to be 222.26 mmol m⁻² d⁻¹. This suggests that the deposited carbon from the water column was not fully preserved in the sediment. Therefore, future studies in the sediment carbon reservoirs should consider both carbon burial and removal, and carbon efflux across the sediment-water interface should not be ignored in achieving precise benthic carbon sink in mariculture areas.
 

Mariculture; Carbon exchange; Sediment-water interface; Isotopic tracing; Sansha Bay.