Wetlands play an important role in the global carbon cycle but are intensively disturbed by humans. Estimating the gaseous carbon budget of degraded wetlands has great significance for wetland conservation. The Shanyutan wetland is a degraded tidal wetland in Southeast China. We compared the landscape patterns of Shanyutan in 2009 and 2019 based on remote sensing images and determined the sediment CO₂ flux (excluding root respiration) in various land types. We combined the sediment CO₂ flux with the wetland CH₄ flux, and the CH₄ and CO₂ fluxes of aquaculture ponds, as well as net plant carbon sequestration (NPCS) from previous studies, and calculated the gaseous carbon budget of Shanyutan for the 10-year period. Our results show that the areas of aquaculture ponds and mudflats increased over the 10-year period, whereas those of vegetated marsh and sand decreased. Determination of the sediment CO₂ flux indicates that sediment CO₂ flux is higher in vegetated marsh and lower in bare land, with the highest annual flux in Spartina alterniflora marsh and the lowest in sand. The gaseous carbon budget shows that aquaculture ponds and bare land are sources of atmospheric carbon, whereas vegetated marsh serves as a sink. The entire wetland was an atmospheric carbon sink in 2009, with a carbon sequestration rate of 1364.4 tC·a⁻¹; however, it became a source in 2019 due to destruction, with a carbon efflux of 1072.6 tC·a⁻¹. Moreover, the gaseous carbon balance in Shanyutan had a climate-warming potential, with an equivalent CO₂ production of 5971.8 t·a⁻¹ in 2009, and this potential increased ~9 times over the 10-year period. Finally, we conclude that restoring the carbon cycle of Shanyutan has considerable future economic value.