The budget of dissolved inorganic carbon in the shellfish and seaweed integrated mariculture area of Sanggou Bay, Shandong, China

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Abstract A dissolved inorganic carbon (DIC) budget was constructed for Sanggou Bay, Shandong, China. This was based on field data on sea-air flux, primary production, river runoff, advection flux, etc. during four cruises from April 2013 to January 2014, and these data were combined with those taken from the literature related to sediment remineralization, annual river discharge, etc. Results showed that Sanggou Bay acted as a net importer of DIC. The DIC flux exchanged across the sea-air interface was the largest contribution to the net DIC input of this bay, comprising 59.3% of the total DIC net input. Other inputs, in order of importance, were sediment remineralization (18.1%), horizontal advection (16.7%), submarine groundwater discharge (4.2%) and river runoff (1.7%). Seaweeds ( Saccharina japonica and Gracilaria lemaneiformis ) as well as phytoplankton were greatly involved in the carbon biogeochemical cycle and acted to update inflowing DIC. The total amount of DIC sequestration caused by photosynthesis was about 1.36 × 10 5 t. Although forms of the scallop ( Chlamys farreri ) and oyster ( Crassostrea gigas ) absorb a certain amount of DIC into their shells, the DIC released from respiration and calcification processes counterbalance this sequestration. In terms of the bay scale, Sanggou Bay acted as a net DIC sink with an annual mean uptake of DIC estimated at 1.39 × 10 5 t. These findings provided powerful support for revealing the role of Sanggou Bay in the carbon cycle. Statement of relevance This study is relevant for understanding the effect of mariculture on the marine carbon cycle.