- The carbonate system and its controlling factors in a mariculture area were studied.
- Massive bay scallop farming was a potential factor for coastal acidification.
- Scallop calcification reduced 75.66 μmol kg−1 of total alkalinity in surface water.
- Biochemical and physical processes jointly controlled the other CO2 parameters.
Seven cruises were carried out in a bay scallop (Argopecten irradians) farming area and its surrounding waters, North Yellow Sea, from March to November 2017 to study the dynamics of the carbonate system and its controlling factors. Results indicated that the studied parameters were highly variability over a range of spatiotemporal scales, comprehensively forced by various physical and biochemical processes. Mixing effect and scallop calcification played the most important role in the seasonal variation of total alkalinity (TAlk). For dissolved inorganic carbon (DIC), in addition to mixing, air-sea exchange and microbial activity, e.g. photosynthesis and microbial respiration processes, had more important effects on its dynamics. Different from the former, the changes of water pHT, partial pressure of CO2 (pCO2) and aragonite saturation state (ΩA) were mainly controlled by the combining of the temperature, air-sea exchange, microbial activity and scallop metabolic activities. In addition, our results suggested that massive scallop farming can significantly increase the DIC/TAlk ratio by reducing the TAlk concentration in seawater, thereby reducing the buffering capacity of seawater to the carbonate system especially for ΩA. Preliminary calculated, ~75.7 μmol kg−1 and ~45.5 μmol kg−1 of TAlk was removed from the surface and bottom water in one scallop cultivating cycle. If these carbonates cannot be replenished in time, it is likely to accelerate the acidification process of coastal waters. This study highlighted the control mechanism of the carbonate system under the influence of bay scallop farming, and provided useful information for revealing the potential link between human activities (shelled-mollusc mariculture) and coastal acidification.