*Article* **Marine Environmental Capacity in Sanmen Bay, China**

**Yanming Yao <sup>1</sup> , Jiahao Zhu <sup>1</sup> , Li Li 1,2,\* , Jiachen Wang <sup>1</sup> and Jinxiong Yuan <sup>3</sup>**


**Abstract:** Estuarine environmental capacity is the foundation for coastal biological diversity and selfpurification capacity. Hence, studies on the marine environmental capacity (MEC) are the foundation for the total discharge control and water quality improvement of land-based pollutants. In the article, A calibrated two-dimensional hydrodynamic model was used to study the environmental characteristics of Sanmen Bay, including the tides, the residual currents, the tidal prism, and water exchange abilities. The model results were used to estimate the environmental capacity of the bay. Taking the pollution problem in Sanmen Bay as an example, the method of response factor, the sub-unit control method, and the phased control method were used to estimate the environmental capacity, pollutant amounts, and the pollutant reduction in the bay. The concentrations of COD, inorganic nitrogen, and acid salt in Sanmen Bay are spatially varied, with higher values occurring in the western part and in the inner bay. The half exchange time of the whole bay is about 23 days, and the exchange time of 95% water body is about 60 days. The evaluation of MEC cannot only provide technical support for the offshore aquaculture industries but also provide a scientific basis for the total control of terrigenous pollutants in coastal cities in Southern Zhejiang Province.

**Keywords:** marine environmental capacity (MEC); response factor; water exchange; residual; Sanmen Bay
