Coastal carbon sink accounting toward construction of three-dimensional ocean carbon sink field

Developing a low-carbon economy is an important means of implementing the United Nations 2030 Sustainable Development Goals, and mastering the carbon sequestration potential of coastal ecosystems is the foundation for implementing carbon neutrality and developing a low-carbon economy. The net sequestrated carbon by phytoplankton and macro-algae is calculated in the Yancheng coastal waters in the west Yellow Sea by subtracting the amount of carbon released through respiration from the amount of photosynthetic carbon sequestration. The annual sequestrated carbon of shellfish is calculated using the carbon content of shells. From 2019 to 2021, the sequestrated carbon of the coastal ecosystem in Yancheng was 67.5431, 72.4331, and 69.5343 million tons of carbon, with an average annual growth rate of 2.95%. The carbon sequestration in the coastal ecosystem of Yancheng is mainly provided by phytoplankton, while the carbon sequestration of macro-algae such as lavers and shellfish such as clams is relatively very low. During these three years, the sequestrated carbon of phytoplankton increased at an average annual rate of 2.96%. However, the carbon sequestration by macro-algae and clams decreased at an average annual rate of 56.08% and 21.11% respectively. The decrease in carbon sequestration by large algae and shellfish is caused by the decrease in the cultivation area of laver and clam in Yancheng in 2021. The construction of a 3-dimensional coastal carbon sink farm consisting of a suspended raft laver mariculture at the surface layer, phytoplankton in the seawater column, and benthic clam mariculture was recommended to the local government.