Evaluation Of Carbon Sink Capacity And Potential Of Coastal Wetlands In Fujian Province Based On Land Use Change

Coastal ecosystems such as mangroves and salt marshes have high carbon sequestration efficiency and are greatly affected by human activities.Blue carbon play an important role in coping with global climate change.Conservation of coastal wetlands and the enhancement of blue carbon stock as a natural-based solution to the global increase in greenhouse gases are gaining increasing attention.Many documents in the "13th Five-Year Plan" have made arrangements for the construction of blue carbon.The improvement of blue carbon capacity will make important contributions to accelerating the realization of "Carbon Peak" and "Carbon Neutrality".However,the understanding of carbon sequestration capacity and carbon storage in China is not enough,so it is urgent to strengthen the research in this area and promote the construction of blue carbon database system and standardization.Based on the InVEST blue carbon model,the spatial distribution,carbon sink capacity,carbon sink potential and economic value of blue carbon in coastal wetlands of Fujian province from 1989 to 2019 were evaluated by using multi-source and multi-temporal Landsat image supervised classification algorithm,provide scientific support for government decisionmaking.The results showed that:(1)The total area of mangrove and salt marsh in Fujian province increased from 1989 to 2019,reaching 851 ha and 12,767 ha respectively in 2019,with an average annual growth rate of 5.4%and 3.8%respectively.The districts with the largest mangrove area are Longhai City,Hui’an County,Yunxiao County and Xiang’an District,and the districts with the largest salt marsh area are Xiapu County,Jiaocheng District,Lianjiang County and Fu’an City.In 1989,the mangrove and salt marsh areas in Fujian province were 419 hectares and 4,662 hectares respectively.After 30 years of evolution,27%of the original mangrove forests were converted into breeding ponds and 19%into construction land;30%of the original salt marshes were converted into breeding ponds,27%converted to construction land.(2)The carbon density of mangrove and salt marsh in Fujian province were 282.8 t ha-1 and 108.75 t ha-1,respectively,and the carbon accumulation rate of mangrove and salt marsh were 12.87 t ha-1 a-1 and 13.71 t ha-1 a-1,respectively.From 1989 to 2019,the blue carbon storage in Fujian province showed an upward trend,with an average annual net sequestration of 30,000 tons per year and an average annual growth rate of 3.1%.In 2019,the blue carbon storage in Fujian province reached 1.54 million tons.From 1989 to 2019,the blue carbon storage increased in most areas of Fujian province.According to the statistics of administrative districts,the carbon storage showed the characteristics of North>South>Middle.The regions with the highest carbon reserves are Xiapu County,Jiaocheng District,Lianjiang County,Fu’an City and Longhai City,with 4.0×105 t,1.9×105 t,1.6×105t,1.4×105 t,1.4×105 t respectively.(3)According to the mangrove planting area in the special action plan for mangrove conservation and restoration of Fujian province,combined with the mangrove carbon density in this paper,the newly added carbon sink of Fujian province will reach 190,000 tons,which is 12%of the existing blue carbon reserves,annual carbon net sequestration will increase by 8,626.5 tons per year,amount to 17%of 2019 net sequestration.The region with the greatest potential for carbon sinks is Jinjiang,with 55,000 tons.(4)Through the analysis of typical estuaries,the mangroves and salt marshes of Zhangjiang estuary,Jiulong River estuary,Quanzhou Bay and Fuqing Bay are well protected,and their carbon sequestration capacity and carbon storage are enhanced.But in Sansha Bay and LuoyuanBay,some of salt marshes have been removed and converted into aquaculture ponds and construction sites,which have lost some of their carbon sequestration capacity.There has been a large increase in aquaculture ponds and construction in the coastal area.The establishment and good operation of nature reserves play a significant role in enhancing the carbon sequestration capacity of coastal wetlands.(5)The blue carbon economic value of Fujian province from 1989 to 2019 presented an overall rising tendency.The calculation is based on the maximum(133.26 USD t-1 CO2e),average(20.36 USD t-1 CO2e)and minimum(0.35 USD t-1 CO2e)prices of the world bank’s "Carbon tax" and "Carbon trading" in 2020.The 30-year total carbon sequestration value is between $2.60 and $986.71 million,with an average value of$150.75 million.The net blue carbon sequestration value in 2019 was $0.66～$24.94 million,with an average value of $3.81 million.