Study On Sedimentation And Carbon Burial Characteristics And Vulnerability Of Mangroves Based On Storm Surge History In Guangxi

Mangroves are widely distributed in the upper part of intertidal zone in tropical and subtropical regions.They are characterized by high productivity and sedimentary rates,and are of great significance for preventing coastal erosion and organic carbon.Typical mangrove wetlands along the coast of Guangxi were used as the research object,and columnar samples of mangrove sediments were collected.Based on the²¹⁰Pb dating method and the high-energy storm surge in the coarse-grained sedimentary layer in the forest,the sedimentary rates of the mangroves were estimated,the grain size characteristics and the temporal and spatial changes of the sedimentary rates were studied.In addition,the distribution characteristics and formation reasons of the buried organic carbon horizon were analyzed,and the carbon burial rates were estimated.Finally,under the threat of sea level rise,the vulnerabilities of typical mangrove forests in Guangxi were assessed by using exposure,sensitivity and adaptability assessment models and combined with mangrove habitat characteristics and sedimentary rates.The ²¹⁰Pb dating method showed that the sedimentary rates of mangroves in Guangxi were between 1.9～14.3 mm/a,and the storm surge dating method estimated that the long-term average sedimentary rates of the mangroves in Guangxi were between 1.5～22.0 mm/a.The storm surge dating method was highly reliable in sedimentary environment in mangroves,and could be used as a comparison and supplement to the ²¹⁰Pb dating method.The sedimentary rates were affected by the supply of sediment and the deposition environment.The wave-controlled mangroves were represented by Jinhai Bay,where the tidal ditches were not developed.In recent years,due to frequent storm surge disturbances,the sedimentary rates on the inside mangroves were greater than that on the outside.The tide-controlled mangroves were represented by Pearl Bay with developed tidal ditches,and the sedimentary rates depended on the distance between the sample point to main tidal ditch.The estuary-type mangrove forest was represented by the Nanliu River estuary,which belongs to the strong-tide sea area and the tidal ditches were relatively developed.The sedimentary rates were controlled by the estuary incoming sediment and high-energy tidal water.The average organic carbon content of mangrove sedimentary columns in Guangxi ranged from 0.9%to 2.2%,and the organic carbon content of the mangrove layer ranged from 0.7%to 4.3%.Both of them were found to be the highest in the inner mangroves of the Nanliu River estuary and the lowest in Yuzhou Flat.The organic carbon burial rates were between 44.0 g·m^-2·a^-1to 444.1 g·m^-2·a^-1,which controlled by the sedimentary rate.The highest was found on the front edge of the Nanliu River estuary,and the lowest was found on the inner side of Yuzhou Flat.Based on the dynamic sedimentary rates of mangroves and the prediction of sea level rise,the mangroves in Yuzhou Flat may face the threat of inundation.Based on field trips and vulnerability model calculations,mangroves with highest vulnerability in Guangxi were at the front mangroves in Jinhai Bay,where were affected by low sedimentary rates and increased storm surge frequency.Due to the low sedimentary rates and human activities,the mangroves in the transitional zone of Pearl Bay and Yuzhou Flat were highly vulnerable.The estuary area was relatively rich in sediment sources with high sedimentary rates,and the mangroves with lowest vulnerability were found in the front of the Nanliu River estuary.The results can be used for reference in study of mangrove sedimentation and carbon burial potential,and can also provide a feasible scheme for the vulnerability assessment of mangroves in Guangxi.