Below-ground organic carbon distribution and burial characteristics of the Gaoqiao mangrove area in Zhanjiang, Guangdong, Southern China

Mangroves are one of the most productive ecosystems of the world,that continually sequester organic carbon and play an important role in global carbon cycles and biogeochemical processes. This study aimed to analyze carbon sequestration and below-ground carbon storage in mangroves,to provide a reference for carbon accounting in mangrove wetlands. The Gaoqiao mangrove area in the Zhanjiang Mangrove National Nature Reserve was chosen as the study area; 6sediment cores were collected along two sample lines,which were perpendicular to the coastline,and the physical and chemical properties were examined. Based on the potassium dichromate oxidation-external heating method,the spatial distribution of below-ground organic carbon content in the sediment cores profile was analyzed. The burial rate of organic carbon was determined using radiometric dating ~(210)Pb of the six sediment cores,organic carbon density,and depth ratio ofmangrove wetlands were also analyzed. The results showed a below-ground organic carbon content of 2. 14-36. 94 g / kg,with an average of( 12.79 + or - 9.91) g / kg. Below-ground organic carbon density in the mangroves was( 0.0100 + or - 0.0056) g /cm3,and the spatial distribution of organic carbon density varied sharply. Horizontally,the peak of organic carbon density appeared at the middle zone,and organic carbon density at the landside was greater than that at the seaside. Vertically,the peak of organic carbon density appeared at the surface both at the landside and the seaside,while it was not clear at the middle zone,and that appeared stratification. In this study area,the century-scale sedimentation rate of mangroves soil was6.5-11 mm / a,the sedimentation rate of the seaside was faster than that of the landside,and it was generally in accordance with the current rate of sea-level rise. Spatial distribution of organic carbon burial rate of the samples varied at different sites,which was affected by the tide level and plant community type. The burial rate of organic carbon at the seaside was( 34.58+ or -7.67) g m-2a-1,while that at the middle zone was150.56 g m-2a-1. The distribution of soil organic carbon was affected by the tidal site in the mangrove wetland; organic carbon content and carbon density were higher at the higher tide site and at the surface,while the low tide site had a faster sediment rate. Below-ground organic carbon content and density at the study site were lower than those at lower latitudes,but higher than those in