湛江高桥红树林湿地有机碳分布及埋藏特征

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

红树林是世界上单位生产力最高的生态系统之一,其能够持续地固定有机碳,对全球碳平衡和生物地球化学循环有着深远影响。以广东湛江国家级红树林自然保护区高桥核心区为研究区,旨在分析我国典型红树林湿地的固碳潜力,为红树林湿地碳计量提供依据。在垂直于海岸线的两条样线上选取6个不同潮位的样点进行沉积柱取样分析,通过重铬酸钾氧化-外加热法测定有机碳含量,基于放射性同位素^(210)Pb定年推演沉积率,并对湿地有机碳密度和埋藏率进行计算。结果表明:研究区红树林湿地有机碳含量2.14—36.94 g/kg,平均(12.79±9.91)g/kg。红树林湿地有机碳密度为(0.0100±0.0056)g/cm3,空间上差异显著显著,水平方向上两条样线均以中带样点的有机碳密度最大,近陆侧(内带)样点的有机碳密度高于近海侧(外带);垂直方向上,内带和外带样柱的有机碳密度均以表层最高,而且随深度增加而减小。研究区红树林湿地百年尺度上沉积率为6.5—11mm/a,且外带样点沉积速率显著快于内带样点。有机碳埋藏率空间差异大,外带样点为(34.58±7.67)g m-2a-1,而中带样点可达150.56 g m-2a-1。红树林湿地有机碳的分布受潮位的影响大,更高潮位点和表层的有机碳含量和密度更高,而处于低潮位的外带样点的有机碳沉积更快。研究区红树林湿地有机碳含量和密度比更低纬度带低,但均高于地带性陆地植被,且其能够通过持续的沉积过程来捕捉和固定有机碳,固碳潜力大。

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; 6 sediment 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 210Pb of the six sediment cores, organic carbon density, and depth ratio of mangrove 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± 9.91 ） g/kg. Below-ground organic carbon density in the mangroves was （0.0100 ± 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 was 6.5--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 ＆fleeted by the tide level and plant community type. The burial rate of organic carbon at the seaside was （34.58±7.67） g m-2a-1, while that at the middle zone was150.56 g m-2 a-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 zonal terrestrial vegetation; thus, its potential for carbon sequestration was huge because of the continuous deposition process.