Estimating Change in Sedimentary Organic Carbon Content During Mangrove Restoration in Southern China Using Carbon Isotopic Measurements

Based on total carbon (C) and C isotopes in sediment cores, sedimentary organic carbon (SOC) was quantified in three types of mangrove sites (barren flat sites without mangroves, mangrove plantations, and natural mangrove forests), which were considered to represent a continuum from least restored to most restored sites in southern China. SOC densities in the barren sites, plantations, and natural forests were 90, 170 and 288 Mg ha(-1), respectively. We inferred that mangrove restoration increased SOC accumulation in coastal areas. At 0-70 cm depth, SOC delta C-13 values in both mangrove sites ranged from -27.37 parts per thousand to -23.07 parts per thousand and exhibited gradual enrichment with depth. In contrast, the values in the barren flat sites remained around -22.19 parts per thousand and fluctuated slightly with depth. At 0-60 cm, the C-14 ages of the SOC in the barren flat site, the natural mangrove site, and the artificial mangrove site ranged from 1 397 to 2608, 255 to 2453, and 391 to 2 512 years BP, respectively. In both types of mangrove sites but not in the barren flat sites, the enrichment of delta C-13 with depth was related to increases in SOC decay and SOC age with depth. According to analysis of C-14 age, much of the mangrove-derived C was transported and stored at 0-60 cm depth under anaerobic conditions in both mangrove sites. The sediments of mangrove forests in southern China sequester large quantities of SOC during mangrove restoration.