Assessment of Heavy Metal Concentrations and Biological Blue Carbon Sequestration Process in Mangrove Forest Ecosystems

Mangrove forests play a critical role in coastal carbon sequestration and act as natural filters for heavy metal contaminants. This study investigated the physicochemical characteristics, heavy metal distribution, and carbon dynamics of R. apiculata and Avicennia spp (A. alba) in the Bangkhunthian mangrove ecosystem over three years. Surface water and sediment analyses revealed elevated concentrations of Hg, Cd, Cr, Cu, Ni, Pb, and Zn at upstream stations, with sediments serving as the primary metal reservoir due to their high organic matter and clay content. Physicochemical parameters, including pH (6.8–7.6), color (16–25 Pt-Co), and turbidity (124–145 NTU), indicated a near-neutral, turbid environment that promotes metal adsorption and organic carbon retention. Above-ground biomass carbon (AGBC) and below-ground biomass carbon (BGBC) of both species increased exponentially, with R. apiculata AGBC rising from 0.15 to 2.49 Mg C/ha and BGBC from 0.019 to 0.848 Mg C/ha, and Avicennia spp (A. alba) showing similar trends. The total carbon stock (TCS) steadily increased, reaching 15.94 Mg C/ha for R. apiculata and 17.60 Mg C/ha for Avicennia spp (A. alba) by the third year. These findings highlight the high carbon sequestration potential of young mangrove stands and underscore the importance of mangrove restoration and conservation for climate change mitigation and coastal ecosystem management.