Enrichment of trace elements by blue carbon habitats in Maoyan Island of Yueqing Bay, China

Mangroves and saltmarshes are coastal blue carbon ecosystems with important eco-environmental functions. In this study, profile samples from five habitats (mangrove, saltmarsh, mudflat, paddy field, and mountain forest) were collected in the Maoyan Island of Yueqing Bay, China, to measure the concentrations of trace elements (TEs) (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, and Zn) among the five ecosystems and to assess their hazardous potentials on the environment. Our results showed that, compared to other sites, concentrations of TEs (except Cd, Pb, and Zn) in mangrove sediment were higher at the top 50 cm of the profile. Besides, significant enrichment of most of the TEs (except Cd, Ni, and Pb) in mangrove and Cd, Pb, and Zn in saltmarsh sediment was observed after the colonization of mangrove and saltmarsh vegetation. Correlation and principal component analysis suggested that the Co, Fe, Mn, and Ti in mangrove, saltmarsh, and mudflat sediments mainly derived from natural sources; whereas Cd, Cr, Cu, Ni, Pb, and Zn possibly came from both natural and anthropogenic sources. The results of contamination indices showed that there was no serious prevalence of TEs (Cd, Cr, Cu, Ni, Pb, and Zn) contamination across the sedimentary profile of all habitats, and the potential hazards of these six elements were low. This study indicates that coastal blue carbon ecosystems not only sequester a considerable amount of carbon but also enrich a substantial portion of trace elements that can minimize the adverse impacts of TEs on marine environments.