Distribution and assessment of mercury (Hg) in surface sediments of Futian mangrove forest, China

To investigate the distribution of mercury (Hg) in Futian mangrove wetland, surface sediments from land to sea were collected, including Kandelia obovata, Avicennia marina, Sonneratia caseolaris, and mud flat. The ecological risks of Hg in sediments were also assessed. The results showed that mangrove forests acidified sediments and promoted the accumulation of salinity and organic matter in sediments. Hg concentrations in both mangrove forests (154.7–218.4 ng g−1) and mud flat sediments (226.3–251.9 ng g−1) surpassed the background level (71.0 ng g−1). Furthermore, Hg concentrations in sediments decreased gradually from sea to land at all depth. From the bottom to the top layer sediment, Hg concentration decreased gradually in the sediments near land, while it kept vertically stable in the coastal area, indicating its pollution may mainly come from the coastal area rather than the land to some extent. Although the mean values of geo-accumulation indexes revealed uncontaminated to moderately contaminated levels, the mean values of potential ecological risk coefficients revealed considerable ecological risk of Hg to the environment, deserving further attention.