Assessment of Heavy Metal Contamination and Ecological Risk in Mangrove Marine Sediments Inside and Outside Zhanjiang Bay: Implications for Conservation

Mangrove ecosystems effectively sequester heavy metals, making their sediment distribution and ecological risk assessment vital for coastal protection. This study focuses on the mangrove forests on both sides of the Donghai Island embankment in Huguang Town, Zhanjiang Bay, analyzing the content, spatial distribution, and potential ecological risks of heavy metals (Cu, Zn, Cd, Pb, Cr, As, Hg) in surface and vertical sediment profiles through systematic sampling. The results show higher, more uniform heavy metal concentrations inside the bay, with Cd, Cr, and As showing significant accumulation, while outside, levels are lower but with Pb and As at sites like DW-Z-1 and DW-Z-4 nearing Class I Marine Sediment Quality Guideline limits. Vertically, concentrations inside the bay increase with depth due to long-term pollution, geoaccumulation and potential ecological risk indices, Cd emerges as the primary pollutant, posing a high risk (Er Class 3) inside the bay (RI Class 2) and a low to moderate risk outside. Pollution sources inside stem from industrial, urban, and aquaculture inputs, while tidal dynamics and mangroves pose purification mitigate risks outside. This study underscores Cd control needs and supports the ecological conservation of Zhanjiang Bay.