Seasonal Variation and Ecological Risk Assessment of Heavy Metal in an Estuarine Mangrove Wetland

Abstract

Potential toxic metal pollution in mangroves has attracted extensive attention globally; however, the seasonal variation of potential toxic metals in mangrove wetlands is still poorly understood. Herein, we investigated the variation of content as well as chemical speciation of typical metals (Pb, Cr, Zn and Cu) in the sediments from the Zhangjiang Estuary mangrove wetland, China. The potential risk of metal contamination was also investigated. Compared to the wet season, we found that sediment metal content was higher in the dry season. Mangrove sites show accumulated significant metals than does the mudflat both in wet and dry seasons. Geo-accumulation (Igeo) shows moderate pollution, probably because of the dilution as result of runoff and tidal hydrodynamics in the wet season. Increased concentrations of all metals in the acid-soluble fraction and decreased metal contents in the residue fraction were found in the dry season. Risk assessment indicated that the concentrations of Pb poses a higher environmental risk in the dry season. These results can increase awareness of metal pollution in the dry season and provide information for potential toxic metal management in mangrove wetlands.