Abstract
The Beibu Gulf (also named the Gulf of Tonkin), located in the northwest of the South China Sea, is representative of a bay suffering from turbulence and contamination associated with rapid industrialization and urbanization. In this study, we aim to provide the novel baseline levels of heavy metals for the research area. Concentrations of five heavy metals (i.e., Cu, Pb, Zn, Cd and Cr) were determined in surface sediments from 35 sites in the eastern Beibu Gulf. The heavy metal content varied from 6.72 to 25.95 mg/kg for Cu, 16.99 to 57.98 mg/kg for Pb, 73.15 to 112.25 mg/kg for Zn, 0.03 to 0.12 mg/kg for Cd, and 20.69 to 56.47 mg/kg for Cr, respectively. With respect to the Chinese sediment quality criteria, sediments in the eastern Beibu Gulf have not been significantly affected by coastal metal pollutions. The results deduced from the geoaccumulation index (Igeo) showed that the study area has been slightly polluted by Pb, which might be caused by non-point sources. Relatively high concentrations of Cu, Pb and Cd were found around the coastal areas of Guangxi province, the Leizhou Peninsula and the northwest coast of Hainan Island, whereas the highest concentrations of Zn and Cr were found on the northwest coast of Hainan Island. Spatial distribution patterns of the heavy metals showed that bioavailable fractions of Pb were higher than in the residual fractions, while Cu and Cd concentrations in exchangeable and carbonate fractions were relatively higher than those in the bioavailable fractions. Hierarchical clustering analysis suggested that the sampling stations could be separated into three groups with different geographical distributions. Accompanying their similar spatial distribution in the study area, significant correlation coefficients among Cu, Cd and Pb were also found, indicating that these three metals might have had similar sources. Overall, the results indicated that the distribution of these heavy metals in the surface sediments collected from the Beibu Gulf was complex.
Highlights
The Beibu Gulf (i.e., Gulf of Tonkin), located in the northwest of the South China Sea (SCS), is representative of a tropical sea regime that is significantly affected by the monsoon
In the northernmost portion of study area, the weathering rock from surrounding land maybe influences the distribution of clay, organic carbon and sulfide [29]
High concentrations of Cu, Pb and Cd were found in the coastal areas of Guangxi Province, Leizhou Peninsula and off the northwest coast of Hainan Island, while high levels of Zn and Cr were observed off the northwest coast of Hainan Island
Summary
The Beibu Gulf (i.e., Gulf of Tonkin), located in the northwest of the South China Sea (SCS), is representative of a tropical sea regime that is significantly affected by the monsoon. As the largest area of extant mangrove and sea grass in China, the Beibu Gulf is a main source of fishery products for coastal cities, such as clam, crabs and varieties of fishes [1,2,3,4]. It is a significant fishery and has become the largest free trade area in South China [5,6]. Total production increased at a rate of 15.6%
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