Heavy Metals in Sediments from the Haizhou Bay Marine Ranching Based on Geochemical Characteristics

Abstract

Marine ranching is a new sustainable production method, which plays an important role in the transformation of China's marine economy. In this paper, Haizhou Bay marine ranching was divided into 3 areas according to the intensity and delivery time of the submarine structures. Five geochemical indicators of temperature (T), pH, oxidation-reduction potential (Eh), grain size (D[3,2]) and total organic carbon (TOC) were determined on-site. A modified European Community Bureau of Reference(BCR)sequential extraction procedure was applied to determine the chemical speciation of different heavy metals (i.e. Cr, Cu, Ni, Zn, Pb, and Cd). The results showed a horizontal distribution of the Eh was influenced by the submarine structures. The TOC content ranged from 11.7 to 13.5 g·kg-1, which had a significant negative correlation with pH. Pb and Cd mainly present in the secondary phase of iron manganese oxide forms (F2), which were controlled by the Eh, however, Cu, Zn, Ni, and Cr were mainly present in the primary phase. A correlation and cluster analysis indicated that the Cr, Cu, Ni, and Zn present in sediments were from natural sources, while the Cd and Pb content obviously came from anthropogenic metal sources. The exchangeable and carbonate fractions (F1) of Cr, Ni, Cu, Zn, Pb, and Cd were significantly correlated with TOC. The residuals (F4) of Cr, Ni, Cu, Zn, Pb, Cd were significantly correlated with the grain size of sediments as well as the iron-manganese oxide forms (F2) of Cr, Ni, Cu, and Zn. A different speciation of Cd was controlled by multiple geochemical characteristics of the sediment. The heavy metal levels of the primary and secondary phases in the central and lateral areas were lower than the control and medial areas because of differences in the submarine structures and hydrodynamics. The enrichment and adsorption of Cr, Ni, Cu, and Zn in sediment was stronger than the release of particles that were resuspended. While the influence of fine particles and organic matter from the sediment in the central and outer areas was limited, an enrichment factor analysis suggested that Cd in sediment showed enrichment to some extent. This paper provides a scientific basis for the construction of marine ranching and ecological restoration in Haizhou Bay.