It is well recognized that the ecosystem of the Bohai Sea is being rapidly degraded and the Sea has basically lost its function as a fishing ground. Billions of funds have been spent in slowing down, halting and finally reversing the environmental deterioration of the Bohai Sea. Although trace metals are routinely monitored, the data with high temporal resolution for a clear understanding of biogeochemical processes in the ecosystem of the Bohai Sea are insufficient, especially in the western literature. In this review, status of trace metal contamination in the Bohai Sea is assessed based on a comprehensive review of their concentrations recorded in the waters, sediments and organisms over the past decades. Studies show that metal contamination in the Bohai Sea is closely associated with the fast economic growth in the past decades. Concentrations of trace metals are high in coastal areas especially in the estuaries. Alarmingly high metal concentrations are observed in the waters, sediments and organisms from the western Bohai Bay and the northern Liaodong Bay, especially the coasts near Huludao in the northernmost area of the Bohai Sea, which is being polluted by industrial sewage from the surrounding areas. The knowledge of the speciation and fractionation of trace metals and the influence of submarine groundwater discharge on the biogeochemistry of trace metals in the Bohai Sea is far from enough and related work needs to be done urgently to get a better understanding of the influence of trace metals on the ecosystem of the Bohai Sea. A clear understanding of the trace metal pollution status of the Bohai Sea could not be achieved presently for lack of systematic cooperation in different research fields. It is quite necessary to apply the environmental and ecological modeling to the investigation of trace metals in the Bohai Sea and then provide foundations for the protection of the environment and ecosystem of the Bohai Sea.

No abstract

Concentrations of eight heavy metals (i.e., Fe, Mn, Cr, Ni, Cu, Zn, Cd and Pb) in the seawater, suspended particulate matter (SPM) and sediments of the Zhanjiang Bay were investigated in 2014. The concentrations of metals were generally low in the seawater and sediments of the Zhanjiang Bay in winter and summer, indicating good environmental quality in the bay. The distribution patterns of Fe and Mn in three phases indicated the influence of terrestrial inputs. The partition coefficients log(Kd) between the dissolved and particulate phases showed a general decrease in the order of Pb≈Cd>Fe≈Mn>Ni≈Cr>Zn>Cu. The concentrations of some metals in the dissolved and particulate phases showed seasonal variations. Phytoplankton production and complexation reactions may contribute to this phenomenon. The relationships among metals in different phases were different, and there were few close relationships among metals in the dissolved phase, many close relationships in the particulate phase, and more close relationships in the sedimentary phase. This finding may be related to the different mobility levels of metals in different phases.

Geochemical characteristics of phosphorus (P) in the surface sediments of the East China Sea shelf (ECSS) were studied in spring and autumn, 2014. Distributions, seasonal variations, transformations and their influencing factors were discussed. Besides, burial fluxes of P in different seasons were also calculated. Five operationally defined forms of P, namely exchangeable or loosely sorbed P (Ads-P), iron-bound P (Fe-P), authigenic P (Au-P), detrital apatite plus other inorganic P (De-P) and organic P (OP), were obtained using a sequential extraction procedure. Generally, the concentrations of Ads-P, Fe-P, Au-P and OP decreased seaward and the concentrations of De-P increased seaward in both seasons. In spring, the average concentrations of Ads-P, Fe-P, Au-P, De-P and OP were 13.8 ± 5.0, 21.9 ± 7.6, 148.5 ± 44.5, 153.1 ± 55.8 and 91.7 ± 21.5 μg g −1 , respectively. The corresponding concentrations in autumn were 11.4 ± 4.3, 20.0 ± 10.9, 170.4 ± 53.6, 225.6 ± 101.7 and 77.1 ± 33.9 μg g −1 , respectively. The average percentages of P fractions in total P (TP) in spring and autumn were both in the order: De-P N Au-P N OP N Fe-P N Ads-P. The average concentrations of Bio-available P (Bio-P) were 127.4 ± 31.4 μg g −1 in spring and 108.5 ± 47.2 μg g −1 in autumn, accounting for 29.8% ± 7.3% and 21.5% ± 8.2% of corresponding TP, respectively. Seasonal variations of the primary production, hydrodynamic conditions, hypoxia and other environmental conditions were responsible for the seasonal variations of different phosphorus forms. The calculation of burial fluxes reflected that, in most parts of the studied area, TP had relative high burial fluxes in autumn, while Bio-P had relatively high burial fluxes in spring. The burial fluxes of other phosphorus forms also showed different seasonal variations in different parts of the studied area.

A comprehensive, depth specific (near‐surface to 3,700 m) water isotope (δD and δ18O) data set of 237 water samples collected from 20 different locations from the Northwest Pacific through the Luzon Strait to the Northern South China Sea (NSCS) are used to clarify the deeper understanding of water mass processes using δ18O‐salinity (S) and δD‐δ18O relations. Our study reveals that the δD‐δ18O correlation has a low slope and the δ18O‐S correlation has a high slope, which are related to the intrusion of the Kuroshio water and the influence of the coastal current above 200 m on the NSCS, respectively. The isotope mixing model showed that 15% is from the Kuroshio water, 40% from the South China Sea (SCS) Tropical Water, and 45% from the coastal current for water above 200 m in the NSCS. In the intermediate layer (300–1,200 m), a significant δ18O‐S correlation was found at depths of 300–700 m on the NSCS side, but no correlation was found on the western Pacific side, suggesting that the mixing of the water masses of the South China Sea Intermediate Water and the North Pacific Intermediate Water mainly occurs at depth in the NSCS. In the deeper water (below 1,200 m), positive isotopic values were found at depths below 1,500 m, which refuted the previous knowledge that positive isotopic values only exist in the Luzon Strait at depths above 1,000 m, and the positive isotope water mass would flow with the Deep Pacific Water into the deeper water of the SCS.

No abstract

a b s t r a c tZaozhuang Segment of the Beijing-Hangzhou Grand Canal is an important water conveyance line on the eastern route of the South-North Water Transfer Project in China and its water environment condition can exert a significant influence on diversion water quality safety. This paper analyzed contents of five heavy metals such as Cd, Cu, Ni, Pb and Zn as well as their chemical forms in surface sediments in this region. Methods including Threshold Effects Level-Probable Effects Level (TEL-PEL), Risk Assessment Code (RAC)and Acid Volatile Sulfide-Simultaneously Extracted Metals (AVS-SEM) were also employed to evaluate the quality of sedimentary environment in this region. With the aim to assess the eco-environmental risk revealing the information of the concentration, the chemical fractionation, the toxicity of heavy metals, a new assessment index known as Multivariable Evaluation Index (MEI) was introduced into this paper. Results indicated that contents of such five heavy metals in surface sediments were generally low. Overall, ecological risk was in the medium-low grade in addition to several locations where the level of risk was high. However, certain differences still existed among various assessment results. Comparing with other single evaluation methods, MEI may be able to reflect contamination status and ecological risks of heavy metals in sediments of a specific region more comprehensively. MEI also seemed able to overcome the limitations of other prevalent aggregated indexes to assess potential sediment pollution risk in aquatic systems.

Elemental (total organic carbon (TOC) and total nitrogen (TN)) and stable carbon and nitrogen isotope compositions (δ13C and δ15N, respectively) in the surface sediment of Zhanjiang Bay (ZJB) in spring and summer were measured to study the spatial and seasonal changes of organic matter (OM) and assess the human-induced and environment-induced changes in the area. The OM in the surface sediment of ZJB was a mixture of terrestrial and marine sources, and was dominated by marine OM (54.9% ± 15.2%). Compared to the central ZJB, the channel and coastal ZJB areas had higher δ13C and δ15N values, higher TOC and TN concentrations, and lower TOC/TN ratios, indicating higher primary productivity and higher percentages of marine OM in the latter two subregions. Mariculture activities, sewage inputs, and dredging were responsible for these phenomena. Clear seasonal variations in OM were observed in ZJB. The average proportions of terrestrial OM in summer increased by 10.2% in the ZJB channel and 26.0% in the coastal ZJB area compared with those in spring. Heavy rainfall brought a large amount of terrestrial OM into the channel and coastal ZJB areas, leading to the increase of the terrestrial OM fraction in these two subregions in summer. In summary, anthropogenic influences had a significant influence on the spatial and seasonal variations of sedimentary OM in ZJB.