Biogeochemical Characteristics Of Heavy Metals And The Environmental Change Signals Under The Influence Of Human Activities In The Jiaozhou Bay Sediments

The studies on the eco-environmental changes of the Jiaozhou Bay, which is a typical bay under the influence of human activities, have practical significance for the sustainable utilization of offshore environment. In this study, the biogeochemical characteristics, eco-environmnental risks, sources of heavy metals（Cr, Cu, Ni, Zn, Cd, Sb, Sn, Pb） in the surface sediments of the Jiaozhou Bay were systematically analyzed; The simple and effective methods to extract the labile fractions of elements were established;The indicator significance of heavy metals in different size fractions in core sediments was identified. The major results were as follows: 1. The distribution pattern of heavy metals in surface sediments were attributed to the dilution by biological deposition, the contents of TOC and clay; The speciation pattern of heavy metals was affected synthetically by the sources, element geochemistries and sediment characteristics. The residual fractions mainly came from the natural input, whereas the non-residual fractions were attributed to the anthropogenic activities, suggesting that he speciation of heavy metals in sediments plays a more important role to reflect the human activities. The risk assessment codes and enrichment factors（EF）suggested that the potential ecological risk of Cd was high.The high values of heavy metals appeared at the north area, the central bay and the bay mouth, where the content of Ca, Sr and Ba were low. The heavy metals had significant correlation with Ca, Sr and Ba, indicating that the content of heavy metals in surface sediments may be diluted by biological deposition. The quantities of heavy metals added by human activities cannot be reflected by the total concentrations. Besides, the content of heavy metals had significant correlation with the clay and TOC content, indicating that the metals were enriched in fine-sized particles.The speciation pattern of heavy metals was controlled by the sources, element geochemistries and sediment characteristics. Anthropogenic activities effected the percentage of non-residual fractions; The correlation analysis and principal component analysis indicated that non-residual fractions（acid-soluble, reducible and oxidizable forms） of heavy metals mainly came from industrial and agricultural productions, whereas the residual fractions mainly came from crustal inputs. In addition, the main non-residual fraction were determined by element geochemical characteristics and sedimentary environment（p H, oxidation-reduction）.The risk assessment codes and enrichment factors（EF）suggested that EF（Cd）>1.5, and Cd was at moderate pollution level; EF（ Pb, Sn, Sb）>1.5, but at low pollution level; EF（ Cr, Pb, Sb） <1.5, but at moderate pollution level. 2. To explore a concise and effective method to detect anthropogenic metal contamination, we compared the extraction efficacy of 0.1 mol/L HCl（method 1）, 1 mol/L HCl（method 2） and 1 mol/L HCl+1.75 mol/L HNO（method 3）. The results indicated that 0.1 mol/L HCl, which was similar to the BCR procedure, was superior in its ability to characterize the degree of anthropogenic contamination. The spatial distribution of labile fractions of Cu, Pb and Zn extracted by 0.1 mol/L HCl, which were consistent with the actual contamination pattern, showed significant anthropogenic signals obviously. All data indicated that the 0.1 mol/L HCl leach was a valuable, rapid, and cost-effective analytical tool in contamination assessment of heavy metals.Average extraction ratios of the clastic elements（Al、Sc、Ti、Th、Fe） in sediments using three extraction methods showed an order of method3>method2>method1, indicating that method1 had minimum impact on the alumino-silicate matrix of solids. The average extraction ratio of trace rare elements extracted by method2 and method3 were significantly different from that of the BCR procedure, indicating these two methods were not appropriate to served as alternative methods to the BCR procedure.The ASI of metals extracted by method2 and 3 were low, which may be due to that the non-labile fractions of heavy metals in the inner layer of large particles were leached out by the higher acidity, enhancing the pollution signals of heavy metals in sediments. The metals extracted by the method1 had the highest anthropogenic signal index（ASI）, indicating that the method1 had the highest extraction efficiency for labile fractions of metals among the three methods. Furthermore, the higher values of Cu, Pb and Zn extracted by method1 appeared at the east coastal area, which was consistent with the actual contamination pattern, demonstrating that 0.1 mol/L HCl can be recommended as an optimal partial decomposition procedure for assessing non-residual fractions of heavy metals in sediments. 3. The responses of different size fractions in core sediment were variant to the natural changes and human activities. Heavy metals in the fine-grained（<32μm） and middle-sized fractions（32-63μm）apparently recorded the informations and degrees of human activities, while the vertical variations of heavy metals in the sand-sized fractions（>63μm） reflected historical climate changes.The geoaccumulation index(I_geo) and enrichment factor（EF） indicated that the fine-grained and middle-sized fractions of the core sediment had high degree of enrichment for anthropogenic heavy metals. According to the anthropogenic factor（AF） of heavy metals in fine-grained and middle-sized fractions, the environmental evolution of the Jiaozhou Bay was divided into three periods, before 1940 s, from 1940 s to 2000 s and after 2000 s. In the first period, human activities had low effects on the Bay with lower AF and slow development of industry and agriculture. During the second period, Qingdao had progressively developed and the AF gradually increased which declaring high influence of human activities on the bay. In the third period, the sediment environment had been improved due to growing concerns of environments and increasing supervision from the government. Whereas the content of heavy metals in the sand-sized fractions was gradually decreased from bottom to the top corresponding to upregulated temperature and enhanced weathering of terrigenous detrital particles during the last century.