BGC-01 Mercury biogeochemical cycling in the ocean
Spatial and Temporal (1936-2019) variation in the Pollution Status and Sources of Mercury in the Jiaozhou bay
Zhengwen Zhou* , Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education and College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China
Zhekai Tang, Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education and College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China
Huiling Wang, Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education and College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China
Xiaotong Xiao, Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education and College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China
Yanbin Li, Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education and College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, 266100, China

Jiaozhou Bay (JZB) is located at the west coast of the Yellow Sea surrounded by Qingdao city. More than 10 rivers and several wastewater sewage treatment plants discharge large quantities of pollutants including Hg into the JZB. Elevated Hg has been detected in the seafood of the JZB, highlighting the importance of investigating Hg cycling in this system. In this study, Hg concentrations and its isotope composition in the surface sediments and sediment cores of the JZB were analyzed. Mercury in the surface sediment ranged from 7 to 163 ng/g, with an average of 60 ± 35 ng/g, which is significantly higher than that in China marginal seas. Mercury concentrations in the eastern area of the bay were higher than that in the western region, possibly due to the larger input fluxes of Hg from the rivers. The surface sediments have negative MDF (δ202Hg: −0.85 ± 0.12‰, −1.08‰ to −0.61‰) and near-zero MIF (Δ199Hg: 0.02 ± 0.04 ‰, −0.08 to 0.13‰). Low δ202Hg and Δ199Hg values were observed in the northeast area of the JZB, indicating the weak photochemical reactions possibly caused by the riverine input of high-turbidity water. From 1936 to 2019, the Hg concentrations in core 14 and 20 showed a fluctuating upward trend, while the core-28 at the Licun river estuary showed a decreasing trend owing to the dam construction in the upper reaches of the river. The δ202Hg of core 14 and 20 fluctuated around the mean value of −0.83‰ and −0.91‰, respectively, while it increased from −1.12‰ to −0.68‰ at core 28 during ∼1940 – 2019. An isotope mixing model was adopted to estimate the relative contributions of industrial source, riverine source, and atmospheric source to Hg in the sediment of JZB. The results suggested that industrial Hg is the major source of Hg in the JZB. The variation of Hg in the sediment cores is controlled by the change in the industrial and riverine input of Hg into the JZB.