BGC-01 Mercury biogeochemical cycling in the ocean
Suspended particulate matter controls distribution, partitioning and transport of mercury in the Yellow River and nearby Estuary
Xiaoquan Liu, School of Environmental Science and Engineering, Shandong University
Yingjun Wang* , School of Environmental Science and Engineering, Shandong University
Yanbin Li, Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China.
Guangliang Liu, Department of Chemistry & Biochemistry, Florida International University
Yong Cai, School of Environmental Science and Engineering, Shandong University

The river export is the main source of Hg to estuary and coastal oceans and be significant to the oceanic burden of mercury. Yellow River is an extremely high-sediment river, which may result in different behaviors and export variations of Hg compared to other rivers. In this study, we investigated the fates of Hg and methylmercury (MeHg) in the downstream areas of Yellow River and its estuary by sampling in November 2021. The unfiltered total and particulate Hg volume concentrations (UTHg and PHg) of surface water in the Yellow River showed an decreasing trend (p<0.05) along the current to the river mouth, similar with SPM. However, the corresponding MeHg volume concentrations (UTMeHg and PMeHg) of surface water in the Yellow River gradually increased. PHg and PMeHg were dominant species with the mean proportions of 99.1 ± 0.74% and 83.2 ± 16.3%, respectively. The gradually increased log-transformed partition coefficients (log Kd) of Hg and MeHg along the current to the river mouth suggesting that the adsorption of Hg and MeHg by SPM was steadily enhanced. Furthermore, Significant correlations (p<0.05) were observed between the logKd of Hg and SPM, as well as pH and DOC. The SPM dynamics modulated the distribution, partitioning and transport of Hg and MeHg species in the water and sediments. The Hg (43.4 ± 20.6 ng/g) and MeHg concentrations (85.6 ± 43.3 pg/g) of estuarine sediments was higher than that of riverine (9.46 ± 2.72 pg/g and 12.3 ± 8.71 pg/g, respectively) because of the finer can be exported to estuary easily than coarse particles. The transport models indicated that about 52.1% of suspended particles deposited from the Lijin Monitoring Station (approximately 105 km upstream from the river mouth) to the river mouth, and the rest 47.9% of SPM finally exported into the estuary. This resulted in about 27.2% of THg and 27.5% of PHg were settled on the river. On the contrary, the TMeHg and PMeHg from the river mouth were increased by 110% and 64.8% compared with the Lijin Monitoring Station. In conclusion, our results showed that the SPM can enhance the Hg burden and risk to coastal ecosystem of the Bohai sea.