Transport of particulate mercury along the reservoir- downstream - estuary continuum during the water-sediment regulation scheme period of Yellow River in 2018

As an important link of mercury (Hg) migration and transformation from land to ocean, rivers have been significantly influenced by anthropogenic activities, resulting in unpredictable environmental influences on the basin and offshore areas. In this study, the particulate Hg content of sediments in Xiaolangdi Reservoir (XLDR), Lijin Hydrological Station, and the Yellow River estuarine area during the water-sediment regulation scheme (WSRS) period in 2018 were analyzed, the characteristics and influencing factors of particulate Hg transport were explored. Our results revealed that the transport flux of particulate Hg into the sea during WSRS was 8.7 t, accounting for 68.8 % of the annual flux. High Hg content derived from the anthropogenic sources was observed in XLDR sediment, and Hg content in sediments of the lower reaches and estuary was elevated due to the sediments were mainly from XLDR during the sediment regulation stage. Under the influence of WSRS, the Hg content in the sediments of the lower reaches to estuary continuum was affected by the variation of sediment particle size, which was caused by the difference of sediment sources. In addition, WSRS led to a change in the binding forms of Hg in sediments, from mostly binding with organic matter in the XLDR to being comprehensively restricted by organic matter, iron and manganese oxides and carbonate minerals. Therefore, the transport behaviors and deposition patterns of particulate Hg in the reservoir-downstream-estuarine continuum has a good response to the implementation process of WSRS.