Distribution and Controlling Factors of Dissolved Gaseous Mercury and Reactive Mercury in Seawater Near Yangtze River Estuary

Complex hydrocultural conditions in the estuary affect the migration and transformation of mercury. Using two voyages in July and October 2018, Dissolved Gaseous Mercury (DGM) and Reactive Mercury (RHg) were determined to explore the source, transformation and influence of DGM content in the adjacent waters of Yangtze River Estuary in summer and autumn. The results showed the contents of DGM and RHg in summer were higher than those in autumn, and both of them were higher than those in open sea. In summer and autumn, the Yangtze River brought a higher concentration of DGM, and different flow direction and runoff resulted in differences in the high value region of the surface. The emergence of low-oxygen zones in summer was conducive to the production of DGM. In autumn, windy weather allowed seawater disturbances to promote the release of mercury from the underlying sediments, especially in shallow sea in northwest. RHg showed a higher concentration in the offshore than in the open sea in summer, but there was no such trend in autumn, reflecting the influence of less runoff input. DGM is the main product of RHg reduction, and there was a significant positive correlation between DGM and RHg in summer ( r = 0.356, P