Study on particulate mercury and dissolved mercury in adjacent waters of the Yangtze River Estuary in summer and autumn

The distribution trend and influence of particulate mercury (PHg) and dissolved mercury (DHg) in adjacent waters of the Yangtze River Estuary were studied by the Science 3 scientific research vessel in July and October 2018, respectively. The results showed that PHg and DHg had a large variance in the surface seawater, and the difference was obvious in different seasons. In summer, PHg in surface water decreased from nearshore to the open seas. In the autumn period, this trend was not obvious. DHg accounted for a larger proportion in this sea area. DHg was higher in autumn than that in summer, and the surface water was higher than the bottom water. In summer, the particle-water partition coefficients in surface and the bottom water increased from nearshore to the open seas; PHg correlated with TSM significantly in the surface and bottom water and PHg/TSM increased exponentially with salinity (R²=0.3365, p<0.01). The main reason for the change in the temporal and spatial distribution of surface PHg was the decrease of Changjiang diluted water and more windy weather. The distribution characteristics of DHg were controlled by small particle diameter and more marine organic particles. While the higher concentration of DHg at 30°N reflected the effects of river transport and surrounding pollution discharge.