Mercury release flux and its influencing factors at the air-water interface in paddy field in Chongqing, China

The exchange of mercury （Hg） across the air-water interface is an important part of Hg biogeochemical cycle. Mercury fluxes across the air-water interface in paddy fields were measured by a Dynamic Flux Chamber （DFC） coupled with a Lumex multifunctional mercury analyzer RA-915＋ at two sites （Chengjiang （C J） and Caoshang （CS）） in Beibei, Chongqing, China in 2008. The results showed that mercury emission followed a power-law relationship with solar radiation and air temperature,, and it increased exponentially with water temperature at both sites. Mercury emission was mainly influenced by the solubility of gaseous elemental Hg, photo-thermal effect, electron activity （Eh） and air Hg concentrations. Solar radiation made the greatest direct contribution to mercury emission during the daytime （0.80）, with an 83.60% contribution, whereas at nighttime the water temperature （0.72） contributed to 71.65% of emissions. The temperature gradient between water and air might also influenced mercury emis- sion across the air/water interface at nighttime. These findings suggest that paddy fields could act as a significant source of atmospheric mercury, and it can contribute significantly to the atmospheric mercury in a local region.