Mercury fluxes from air/surface interfaces in paddy field and dry land

In order to provide insight into the characteristics of Hg exchange in soil/water–air surface from cropland (including paddy field and dry land), Hg fluxes were measured in Chengjiang. Mercury fluxes were measured using the dynamic flux chamber method, coupled with a Lumex® multifunctional Hg analyzer RA-915+ (Lumex Ltd., Russia). The Hg fluxes from paddy field and dry land were alternatively measured every 30 min. Data were collected for 24–48 h once per month for 5 months. Mercury fluxes in both fields were synchronously measured under the same conditions to compare Hg emissions between paddy field and dry land over diurnal and seasonal periods and find out what factors affect Hg emission on each surface. These results indicated that air Hg concentrations at the monitoring site was double the value observed at the global background sites in Europe and North America. The Hg release fluxes were 46.5 ± 22.8 ng m−2 h−1 in the warm season, 15.5 ± 18.8 ng m−2 h−1 in the cold season for dry land, and 23.8 ± 15.6 ng m−2 h−1 in the warm season, 6.3 ± 11.9 ng m−2 h−1 in the cold season for paddy field. Solar radiation is important in the emission of Hg over both sites. Hg exchange at the soil/air and water/air interfaces showed temporal variations. The amount of Hg emission from dry land was higher than that from the paddy field, and the emission in daytime was higher than that at night. Moreover, Hg emissions from land covered by crops, was lower than that for bare land.

Research highlights
► It was found that agricultural fields are important local atmospheric Hg sources in the region.
► The Hg emissions from dry cornfield were higher than those from the flooded rice paddy, higher mercury emissions in the warm season than the cold season, and during daytime than at night.
► Mercury evasion is strongly related to solar radiation which is important in the emission of Hg at both sites.