Mercury emissions from natural surfaces highly impacted by human activities in Guangzhou province, South China

In situ measurements of mercury (Hg) exchange fluxes between natural surfaces and atmosphere were carried out at 14 sampling sites in Guangdong province, southern China, which is the most populated and industrialized area in China. It is found Hg fluxes varied significantly from different landscapes. The average fluxes of Hg from agricultural bare soils, dry paddy soils, and wet paddy fields were in the ranges of 18.2-135, 2.7―14.2, and 1.4―22.8 ng m―2 h―1, respectively. Average fluxes for bare soil and forest soil were 135 and 6.6 ng m―2 h―1, respectively. We did not observe significant correlations between Hg fluxes and soil Hg concentrations for all the sampling sites, and this is probably due to the different soil utilizations at the sampling sites. Dry paddy soils and wet paddy fields exhibited relatively lower Hg fluxes than other agricultural soils. Dry paddy soils had low soil porosity which might minimize the interface of soil to the atmosphere. Besides, low penetrations of solar radiation and relevant biotic activities in dry paddy soils might also result in low air Hg concentrations in soil pool which in turn result in minimal diffusions of Hg to the atmosphere. Hg fluxes from wet paddy fields were mainly controlled by soil Hg concentrations, which affected the Hg contents of above water layer and could also release Hg0 through the water layer to the atmosphere. It was also found that sites close to large anthropogenic point sources exhibited relatively higher emission fluxes, indicating potential of Hg reemissions from historical deposited Hg from anthropogenic sources.