Abstract. The pattern of air–surface gaseous mercury (mainly Hg(0)) exchange in the Qinghai-Tibet Plateau (QTP) may be unique because this region is characterized by low temperature, great temperature variation, intensive solar radiation, and pronounced freeze-thaw process of permafrost soils. However, air–surface Hg(0) flux in the QTP is poorly investigated. In this study, we performed filed measurements and controlled field experiments with dynamic flux chambers technique to examine the flux, temporal variation and influencing factors of air–surface Hg(0) exchange at a high-altitude (4700 m a.s.l.) and remote site in the central QTP. The results of field measurements showed that surface soils were net emission source of Hg(0) in the entire study. Hg(0) flux showed remarkable seasonality with net high emission in the warm campaigns and net low deposition in winter campaign, and also showed the diurnal pattern with emission in daytime and deposition in nighttime, especially on days without precipitation. Rainfall events on the dry soils induced large and immediate increase in Hg(0) emission. Snowfall events did not induce the pulse of Hg(0) emission, but snow melt resulted in the immediate increase in Hg(0) emission. Daily Hg(0) fluxes on rainy or snowy days were higher than those of days without precipitation. Controlled field experiments suggested that water addition to dry soils significantly increased Hg(0) emission both in short and relatively long timescales, and also showed that UV radiation was primarily attributed to Hg(0) emission in the daytime. Our findings imply that a warm climate and environmental change could facilitate Hg release from the permafrost terrestrial ecosystem in the QTP.
Air–surface exchange of gaseous mercury over permafrost soil: an
investigation at a high-altitude (4700 m a.s.l.) and remote site in the central
Qinghai-Tibet Plateau
