Gaseous elemental mercury (GEM) exchange flux from soil-vegetation to atmosphere at a meadow steppe

Gaseous elemental mercury (GEM) exchange between terrestrial surfaces and the atmosphere plays an important role in the global Hg cycle, but there are large uncertainties in estimating the quantity of grassland air-soil exchange of elemental mercury vapor (Hg-0). Our study investigated GEM exchange fluxes over the soil covered by two vegetation communities (including four conditions: L. chinensis coverage and removal, L. chinensis + forbs coverage and removal). We collected flux data during the growing season (from May to September) in 2018, highlighting the interactive effects of plant coverage and meteorological conditions. For the four different treatments, the daily mean values of GEM in the air ranged from 12.5 +/- 3.7 to 17.4 +/- 5.7 ng m(-3) and the total Hg concentrations in the soil ranged as 32.8-36.2 ng g(-1). GEM fluxes under the four treatments were net emissions from soil (daily mean 4.1 +/- 8.4-9.0 +/- 14.7) (ng m(-2) h(-1)), varying diurnally with releasing (10.3 +/- 6.3-20.0 +/- 8.1) (ng m(-2) h(-1)) in daytime, and depositing (4.3 +/- 1.7-8.7 +/- 4.6) (ng m(-2) h(-1)) in nighttime. The significant difference of flux between vegetation coverage and removal were observed during the -growing season, but the differences between L. chinensis and L. chinensis + forbs coverage only were confirmed in July (p < 0.05). The positive correlation between fluxes and solar radiation, air/soil temperature suggested these meteorological factors could promote the Hg emission (p < 0.05). Together, we demonstrated that meadow steppe served as a source for atmospheric Hg during the growing season and the plant community played an importantly catabatic role in the Hg exchange between soil and atmosphere.

Automated summary

This study investigated the GEM exchange fluxes over soil covered by two vegetation communities and found that plant coverage and meteorological conditions significantly affected GEM exchange. The results demonstrated that grassland served as a source for atmospheric mercury during the growing season and the plant community played an important role in mercury exchange between soil and atmosphere.