Air/Surface Exchange of Gaseous Elemental Mercury at Different Landscapes in Mississippi, USA

• Main Authors: James V. Cizdziel, Yi Zhang, Divya Nallamothu, J. Stephen Brewer, Zhiqiang Gao
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Atmosphere
• Subjects: mercury; air-surface exchange; dynamic flux chamber; soils; wetland; forest floor; pond
• Online Access: https://www.mdpi.com/2073-4433/10/9/538

Mercury (Hg) is a global pollutant with human health and ecological impacts. Gas exchange between terrestrial surfaces and the atmosphere is an important route for Hg to enter and exit ecosystems. Here, we used a dynamic flux chamber to measure gaseous elemental Hg (GEM) exchange over different landscapes in Mississippi, including in situ measurements for a wetland (soil and water), forest floor, pond, mowed field and grass-covered lawn, as well as mesocosm experiments for three different agricultural soils. Fluxes were measured during both the summer and winter. Mean ambient levels of GEM ranged between 0.93−1.57 ng m^−3. GEM emission fluxes varied diurnally with higher daytime fluxes, driven primarily by solar radiation, and lower and more stable nighttime fluxes, dependent mostly on temperature. GEM fluxes (ng m^−2 h^−1) were seasonally dependent with net emission during the summer (mean 2.15, range 0.32 to 4.92) and net deposition during the winter (−0.12, range −0.32 to 0.12). Total Hg concentrations in the soil ranged from 17.1 ng g^−1 to 127 ng g^−1 but were not a good predictor of GEM emissions. GEM flux and soil temperature were correlated over the forest floor, and the corresponding activation energy for Hg emission was ~31 kcal mol^−1 using the Arrhenius equation. There were significant differences in GEM fluxes between the habitats with emissions for grass > wetland soil > mowed field > pond > wetland water ≈ forest ≈ agriculture soils. Overall, we demonstrate that these diverse landscapes serve as both sources and sinks for airborne Hg depending on the season and meteorological factors.