Soil–atmosphere exchange flux of total gaseous mercury (TGM) at subtropical and temperate forest catchments

Abstract

Abstract. Evasion from soil is the largest source of mercury (Hg) to the atmosphere from terrestrial ecosystems. To improve our understanding of controls and in estimates of forest soil–atmosphere fluxes of total gaseous Hg (TGM), measurements were made using dynamic flux chambers (DFCs) over 130 and 96 d for each of five plots at a subtropical forest and a temperate forest, respectively. At the subtropical forest, the highest net soil Hg emissions were observed for an open field (24 ± 33 ng m−2 h−1), followed by two coniferous forest plots (2.8 ± 3.9 and 3.5 ± 4.2 ng m−2 h−1), a broad-leaved forest plot (0.18 ± 4.3 ng m−2 h−1) and the remaining wetland site showing net deposition (−0.80 ± 5.1 ng m−2 h−1). At the temperate forest, the highest fluxes and net soil Hg emissions were observed for a wetland (3.81 ± 0.52 ng m−2 h−1) and an open field (1.82 ± 0.79 ng m−2 h−1), with lesser emission rates in the deciduous broad-leaved forest (0.68 ± 1.01 ng m−2 h−1) and deciduous needle-leaved forest (0.32 ± 0.96 ng m−2 h−1) plots, and net deposition at an evergreen pine forest (−0.04 ± 0.81 ng m−2 h−1). High solar radiation and temperature during summer resulted in the high Hg emissions in the subtropical forest and the open field and evergreen pine forest at the temperate forest. At the temperate deciduous plots, the highest Hg emission occurred in spring during the leaf-off period due to direct solar radiation exposure to soils. Fluxes showed strong positive relationships with solar radiation and soil temperature and negative correlations with ambient air TGM concentration in both the subtropical and temperate forests, with area-weighted compensation points of 6.82 and 3.42 ng m−3, respectively. The values of the compensation points suggest that the atmospheric TGM concentration can play a critical role in limiting TGM emissions from the forest floor. Climate change and land use disturbance may increase the compensation points in both temperate and subtropical forests. Future research should focus on the role of legacy soil Hg in reemissions to the atmosphere as decreases in primary emissions drive decreases in TGM concentrations and disturbances of climate change and land use.

Measurement of the Vertical Distribution of Gaseous Elemental Mercury Concentration in Soil Pore Air of Subtropical and Temperate Forests

“…A major objective of our soil pore Hg(0) study was to investigate relationships between Hg(0) in vertical soil pore profiles and evasion of Hg(0) from the soil surface. The variation of soil–air Hg(0) fluxes is shown in Figures S2 and S3 . No relationship was found between soil pore Hg(0) flux and soil pore Hg(0) concentrations at 20 and 50 cm depths.…”

“…In eq , F can be derived from the diffusion of pore Hg(0) or from the photochemical reduction of Hg­(II) on the soil surface during daytime. Combining the simultaneous measurement of soil–air Hg(0) exchange, we estimated the diffusion coefficient between the soil at 3 cm and the atmosphere during daytime ( D s day ) and night-time ( D s night ) and for the entire day ( D s day + night ). In the subtropical forest, the estimated D s day , D s night , and D s day + night were 0.015, 0.013, and 0.014 m 2 h –1 for plot S-A and 0.0098, 0.0096, and 0.0097 m 2 h –1 for plot S-B in the Masson pine forest and 0.010, 0.0076, and 0.0079 m 2 h –1 for plot S-C in the camphor forest, respectively.…”

Isotopic Characterization of Mercury Atmosphere–Foliage and Atmosphere–Soil Exchange in a Swiss Subalpine Coniferous Forest

“…The regression equations of the Hg 0 flux versus the inverse of the temperature follow the Arrhenius equation (Figure S5). Previous studies also have shown that temperature is one of the main factors determining the atmosphere–soil Hg 0 flux in forest ecosystems. ,, …”

“…The atmospheric Hg 0 concentration correlates typically positively with atmosphere−soil Hg 0 exchange at remote sites. 19,71,72 The average atmospheric Hg 0 concentration measured during the atmosphere−soil flux investigations was 0.82 ± 0.16 ng m −3 in Davos-Seehornwald, which was much lower than the background concentrations of Hg 0 in the Northern Hemisphere (1.5−1.7 ng m −3 ). 63 Thus, lower atmospheric Hg 0 concentrations could lead to a higher potential of Hg re-emission from the forest soils in Davos-Seehornwald.…”

Health risk assessment of gaseous elemental mercury (GEM) in Mexico City

“…Additionally, we provide information on standard meteorological parameters (including temperature (T), relative humidity (RH), wind speed (WS), and wind direction (WD)) and trace gases (particulate matter (PM), CO, NO 2 , and SO 2 ), since many factors affecting the variability of GEM emissions include T, atmospheric turbulence, and sunlight, among others (Cizdziel et al, 2019 ; Zhou et al, 2020 ). Meteorological data and trace gas concentrations were downloaded from the Automated Atmospheric Monitoring Network (Red Automática de Monitoreo Atmosférico (RAMA) and Red de Meteorología y Radiación Solar (REDMET)) available at http://www.aire.cdmx.gob.mx/ .…”