Abstract
Terrestrial air-surface exchange of mercury (Hg) forms an important component of the global Hg cycle, with drivers varying across spatial and temporal scales. These drivers include substrate properties, atmospheric chemistry, and meteorological factors. Vegetation uptake represents the dominant pathway of atmospheric Hg deposition to terrestrial surfaces. This study investigated the drivers of net ecosystem exchange of gaseous elemental mercury (Hg0) across multiple seasons in order to gain an understanding of the influence of vegetation and other environmental parameters on the Hg0 air-surface exchange. Measurements were made continuously using a micrometeorological aerodynamic flux gradient method at a low-vegetated background site in south-eastern Australia, over 14 months. Mean Hg fluxes and atmospheric concentrations across the entire study period were 0.002 ng m–2 h–1 (SD ± 14.23 ng m2 h–1) and 0.68 ng m–3 (SD ± 0.22 ng m–3), respectively. Variability was observed across seasons, with the highest average rate of emissions occurring in austral summer (December, January, February) (0.69 ng m–2 h–1) and the highest rate of deposition observed in autumn (March, April, May) (–0.50 ng m–2 h–1). Vegetation uptake dominated Hg flux during the winter and spring when meteorological conditions were cold and light levels were low. This is supported by CO2 flux data, with a daytime winter mean of 0.80 µmol m–2 h–1 and a spring daytime mean of 1.54 µmol m–2 h–1. Summer Hg fluxes were dominantly emission due to higher solar radiation and temperature. Climatic conditions at Oakdale allowed plant production to occur year-round, however the hot dry conditions observed in the warmer months increased evasion, allowing this site to be a small net source of Hg0 to the atmosphere.
Highlights
Mercury (Hg) is a globally transported atmospheric pollutant that can have adverse environmental and human health effects (Carpi and Lindberg, 1997; Schroeder and Munthe, 1998)
This study investigated the drivers of net ecosystem Hg exchange across multiple seasons in order to gain an understanding of the influence of vegetation and environmental parameters on Hg air-surface exchange across seasonal time scales
Mercury fluxes observed at Oakdale where highly variable and low throughout the study duration making it difficult to definitely determine the strength of relationships with environmental parameters
Summary
Mercury (Hg) is a globally transported atmospheric pollutant that can have adverse environmental and human health effects (Carpi and Lindberg, 1997; Schroeder and Munthe, 1998). Mercury is released into the atmosphere naturally, anthropogenically, or through re-emission of naturally- and anthropogenicallyderived Hg (Amos et al, 2013; Gustin et al, 2008). This emission of Hg from surfaces is an important component of the global Hg cycle, as it is what allows Hg to remain in the environment for long periods of time and to be globally distributed (Hintelmann et al, 2002; Schroeder and Munthe, 1998). Terrestrial air-surface exchange of Hg is heavily influenced by substrate properties, atmospheric chemistry and meteorological factors, which vary across time and sites and make it difficult to adequately assess the key controls (Agnan et al, 2016; Gabriel et al, 2011; Lin et al, 2010; Wang et al, 2006; Zhang et al, 2001)
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