Abstract
In order to estimate the air-surface mercury exchange of grasslands in temperate climate regions, fluxes of gaseous elemental mercury (GEM) were measured at two sites in Switzerland and one in Austria during summer 2006. Two classic micrometeorological methods (aerodynamic and modified Bowen ratio) have been applied to estimate net GEM exchange rates and to determine the response of the GEM flux to changes in environmental conditions (e.g. heavy rain, summer ozone) on an ecosystem-scale. Both methods proved to be appropriate to estimate fluxes on time scales of a few hours and longer. Average dry deposition rates up to 4.3 ng m-2 h-1 and mean deposition velocities up to 0.10 cm s-1 were measured, which indicates that during the active vegetation period temperate grasslands are a small net sink for atmospheric mercury. With increasing ozone concentrations depletion of GEM was observed, but could not be quantified from the flux signal. Night-time deposition fluxes of GEM were measured and seem to be the result of mercury co-deposition with condensing water. Effects of grass cuts could also be observed, but were of minor magnitude.
Highlights
The continued use of mercury in a wide range of products and processes and its release into the environment lead to deposition of mercury in ecosystems yet unspoiled
Mercury sequestered by terrestrial ecosystems might eventually be disconnected temporarily from the atmosphere-biosphere cycle, which would lead to a decrease in the pool of atmospheric mercury
In Neustift and Oensingen the data coverage of the gaseous elemental mercury (GEM) fluxes calculated by the modified Bowen ratio (MBR) method was considerably reduced due to failure of the eddy covariance systems
Summary
The continued use of mercury in a wide range of products and processes and its release into the environment lead to deposition of mercury in ecosystems yet unspoiled. Meteorological conditions and physicochemical properties of the soils mercury may be cycled fairly rapidly between terrestrial surfaces and the atmosphere (Gustin and Lindberg, 2005). It remains unclear whether deposited mercury is retained in background soils or whether terrestrial surfaces are even a net source of mercury (Pirrone and Mahaffey, 2005). Mercury sequestered by terrestrial ecosystems might eventually be disconnected temporarily from the atmosphere-biosphere cycle, which would lead to a decrease in the pool of atmospheric mercury
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