Salt-marsh plants as potential sources of Hg0 into the atmosphere

Publication date: March 2017
Source:Atmospheric Environment, Volume 152
Author(s): João Canário, Laurier Poissant, Martin Pilote, Miguel Caetano, Holger Hintelmann, Nelson J. O'Driscoll
To assess the role of salt-marsh plants on the vegetation-atmospheric Hg⁰ fluxes, three salt marsh plant species, Halimione portulacoides, Sarcocornia fruticosa and Spartina maritima were selected from a moderately contaminated site in the Tagus estuary during May 2012. Total mercury in stems and leaves for each plant as well as total gaseous mercury and vegetation-air Hg⁰ fluxes were measured over two continuous days. Mercury fluxes were estimated with a dynamic flux Tedlar^® bag coupled to a high-resolution automated mercury analyzer (Tekran 2537A). Other environmental parameters such as air temperature, relative humidity and net solar radiation were also measured aside. H. portulacoides showed the highest total mercury concentrations in stems and leaves and the highest average vegetation-air Hg⁰ flux (0.48 ± 0.40 ng Hg m⁻² h⁻¹). The continuous measurements converged to a daily pattern for all plants, with enhanced fluxes during daylight and lower flux during the night. It is noteworthy that throughout the measurements a negative flux (air-vegetation) was never observed, suggesting the absence of net Hg⁰ deposition. Based on the above fluxes and the total area occupied by each species we have estimated the total amount of Hg⁰ emitted from this salt-marsh plants. A daily emission of 1.19 mg Hg d⁻¹ was predicted for the Alcochete marsh and 175 mg Hg d⁻¹ for the entire salt marsh area of the Tagus estuary.



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