Organic Matter in Rain: An Overlooked Influence on
Mercury Deposition
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Abstract
The importance of Hg emissions for
deposition will be scrutinized
in the future as new legislation to control emissions of Hg to the
atmosphere comes into effect. We show that mercury (Hg) concentrations
in rainfall are closely linked to organic matter (OM) with consistent
Hg/TOC ratios over large spatial scales decreasing from that in an
open field (OF, 1.5 μg g<sup>–1</sup>) to that in throughfall
(TF, 0.9 μg g<sup>–1</sup>). The leaf area index was
positively correlated with both TF [Hg] and total organic carbon ([TOC]),
but not the Hg/TOC ratio. This study shows that the progression in
the Hg/TOC ratio through catchments starts in precipitation with Hg/TOC<sub>bulk dep</sub> > Hg/TOC<sub>soil water</sub> > Hg/TOC<sub>streamwater</sub>. These findings raise an intriguing question about
the extent to which it is not just atmospheric [Hg] but also OM that
influences [Hg] in precipitation. This question should be resolved
to improve the ability to discern the importance of changing global
Hg emissions for deposition of Hg at specific sites