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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  26 Aug 2020

26 Aug 2020

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This preprint is currently under review for the journal BG.

A bottom-up quantification of foliar mercury uptake fluxes across Europe

Lena Wohlgemuth1, Stefan Osterwalder2, Carl Joseph1, Ansgar Kahmen1, Günter Hoch1, Christine Alewell1, and Martin Jiskra1 Lena Wohlgemuth et al.
  • 1Department of Environmental Sciences, University of Basel, Basel, Switzerland
  • 2Institut des Géosciences de l'Environnement, Université Grenoble Alpes, CNRS, IRD, Grenoble INP, Grenoble, France

Abstract. The exchange of gaseous elemental mercury, Hg(0), between the atmosphere and terrestrial surfaces remains poorly understood mainly due to difficulties in measuring net Hg(0) fluxes on the ecosystem scale. Emerging evidence suggests foliar uptake of atmospheric Hg(0) to be a major deposition pathway to terrestrial surfaces. Here, we present a bottom-up approach to calculate Hg(0) uptake fluxes to aboveground foliage by combining foliar Hg uptake rates normalized to leaf area with species-specific leaf area indices. This bottom-up approach incorporates systematic variations in crown height and needle age. We analyzed Hg content in 583 foliage samples from six tree species at 10 European forested research sites along a latitudinal gradient from Switzerland to Northern Finland over the course of the 2018 growing season. Foliar Hg concentrations increased over time in all six tree species at all sites. We found that foliar Hg uptake rates normalized to leaf area were highest at the top of the tree crown. Foliar Hg uptake rates decreased with needle age of multi-year old conifers (spruce and pine). Average species-specific foliar Hg uptake fluxes during the 2018 growing season were 18 ± 3 µg Hg m−2 for beech, 26 ± 5 µg Hg m−2 for oak, 4 ± 1 µg Hg m−2 for pine and 11 ± 1 µg Hg m−2 for spruce. For comparison, the average Hg(II) wet deposition flux measured at 5 of the 10 research sites during the same period was 2.3 ± 0.3 µg Hg m−2, which was four times lower than the site-averaged foliar uptake flux of 10 ± 3 µg Hg m−2. Scaling up site-specific foliar uptake rates to the forested area of Europe resulted in a total foliar Hg uptake flux of approximately 20 ± 3 Mg during the 2018 growing season. Considering that the same flux applies to the global land area of temperate forests, we estimate a foliar Hg uptake flux of 108 ± 18 Mg. Our data indicate that foliar Hg uptake is a major deposition pathway to terrestrial surfaces in Europe. The bottom up approach provides a promising method to quantify foliar Hg uptake fluxes on an ecosystem scale.

Lena Wohlgemuth et al.

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Lena Wohlgemuth et al.

Data sets

Dataset of foliar Hg concentrations at 10 forest research sites Lena Wohlgemuth

Lena Wohlgemuth et al.


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Short summary
Mercury (Hg) uptake by trees from the air is an important mechanism for the distribution of Hg in the environment. However, on the scale of a whole forest the amount of net Hg uptake is rarely measured which motivated us to our study. We determined Hg uptake fluxes by leaves and needles at 10 European forests and found that these Hg uptake fluxes are indeed large relative to other fluxes. The amount of Hg uptake by leaves and needles depended on their age and growing height on the tree.
Mercury (Hg) uptake by trees from the air is an important mechanism for the distribution of Hg...