14 Jun 2022
14 Jun 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Internal tree cycling and atmospheric archiving of mercury: examination with concentration and stable isotope analyses

David S. McLagan1,2,3, Harald Biester1, Tomas Navrátil4, Stephan M. Kraemer5, and Lorenz Schwab5,6 David S. McLagan et al.
  • 1Institute of Geoecology, Technical University of Braunschweig, Braunschweig, 38106, Germany
  • 2Dept. of Physical and Environmental Sciences, University of Toronto Scarborough, M1C1A4 Canada
  • 3School of Environmental Studies and Dept. of Geological Sciences and Geological Engineering, Queen’s University, K7L3N6 Canada
  • 4Institute of Geology of the Czech Academy of Sciences, Prague, 117 20, Czech Republic
  • 5Department for Environmental Geochemistry, Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, 1090, Austria
  • 6Doctoral School in Microbiology and Environmental Science, University of Vienna, Vienna, 1090, Austria

Abstract. Trees predominantly take up mercury (Hg) from the atmosphere via stomatal assimilation of gaseous elemental Hg (GEM). Hg is oxidised in leaves/needles and transported to other tree anatomy including bole wood where it can be stored long-term. Using Hg associated with growth rings facilitates archiving of historical GEM concentrations. Nonetheless, there are significant knowledge gaps on the cycling of Hg within trees. We investigate Hg archived in tree rings, internal tree Hg cycling, and differences in Hg uptake mechanisms in Norway spruce and European larch sampled within 1 km of a HgCl2 contaminated site using total Hg (THg) and Hg stable isotope analyses. Tree ring samples are indicative of significant increases in THg concentrations (up to 521µg·kg-1) from background period (BGP; facility closed; 1992—present) to secondary industrial period (2ndIP; no HgCl2 wood treatment; 1962–1992) to primary industrial period (1stIP; active HgCl2 wood treatment; ≈1900–1962). Mass dependent fractionation (MDF) Hg stable isotope data are shifted negative during industrial periods (δ202Hg: 1stIP: 4.32±0.15 ‰; 2ndIP: 4.04±0.32 ‰; BGP: 2.83±0.74 ‰; 1SD). Even accounting for a ≈ 2.6 ‰ MDF shift associated with stomatal uptake, these data are indicative of emissions derived from industrial activity being enriched in lighter isotopes associated with HgCl2 reduction and Hg0 volatilisation. Similar MDF (δ202Hg: 3.90±0.30 ‰; 1SD) in bark Hg (137±105µg·kg-1) suggests that stomatal assimilation and downward transport is also the dominant uptake mechanism for bark Hg (reflective of negative stomatal uptake MDF shift) rather than deposition to bark. THg was enriched in sapwood of all sampled trees across both tree species. This may indicate long-term storage of a fraction of Hg in sapwood or xylem solution. These data advance our understanding of the physiological processing of Hg within trees and provide critical direction to future research into the use of trees as archives for historical atmospheric Hg.

David S. McLagan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-124', Anonymous Referee #1, 28 Jun 2022
    • AC1: 'Reply on RC1', David McLagan, 26 Jul 2022
    • AC3: 'Reply on RC1', David McLagan, 26 Jul 2022
  • RC2: 'Comment on bg-2022-124', Anonymous Referee #2, 18 Jul 2022
    • AC2: 'Reply on RC2', David McLagan, 26 Jul 2022

David S. McLagan et al.

David S. McLagan et al.


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Short summary
Spruce and larch trees are effective archiving species for historical atmospheric mercury using growth rings of bole wood. Mercury stable isotope analysis proved an effective tool in helping to characterise industrial mercury signals and assess mercury uptake pathways (leaf uptake for both wood and bark) and mercury cycling within the trees.