New Insights on Ecosystem Mercury Cycling Revealed by Stable Isotopes of Mercury in Water Flowing from a Headwater Peatland Catchment
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Environmental Science & Technology
Stable isotope compositions of mercury (Hg) were measured in the outlet stream and in soil cores at different landscape positions in a 9.7-ha boreal upland-peatland catchment. An acidic permanganate/persulfate digestion procedure was validated for water samples with high dissolved organic matter (DOM) concentrations through Hg spike addition analysis. We report a relatively large variation in mass-dependent fractionation (δ202Hg; from −2.12 to −1.32‰) and a smaller, but significant, variation of mass-independent fractionation (Δ199Hg; from −0.35 to −0.12‰) during two years of sampling with streamflow varying from 0.003 to 7.8 L s−1. Large variations in δ202Hg occurred only during low streamflow (<0.6 L s−1), which suggest that under high streamflow conditions a peatland lagg zone between the bog (3.0 ha) and uplands (6.7 ha) becomes the dominant source of Hg in downstream waters. Further, a binary mixing model showed that except for the spring snowmelt period, Hg in streamwater from the catchment was mainly derived from dry deposition of gaseous elemental Hg (73−95%). This study demonstrates the usefulness of Hg isotopes for tracing sources of Hg deposition, which can lead to a better understanding of the biogeochemical cycling and hydrological transport of Hg in headwater catchments.
Woerndle, Glenn E.; Tsz-Ki Tsui, Martin; Sebestyen, Stephen D.; Blum, Joel D.; Nie, Xiangping; Kolka, Randall K. 2018. New Insights on Ecosystem Mercury Cycling Revealed by Stable Isotopes of Mercury in Water Flowing from a Headwater Peatland Catchment. Environmental Science & Technology. 52(4): 1854-1861. https://doi.org/10.1021/acs.est.7b04449.