Investigating sources of seasonal variation in mercury exported from an upland-peatland ecosystem in northern Minnesota using mercury stable isotopes

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Glenn Woerndle (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Martin Tsui

Abstract: Boreal peatland ecosystems are well known as an important sink of atmospheric mercury (Hg) as well as a source of highly toxic methylmercury (MeHg) to downstream ecosystems. Therefore, a thorough understanding on the complex Hg cycling in these northern ecosystems is important. For the first time, stable Hg isotopes were evaluated as a tool to investigate Hg cycling in an upland-peatland ecosystem in northern Minnesota. Hg stable isotopes undergo both mass-dependent fractionations (MDF; e.g., d202Hg) and mass-independent fractionations (MIF; e.g., ?199Hg) during biotic, abiotic, and photochemical reactions, and are diagnostic of complex Hg cycling processes in natural ecosystems. In this study, we examined the variability of stable Hg isotopes in a relatively well characterized small peatland-upland watershed (S2) in Marcell Experimental Forest in northern Minnesota, U.S.A. Water samples at the watershed outlet were collected biweekly when the stream flowed in both 2014 and 2015. We also collected surface and subsurface runoff from upland soils, porewater from the lagg zones, bog cores, upland soil, foliage and litter, for determining total-Hg, MeHg, and Hg stable isotope compositions. Data on exported water over time (2014- 2015) show a large range of d202Hg (-2.1 to -1.3 permil; n=21) but only a small range of ?199Hg (-0.35 to -0.1 permil; n=21), with ?199Hg resembling the isotopic values of Hg in bog/foliage samples. Samples with more positive d202Hg in the exported water were collected during the spring snow melt event, and these d202Hg values are similar to the values of surface and subsurface runoff from the upland (i.e., -1.4 to -1.2 permil; n=4). Our results suggest that the temporal variation of Hg isotopes are large in this small upland-peatland watershed and such variation can potentially offer new insight into complex Hg cycling in these ecosystems.

Additional Information

Language: English
Date: 2016
Mercury, Mercury biogeochemistry, Mercury stable isotopes, S2, Sources of inorganic mercury, Wetland mercury cycling
Mercury cycle (Biogeochemistry) $z Minnesota $z Marcell Experimental Forest
Wetland ecology $z Minnesota $z Marcell Experimental Forest

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