Increased mercury in forest soils under elevated carbon dioxide
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Fossil fuel combustion is the primary anthropogenic source of both CO2 and Hg to the atmosphere. On a global scale, most Hg that enters ecosystems is derived from atmospheric Hg that deposits onto the land surface. Increasing concentrations of atmospheric CO2 may affect Hg deposition to terrestrial systems and storage in soils through CO2-mediated changes in plant and soil properties. We show, using free-air CO2 enrichment (FACE) experiments, that soil Hg concentrations are almost 30% greater under elevated atmospheric CO2 in two temperate forests. There were no direct CO2 effects, however, on litterfall, throughfall or stemflow Hg inputs. Soil Hg was positively correlated with percent soil organic matter (SOM), suggesting that CO2-mediated changes in SOM have influenced soil Hg concentrations. Through its impacts on SOM, elevated atmospheric CO2 may increase the Hg storage capacity of soils and modulate the movement of Hg through the biosphere. Such effects of rising CO2, ones that transcend the typically studied effects on C and nutrient cycling, are an important next phase for research on global environmental change.
KeywordsGlobal change Soil organic matter Hg deposition Throughfall Free-air carbon dioxide enrichment
We thank D. Richter for soil samples, E. A. Leger and F. J. Rohlf for statistical advice, C. Iversen, R. Oren and the FACE staff for field support, J. Lichter for conversations and data on pre-treatment soils, R. K. Kolka for advice on stemflow collectors, S. Lindberg and N. Bloom for throughfall sampling advice, J. Varekamp for use of his DMA-80, W. Schlesinger for advice during manuscript preparation, and H. Heilmeier and two anonymous reviewers for comments on this manuscript. This work was supported by the US Department of Energy, Office of Science-Biological and Environmental Research, and fellowships from the National Science Foundation (S. M. N.) and Department of Energy (S. M. N.).
- Expert Panel on Mercury Atmospheric Processes (EPMAP) (1994) Mercury atmospheric processes: a synthesis report. Workshop Proceedings, EPRI/TR–104214, Tampa, FLGoogle Scholar
- Finzi AC, Allen AS, DeLucia EH, Ellsworth DS, Schlesinger WH (2001) Forest litter production, chemistry, and decomposition following two years of free-air CO2 enrichment. Ecology 82:470–484Google Scholar
- Fitzgerald WF, Lamborg CH (2003) Geochemistry of mercury in the environment. In: Holland HD, Turekian KK (eds) Treatise on geochemistry, vol 9. Elsevier, San Diego, pp 107–148Google Scholar
- IPCC (2007) Climate change 2007: the physical scientific basis. In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (eds) Contribution of Working Group I to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press, New York, p 966Google Scholar
- Lubowski RN, Vesterby M, Bucholtz S, Baez A, Roberts MJ (2006) Major land uses in the United States. US Department of Agriculture economic information bulletin (EIB–14)Google Scholar
- Riggs JS, Tharp ML, Norby RJ (2007) ORNL FACE weather data. Carbon Dioxide Information Analysis Center, US Department of Energy, Oak Ridge National Laboratory, Oak RidgeGoogle Scholar
- US Environmental Protection Agency (US EPA) (1997a) Mercury study report to Congress, vol. VII. Characterization of human health and wildlife risks from mercury exposure in the United States, EPA-452/R-97-009Google Scholar
- US Environmental Protection Agency (US EPA) (1997b) Mercury study report to Congress, vol. III. Fate and transport of mercury in the environment, EPA-452/R-97-005Google Scholar