2010 Progress Report: Effects of Global Change on the Atmospheric Mercury Burden and Mercury Sequestration Through Changes in Ecosystem Carbon Pools

EPA Grant Number: R833378
Title: Effects of Global Change on the Atmospheric Mercury Burden and Mercury Sequestration Through Changes in Ecosystem Carbon Pools
Investigators: Obrist, Daniel , Johnson, Dale W. , Lindberg, Steve , Luo, Yiqi
Institution: Desert Research Institute , University of Oklahoma , University of Nevada - Reno
Current Institution: Desert Research Institute , University of Nevada - Reno , University of Oklahoma
EPA Project Officer: Chung, Serena
Project Period: May 1, 2007 through April 30, 2012
Project Period Covered by this Report: May 1, 2010 through April 30,2011
Project Amount: $899,091
RFA: Consequences of Global Change For Air Quality (2006) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Climate Change , Air

Objective:

Terrestrial carbon (C) pools play an important role in uptake, deposition, sequestration, and emission of atmospheric mercury (Hg). Biomass and soil C pools are highly sensitive to climate and land use changes with potentially serious consequences for the fate of large Hg pools, including past atmospheric Hg pollution, associated within these C pools. Our overall objective is to assess how global change during the next 100 years is likely to affect Hg cycling processes (i.e., atmospheric Hg uptake, sequestration, and emission) associated with vegetation and soil C pools. This will be achieved by developing a first systematic inventory of Hg concentrations and pools associated with and sequestered in U.S. forest ecosystems, assessing how global change will affect plant-derived atmospheric Hg inputs to ecosystems via changes in plant productivity, plant senescence, and litterfall; assessing fate processes of Hg sequestered in terrestrial C pools during decomposition processes; and modeling how global change impact on above processes may feedback on the future atmospheric Hg burden.

The work is implemented during a four-year period through the following tasks:

    Task 1: We will systematically quantify present-day Hg concentrations associated with vegetation, litter, and organic soil horizons in forested ecosystems across the United States.

    Task 2: We will assess the fate of Hg during C mineralization processes using controlled laboratory incubation and field studies to evaluate to what degree decomposition of organic matter leads to emission and re-emission of Hg to the atmosphere, increased mobilization within terrestrial ecosystems, or long-term sequestration by incorporation and accumulation of Hg in the remaining C matter fraction.

    Task 3: We will statistically evaluate and model the dependence of atmospherically derived plant and organic Hg pools and fluxes to climatic conditions.

    Task 4: We will integrate data on measured plant, litter, and soil Hg pools and fluxes—along with the hierarchy of climatic factors—into an existing terrestrial C model and use model results to explore possible mitigation measures for atmospheric Hg and land management options to stabilize Hg pools associated with terrestrial C pools.

Progress Summary:

After completion of Task 1 in previous years, we also have now completed Task 2 of the study and are nearing completion of Task 3. Data from the systematic investigation of present-day Hg concentration and pools across U.S. forests (Task 1) now have been published in several manuscripts (Obrist, et al., 2011, ES&T ; Obrist, et al., 2011, JPNSS; Obrist, et al., Biogeosciences, 2009), and addtional publications, including one on methylated Hg patterns, are in preparation. Experimental studies to assess fate of Hg during C mineralization and biogeochemical links between terrestrial carbon and mercury (Task 2) have been completed, results have been analyzed and published (Teisserenc, et al., L&O , in press; Pokharel and Obrist, Biogeosciences, in press; Fain, et al, GCA, 2011; Obrist, et al., STOTEN, 2010; Zhang, Lindberg, et al., AE, 2008), and further manuscripts are in preparation for publication (Pokharel and Obrist, in preparation). Task 3 has been addressed based on results obtained through Task 1 and has formed the basis for the first published spatial distribution maps of mercury in forests of the United States (Obrist, et al., 2011; ES&T ). Task 4, focused on modeling effects of global change on Hg sequestration in terrestrial ecosystems, currently is fully under way and will continue to the end of this study. We also completed tasks outlined in the cooperative agreement (methyl-mercury analysis) and these data currently are being written up for publication (Obrist, et al., in preparation).

Task 1. Systematic quantification of Hg concentrations associated with vegetation, litter, and organic soil horizons and carbon pools

We finished a 3-year sampling campaign to develop the first systematic database on Hg concentration and stocks in terrestrial ecosystems and to assess the degree terrestrial Hg is associated with terrestrial carbon (C). In 14 forest sites, we collected, in a systematic and replicated way, 11 major vegetation and soil compartments to analyze for Hg concentrations and stocks, C concentrations and stocks, Hg/C ratios, N concentrations, and texture (for soils). In addition, subsets of samples have been analyzed for methylmercury as part of a cooperative agreement with EPA (see below). This activity addressed the following project goals: (1) to quantify total Hg pools associated with terrestrial C pools; (2) to estimate atmospheric Hg inputs and sequestration through leaf litterfall and plant senescence; (3) to evaluate total Hg pools sequestered across forests of the United States; (4) to determine resilience and turnover times of Hg sequestered in vegetation and soil pools; and (5) to assess relationships between total mercury and methylmercury concentrations in terrestrial ecosystems. Detailed results and discussions are presented in the full report and in several published manuscripts (Obrist, et al., 2011, ES&T ; Obrist, et al., 2011, JPNSS; Obrist, et al., 2009, Biogeosciences).

Task 2: Assessing the fate of Hg during C mineralization processes using controlled laboratory incubation and field studies

This task aimed to quantify fate processes of Hg associated with C pools during decomposition processes. We have implemented and completed multiple experimental studies to assess fate of Hg during C mineralization, including (i) stoichiometric comparisons of Hg and C in variously decomposed layers in samples of the 14 forest sites; (ii) controlled laboratory flux studies to synchronously measure Hg degassing and soil respiration (i.e., CO2 fluxes) from soils; (iii) continuous, in situ measurement of soil gas Hg and CO2 concentrations at various depths to assess linkages between CO2 and Hg0 production (and atmospheric emissions); and (iv) long-term controlled laboratory litter decomposition studies incubation to measure losses of Hg during C decomposition processes. In addition, we participated in additional field studies to assess the relationships of terrestrial Hg cycling with carbon at the scale of whole watersheds (e.g., Fain, et al., 2011, GCA; Teisserenc, et al., L&O , in press).

Further details on the results of Task 2 can be seen in published manuscripts (Pokharel and Obrist, Biogeosciences, in press; Obrist, et al., STOTEN, 2010; Zhang, Lindberg, et al., AE, 2008).

Task 3 and 4: Statistical evaluation of pools and fluxes in respect to climatic conditions and other variables and integration of data into terrestrial C models.

We statistically evaluated relationships of spatial Hg and Me-Hg distribution patterns to climatic conditions and other variables to assess how environmental conditions and ecosystem processes favour sequestration of atmospheric Hg versus emission/re-emission of Hg from terrestrial surfaces to the atmosphere. Our statistical evaluation showed that key variables associated with high Hg sequestration potentials are latitude, contents, precipitation, and soil carbon and soil clay contents. A particularly strong link was observed between Hg levels and C/N ratios, which we attribute to the fact that sites with older, highly decomposed carbon pools have been exposed to a long-term legacy of atmospheric Hg deposition. Methyl-Hg concentrations in general follow trends of total Hg, and as such are driven by similar variables. However, the spatial distribution of Me-Hg concentration also is co-determined by C/N ratios of soils and soil clay contents, implying additional biogeochemical controls on methyl-Hg distribution.

Observed relationships of Hg distribution patterns to key variables (see Obrist, et al., 2011, ES&T ), including geographic (i.e., latitude), climatic (i.e., precipitation), and ecosystem (i.e., carbon and clay content) variables, now allow us to predict future Hg distribution trends and assess possible feedbacks on atmospheric Hg loads. There are ongoing efforts for modeling and sensitivity analyses of future terrestrial Hg distribution and the implications of climate change for atmospheric Hg loads.

Future Activities:

Final activities of this project will focus on completion of manuscripts relating to Tasks 1, 2, and 3, and completion of modeling Task 4 to predict effects of climate change on terrestrial Hg storage and the implication for atmospheric Hg burden. A specific task will involve a comprehensive analysis and discussion of all combined project tasks to provide EPA with a comprehensive report on how climate change is likely to affect the terrestrial cycling and storage of Hg, and how this will feedback on air Hg loads in the future based on experimental and modeling tasks of this study.


Journal Articles on this Report : 9 Displayed | Download in RIS Format

Other project views: All 64 publications 21 publications in selected types All 21 journal articles
Type Citation Project Document Sources
Journal Article Fain X, Obrist D, Pierce A, Barth C, Gustin MS, Boyle DP. Whole-watershed mercury balance at Sagehen Creek, Sierra Nevada, CA. Geochimica et Cosmochimica Acta 2011;75(9):2379-2392. R833378 (2010)
R833378 (Final)
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  • Journal Article Graydon JA, St. Louis VL, Hintelmann H, Lindberg SE, Sandilands KA, Rudd JWM, Kelly CA, Tate MT, Krabbenhoft DP, Lehnherr I. Investigation of uptake and retention of atmospheric Hg(II) by boreal forest plants using stable Hg isotopes. Environmental Science & Technology 2009;43(13):4960-4966. R833378 (2010)
    R833378 (Final)
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  • Journal Article Obrist D, Hallar AG, McCubbin I, Stephens BB, Rahn T. Atmospheric mercury concentrations at Storm Peak Laboratory in the Rocky Mountains: evidence for long-range transport from Asia, boundary layer contributions, and plant mercury uptake. Atmospheric Environment 2008;42(33):7579-7589. R833378 (2009)
    R833378 (2010)
    R833378 (Final)
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  • Journal Article Obrist D, Johnson DW, Lindberg SE. Mercury concentrations and pools in four Sierra Nevada forest sites, and relationships to organic carbon and nitrogen. Biogeosciences 2009;6(5):765-777. R833378 (2009)
    R833378 (2010)
    R833378 (Final)
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  • Journal Article Obrist D, Fain X, Berger C. Gaseous elemental mercury emissions and CO2 respiration rates in terrestrial soils under controlled aerobic and anaerobic laboratory conditions. Science of The Total Environment 2010;408(7):1691-1700. R833378 (2009)
    R833378 (2010)
    R833378 (Final)
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  • Journal Article Obrist D, Johnson DW, Lindberg SW, Luo Y, Hararuk O, Bracho R, Battles JJ, Dail DB, Edmonds RL, Monson RK, Ollinger SV, Pallardy SG, Pregitzer KS, Todd DE. Mercury distribution across 14 U.S. forests. Part I: Spatial patterns of concentrations in biomass, litter, and soils. Environmental Science & Technology 2011:45(9):3974-3981. R833378 (2010)
    R833378 (Final)
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  • Journal Article Obrist D, Johnson DW, Edmonds RL. Effects of vegetation type on mercury concentrations and pools in two adjacent coniferous and deciduous forests. Journal of Plant Nutrition and Soil Science 2012;175(1):68-77. R833378 (2010)
    R833378 (Final)
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  • Journal Article Pokharel AK, Obrist D. Fate of mercury in tree litter during decomposition. Biogeosciences 2011;8(9):2507-2521. R833378 (2010)
    R833378 (Final)
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  • Journal Article Zhang H, Lindberg SE, Kuiken T. Mysterious diel cycles of mercury emission from soils held in the dark at constant temperature. Atmospheric Environment 2008;42(21):5424-5433. R833378 (2007)
    R833378 (2009)
    R833378 (2010)
    R833378 (Final)
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  • Supplemental Keywords:

    RFA, Scientific Discipline, Air, climate change, Air Pollution Effects, Environmental Monitoring

    Relevant Websites:

    http://www.dri.edu/People/Daniel.Obrist/ Exit

    Progress and Final Reports:

    Original Abstract
  • 2007 Progress Report
  • 2008 Progress Report
  • 2009 Progress Report
  • Final Report