2009 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, 2009 through April 30,2010
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 US 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 4-year period through the following tasks:
Task 1:    We will systematically quantify 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 on 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:

In year 3 of the study, we have completed task Task 1 and have finished an intense,  3-year field sampling campaign and analyzed field samples for Hg, C, N, and auxiliary measurements, in order to build a first systematic database on Hg distribution across U.S. forests. Several field and laboratory experiments to assess the fate of Hg during C mineralization (Task 2) have been performed; most of these studies have been finished or are nearing completion. We have made considerable progress in Task 3 (i.e., assessing spatial and statistical relationship that cause Hg distributions) as spatial mercury data are now available from all 14 sites. Task 4, which is focused on modeling and scaling of observed Hg patterns, is in progress, and we are developing the first spatial maps of mercury distributions across the United States using a modified ecosystem carbon model. Implementation of global change factors on Hg fluxes and pools associated with vegetation and carbon dynamics is a main task for remaining project period. We also have made progress in the cooperative agreement task (methyl-mercury analysis), and have completed analysis of subsets of field samples for methyl-mercury levels.
Task 1. Systematic quantification of Hg concentrations associated with vegetation, litter, and organic soil horizons and carbon pools

Table 1: List of 14 sites where samples were collected for this project.

 

 

 

 

 

 

 

 

We have finished an intentense 3-year sampling campaign to develop a systematic database on Hg stocks associated with terrestrial C pools across US forest ecosystems.  In 14 forest sites (see Table 1), we have collected, in a systematic and coherent way, 11 vegetation and soil compartments and analyzed for Hg concentrations, Hg/C ratios, N concentrations, texture (for soils). In addition, subsets of samples have been analyzed for methylmercury. This activity addresses 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.

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

This project also aims to quantify fate processes of Hg associated with C pools during decomposition processes.  We have implemented multiple approaches to study fate of Hg during C mineralization, including (i) stoichiometric comparisons of Hg and C pools in variously decomposed substrates in the field; (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 hence atmospheric emissions) in soils; and (iv) long-term (1.5 year) controlled laboratory incubation and field exposure studies of forest litter to assess C and Hg changes during decomposition. The status of these approaches is as follows:
(i)    Field sampling (see Task 1) has been finished and data analysis is ongoing to assess stoichiometric changes of variously decomposed substrates in the field.
(ii)   Controlled laboratory flux experiments to evaluate dependence of mercury soil emission from mineralization processes have been finished.
(iii)  Continuous soil gas measurements (to assess linkage between soil CO2 and Hg0 concentrations and diffusion profiles in the field) has been completed in one field site in one site and is in progress in a second field site,.
(iv)  Long-term (1.5 years) laboratory litter incubation studies have been finished and samples and results have been analyzed up to 1 year (1.5 year sample analysis in progress). Litter samples exposed in the field are currently being collected for analysis and comparison to laboratory incubation results. 
Task 3 and 4: Statistically evaluation of pools and fluxes in respect to climatic conditions and other variables and integration of data into terrestrial C models.
These tasks aim to statistically evaluate spatial patterns of mercury distribution in terrestrial ecosystem across the United States, with a specific emphasis on how vegetation and carbon pools determine atmospheric mercury sequestration and emissions. The results of field Hg concentrations and pools will be integrated in terrestrial C models to assess how climate change changes atmospheric mercury loads through interactions with vegetation and ecosystem carbon pools.
(i)    Availability of data from all 14 sites and all ecosystem components now allows to statistically and spatially analyze mercury distribution in terrestrial ecosystems, and assess how mercury distribution is co-determined by climatic variables, meteorology, regional pollution loads, and vegetation and ecosystem properties. We have performed a multitude of statistical tests, including linear and non-linear regression analyses, step-wise multiregression models, and Principal Component Analysis to analyze spatial patterns.
(ii)   An emphasis of spatial analysis includes how mercury loads in forest are co-determined by local and regional atmospheric pollution. Our results show that the large-scale distribution of Hg in the United States is largely independent of regional pollution loads, but that continental-scale abiotic (e.g., latitude, precipitation) and biotic (e.g., availability of soil C) processes control Hg levels in remote environments.
(iii)  We have used statistical relationships using a multiple regression model to create U.S. distribution maps of Hg concentrations in terrestrial ecosystems. The model includes a strong control of soil carbon, which we model using terrestrial carbon models. The model has now been parameterized and will be further used for scaling and to model effects of global change factors (i.e., to assess how changes in vegetation and soil carbon dynamics will feedback on atmospheric Hg uptake, sequestration, and emissions).

Future Activities:

The activities of the remaining project period will focus on: 
(1) Completion of ongoing  experimental studies, specifically in regards to fate process of mercury associated with carbon mineralization.
(2) Completion of data analysis of large systematic field sampling database. A key component is to analyze and discuss cause and effects of observed spatial distribution of mercury in remote, terrestrial environments.
(3) Modeling of effects of climate change through effects of changes in vegetation and carbon dynamics, with a special emphasis how this may affect future atmospheric mercury levels.
(4) Writing of publications and presentations of results.


Journal Articles on this Report : 5 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 Graydon JA, St. Louis VL, Hintelmann H, Lindberg SE, Sandilands KA, Rudd JW, Kelly CA, Hall BD, Mowat LD. Long-term wet and dry deposition of total and methyl mercury in the remote boreal ecoregion of Canada. Environmental Science & Technology 2008;42(22):8345-8351. R833378 (2009)
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 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:

    N/A, RFA, Scientific Discipline, Air, climate change, Air Pollution Effects, Environmental Monitoring

    Relevant Websites:

    http://www.dri.edu/People/Daniel.Obrist/exit EPA 

     

    Progress and Final Reports:

    Original Abstract
  • 2007 Progress Report
  • 2008 Progress Report
  • 2010 Progress Report
  • Final Report