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Wetlands exchange significant amounts of carbon dioxide (CO2) and methane (CH4)---two major greenhouse gases (GHG), and thus have significant impacts on the Earth's climate. In this study, fluxes of CO2 and CH4 were measured in a cattail-dominated marsh in Eastern Ontario, Canada. Eddy covariance measurements of net ecosystem CO2 exchange (NEE) revealed that the marsh was an annual sink of 264 g C m-2, and that growing season net CO2 fluxes were strongly correlated with vegetation biomass and leaf area index. Fluxes of CH4 were measured from water, soil and plants using closed chambers and resulted in a net annual area-weighted emission from the marsh of 206 g C m-2. Consequently, the net (CO2 + CH4) annual carbon (C) balance of this wetland corresponded to a sink of 58 g C m-2. A simple radiative forcing model based on the marsh CO 2 and CH4 emission patterns suggests that, despite the net carbon uptake, this wetland is contributing to atmospheric warming because of the large CH4 efflux. Future potential climate impacts of this marsh were evaluated using different emission scenarios that could result in response to climatic or environmental changes. Overall, short-term impacts are driven by CH4 emission rate, while the CO2 flux determines the impacts on longer time horizons. Uncertainties in predicting future wetland GHG balance arise from uncertain feedbacks and responses. Future alterations of the marsh GHG emission and uptake patterns resulting from land use or climatic changes could lead to a shift in the marsh C balance, showing the importance of wetland ecosystems in national and global C budgets and GHG-related political decisions.

Carbon dioxide and methane fluxes were measured between May 2003 and August 2004 on vegetated surfaces and pools of three peatlands located in the La Grande Riviere watershed, James Bay lowland, Quebec, Canada. Gas flux measurements were made using static chambers on a variety of sites in the three peatlands, chosen to represent the different biotypes present, from hummocks with water table position 35 cm below the surface to pools 100 cm deep. / Average CH4 fluxes for the different biotypes on vegetated surfaces sampled during summer 2003 ranged from 3.5 to 197 mg m-2 d-1 while summer 2004 average floating chamber pool fluxes ranged between 6.2 and 3165 mg CH4 m-2 d -1. Mean daily CH4 fluxes on vegetated surface are strongly correlated (r2 > 0.75) with summer average water table depth, greater fluxes occurring where water table is close to the surface. The vegetated surface CH4 fluxes were also correlated with peat temperature as fluxes increase with increasing peat temperature during the summer. / Most net ecosystem productivity values calculated for the different biotypes in the three peatlands showed release of CO2 during both early and mid growing season periods. An annual budget calculated for the LG2 peatland showed that the peatland emitted CO2 to the atmosphere at a rate of 0.77 g m-2 d-1. The overall release of CO 2 may have been caused in part by dry conditions in the peatlands during summer 2003, due to high temperature and low precipitation.

Beaver ponds are important parts of peatland landscapes and have high fluxes of CO2 and CH4. This study was undertaken in Mer Bleue Bog, Ontario, to determine the response of a beaver pond to drainage (lowering by 25 cm) as a sink or source of carbon. Plant distribution was changed in response to a new water table gradient. Each vegetation community and the remaining beaver pond were sampled for fluxes of CO2 and CH4 from mid-April to end-November, 1999, one year after the water table was lowered. / A flow-through chamber system was used to measure CO2 flux from vegetated sites. Mean daily CO2 flux ranged from 0.4--1.6 g CO2-C M-2 (positive denoting uptake from the atmosphere). Variations in CO2 flux amongst the sites along the gradient could not be related to differences in plant species composition, peat temperature, or water table. The mean daily CO2 emission measured by a static floating chamber on the pond area was -24.1 g CO2-C m-2. / A closed chamber was used to measure CH4 on vegetated sites. Daily CH4 fluxes ranged from 1 to -159 mg CH4-C m-2, increasing from the beaver pond margin to the open water surface. The water table explained 83% of the seasonal average CH 4 flux variability and the vegetation added another 11%. The mean daily CH4 flux measured by a static floating chamber on the pond area was -54 mg CH4-C m-2. / The seasonal measurements were integrated into an areal estimate of CO 2 and CH4 flux for the beaver pond area prior to and after drainage. The beaver pond area sequestered 96 g m-2 before drainage (104 g CO2-C m-2 and -8 g CH 4-C m-2), and the same area more than doubled the uptake to 231 g m-2 after being drained (233 g CO 2-C m-2 and -3 g CH4-C m -2).

CH$ sb4$ and CO$ sb2$ fluxes were measured in upland boreal forest soils, over the period May 16$ sp{ rm th}$ through Sept. 16$ sp{ rm th}$, 1994, among a variety of vegetation and drainage characteristics. Most upland soils consumed CH$ sb4$, (0.6 to $-$2.6 mg CH$ sb4$ m$ sp{-2}$ d$ sp{-1}$), and produced CO$ sb2$, (0.2 to 26.8 g CO$ sb2$ m$ sp{-2}$ d$ sp{-1}$). CH$ sb4$ consumption showed no seasonal trend, however CO$ sb2$ flux displayed an increasing rate until late August, after which flux rates began to decrease. Differences among the sites examined showed soil temperature and organic matter content to be the primary controls in predicting seasonal mean CH$ sb4$ flux rates. Similarly for CO$ sb2$ flux, soil temperature and C content proved to be the best predictors of seasonal mean differences among the range of sites examined. / Sites could be divided into 2 categories, strong CH$ sb4$ consuming and CO$ sb2$ producing sites, Gillam Aspen, Gillam Pine, OBS Aspen, Burn Moss, Palsa Birch, and YJP Dry and weak CH$ sb4$ consuming and CO$ sb2$ producing sites, Gillam Spruce, OBS Spruce, YJP Wet, Burn Spruce and Palsa Moss. The strong flux sites all exhibited similar trends in soil characteristics as they were the warmest, driest sites with faster nutrient cycling processes and thin ($ sim$2 to 10 cm) organic layers. The weak flux sites were colder, wetter, with slower nutrient cycling, and a thick organic/peat layer ($ sim$20 to 50 cm). The primary visual distinction between these two groups was the presence of a Sphagnum sp. ground cover, which was characteristic of weak CH$ sb4$ consuming and CO$ sb2$ producing sites.

Tropospheric oxidation modulates pollution chemistry and greenhouse gas lifetimes. The hydroxyl radical (OH) is the primary oxidant and the main sink for methane, the second-most influential anthropogenic contributor to climate change. OH is produced following the photolysis of ozone, an oxidant, respiratory irritant and greenhouse gas. Trends in methane or ozone are frequently attributed to their sources, but sink-driven variability is less often considered. I investigate the influence of fluctuations in turbulent loss to the Earth’s surface, also known as deposition, on tropospheric ozone concentrations and chemistry over the relatively polluted eastern United States. I use idealized sensitivity simulations with the global chemistry-climate model AM3 to demonstrate that coherent shifts in deposition, on the order recently observed at a long-term measurement site, affect surface ozone concentrations as much as decreases in its precursor emissions have over the past decade. I conclude that a sub-regional deposition measurement network is needed to confidently attribute trends in tropospheric ozone. Next, I turn to the remote marine troposphere to evaluate two theoretical proxies for variability in the methane sink, OH, with observations from the NASA Atmospheric Tomography (ATom) aircraft campaign. The low concentration and short lifetime of OH preclude the development of a representative measurement network to track its fluctuations in space and time. This dearth of constraints has led to discrepancies in the methane lifetime across models that project atmospheric composition and climate. Observational and modeling studies suggest that few processes control OH fluctuations in relatively clean air masses, and the short OH lifetime implies that it is at steady-state (total production is equal to loss). I leverage this chemistry by evaluating a convolution of OH drivers, OH production scaled by the lifetime of OH against its sink with carbon monoxide, as a potential “steady-state” proxy. I also assess the predictive skill of formaldehyde (HCHO), an intermediate product of the methane and OH reaction. I find that both proxies broadly reflect OH on sub-hemispheric scales (2 km altitude by 20° zonal bins) relative to existing, well-mixed proxies that capture, at best, hemispheric OH variability. HCHO is produced following methane loss by reaction with OH and reflects the insolation influence on OH, while the steady-state proxy demonstrates a stronger relationship with OH and offers insight into its sensitivity to a wider array of drivers. Few components—water vapor, nitric oxide, and the photolysis rate of ozone to singlet-d atomic oxygen—dominate steady-state proxy variance in most regions of the remote troposphere, with water vapor controlling the largest spatial extent. Current satellite instruments measure water vapor directly, and other retrievals like nitrogen dioxide columns or aerosol optical depth or could be used to infer nitric acid or the rate of ozone photolysis. Thus satellite observations may be used to derive a steady-state proxy product to infer OH variability and sensitivity in the near-term. HCHO is also retrieved from satellite instruments, and an OH product using satellite-observed HCHO columns is already in development. The relatively high fluctuation frequency of HCHO or the steady-state proxy advances our insight into the connection between OH and its drivers. The observed steady-state proxy demonstrates a widespread sensitivity to water vapor along the ATom flight tracks, and I conclude that an improved and consistent representation of the water vapor distribution is a necessary step in constraining the methane lifetime across global chemistry-climate models.