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Methane Fluxes from a Wetland using the Flux-Gradient Technique

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  • Kware Software Systems Inc.
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Abstract

Methane emissions were measured from a bog and lake in the Experimental Lakes Area in Northern Ontario in 1992 and 1993, prior to and following flooding. Bog fluxes were small in 1992 (0.27 mg m −2 d −1) but increased 5-fold in 1993 after flooding. Over the bog, there was a diel cycle of nighttime emission and daytime uptake in 1992 in contrast to constant emission in 1993. Lake emissions decreased after flooding but were much greater than bog emissions in both years (average = 7.3 mg m −2 d −1). Seasonally, the bog flux was correlated with ground temperatures after flooding. In 1992, lake fluxes were correlated with air temperature on a daily basis. In contrast, seasonal lake fluxes were correlated with water and sediment temperatures in 1992, but only with sediment temperatures in 1993. These results are explained with respect to the effects of flooding on lake and bog dynamics.

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... Other custom-made TDL based trace gas analyzers are available (e.g., TDL-36, Aerodyne Research, Billerica, MA, USA), and have been used by several research teams in Europe and USA (Weinhold et al., 1994; Zahniser et al., 1995; Laville et al., 1999). The TGA100 has been used extensively to measure trace gas concentration gradients in order to determine the flux using the flux-gradient technique (Edwards et al., 1994Edwards et al., , 2001Edwards et al., , 2003 Wagner-Riddle et al., 1996a,b; WagnerRiddle and Thurtell, 1998; Simpson et al., 1995 Simpson et al., , 1997 Pattey, 1999, 2003). The flux-gradient technique is chosen over the more direct eddy covariance method as it permits the use of one TGA100 to measure fluxes over several locations sequentially. ...
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... If CH 4 and/or N 2 O fluxes need to be measured at more than one site, site valves (Whitey SS- 63TF6-142AC 2-way AC powered ball valve, Ottawa, ON) can be used to sequentially alternate between the sites every 30 min for example (Fig. 1). The tunable diode laser (model TGA100) has been used extensively to measure gas concentration gradients in order to determine the trace gas flux (Edwards et al., 1994Edwards et al., , 2001Edwards et al., , 2003 Wagner-Riddle and Thurtell, 1998; WagnerRiddle et al., 1996a, 1996b Simpson et al., 1995 Simpson et al., , 1997; Pattey, 1999, 2003). The TDL instrument and noise characteristics for gradient measurement are described by Edwards et al. (2003). ...
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Boreal wetlands are thought to be a large source of atmospheric methane, but this idea is based on very few measurements. Thus a regional survey in the low boreal forest region of central Ontario, Canada, consisting of 24 sites over 12 wetlands and 3 beaver ponds was conducted to determine the temporal and spatial trends in emissions and the net annual methane (CH4) flux. Conifer swamps represented nearly 50% of the wetland coverage, but emit a small amount of CH4 (seasonal means < 8 mg m−2 d−1). The significant emitters of CH4, in order from highest to lowest seasonal means, were beaver ponds (30–90 mg m−2 d−1), thicket swamps (0.1–88 mg m−2 d−1), and bogs (6–21 mg m−2 d−1). Mixed swamps, marshes, and fens emitted very little CH4 (< 3 mg m−2 d−1). Moisture saturation was the key determinant of high emissions, and when satisfied, differences in emissions could be explained by peat and sediment temperatures. On the basis of the areal extent of wetlands from peatland inventories we calculate that the low boreal region of Canada contributes approximately 0.15Tg CH4 yr−1 to the atmosphere. This is an order of magnitude lower than the flux would be using the estimate of Aselmann and Crutzen (1989) for the same boreal region.
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Article
The surface-atmospheric exchange of CO2 and CH 4 was measured continuously using the flux gradient approach from a beaver pond in the northern study area of the Boreal Ecosystem-Atmosphere Study between May 22 and September 19, 1994. The beaver pond was a large source of CO2 and CH 4 for the entire study period. 2 1 The half-hourly mean flux of CO2 and CH 4 ranged from -0.498 to 1.135 mg CO2 m- s- and from -0.805 to 37.5/xg CH 4 m -2 s -1, respectively, while the seasonal mean fluxes were 0.072 _+ 0.095 mg CO2 m -2 s -1 and 1.26 _+ 1.87/xg CH 4 m -2 s -1. The beaver pond rarely took up CO2. There was a large flux of both gases during the daytime. This increase is related to the transfer of the gases rather than to specific controls on production. The total efflux of CO2 and CH4for the 120 days of the study was 678 g CO2 m -2 and 11.3 g CH 4 m -2, or 183 and 8.4 g C m -2, respectively. When the measurements ceased, the sediment temperatures were >10øC, so it is reasonable to expect that the fluxes of CO2 and CH 4 continued into the late fall. This indicates that the beaver pond released more than 200 g C m -2 yr -.
Article
Variations in hydrostatic pressure controlled by diurnal tides triggered ebullition from subtidal freshwater sediments dominated by methanogenesis in the White Oak River estuary, North Carolina. Pulses of gas consisting of 50–80% methane were released when the tidal cycle reached its nadir. In August, site‐to‐site variations in these fluxes ranged from 60 to 650 ml (39–425 mg) CH 4 m ⁻² d ⁻¹ . At a single site, ebullition made up 50% of the total CH 4 flux out of the sediments; the remainder was transported across the sediment‐water interface by molecular diffusion. The sedimentary gas bubble reservoir varied seasonally between 2.6 and 14.8 liters m ⁻³ at two White Oak sites. These quantities represented 10–30% of the total sedimentary CH 4 inventory, the balance of which was dissolved in pore waters. Methane shifted between the two pools with seasonal changes in temperature as bubble methane partial pressure maintained equilibrium with dissolved CH 4 . Factors controlling the composition of sedimentary gas bubbles were investigated by collecting samples from several environments. These bubbles consisted primarily of CH 4 , N 2 , and CO 2 . The ratio of CH 4 to N 2 was found to be a useful indicator of mechanisms transporting gases from sediments and was controlled by both the ebullition rate and the presence of rooted emergent macrophytes.
Article
Data obtained in an intensive field study of the dry deposition of sulfur dioxide, ozone, and nitrogen dioxide, conducted in 1985 in central Pennsylvania, are used to illustrate the factors that must be considered to assure that high quality results are derived. In particular, the quality of the site must be such that flux measurements made above the surface are representative of surface values. For this purpose, tests involving momentum transfer and the surface energy budget are especially useful. In addition, conditions must not be changing rapidly, and the statistical uncertainty associated with flux measurement must be low. For the set of data presented here, conservative quality-assurance guidelines are used to reject potentially erroneous flux data. For ozone, most of the measured fluxes are of use in deriving surface resistances. For SO2, far fewer data points are available. For NO2, fluxes appear to lack the order of the O3 and SO2 fluxes, and do not enable surface resistances to be computed. The highest-quality SO2 and O3 data yield surface resistances in fair average agreement with model predictions for SO2, but substantially higher than predictions for O3.
Article
The potential aerobic methane oxidation (an estimate of the viable biomass of methane-oxidizing microorganisms) was assessed in various plant communities of a boreal, Sphagnum-dominated, mixed mire in Sweden. The relationships between potential oxidation and probable controlling environmental factors, such as water table depth, soil temperature and pore-water methane concentrations were also examined. Finally, the relationship between potential methane oxidation and the rate of net methane emission was evaluated. Potential methane oxidation ranged between 0.0 and 4.7 μg CH4 g−1 wet peat h−1, and the areal estimates for the 0–40 cm depth interval ranged between 0.04 and 16 g CH4 m−2 d−1. The depth of maximal potential oxidation was correlated with the depth of the water table (r2 = 0.64). Most communities showed a positive relationship between average rate of potential methane oxidation and water table depth (r2 = 0.66), i.e. the greater the vertical extension of aerated surface peat, the higher the methane oxidation capacity. In non-waterlogged communities (water table more than 5 cm below the vegetation surface), a positive correlation was found between the potential oxidation and methane concentration in peat pore-water (r2 = 0.44). These results suggest that the supplies of methane and oxygen largely control the biomass of methanotrophs across plant communities. Overall, net methane emission rates were negatively, but only weakly, correlated with the potential oxidation, suggesting that aerobic oxidation often controls emission rates from comparatively dry communities of Sphagnum peatlands, but that other factors also influence the emission.
Article
Wetlands are significant sources of atmospheric methane, an important radiatively active ‘greenhouse’ gas that accounts for an estimated 12% of total greenhouse warming. Since global climate models predict the greatest temperature and precipitation changes at high latitudes, and as the largest areas of wetland (346 × 106ha) are in the boreal and subarctic regions (40–70°N), recent research has focused on Identifying the factors that control methane emission from northern wetlands. Over the past few years, the database has expanded tremendously, and much progress has been made in understanding the environmental controls on methane emission at small spatial and temporal scales. However, we now need to broaden our understanding of regional differences in methane emission, ecological responses of northern wetlands to climate change, and the effect of other perturbations such as drainage and flooding.
Article
There is no clear consensus on how environmental and biotic factors control microbiallymediated methane production in wetlands, as well as emission of this important ‘greenhouse gas’ from wetlands into the atmosphere. To provide insight, I studied rates of methane production and emission into the atmosphere, as well as factors controlling those rates, along a toposequence from non-flooded to seasonally flooded in a coastal meadow and in a fen in Denmark. Methane production was estimated from anaerobic soil slurries while emission was estimated from static flux chambers. Methane emission into the atmosphere averaged 0.04 μg C-CH4 dm−2 h-−1 in the coastal meadow and 1.9 μg C-CH4 dm−2 h−1 in the fen. A comparison of potential CH4 production and CH4 emission into the atmosphere showed that in the coastal meadow, but not in the fen, emission increased when production increased during summer. Relationships between potential CN4 production and soil water content as well as soil temperature are discussed. Arrhenius plots indicated strikingly similar temperature responses of CH4 production in the two wetlands. Also, both wetlands showed different temperature responses in saturated soils (Q10 = 3.1 and 3.6; Eh=79 and 84 kJ mol−1) compared to unsaturated soils (Q10 = 8.1 and 8.7; eh = 138 and 142 kJ mol−1). My results suggest that different types of methanogens inhabit saturated and unsaturated soils in both a coastal meadow and a fen. Overall, the study indicates that CH4 production in wetlands and CH4 emission into the atmosphere from wetlands are controlled by a complex set of environmental and biotic factors which differ between wetlands.
Article
When the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived. If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre‐dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required. If the constituent's density fluctuations or mean gradients are measured directly in the air in situ , then corrections arising from both heat and water vapour fluxes are required. These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.
Article
As part of the Canadian Northern Wetlands Study (NOWES) measurements of methane flux were made at the Kinosheo Lake tower site for a 1-month period during the 1990 summer intensive. The measurements were made with a diode-laser-based methane sensor using the eddy correlation technique. Measurements of the methane fluxes were made at two levels, 5 or 18 m. Approximately 900 half-hour average methane flux measurements were obtained. Weak temporal and diurnal trends were observed in the data. Fluxes averaged over the study period showed an overall methane emission of 16 mg CH4 m(exp -2)/d with a daytime average of 20 mg CH4 m(exp -2)/d and a nighttime average of 9 mg CH4 m(exp -2)/d. The effect of emission footprint was evident in the data. A strong relationship between the daily average methane flux and wet bog temperature at 20-cm depth was observed.
Methane: Processes of Production and Consumption', in Agricultural Ecosystem Effects on Trace Gases and Global Climate Change
  • R Knowles
Knowles, R.: 1993, 'Methane: Processes of Production and Consumption', in Agricultural Ecosystem Effects on Trace Gases and Global Climate Change, ASA special publication no. 55, American Society of Agronomy, Madison, Wisconsin, U.S.A., pp. 145-155.
Methane emissions from a Swedish peatland area: Temporal and spatial variation
  • C Mikkela
  • I Sundh
  • J Eilertsson
  • B H Svennson
  • M Nilsson
Mikkela, C., Sundh, I., Eilertsson, J., Svennson, B. H. and Nilsson, M.: 1992, 'Methane emissions from a Swedish peatland area: Temporal and spatial variation', in Proceedings of the 9th International Peat Congress (IPS), Swedish National Committee of the IPS, Vol. 3, 152-165.
  • P Boeckx
  • O Van Cleemput
Boeckx, P. and Van Cleemput, O.: 1997, 'Methane emissions from a freshwater wetland in Belgium', Soil Sci. Soc. Am. J. 61, 1250-1256.
  • N T Roulet
  • P M Crill
  • N T Comer
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  • R A Boubonniere
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