Trace Gas Production Research Articles

Microbial oxidation of methane, ammonium and carbon monoxide, and turnover of nitrous oxide and nitric oxide in soils

The effect of soil microbial processes on production and/or consumption of atmospheric trace gases was studied in four different soils which were preincubated in the presence of elevated concentrations of CH4, NH 4 + or CO, to simulate the growth of the resident populations of methanotrophic, nitrifying, or carboxydotrophic bacteria, respectively. Oxidation of CH4, both at atmospheric (1.8 ppmv) and at elevated (3500 ppmv) CH4 mixing ratios, was stimulated after preincubation with CH4, but not with NH 4 + or CO, indicating that CH4 was oxidized by methanotrophic, but not by nitrifying or carboxydotrophic bacteria. However, the oxidation of CH4 was partially inhibited by addition of NH 4 + and CO. Analogously, oxidation of NH 4 + was partially inhibited by addition of CH4. Oxidation of CO at elevated mixing ratios (2300 ppmv) was stimulated after preincubation with CO, indicating oxidation by carboxydotrophs, but was also stimulated at a small extent after preincubation with CH4, suggesting the involvement of methanotrophs. At atmospheric CO mixing ratios (0.13 ppmv), on the other hand, oxidation of CO was stimulated after preincubation with NH 4 + , indicating that the activity was due to nitrifiers. NO uptake was stimulated in soils preincubated with CH4, indicating the involvement of methanotrophs. However, production of N2O was only stimulated, if CH4 was added as a substrate. The results indicate that especially the methanotrophic and nitrifying populations in soil not only oxidize their specific substrates, but are also involved in the metabolism of other compounds.

A new test gas generator for atmospheric trace compounds

A new device for generating atmospheric trace gases for calibration purposes is described, which allows to adjust test gas concentrations with fast response times and constant carrier gas flow. It consists of a permeation tubing surrounded by a solution of the substance of interest. Inside of the tubing a movable piston is placed. The position of this piston determines the available fraction of the permeation surface and hence the output of the test gas source. The device has been tested for the trace gas production of SO2 and formaldehyde in the ppbv range. It shows linear dependence of the produced concentrations on the position of the piston, fast response times and good reproducibilities.

Processes Regulating Soil Emissions of NO and N^2O in a Seasonally Dry Tropical Forest

While much is known about control of production of NO and N2O by nitrifying and denitrifying bacteria at the cellular level, application of this knowledge to field studies has not yielded unifying concepts that are widely applicable and that foster understanding of global sources of these atmospheric trace gases. We applied a simple conceptual model to the investigation of sources of NO and N2O and the environmental factors affecting fluxes in a drought—deciduous forest of Mexico. Fluxes of NO and N2O were higher in the wet season than the dry season, but addition of water to dry soil caused large pulses of CO2, NO, and N2O emissions. Immediate increases of extractable soil NH4+ and high rates of gross N mineralization and gross nitrification also were observed following wetting of dry soil NO2— had accumulated during the dry season, and that NO2— plus the pulse of increased soil NH4+ were mostly consumed within 24 hours of wetting. This dynamic microbial processing of soil inorganic N coincided with the pulses of NO and N2O production following wetting of dry soil. Acetylene inhibition experiments indicated that NO production was dependent on nitrification, that nitrification was the dominant source of N2O when the soil was wetted at the end of the dry season, and that dentrification might be an important source of N2O during the wet season. Post—wetting soil moisture was correlated negatively with NO fluxes and positively with N2O fluxes. These results support a conceptual model in which N trace gas production is generally constrained by the rates of N mineralization and nitrification, while the specific ratios of NO and N2O fluxes and the contributions from nitrifying and denitrifying bacteria are controlled largely by soil moisture.

Surface Level and Water Table Fluctuations in a Subarctic Fen

Fluctuations in the surface level of a subarctic fen, near Schefferville, Quebec, were measured from early June to mid-August 1988. Surface level, water table, and depth of thaw were measured at four sites representing three different topographic units of the fen: a flat central area; hummocks, islands and ridges; and the fen perimeter. Surface level changes of several centimeters a day were measured in the central portion of the fen, while the change was much less in the ridge and perimeter areas. Change in surface level at the perimeter and ridge sites was controlled by the depth of thaw. Levels of the central area were controlled by changes in water storage. A simple water balance model adequately predicted the lowering of the surface level of the central area of the fen. However, the same model underestimated rising surface levels. The adjusting surface level in the central area of the fen lead to a constantly saturated peat surface even during periods of persistent exfiltration. The constancy of saturation has important implications on the rate and magnitude of many biotic and abiotic processes, such as the biogenic production and consumption of trace gases and evapotranspiration.

Carbon dioxide and nitrogenous gases in the soil atmosphere

Carbon dioxide and nitrogenous trace gases (N2O, NO) in the soil atmosphere are mainly the products of microbially mediated processes. Once produced, these gases pass to the overlying atmosphere primarily via molecular diffusion, a process which is described by Fick's law of diffusion. In a diffusion-dominated soil, the partial pressure, or concentration, of CO2 in the soil atmosphere varies as a function of soil depth and is dependent on the production rate and diffusivities. Since these parameters are highly variable, CO2 concentrations vary widely both between, and within, differing ecosystems. In a compilation of data from around the world, arranged according to an ecosystem classification, soil CO2 concentrations varied from 0.04 to 13.0% by volume in the upper several meters of soil. These data also highlight the importance of organic substrate (soil organic matter, roots, root exudates), temperature, and (to some extent) moisture on CO2 production and the resulting concentration in soil profiles. The δ13C of the soil CO2 also varies as a function of depth due to differences in the δ13C of the organic substrate undergoing decomposition and the mixing with CO2 of the overlying atmosphere. Recent work suggests that the δ18O of the soil CO2 may hold some promise in estimating the δ18O of soil water. Biological production and consumption of N2O and NO results primarily from activity of nitrifying and denitrifying bacteria. Ammonium limitation of nitrification and organic carbon limitation of denitrification usually restricts these processes to surface soil horizons, although denitrification may be an important process for reducing NO3− in groundwater. These microbial processes and the relative proportions of their gaseous end products are strongly influenced by redox conditions. Microsite variation in sources of electron donors and acceptors is critical to understanding rates and distributions of N trace gas production. Several abiological oxidation and reduction reactions are also important, and interaction of biological and abiological processes deserves more research attention.

Cross‐system comparisons of soil nitrogen transformations and nitrous oxide flux in tropical forest ecosystems

Soil nitrogen transformations and nitrous oxide flux across the soil‐air interface were measured in a range of tropical forest sites in Costa Rica, Brazil, and Hawaii. Nitrogen mineralization and nitrification potentials were high in the relatively fertile Costa Rica sites and the Amazonian oxisol/ultisols (>1.5 μg g−1 d−1 of N mineralized), intermediate in Amazonian white sand soils (0.5‐0.8 μg g−1 d−1) and low in the Hawaiian montane sites (<0.5 μg g−1 d−1). Nitrous oxide fluxes ranged from 0 to 6.2 ng cm−2 h−1 of N; mean flux per site was highly correlated with mean nitrogen mineralization across 26 sites. These correlated patterns of nitrogen cycling and trace gas production could be useful in the development of regional‐ and global‐scale estimates of nitrous oxide fluxes from tropical forests.

The behavior of trace gases in the troposphere

Several man-made trace gases, accumulating in the Earth's atmosphere, may lead to a global warming in the future or may cause a depletion of stratospheric ozone. Although increased amounts of individual trace gases may add little to the Earth's natural greenhouse effect, together they may rival the effects expected from the increasing levels of CO 2. The primarily natural trace gases, N 2O and CH 4, now increasing because of human activities, are likely to add to the Earth's greenhouse effect, and among the man-made halocarbons, CCl 3F (F-11) and CCl 2F 2 (F-12) are expected to be the most important contributors to the future warming of the Earth. The increase of CH 4 may also affect the characteristics of the atmosphere by increasing ozone levels in the troposphere and stratosphere. We will discuss the record of the concentrations of anthropogenic trace gases that reveals increasing trends of CCl 3F, CCl 2F 2, CCl 4, CH 3CCl 3, and other man-made halocarbons. Some man-made halocarbons, although they exist individually at concentrations too low to affect the environment significantly, may be used as intrinsic tracers of local, regional, and even global transport of air pollution. Recent research on the global production, removal, and transport of both man-made and natural trace gases are reviewed.

Production, modification, and consumption of atmospheric trace gases by microorganisms

Some trace gases are contained in the atmosphere in appreciable amounts: methane, carbon monoxide, hydrogen, nitrous oxide. The bulk of these gases is of biological origin. Hydrogen is a primary product of microbial metabolism under anaerobic conditions. However, before reaching the atmosphere, it is converted by methane bacteria to methane, by nitrate reducing bacteria to nitrogen and to nitrous oxide and by sulfate reducing bacteria to hydrogen sulfide. Carbon monoxide is produced from certain organic compounds. Hydrogen, methane, and carbon monoxide are quickly oxidized by microorganisms under aerobic conditions. However, especially methane and carbon monoxide reach the atmosphere. The literature dealing with the microorganisms and biochemical reactions involved in the production and conversion of trace gases is reviewed. DOI: 10.1111/j.2153-3490.1974.tb01947.x

Production, modification, and consumption of atmospheric trace gases by microorganisms

Some trace gases are contained in the atmosphere in appreciable amounts: methane, carbon monoxide, hydrogen, nitrous oxide. The bulk of these gases is of biological origin. Hydrogen is a primary product of microbial metabolism under anaerobic conditions. However, before reaching the atmosphere, it is converted by methane bacteria to methane, by nitrate reducing bacteria to nitrogen and to nitrous oxide and by sulfate reducing bacteria to hydrogen sulfide. Carbon monoxide is produced from certain organic compounds. Hydrogen, methane, and carbon monoxide are quickly oxidized by microorganisms under aerobic conditions. However, especially methane and carbon monoxide reach the atmosphere. The literature dealing with the microorganisms and biochemical reactions involved in the production and conversion of trace gases is reviewed. DOI: 10.1111/j.2153-3490.1974.tb01947.x