Showing papers on "Atmospheric methane published in 1986"
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TL;DR: In this paper, the authors measured the CH4 emissions from rice paddies during a complete vegetation period, using a static box system, and found that CH4 is almost exclusively emitted into the atmosphere by gas bubbles during the first 6 weeks after flooding the rice fields, that is, on fields without vegetation.
Abstract: CH4 release rates from rice paddies were measured in Vercelli, Italy, in 1983 during a complete vegetation period, using a static box system. The rice paddies were found to be a source of atmospheric methane during the time of flooding. The CH4 release rates range between a few milligrams of CH4 per square meter per hour and 51 mg CH4 m−2 h−1 and show a seasonal variation with maximum emission rates between tillering and flowering. Averaged over the complete vegetation period, the CH4 release rate accounts for 16 mg m−2 h−1. Significant differences in the CH4 release rates of unfertilized field plots and plots fertilized with mineral fertilizer (CaCN2) were not observed. The CH4 release rates show strong diurnal variations, with highest values in the late afternoon and lowest values in the early morning, which coincides with the temperature variation in the upper soil layer (1–10 cm). These variations must be taken into account in estimating reliable global CH4 emission rates from rice paddies. CH4 is almost exclusively emitted into the atmosphere by gas bubbles during the first 6 weeks after flooding the rice paddies, that is, on fields without vegetation. Afterwards, 80% of the observed CH4 transport from the paddy soil into the atmosphere was due to diffusion through the stems of the rice plants. Transport by diffusion through the paddy water appeared to be of minor importance. The global annual CH4 emission from rice paddies is estimated to be of the order of 39–94 Tg yr−1 (Tg = 1012 g) for 1940 conditions and 70–170 Tg yr−1 for 1979 conditions, indicating a secular trend of the CH4 emission by rice paddies of about 1.6% per year during the last 35 years.
346 citations
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TL;DR: In the tundra, average CH 4 emission rates varied from 4.9 mg CH 4 m -2 d −1 (moist tundras) to 119 mg CH4 m −2 d -1 (waterlogged tundrains) as mentioned in this paper.
Abstract: Methane (CH 4 ) flux measurements from Alaskan tundra bogs, an alpine fen, and a subarctic boreal marsh were obtained at field sites ranging from Prudhoe Bay on the coast of the Arctic Ocean to the Alaskan Range south of Fairbanks during August 1984. In the tundra, average CH 4 emission rates varied from 4.9 mg CH 4 m -2 d -1 (moist tundra) to 119 mg CH 4 m -2 d -1 (waterlogged tundra). Fluxes averaged 40 mg CH 4 m -2 d -1 from wet tussock meadows in the Brooks Range and 289 mg CH 4 m -2 d -1 from an alpine fen in the Alaskan Range. The boreal marsh had an average CH 4 emission rate of 106 mg CH 4 m -2 d -1 . Significant emissions were detected in tundra areas where peat temperatures were as low as 4°C and permafrost was only 25 cm below the ground surface. Emission rates from the 17 sites sampled were found to be logarithmically related to water levels at the sites. Extrapolation of our data to an estimate of the total annual CH 4 emission from all arctic and boreal wetlands suggests that these ecosystems are a major source of atmospheric CH 4 and could account for up to 23% of global CH 4 emissions from wetlands. DOI: 10.1111/j.1600-0889.1986.tb00083.x
226 citations
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TL;DR: In this article, the mass-weighted average isotopic composition of all sources should equal the mean C-13 of atmospheric methane, corrected for a kinetic isotope effect in the OH attack of CH4.
Abstract: Ratios of C-13/C-12 have been measured in atmospheric methane and in methane collected from sites and biota that represent potentially large sources of atmospheric methane. These include temperate marshes (about -48 percent to about -54 percent), landfills (about -51 percent to about -55 percent), and the first reported values for any species of termite (-72.8 + or - 3.1 percent for Reticulitermes tibialis and -57.3 + or - 1.6 percent for Zootermopsis angusticollis). Numbers in parentheses are delta C-13 values with respect to PDB (Peedee belemnite) carbonate. Most methane sources reported thus far are depleted in C-13 with respect to atmospheric methane (-47.0 + or - 0.3 percent). Individual sources of methane should have C-13/C-12 ratios characteristic of mechanisms of CH4 formation and consumption prior to release to the atmosphere. The mass-weighted average isotopic composition of all sources should equal the mean C-13 of atmospheric methane, corrected for a kinetic isotope effect in the OH attack of CH4. Assuming the kinetic isotope effect to be small (about -3.0 percent correction to -47.0), as in the literature, the new values given here for termite methane do not help to explain the apparent discrepancy between C-13/C-12 ratios of the known CH4 sources and that of atmospheric CH4.
82 citations
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TL;DR: In this paper, a photochemical model is used to look backwards in time by simulating the trace-gas composition of the unpolluted troposphere at the start of the industrial era (taken as 1860) and at intervals up to 1985.
Abstract: Studies have shown that atmospheric methane, CO and the gaseous OH radical are interdependent: if CH4, CO or OH is perturbed, background concentrations of the other two constituents are affected. Perturbations to OH alter photooxidation rates of numerous natural and anthropogenic trace gases and affect lifetimes of those species that pass from the earth's surface to the free troposphere and stratosphere. It is now known that global atmospheric methane concentrations are increasing; less definite data suggest that carbon monoxide is also increasing. Even before the measurements reported in nine literature references, modeling studies of CH4-CO-OH coupling had led to predictions (Chameides, Liu and Ciceronne, 1977; Sze, 1977; and Hameed, Pinto and Stewart 1979) of future increases of CH4 and CO. A photochemical model is used to look backwards in time by simulating the trace-gas composition of the unpolluted troposphere at the start of the industrial era (taken as 1860) and at intervals up to 1985. It is found that the OH concentration in the background troposphere has decreased significantly and O3 has increased due to increases of CH4 and CO; calculated changes depend on temporal trends of NOx (NOx = NO + NO2), for which no historical data are available. The calculations allow recent trace-gas trends affecting background chemistry and climate to be viewed in a longer-term context.
52 citations
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TL;DR: Results show that the rate of increase in methane undergoes interannual variations; the most prominent of these coincided with the last major El Ni�o—Southern Oscillation, when methane concentrations fell far below expected levels.
Abstract: Nearly continuous measurements at Cape Meares, Oregon, revealed that methane was increasing in the earth's atmosphere and that its concentration varied cyclically with the seasons. After 6 years of measurements, results show that the rate of increase in methane undergoes interannual variations; the most prominent of these coincided with the last major El Nino-Southern Oscillation, when methane concentrations fell far below expected levels. One of the consequences of the interannual variability is that the long-term rate of increase at Cape Meares is now about 16 parts per billion by volume per year, or about 1 percent annually, which is significantly less than that indicated by the earliest calculations.
37 citations
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TL;DR: In this paper, a rough estimate of the present rate of this biologically mediated feedback on the climate system indicates that it might account for as much as 30 percent of the observed methane increase and speed up the greenhouse forcing by up to 15 percent.
Abstract: It is well established that plants tend to increase net photosynthesis under increased carbon dioxide. It is also well established that a large fraction of atmospheric methane is produced by microbial metabolism of organic sediments in paddies and freshwater wetlands, where a major source of organic debris is local plant growth. As CO2 increases, it may lead to increased methane production and a resulting enhancement of the expected greenhouse warming. A rough estimate of the present rate of this biologically mediated feedback on the climate system indicates that it might account for as much as 30 percent of the observed methane increase and speed up the greenhouse forcing by as much as 15 percent.
22 citations
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TL;DR: There are increasing concentrations of the trace species CCl3F, CCl2F2, CCL4, CH3CCl3, and CH4 in the atmosphere because of the increasing use by humans.
Abstract: Publisher Summary There are increasing concentrations of the trace species CCl3F, CCl2F2, CCl4, CH3CCl3, and CH4 in the atmosphere because of the increasing use by humans. Further increases in these and other trace chemical species will certainly occur in the coming decade and in the foreseeable future. These increases are connected with potentially important alterations of the environment through the depletion of ozone at 40 km and through the infrared greenhouse effect. Control procedures toward the atmospheric emissions of these compounds have been limited to CCl3F and CCl2F2 and to their specific uses as aerosol propellant gases in the United States, Canada, and several Scandinavian countries. The most significant environmental concern is that the concentrations are increasing for most of the trace species that have been quantitatively studied in the atmosphere. With so many chemical compounds exhibiting a trend in the same direction, the possibility for eventual serious alterations in the entire structure of the atmosphere needs to be very carefully monitored and evaluated.
1 citations
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TL;DR: Carbon and methane budgets were prepared for Carlisle Lake and it is suggested that methanogenesis may be indicative of the intensity of nutrient regeneration from sediments and Methanogenesis may indicate the degree of heterotrophic activity in sediments.
Abstract: Although the contribution of sediment-generated methane to dissolved oxygen demand has been well documented in a number of stratified lakes throughout the world, little work on the subject has been performed in shallow, un-stratified lakes. To quantify the role of methane in carbon and oxygen cycling in such environments, carbon and methane budgets were prepared for Carlisle Lake, a small, shallow, unstratified, hypereutrophic lake. The budgets reveal that about 10 percent of the summer oxygen demand is exerted by the bacterial oxidation of methane. Methane production accounts for recycling of about 5 percent of the carbon produced by primary production and about 10 percent of the carbon reaching the sediments. Methanogenesis may indicate the degree of heterotrophic activity in sediments. This work supports such a conclusion and also suggests that methanogenesis may be indicative of the intensity of nutrient regeneration from sediments.