ISSN:0148-0227    

DOI:10.1029/94JD01675

年代:1994

数据来源: WILEY

摘要:

It is generally accepted that methyl iodide is a major contributor to the flux of iodine from the ocean to the atmosphere, but its sources in the ocean are largely unknown, an exception being production by certain species of coastal macrophytic algae. Preliminary results reported here indicate production of methyl iodide in filtered seawater that has been irradiated with either sunlight or an artificial light source having a spectral output closely approximating to sunlight at sea level. The production was enhanced when the water samples were deoxygenated and by the addition of iodide to this water. The results appear to be consistent with a mechanism involving reaction between photochemically produced methyl radicals and iodine atoms. It is estimated that the process is capable of making a significant contribution to global iodine fluxes.

ISSN:0148-0227    

DOI:10.1029/94JD00786

年代:1994

数据来源: WILEY

摘要:

As part of a comprehensive study on tropical land use change and its effect on atmospheric trace gas fluxes, we report the CO fluxes recorded at a natural grassland site and the changes produced when this ecosystem was managed or cultivated. The field site is located in the central part of the savannah climatic region of Venezuela. Fluxes were measured in the dark using the enclosed chamber technique. CO was analyzed with a reduction‐gas detector in combination with a molecular sieve 5A columm for CO separation. At all sites, CO fluxes exhibited a strong diurnal variation, with net emission during daytime and consumption or no fluxes during nightime. In unplowed soils no differences were observed between dry and rainy season. A large disparity was observed between unplowed and plowed grassland soils. Plowed soil shows a much smaller emission during daytime and a larger consumption at night. The 24‐hour integrated fluxes indicate that the nonperturbed grassland switches from being a net source of CO (3.4×1010molecules cm−2s−1) to being a net sink (−1.6×1010molecules cm−2s−1) after plowing. It is likely that burial of surface litter reduces the production of CO in the top soil and that the diffusion of CO to deeper layers (where CO is consumed by microbiological processes) is promoted in decompacted soils. As the rainy season progressed the plowed soil gradually compacted and CO fluxes changed back, and after 3 months the fluxes from plowed soils and the original unplowed soils were equal. Even though the various cultivated fields (corn, sorghum, and pasture) received differing inorganic fertilization treatments, no significant difference in the CO fluxes resulted. Measurements during the dry season suggest that “degrading dry (dead) vegetation” produces CO un

ISSN:0148-0227    

DOI:10.1029/93JD02918

年代:1994

数据来源: WILEY

摘要:

Using closed chamber techniques, soil fluxes of CO2, CO, CH4, N2O, and NO were measured in unplowed and plowed savannah soil from May 23 to June 11, 1991. During the measurement period the gravimetric soil moisture ranged from 1% to 10%, with an average of 2.7%. Results did not show any notable change in CO2, CH4, and N2O fluxes between unplowed and plowed soil, whereas a significant change in CO and NO fluxes was produced. For CO, nonperturbed soil switches from being a net source (16 ng m−2s−1) to being a net sink (−5.3 ng m−2s−1) after plowing, and in the case of NO the plowing leads to a dramatic increase (from 12.3 to 67.5 ng NO‐N m−2s−1) in the emissions. The addition of fertilizer (phosphate, ammonium, and potassium) to the plowed soil did not produce any significant effect. The simultaneous study of these five trace gases strongly suggests that in the short term, plowing of this savannah soil does not significantly alter the activity that produces trace gases and that the large changes in CO and NO fluxes are mainly related to an enhancement of the transport of gases within the soil and to a larger surface area in contact with

ISSN:0148-0227    

DOI:10.1029/94JD00265

年代:1994

数据来源: WILEY

摘要:

Atmospheric samples were collected during rice straw burning at four different locations in Viet Nam during the dry and wet seasons (March 1992, February 1993, and August 1992, respectively). The samples were analyzed for CO2, CO, and COS. The emission ratios relative to CO2for rice straw burning during the dry season were comparable to those observed on samples collected during burning of savanna in Africa or forest in the United States. On the contrary, during the wet season the emission ratios for CO and COS relative to CO2were 2 to 10 times higher. With these emission ratios and estimates of rice production from southeastern Asia, we estimated that burning of rice straw emits annually about 2.1 Tmol of CO (25 Tg C) and 0.6 Gmol of COS (0.02 Tg S) to the atmosphere. Taking into account these new results, CO and COS fluxes from biomass burning could be reevaluated by 5–21% and 10–67%, respectively, with regard to previous estimates of these gas emissions from all biomass burning activit

ISSN:0148-0227    

DOI:10.1029/93JD03521

年代:1994

数据来源: WILEY

摘要:

During the 1991 and 1992 dry seasons (April to October), we collected and analyzed over 100 samples of smoke from savanna fires at the Kapalga Research Station (12°S, 132°E) in Kakadu National Park, Northern Territory, Australia. Samples collected from the ground and from a light aircraft flying at 50–700 m above the fires were analyzed for CO2, CO, CH4, C2H2, C6H6, CH2O, CH3CHO, NOx(= NO + NO2), NH3, HCN, and CH3CN using gas phase Fourier transform infrared (FTIR) spectroscopy, matrix isolation FTIR spectroscopy, and chemiluminescence techniques. In addition, we made detailed analyses of the mass, carbon, and nitrogen loads of the prefire fuel and the postfire ash residue. Molar emission ratios relative to emitted CO2and CO, and emission factors relative to the fuel carbon or nitrogen burned were determined for the measured trace gases. Over 96% of the fuel carbon burned was released to the atmosphere, predominantly as CO2(87±3% of fuel C) and CO (7.8±2.3%). The mean ΔCO/ΔCO2emission ratio of 9.0±2.6% indicates efficient combustion in these fires of grasses and other light fuels. The main nitrogen‐based emissions we measured were NOx(21±8% of fuel N) and NH3(23±13%). The combined emissions of NOx, NH3, N2O, CH3CN, and HCN accounted for only 51±17% of the fuel N released to the atmosphere during combustion. We use these measurements to estimate the annual emissions of several important trace gases from savanna burning

ISSN:0148-0227    

DOI:10.1029/94JD00670

年代:1994

数据来源: WILEY

摘要:

Methane emission rates from wetland rice fields were determined in Los Baños (Philippines) using an automatic system that allows continuous measurements over time. Methane emission was monitored in an irrigated Aquandic Epiaqualf planted to rice cultivar IR72. Urea fertilizer was applied using four modes: (1) broadcast 10 days after transplanting, (2) broadcast at transplanting, (3) broadcast and incorporated at final harrowing, and (4) deep placement as sulfur‐coated granules. The treatments were laid out in a randomized complete block design with four replicates. Measurements were done in the 1991 wet season, 1992 dry season (four treatments), and the 1992 wet season (only treatment 3). Methane emission rates from the experimental plots showed pronounced seasonal and diel variations. The diel pattern of methane emission rates followed a consistent pattern, with highest rates observed in the early afternoon and lowest rates in the early morning. Methane emission rate was generally highest at the ripening stage. The average methane emission rate during the 1992 dry season (190 mg CH4m−2d−1) exceeded the average flux rates of the 1992 wet season (79 mg CH4m−2d−1) by a factor of 2.4. The total methane emitted from these flooded rice fields amounted to 19 g CH4m−2in the dry season with rice yields of 5.2–6.3 t ha−1and 7 g CH4m−2in the wet season with rice yields of 2.4–3.3 t ha−1regardless of the mode of N application. Significant amounts corresponding to 20% of the methane released under waterlogged conditions were released when the soil was drained after harvest. Emission rates increased sharply when the floodwater receded and macropores started to drain. Emission of methane stopped only when the soi

ISSN:0148-0227    

DOI:10.1029/94JD00017

年代:1994

数据来源: WILEY

摘要:

Using the closed chamber method, the methane emission rate from rice paddies was measured during three complete vegetation periods from 1990 to 1992 in the Beijing area. The emission level of this region was found between 15.0 mg/m2/h and 20.4 mg/m2/h. The methane emission rate showed a strong diurnal variation with the maximum and minimum emission rate in the afternoon and in the morning, respectively. The diurnal methane emission rate closely correlated with soil temperature after the tillering stage. A study on the effect of four kinds of chemical fertilizers (ammonium sulfate, urea, ammonium phosphate, ammonium bicarbonate) was carried out in 1991 and 1992. Application of ammonium sulfate and urea resulted in a reduction of methane emission, while application of ammonium phosphate enhanced the methane emission during the effective period of a chemical fertilizer. No significant influence of ammonium bicarbonate was found. Reasonable application of some types of chemical fertilizers in 1992 resulted in a significant reduction of total methane emission from rice paddies.

ISSN:0148-0227    

DOI:10.1029/94JD00815

年代:1994

数据来源: WILEY

摘要:

Methane emission from a rice field in a semiarid, temperate region in China, namely Beijing, has been measured, over an entire growing period. Strong seasonal variation was observed, with two periods of emission in early July and middle August, accounting for more than 70% of the total emission. Organic fertilizer (horse dung), irrigation pattern, and soil temperature were found to be important factors which influence the methane emission rates. Under common management the average flux during the entire growing season of 94 days was 20.4 mg/m2/h. Methane emission variation from control plots with no rice has also been studied.

ISSN:0148-0227    

DOI:10.1029/94JD01154

年代:1994

数据来源: WILEY

摘要:

The role of soil in controlling production and fluxes of biotic greenhouse gases is the focus of research in progress at the International Soil Reference and Information Centre (ISRIC). There are two main goals in this project on World Inventory of Soil Emission Potentials (WISE). The first is to assemble a global soil database in association with the Land and Water Division of the Food and Agricultural Organization (FAO), using a ½° × ½° grid of geographic soil data (1:5 M scale). This “area” data will be linked to a database of soil profile “attribute” data using a geographical information system. The foundations for this work have now been put in place and, providing the soil profile collection programme proceeds satisfactorily, it is anticipated that a preliminary database should begin to emerge by the end of 1993. When the soil database is complete, the second thrust will be to make an inventory of the world's poorly drained soils, providing the geographical framework for an improved estimate of methane production potentials. To do this, controlled long‐term field experiments are required and modeling techniques must be developed and tested. ISRIC is cooperating with the International Rice Research Institute (IRRI) in the Philippines for these aspects of the work. An important corollary to the development of a global soil database is that many requests are being received for soil information relevant for studies of “global change.” At present, much of this information does not exist in an adequate format, so ISRIC is proceeding as rapidly as possible to implement the WISE digital database in a format which is compatible and user‐friendly, for ultimate distribution

ISSN:0148-0227    

DOI:10.1029/93JD03278

年代:1994

数据来源: WILEY