The fast response instrument designed to measure simultaneous fluctuations of carbon dioxide and water vapor is described. The measuring frequency was 30 Hz. The sensing path length of the instrument was 20 cm. This is compatible with the path length of the standard type of a sonic anemometer. The noise level was about 0.8ppm for carbon dioxide measurement and about 0.02g/kg for water vapor measurement. The cospectrum estimate of carbon dioxide and vertical wind velocity showed that the high frequency loss due to smoothing effect of sensing path length was about 2 % for wfc r measurement. This denotes that the present instrument is promising for flux measurements of carbon dioxide by the eddy correlation technique in conjunction with a sonic anemomet er. The carbon dioxide flux measured by the eddy correlation technique showed a well defined diurnal variation over a paddy field characterized by the negative values in the daylight hours and positive values in the nighttime. Examination of the stability dependency of eddy diffusivities for carbon dioxide (Xc), sensible heat (Kh), and momentum (Km) showed that the ratio Kh/Kc is unity, but the ratio Kc/Km increases with increasing instability of the air layer as a function of (1—16z/L)1/4.
The earth warming is now one of the most serious environmental problems. Of all the greenhouse gases, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are deeply related to agriculture. Methane is emitted from paddy fields, and nitrous oxide from upland fields according to fertilizer application, respectively. As is well known, paddy fields are one of the most important sources of methane fluxes. Hitherto, studies on methane fluxes from paddy fields have mainly focused on their quantitative estimation, while production and movement of methane in paddy soils have not been major concern among researchers. Paddy soils are microbially dynamic environment, in which carbon dioxide and methane are produced and emitted through various processes. In this paper, the processes involved in the production and movement of carbon dioxide and methane in paddy soils were reviewed with special consideration to chemical properties of these two gases and the role of percolation water on their fates in paddy soils.
Potential activity of soil and sediment samples along a watershed is determined for the reduction of nitrous oxide (N2O), which is a doubly important trace gas controlling the energy budget of the troposphere and the ozone level in the stratosphere.15N tracer technique is applied for the determination of the potential activity using labelled N2O. Most of the soil and sediment samples have been proved to have large potential activity for reduction of N2O. The potential activity is highest for the river and bay subsurface sediment at the coast, where anaerobic micro site predominates. The present results indicate that the nitrate reduction system of soil and sediment, especially in coastal area is an important process in consuming N2O.
Interest in the atmospheric sulfur (S) budget has developed rapidly because anthropogenic activities are increasing the rates of emission of S gases into the atmosphere. These increase are important because S gases are oxidized in the atmosphere with formation of sulfate, the resulting contributes to environment problems associated with acid rain. There also is evidence that S gases may alter the optical properties of clouds and which could affect global climate. Large uncertainties remain concerning the chemical speciation and the magnitude of natural emission of S gases to the atmosphere. It has been well documented that dimethylsulfide (DMS) is most important in ocean, which have been estimated to contribute 40 Tg or 15 TgS to the atmosphere as S gases each year. The annual amounts of S evolved from soil have been estimated to be 7 to 77 TgS. Very little is known concerning emissions from paddy field, which are abundant in many parts of the world. The purpose of this report is to summarize the results of recent measurements of emissions of biogenic S gases from rice paddies in Japan. Emissions were measured in laboratory studies to learn more about the kinds and sources of S gases produced. Emissions were measured in paddy lysimeters and in paddy fields to gain better information about the amounts of DMS, carbonyl sulfide (COS), and carbon disulfide (CS2) emitted, the seasonal and diurnal patterns of emission, and the factors affecting emissions of these gases under field conditions.
To estimate the average chemical structure of humic acids, structural parameters were calculated from the elemental and functional groups analysis and hydrogen distribution estimated by H-NMR ; carbon aromaticity fa, hydrogen to carbon ratio in hypothetical unsubstituted aromatic material Hau/Cau, and number of aliphatic substituent nai. From the Hau/Cau value, condensation degree of aromatic ring was estimated. Number average molecular weight of humic acids were measured by the vapor pressure osmometry. Consequently, Andisol humic acids consist of a few structural subunits assumed to be condensed aromatic rings with short aliphatic substituents and many carboxyl and carbonyl groups. Aquent and Ochrept humic acids consist of many structural subunits assumed to be aromatic ring with relatively long aliphatic substituents. Macroporous, nonionic Amberlite XAD-8 resin was used for fractionation of soil humic acids in order to reduce their complexity. H+-saturated humic acid was adsorbed onto the resin at pH 3 and fractionated into four components by stepwise elution using universal buffers adjusted to pH 7, to pH 11,water, and 50% ethanol. The first components consists of a few structural subunits, assumed to be condensed aromatic rings with short aliphatic substituents and many carboxyl groups. The second component was characterized by phenolic groups, and the third by relatively long aliphatic chains. The fourth component consists of many structural subunits, assumed to be aromatic rings with long aliphatic substituents. These components were termed as carboxylic, phenolic, semi-aliphatic, and aliphatic components, respectively. Andisol humic acids contained abundant amounts of carboxylic component. Aquatic sediment humic acids contained ample amount of aliphatic components. Phenolic component was dominant in humic acids of tropical peats sublayer soils. Component analysis could lead to a new way to estimate the humification processes of humic substances.