Kervella Yagi

© Copyright 1999 by the American Geophysical Union.We have measured emissions of CH3C1, CH3Br, and 2S from Holstein cows. In one experiment, two cows were studied in separate metabolic research chambers for a 24-hour period while on a normal diet and were studied for an additional 24-hour period 1 week later after being placed on a diet enhanced in chloride and bromide. Methyl chloride emissions ranged between 0.4 × 10-3 and 1.5 × 10-3 g cow-1 d-1, while methyl bromide emissions were much smaller, 3 × 10-6-2 × 10∼5 g cow-1 d-1. Daily emissions of methane from these cows were 134-180 g cow-1 d-1, quite similar to values found in many previous studies. A second 24-hour study of two different cows on normal diets yielded daily emissions of 0.6 × 10-3 and 0.9 × 10-3 g CH3C1, 0-1.0 × 10-6 g CH3Br, and 191 and 176 g CH4. If these emissions of CH3C1 and CH3Br are representative of the 1.3 billion head of cattle worldwide, then the global source of atmospheric CH3C1 and CH3Br from cattle would be 0.23-0.70 Gg yr-1 and × 10-3 Gg yr-1, respectively. These emissions of CH3C1 and CH3Br represent <0.02% and <0.005%, respectively, of the total annual global atmospheric sources of these compounds; therefore, emissions of CH3C1 and CH3Br from cattle are insignificant contributors to their total sources. Discovered serendipitously, DMS emissions were between 0.17 and 0.24 g cow-1 d-1, and chloroform emissions were 2 × 10-4-3 × 10-3 g cow-1 d-1. DMS from cattle is not a major source over hemispheric or global scales but could be important in certain geographical regions. Chloroform emissions were similarly detected and quantified, as were those of C2H5X.

We have made measurements of the methane flux and δ13C value in CH4 from rice paddies in Ryugasaki, Japan. This study is the first we are aware of in which a significant change in the δ13C signature of emitted CH4 has been documented over the rice growing season. Nutrient treatments studied were of two kinds: compound mineral fertilizer either with or without rice straw from the previous growing season incorporated into the inorganic fertilizer. The calculated annual emission rates during the 1990 growing season were 43.1 g/m2 and 40.6 g/m2 for the two treatments. In both treatments, CH4 started out relatively enriched in 13C, became lighter in 13C, and then became more enriched again during the latter part of rice growth. The 1991 growing season showed a lower integrated flux in both nutrient treatments than for 1990 but plots of the fluxes versus time had the same general shape as the flux curves in 1990 and a similar although less pronounced trend in δ13CH4 signal. Seasonal changes in δ13C are probably related to changes in CH4 production and oxidation and plant‐mediated transport. The likelihood of each process occurring and its effect on δ13C values is discussed. The range of δ13CH4 values from seasonal effects was ∼12‰ in 1991 for both nutrient treatments. The δ13CH4 range for 1991 was ∼10‰ and ∼5‰. Our data indicate that when using flux‐weighted isotopic signatures to put constraints on the tropospheric CH4 budget, attention should be paid to seasonal changes in isotopic signatures from rice paddy CH4 in a manner similar to that previously suggested from measurements in natural wetlands. Copyright 1994 by the American Geophysical Union.