Investigation of cattle methane production and emission over a 24-hour period using measurements of delta C-13 and delta D of emitted CH4 and rumen water

摘要

We have conducted a series of experiments to determine the effects different diets, including the addition of unsaturated fatty acids, had on isotopic signatures of Cl-L emissions from dairy cattle. Measurements of emitted delta (CH4)-C-13, delta (CO2)-C-13, and deltaD-CH4 were made on gases collected over a 24-hour period from animal chambers containing individual Holstein cows. Some measurements of deltaD-H2O from samples collected directly from the rumen were also made. We observed variation in delta (CH4)-C-13 values with time after feeding and a correlation in VC between emitted gases and diet. The average delta (CH4)-C-13 value, which includes all samples of emitted gases, was -70.6 +/-4.9 parts per thousand (n=57). Measurements of deltaD-CH4 over the 24-hour sampling period had an average value of -357.8 +/- 15.0 parts per thousand, (n=56). These deltaD measurements are among the lightest reported for CH4 produced by cattle, Our cattle data indicate that hydrogen incorporated into the CH4 produced by CO2 reduction in high H-2 concentration environments is fractionated to a greater degree than that incorporated in systems with relatively low H-2 conditions, such as wetlands. Our results support bacterial studies that have demonstrated large hydrogen fractionation in high H-2 concentration systems during methanogenesis. [References: 47]