Global Warming Research Today is a free monthly online journal that collates and summarizes the latest research about Global Warming, including details on causes, effects, impact, facts, myths, information. | ||||||||
|
Methane emissions from free-ranging cattle: comparison of tracer and integrated horizontal flux techniques.Griffith DW, Bryant GR, Hsu D, Reisinger AR Dep. of Chemistry, Univ. of Wollongong, Wollongong, NSW, Australia. Accurate measurements of methane (CH(4)) emission rates from livestock in their undisturbed natural environments are required to assess their impacts on radiative forcing (i.e., enhanced greenhouse effect) and the environment. Here we compare results from two nonintrusive techniques for the measurement of CH(4) emissions from cattle. The cows were kept in an outdoor feeding strip that allowed them to follow natural behavioral patterns but contained them within a well defined space. In the first technique, nitrous oxide (N(2)O) was released as a tracer at the upwind edge of the feeding strip, and the downwind concentrations of N(2)O and CH(4) were measured simultaneously using Fourier transform infrared (FTIR) spectroscopy. Average CH(4) emission per cow was calculated each half-hour on three separate days from the correlation between the two gases. The second technique was the integrated horizontal flux (IHF) or 1-D mass-balance method, in which we used the measured vertical profiles of CH(4) concentration and windspeed downwind of the cows to determine the total CH(4) emission. Comparing the IHF results to the known release rate of N(2)O allowed us to test the IHF technique independently. We found agreement within 10% for all comparisons on all days. The daily CH(4) emission rate averaged over all tracer and IHF measurements was 342 g CH(4) head(-1) d(-1). This is within the range of previous measurements for mature lactating dairy cattle (200-430 g CH(4) head(-1) d(-1)) but higher than expected for yearling cattle. The high CH(4) emissions are accompanied by high CO(2) emissions determined from the FTIR measurements. The bias is most likely due to the measurements being made during and after supplementary feeding of the cattle. Published 26 February 2008 in J Environ Qual, 37(3): 582-91.
© 2004-2008 Global Warming Research Today. All Rights Reserved. |
| ||||||
