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Title: Eddy covariance measurements of methane fluxes over grazed native and improved prairies in Oklahoma

Author
item WAGLE, PRADEEP - University Of Oklahoma
item Gowda, Prasanna
item Steiner, Jean
item XIAO, XIANGMING - University Of Oklahoma
item Neel, James
item Northup, Brian

Submitted to: Grazinglands Research Laboratory Miscellaneous Publication
Publication Type: Proceedings
Publication Acceptance Date: 5/29/2016
Publication Date: 6/14/2016
Citation: Wagle, P., Gowda, P., Steiner, J.L., Xiao, X., Neel, J.P., Northup, B.K. 2016. Eddy covariance measurements of methane fluxes over grazed native and improved prairies in Oklahoma. Pp. 34-39. In: R.W. Todd and A. Campbell (Eds). Proceedings-Great Plains Grazing Field Research Symposium, 14 June 2016, Oklahoma State University, Stillwater, OK. Available at: https://drive.google.com/file/d/0B5YS3Y9RTDyiQV9IUURWY2NNNW8/view?pref=2&pli=1.

Interpretive Summary: Although several studies have reported eddy covariance (EC) measurements at several tallgrass prairie sites to investigate the dynamics of carbon and water vapor fluxes, the EC measurements of methane (CH4) fluxes over grazed tallgrass prairie sites are lacking. CH4 fluxes were measured during the 2014 growing season over co-located native and improved tallgrass prairie sites near El Reno, Oklahoma. Both pastures were grazed (randomly, not confined) periodically. The major objective of this study was to quantify and compare the magnitudes and seasonal patterns of CH4 fluxes between two prairie sites. CH4 fluxes did not show a typical diurnal pattern, and the mean diurnal patterns were different among months at both sites. The magnitudes of monthly ensemble averaged 30 min CH4 fluxes were very small (mostly ranging from -0.1 to 0.1 µmol m-2 s-1). We observed contrasting diurnal patterns of CH4 fluxes between two sites. The native prairie site behaved as a net sink of CH4 for most of the time, whereas the improved prairie site behaved as both sink and source of CH4. The magnitudes of CH4 emissions were also relatively larger at the improved pasture site (~0.1 µmol m-2 s-1) than at the native pasture site (< 0.05 µmol m-2 s-1). Major controlling factors of CH4 emissions or assimilations and the role of grazing cattle on the observed CH4 fluxes will be further investigated

Technical Abstract: Although several studies have reported eddy covariance (EC) measurements at several tallgrass prairie sites to investigate the dynamics of carbon and water vapor fluxes, the EC measurements of methane (CH4) fluxes over grazed tallgrass prairie sites are lacking. CH4 fluxes were measured during the 2014 growing season over co-located native and improved tallgrass prairie sites near El Reno, Oklahoma. Both pastures were grazed (randomly, not confined) periodically. The major objective of this study was to quantify and compare the magnitudes and seasonal patterns of CH4 fluxes between two prairie sites. CH4 fluxes did not show a typical diurnal pattern, and the mean diurnal patterns were different among months at both sites. The magnitudes of monthly ensemble averaged 30 min CH4 fluxes were very small (mostly ranging from -0.1 to 0.1 µmol m-2 s-1). We observed contrasting diurnal patterns of CH4 fluxes between two sites. The native prairie site behaved as a net sink of CH4 for most of the time, whereas the improved prairie site behaved as both sink and source of CH4. The magnitudes of CH4 emissions were also relatively larger at the improved pasture site (~0.1 µmol m-2 s-1) than at the native pasture site (< 0.05 µmol m-2 s-1). Major controlling factors of CH4 emissions or assimilations and the role of grazing cattle on the observed CH4 fluxes will be further investigated.