HR: 1330h
AN: B32B-0379    [PDF]
TI: Methane Consumption and Production in Desert Ecosystems Experiencing Mesquite Invasion and Control
AU: * McLain, J E
EM: jmclain@tucson.ars.ag.gov
AF: USDA-ARS, Southwest Watershed Research Center, 2000 E. Allen Road, Tucson, AZ 85719 United States
AU: Martens, D A
EM: dmartens@tucson.ars.ag.gov
AF: USDA-ARS, Southwest Watershed Research Center, 2000 E. Allen Road, Tucson, AZ 85719 United States
AB: We are studying the influences of vegetation change on soil fluxes of methane (CH$_{4}$) in semi-arid ecosystems. Soils under the natural grass vegetation are a strong sink of atmospheric CH$_{4}$ year-round, consuming -35.1 $\pm$ 8.3 $\mu$g CH$_{4}$ m$^{-2}$ h$^{-1}$ during the monsoon summer and -24.3 $\pm$ 11.2 $\mu$g CH$_{4}$ m$^{-2}$ h$^{-1}$ during winter, but consumption falls to near zero in June. The depth of maximum CH$_{4}$ oxidation varies during the year, corresponding to the presence or absence of surface soil moisture. Invasion of mesquite ({\it Prosopis} spp.) significantly (p $<$ 0.001) reduces the monsoon CH$_{4}$ oxidation (-24.4 $\pm$ 8.3 $\mu$g CH$_{4}$ m$^{-2}$ h$^{-1}$), possibly due to the formation of a moist litter layer impeding CH$_{4}$ diffusion into the soil surface or from ammonium inhibition from the N-rich mesquite litter. CH$_{4}$ consumption is equally high in mesquite and grassland during the winter. Historically, ranchers have attempted to control invasion of mesquite onto grazing lands. Our work indicates that mesquite eradication may result in pockets of strong CH$_{4}$ production (42.3 $\pm$ 17.6 $\mu$g CH$_{4}$ m$^{-2}$ h$^{-1}$) as the mesquite trunk and roots decay. Pool dilution experiments with $^{13}$CH$_{4}$ are being performed to ascertain if CH$_{4}$ production is from soil methanogens or from termites. This work, when coupled with ecosystem C and N inventories and quantification of net N$_{2}$O and CO$_{2}$ respired, will help determine the potential for vegetation management in semi-arid ecosystems to mitigate or force potential climate change.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1615 Biogeochemical processes (4805)
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: 2003 Fall Meeting