HR: 09:35h
AN: B41D-05    [Abstracts]
TI: Land Use Effect on Methane Oxidation and Its Kinetics in Tropical Upland Soils
AU: * Chidthaisong, A
EM: amnat_c@jgsee.kmutt.ac.th
AF: Joint Graduate School of Energy and Environment, King Mongkut's Univ. of Technology Thonburi, 91 Pracha-Uthit Rd., Tungkru, Bangkok, 10140 Thailand
AU: Vanitchang, S
EM: supika_v@yahoo.com
AF: Joint Graduate School of Energy and Environment, King Mongkut's Univ. of Technology Thonburi, 91 Pracha-Uthit Rd., Tungkru, Bangkok, 10140 Thailand
AU: Harvey, N W
EM: nwharvey@jgsee.kmutt.ac.th
AF: Joint Graduate School of Energy and Environment, King Mongkut's Univ. of Technology Thonburi, 91 Pracha-Uthit Rd., Tungkru, Bangkok, 10140 Thailand
AU: Conrad, R
EM: onrad@staff.uni-marburg.de
AF: Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straáe, D-35043 Marburg, Marburg, D-35043 Germany
AB: Upland soil represents the important biological sink for atmospheric methane. In the tropics, one of the most remarkable changes in land use in the past decades is deforestation. It is estimated that deforestation rates in the tropic are as rapid as 2% yr$^{-1}$. Such land use change may lead to loss of methane oxidation and thus may have implicated the global methane budgets. However, little information is available on magnitudes and variations of methane oxidation upon changing land use in the tropics. Here we report methane oxidation in three land use types in Thailand; a natural forest (SK soil), a reforested site (AC soil), and an agricultural field (CF soil). Monthly methane oxidation fluxes were measured with the closed chamber method during January to December 2003. Soil samples were also taken for kinetic study in the laboratory. Results reveal that methane oxidation occurred in all land use types but oxidation rate varied according to season, land use types, and sampling spots. Both SK and AC soils showed the oxidation rates comparable to that found in temperate forests. High rate of methane oxidation was found during the summer months. In raining season, net methane emission was occasionally observed, indicating the importance of soil moisture as the controlling factor. On one-year average basis, soil at both SK and AC forests were the net methane sinks (1.06 and 1.26 mg CH$_{4}$ m$^{-2}$ day$^{-1}$, respectively). On the other hand, high methane emission during raining season made soil at CF site became a net methane source on annual average basis. In SK and AC soils a clear zonation for active methane oxidation layer was detected along the soil depth. The most active oxidation layers in SK and AC soils lied between 15 cm and 40 cm while in CF soil no clear active layer was observed. Stratification of active oxidation zones coincides with the trends of inorganic nitrogen content profile. In SK and AC soils, high concentration of inorganic nitrogen compounds (usually $>$100 mg NO$_{3}$$^{-}$ or NH$_{4}$$^{+}$ kg soil$^{-1}$) was detected in the top 15-cm soil while there was no clear distribution trend found in CF soil. It was assumed that such high concentration of inorganic nitrogen in the topsoil inhibited the activity of methane oxidizing bacteria thus only in the subsoil that methanotrophs were active. Examining kinetic coefficients of these active layers revealed that soil at SK site had high affinity for methane (Km of 52 ppmv) but rather low methanotrophic capacity (Vmax of 0.82 nmol soil$^{-1}$ h$^{-1}$). Soil at AC and CF sites, on the other hand, showed low affinity for methane (Km of 724 ppmv and 1454-2362 ppmv, respectively). However, soils at these two sites were capable of oxidizing high concentration of methane (Vmax about 10 nmol soil$^{-1}$ h$^{-1}$). These results indicate that land use type significantly affects rates, depth distribution and kinetics of methane oxidation in tropical soils.
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting