Presentation on theme: "“Effects of Soil Moisture on Methane Oxidation Rates in the Harvard Forest” Presented by Linda Jane Wan."— Presentation transcript:
“Effects of Soil Moisture on Methane Oxidation Rates in the Harvard Forest” Presented by Linda Jane Wan
Table of Contents INTRODUCTION WHAT is CH 4 OXIDATION? WHY it’s IMPORTANT METHODS The Lowdown on the Drydown Broaden Your Horizons RESULTS Impact of H 2 O DISCUSSION Type A vs. Type O SINK or SOURCE? CONCLUSION Global Import of Climate Change
Universal SOIL The Universal SOUL, as it is called, has an interest in the stacking of hay, the foddering of cattle, and the DRAINING of peat-meadows. - Henry David Thoreau SOIL microorganisms =terrestrial biological SINK Because of this effect, we must study the effect of climate in terms of SOIL MOISTURE on processes influencing microbial consumption within horizons In an effort to study these processes, Woods Hole Research Center (WHRC) is conducting a H.F. study of soil moisture on soils of BOTH the A and O horizons, respectively
Tracing CH 4 Greenhouse gas Product of decomposition of matter in swamps. Primarily used for fuel Natural gas=1/5 of total E consumption & 1/3 in U.S.
Rainfall Exclusion Experiment: The DRYDOWN OBJ: Test effects of soil moisture content on Uptake CH 4 samples collected from May to Aug. ‘01: 3 T & 3C T= Drought Plot (n=4); 4m X 4m, covered completely by transparent PVC rooves 1.5 m high C = Control Plot (n=4); ambient plots sans roof on similar, adjacent soil Each plot: 4 PVC collars
Collecting Chamber Samples Weekly manual gas samples from 3 drought (n=4) & 3 ambient plots (n=4); analyzed with Gas Chromatograph (GC) Ambient/soil temp. measured at each collar Needles attached to syringes inserted thru rubber septum to collect 2 10-mL gas samples after affixing each chamber lid) from each collar Net CH 4 flux = non-linear change in concentration of each chamber.
O n the HORIZON 5 soil samples from L, F, H & A horizons All soil horizon replicates incubated for 24 hr, CH 4 levels analyzed on GC at varying intervals L, F, H & A replicates dried at 105 C for 24 hr to determine SWC
Definitions Microbial CH 4 oxidation by soil methanotrophs: CH 4 + 2O 2 CO H 2 O Soil horizon: layer differentiated based on structure & color.
O n the HORIZON (cont’d) Measured each sample ’ s [CH 4 ] at intervals of.5-10 hr Utilizing linear regression analyses, we ascertained the relationship between weekly means of oxidation rates to soil moisture
OPERATION: GC Separates gas mixtures into component parts 2 certified standards (1050 & 2020 ppb) used for calibration at initiation & end of each incubation to ensure precision CH 4 flux calculated using slope of linear fitting of calibration
[CH 4 ] in Soil Profile
Horizon CH 4 Uptake Rates
Wet, Wet, Wet! The surface of the ground in the Maine woods is everywhere spongy and saturated with MOISTURE. Henry David Thoreau To better assess how future climatic changes will alter the terrestrial methane sink, we need to examine processes influencing CH 4 flux under field conditions. Changes in CH 4 consumption by watered soils paralleled those in soil moisture.
Soil H 2 O Content Weekly averages of CH4 oxidation:
SINK or SOURCE Methanotrophs: active in A, yet inactive in O horizon. Demonstrates differences in CH 4 diffusivity rates of horizons. Soils=NET SINK, hi rates of CH 4 consumption due to > gas diffusivity & well-drained, porous soils for > gas exchange
Living Earth The earth is not a mere fragment of dead history, stratum upon stratum like the leaves of a book, to be studied by geologists and antiquaries chiefly, but living poetry like the leaves of a tree, which precede flowers and fruit,—not a fossil earth, but a LIVING EARTH; compared with whose great central life all animal and vegetable life is merely parasitic. -Henry David Thoreau H.F. soils exhibit very strong uptake, caused by a unique soil texture, propitious for > gas diffusivity-- > uptake. H 2 O content affects CH 4 oxidation thru gas diffusivity Soil moisture significantly affects CH 4 consumption. In such temperate forests as the H.F., soil moisture = the determining factor in regulating oxidation rates.
Acknowledgements As I disembark from this summer experience, in addition to all my Harvard Forest friends & fellow colleagues, I would like to thank my fellow researchers and colleagues at Woods Hole Research Center, Kathleen E. Savage, Werner Borken, and Eric A. Davidson for all their time, efforts, and much appreciated support!