“effects of soil moisture on methane oxidation rates in the harvard forest” presented by linda...
TRANSCRIPT
“Effects of Soil Moisture on Methane Oxidation
Rates in the Harvard Forest”
Presented by Linda Jane Wan
Table of ContentsINTRODUCTION
• WHAT is CH4
OXIDATION?
• WHY it’s IMPORTANT
METHODS
• The Lowdown on the Drydown
• Broaden Your Horizons
RESULTS• Impact of H2O
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 CH4
• 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
• CH4 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 CH4 flux = non-linear change in concentration of each chamber.
On the HORIZON
• 5 soil samples from L, F, H & A horizons• All soil horizon replicates incubated for 24 hr,
CH4 levels analyzed on GC at varying intervals • L, F, H & A replicates dried at 105 C for 24 hr
to determine SWC
Definitions • Microbial CH4
oxidation by soil methanotrophs:
CH4 + 2O2 CO2 + 2 H2O
• Soil horizon: layer differentiated based on structure & color.
On the HORIZON (cont’d)
• Measured each sample’s [CH4] 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
• CH4 flux calculated using slope of linear fitting of calibration
[CH4] in Soil Profile
0
5
10
15
20
25
0 300 600 900 1200 1500 1800
CH4 concentration (ppb CH4)
Soil
dept
h (c
m)
1-D 1-C
Incubation: A-horizon y = 1715.8e-0.3937x
R2 = 0.9986
0
500
1000
1500
2000
012345678910
Time (hours)
CH4 concentration (ppb CH4)
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 CH4 flux under field conditions. Changes in CH4 consumption by watered soils paralleled those in soil moisture.
Soil H2O ContentWeekly averages of CH4 oxidation:
A-horizon
0
5
10
15
20
0 0.2 0.4 0.6 0.8
water content (g H2O g-1 soil)
CH 4
oxid
ation (
ug C
H4 kg-1 s
oil h
r-1 )
SINK or SOURCE
• Methanotrophs: active in A, yet inactive in O horizon.
• Demonstrates differences in CH4 diffusivity rates of horizons.
• Soils=NET SINK, hi rates of CH4 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.
• H2O content affects CH4 oxidation thru gas diffusivity• Soil moisture significantly affects CH4 consumption.
• In such temperate forests as the H.F., soil moisture = the determining factor in regulating oxidation rates.
Climate Change
A UN Conference on Climate Change, held in Kyoto, Japan, in 1997 resulted in an international agreement to fight global warming, which called for sharp reductions in emissions of industrial gases. Not all industrial countries immediately signed or ratified the treaty, however, and obstacles to its implementation remain. In 2001 the G. W. Bush administration announced it would abandon the Kyoto Protocol; because the United States produces about one quarter of the world’s greenhouse gases, this was regarded as a severe blow to the effort to slow global warming.
• The Columbia Encyclopedia, Sixth Edition. Copyright © 2001 Columbia University Press.
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!