Identifying temporal patterns and controlling factors in methane ebullition at Sallie’s Fen, a temperate peatland site, using automated chambers Jordan.
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Identifying temporal patterns and
controlling factors in methane ebullition at
Sallie’s Fen, a temperate peatland
site, using automated chambers
Jordan GoodrichJordan GoodrichAdvisors: Ruth Varner,Advisors: Ruth Varner,
Steve Frolking,Steve Frolking,
Bryan DuncanBryan Duncan
Motivation Recent return to high growth rate in the
atmospheric burden points to northern wetlands as contributor [Dlugokencky et al. 2009]
Thawing permafrost may release large stores of carbon byenhancing CH4 emissions[e.g. Christensen et al. 2004]
Identify local processesand mechanisms to helpconstrain global trendsAbisko, Sweden: CAMEL Project
Wetland CH4
Anaerobic microbial production at depth creates a gradient with the overlying atmosphere
Subsequent transport upward can occur via three pathways: diffusion, plant mediated transport and ebullition (bubbling)
Bubbles form when pCH4(aq) exceeds hydrostatic pressure shown to contain up to 70% CH4
release has been related to falling atmospheric pressure and threshold peat bubble content
Objectives
Use automated chambers to measure CH4 flux and quantify ebullition magnitude and frequency
Characterize the controls on CH4 ebullition at various timescales (seasonal, synoptic, diel)
Estimate the proportion of total CH4 flux contributed by ebullition at Sallie’s Fen
Site & Methods
Sallie’s Fen is located in Southeast NH, USA (43º12.5’N, 71º3.5’W) - peat depth 2.0-4.5 m, basal date ~9500yrs
Ten automated chambers close at random for either six or ten minutes at a time
Chamber head space concentration over time is measured with a cavity ring-down spectroscopy analyzer (one measurement every 2 sec)
* Flux from this curve:185.2 mgCH4 m-2 day-1
Ebullition Frequency
Water Table Effect Reduction in pressure on CH4 stored at depth [Windsor et al. 1992]
Easier to transport through air than water - increased diffusivity [Moore and Roulet, 1993]
No clear relationship withatmospheric pressure - unlikeprevious studies -e.g. Tokida et al. 2005,Tokida et al. 2007,Waddington et al. 2009
Cumulative Summary: Jun-Aug 2009
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
1 2 3 4 5 6 7 8 9 10
Chamber
Cumulative Summer Flux
(gCH
4 m
-
2)
Ebullition Flux
Linear Flux
*
Episodic ebullition as percent of total: 2 - 12%
Conclusions
Peat hydrology exhibits a strong control on CH4 ebullition on synoptic timescales
Episodic ebullition can contribute a significant portion of the total CH4 released during summer months at Sallie’s Fen, but our estimate is smaller than other field chamber studies
Modeling implications Will the proportion of total flux contributed by ebullition increase or decrease in a changing climate?
In permafrost regions, will this pathway lead to significant release from carbon stored at depth?
AcknowledgementsM.S. committee: Ruth Varner, Steve
Frolking, Bryan Duncan
Research & Discover Program (NASA & UNH) Michael Keller (Instrument) & Jack Dibb,
Sallie Whitlow and Nicola Blake (Sallie’s Fen)
Rob Braswell, Jill Bubier, Patrick Crill, Tom Milliman, Tuula Larmola
Fellow students - Haley W., Claire T., Gennie N., Frankie S., Chelsea C., Eric K. Questions?
Ebullition Magnitude Distribution
Arbitrary model units [Coulthard et al. 2009]
Indicative of poorlydecomposed peat with open poor structure (i.e. low bulk density)
Diel Pattern in Ebullition Frequency
Cumulative Summary - Summer only
Scale the daily frequency estimates Based on area of each chamber Based on amount of time the chamber was closed each day
Sample from the magnitude distribution Take random samples as many times as indicated by the scaled frequency estimate for each day
Add them for each day to get a daily sum
Bootstrap the sampling to get uncertainty estimate (95% Confidence Intervals)
Uncertainty in Emission Estimates
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100
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400
500
600
700
WetlandsEnergy
RuminantsLandfills
Rice AgricultureBiomass Burning
TermitesOcean
Hydrates
Waste Treatment
OtherSoil Sink
Stratospheric Loss
OH Sink
Total SourceTotal Sink
Global Methane Flux (Tg CH4/yr)
Minimum Maximum
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