identifying temporal patterns and controlling factors in methane ebullition at sallie’s fen, a...

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

0

100

200

300

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