Spatial Distribution of Methane Spatial Distribution of Methane in Surface Water from Terrestrial in Surface Water from Terrestrial

Sources to Coastal RegionsSources to Coastal Regions

Kaitlyn J. SteeleKaitlyn J. SteeleResearch and Discover 2009Research and Discover 2009

Faculty Advisor: Dr. Ruth K. Varner, EOSFaculty Advisor: Dr. Ruth K. Varner, EOS

Greenhouse gasesGreenhouse gases Carbon dioxide concentration in the atmosphere has increased Carbon dioxide concentration in the atmosphere has increased

from 280 ppm before the Industrial Revolution to 370 ppm in from 280 ppm before the Industrial Revolution to 370 ppm in 20002000

Methane has increased from 700 ppb to 1,745 ppbMethane has increased from 700 ppb to 1,745 ppb

Methane has a global warming potential 23 times greater than Methane has a global warming potential 23 times greater than COCO22

MEA 2005

Sources of Methane to Atmosphere (TgC/yr)

30%

17%

16%

11%

9%

7%

4%3%2%1%

peatlands/wetlands

ruminants

energy

rice paddies

landfills

biomass burning

termites

waste treatment

oceans

methane hydrates

Role of OceansRole of Oceans The coastal marine ecosystem is The coastal marine ecosystem is

attributed with producing 75% of attributed with producing 75% of CHCH4 4 emitted by the world’s oceans emitted by the world’s oceans (Bange et al. 1994)(Bange et al. 1994)

Ebullition and molecular diffusion Ebullition and molecular diffusion are responsible for transport of are responsible for transport of methane out of sediments (Chanton methane out of sediments (Chanton et al. 1989)et al. 1989)

In coastal ecosystems the major In coastal ecosystems the major pathway for bacterial methane pathway for bacterial methane formation is COformation is CO22 reduction by reduction by hydrogen hydrogen

COCO22 + 4 H + 4 H22 → CH → CH44 + 2 H + 2 H22OO4 H4 H22 + HCO + HCO3-3- + H + H++ → CH → CH44 + 3 H + 3 H22OO

Methane also produced by acetate Methane also produced by acetate fermentation but is limited by sulfate fermentation but is limited by sulfate reductionreduction

CHCH33COOH → CHCOOH → CH44 + CO + CO22

Whiticar et al. 1986

Hemond and Fechner-Levy 2000

ObjectivesObjectives Determine the flux of methane produced by anoxic Determine the flux of methane produced by anoxic

coastal sedimentscoastal sediments-Incubation of sediment from tidal flats-Incubation of sediment from tidal flats-Sample surface water of Great Bay estuary-Sample surface water of Great Bay estuary

Examine the spatial distribution of methane from Examine the spatial distribution of methane from freshwater to coastal ecosystemsfreshwater to coastal ecosystems

-Sample surface of rivers flowing into estuary-Sample surface of rivers flowing into estuary-Use GIS to identify sources of methane and evaluate -Use GIS to identify sources of methane and evaluate

transport to transport to coastal regionscoastal regions

Methanogenesis:Acetate fermentation

Wetlands, WWTP, etcOxidation, Diffusive Flux,

Advective Transport

Estuary, saltmarsh

Methanogenesis:CO2 Reduction

Oxidation, Air-Sea Exchange

Oxidation, Air-Sea Exchange

MethodsMethods

IncubationsIncubations Sediment core taken in Great Bay Sediment core taken in Great Bay

Estuary at tidal flatsEstuary at tidal flats

10-20 g of sediment from 0-5, 5-10-20 g of sediment from 0-5, 5-10, 10-15 and 15-20 cm 10, 10-15 and 15-20 cm incubated under anaerobic incubated under anaerobic conditionsconditions

10 mL of headspace sampled 10 mL of headspace sampled daily and analyzed for CHdaily and analyzed for CH44 concentration using GC-FIDconcentration using GC-FID

Water SamplingWater Sampling Surface water collected in Surface water collected in

container and syringe used to container and syringe used to sample 30 mL of watersample 30 mL of water

30 mL of ambient air drawn in 30 mL of ambient air drawn in and syringe shaken to flush and syringe shaken to flush dissolved methane into the dissolved methane into the headspaceheadspace

Headspace injected into GC-FID Headspace injected into GC-FID to obtain CHto obtain CH44 concentration concentration

Methane Concentration in Surface Methane Concentration in Surface WaterWater

Methane Concentration in Methane Concentration in RiversRivers

2008

2009

Examples of Sources:Examples of Sources: Sallie’s Fen

4805 ppmv Durham Wastewater Treatment

Plant44 ppmv

Difference in CHDifference in CH44 Concentration from Concentration from 2008 to 20092008 to 2009

Methane Flux from Rivers to Methane Flux from Rivers to AtmosphereAtmosphere

2008

2009

Soil IncubationsSoil Incubations

Depth (cm)

Moisture Content (%)

Organic Matter (%)

Average Flux (mg CH4/g sed*day)

5 38.9 ± 1.2 5.0 ± 0.5 0.98 ± 0.12

10 33.6 ± 1.8 4.5 ± 1.0 1.59 ± 0.77

15 32.0 ± 0.8 5.3 ± 0.7 2.67 ± 0.68

20 29.2 ± 0.4 4.3 ± 0.5 13.48 ± 13.05

Methane flux from sediment to headspace

0.0 5.0 10.0 15.0 20.0 25.0 30.0

5

10

15

20

Dep

th (

cm)

Methane Flux (mg CH4/g sed*day)

Future WorkFuture Work Methane produced through COMethane produced through CO22 reduction is isotopically light with reduction is isotopically light with

δδ1313C values between -110 and -60‰C values between -110 and -60‰

CHCH44 produced by acetate fermentation has δ produced by acetate fermentation has δ1313C values between -65 C values between -65 and -50‰ and -50‰

Methane oxidation converts some of the methane produced at depth Methane oxidation converts some of the methane produced at depth to carbon dioxide as it rises to a level where oxygen is presentto carbon dioxide as it rises to a level where oxygen is present

Since the Since the 1313C/C/1212C ratios of dissolved COC ratios of dissolved CO22 are affected by the equilibria are affected by the equilibria of many kinetic isotope effects it is necessary to calculate the of many kinetic isotope effects it is necessary to calculate the carbon isotopic fractionation between methane and carbon dioxidecarbon isotopic fractionation between methane and carbon dioxide

Whiticar et al. 1986Whiticar et al. 1986

NASA RelevanceNASA Relevance Evaluating sources of methane can aid in determining Evaluating sources of methane can aid in determining

processes that produce atmospheric methane processes that produce atmospheric methane

TDL spectroscopy from aircraft TDL spectroscopy from aircraft

Remote sensing using AIRS instrument on AQUA Remote sensing using AIRS instrument on AQUA satellitesatellite

AIRS CH4 at 300hPa

AcknowledgementsAcknowledgements

Dr. Ruth VarnerDr. Ruth Varner

Dr. George HurttDr. George Hurtt

Olivia DeMeoOlivia DeMeo

Jordan GoodrichJordan Goodrich

NASA/UNH R&DNASA/UNH R&D

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