spatial distribution of methane in surface water from terrestrial sources to coastal regions kaitlyn...
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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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