Supplement of Atmospheric constraints on the methane emissions ...
Improving Our Process Understanding of Methane Emissions ...
Transcript of Improving Our Process Understanding of Methane Emissions ...
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AGU FALL MEETING 13 December 2017
Improving our process understanding of methane emissions from a mid-latitude reservoir by combining eddy covariance monitoring
with spatial surveys
Sarah Waldo, Jake J. Beaulieu, and John T. Walker USEPA Office of Research and Development
National Risk Management Research Laboratory
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Anthropogenic Methane Budget
Best estimate of global CH4 from reservoirs is uncertain
The IPCC is actively working to establish a methodology for reservoir CH4 emissions
Rice Cultivation 36 Tg/yr
75 Tg/yr
Ruminants 89 Tg/yr
Landfills
Reservoirs ~18 Tg/yr
(12-30) Deemer et al (2016)
Biomass Burning and
biofuels 35 Tg/yr
Fossil Fuels 96 Tg/yr
Sources other than reservoirs from IPCC 5th Assessment
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Background: why and how reservoirs emit methane
Methane (CH4) is produced by methanogens in oxygen-poor, carbon-rich sediment
CH4 makes it to the atmosphere via
diffusion
ebullition
Rate/timing of CH4 emissions are affected by physical and biotic factors
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Acton Lake Study: site description
Cropland
Pasture/Hay
Forest
Developed
Water
Land cover data: http://www.mrl c.gov/nlcd2011. php
https://www.epa.gov/national-aquaticresource-surveys/ecoregional-results-nationallakes-assessment-2012
Acton Lake site description:
Surface area: 2.4 km2
Maximum depth: 10 m
Watershed is 81% agriculturalland
Dam was constructed in 1956
Acton Lake Study: methods
Executed spatially balanced surveys:July 10th – 11th & Aug 31st – Sept 1st
Deployed inverted funnels overnight ( >12 hr)
Measured diffusive fluxes with a floating chamber + ultraportablegreenhouse gas analyzer
Eddy covariance flux towerdeployed at the NW corner of the lake
Monitoring fluxes of CH4, CO2, water vapor, and energy
Pseudo-continuous, 30-minute measurements from Feb 2017 present
flux tower location
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Acton Lake Study: research questions
1. How do magnitudes ofebullitive and diffusive emissions compare?
2. What temporal patterns do we see in CH4 fluxes?
3. What environmental drivers are associated with elevated emissions?
flux tower location
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Emission Pathway: Lake-wide surveys
Results from inverted funnel and chamber measurements of CH4 emissions
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Surprising Spatial Finding: Ebullition vs. Depth
Typical for areas in theriver-reservoir transition area near the inflow to have elevated ebullition rates
• more organic matter fromsedimentation
• deep sites
• suppress bubbling
• more oxidation in water column
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Emission Pathway: Lake-wide surveys
Ebullition Diffusion Ebullition was the main CH4 emission pathway:
• 82% of total lake-wide e missions on July 10th
• 94% of total lake-wide e missions on August 31st
July 10th July 10th Aug 31stAug 31st
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Eddy covariance observations: temporal patternsand relationship with environmental drivers
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400 m
200 m
flux tower location U-14
Temporal Trends: Seasonal
Seasonal trends (numbers reported as mean ± se):
Winter and early spring saw lowemissions. 1 Feb – 1 April:
14.1 ± 2.2 mg CH4 m-2 d-1
Maximum sustained emissions in the late summer. July 25 – Sept 1:
582 ± 31 mg CH4 m-2 d-1
Emissions back to winter baseline by late fall. Oct 25 – Nov 16:
19.3 ± 4.1 mg CH4 m-2 d-1
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Temporal Trends: Seasonal
The lake-wide CH4 emission results from the spatial surveys agreed relatively well with the eddycovariance results
Spatially, would have expected thelake-wide characterizations to be higher than the EC
survey results indicated that the NWportion of the lake had lower emissionsthan the rest of the lake
Temporally, looks like we may havemissed peak emissions
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Temporal Trends: Seasonal
Total hydrostatic pressure(pressure from water column +atmosphere) has a threshold effect
Temperature has a threshold effect as well
Air temperature needs to be above 8 °C for substantial methane emission to occur
Q10 analysis (DelSontro et al.,2016)
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Summary & Future Work
• Summary:
• Ebullition accounted for >80% of summertime CH4 emissions at Acton Lake
• Clear seasonality: summertime emissions were 40xhigher than wintertime
• Temperature and hydrostatic pressure exerted controlon CH4 emissions
• Future work:
• Gap-filling and identification of CH4 flux drivers using wavelet analysis
• Compare and contrast CH4 and CO2 fluxes • Use water temperature profile measurements to
investigate impact of hydrodynamics on air-water gasexchange
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Acknowledgements
• USEPA ORD Cincinnati & RTP
• Karen White • Kit Daniels • Megan Berberich • Ryan Daly • William Yelverton • Bill Mitchell
• Pegasus Technical Services
• Adam Balz • Adin Pemberton • Keith Bisbe • Paul Trygstad • Mia Varner
• Vanni Research Group at Miami University of Ohio
• Mike Vanni • Tanner Williamson • Tera Ratliff • Tom Radford
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Disclaimer The information in this presentation has been reviewed and approved for public dissemination in accordance with U.S.
Environmental Protection Agency (EPA). The views expressed in this presentation are those of the author(s) and do not necessarily
represent the views or policies of the Agency. Any mention of trade names or commercial products does not
constitute EPA endorsement or recommendation for use.
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Questions? Questions?