Seasonalcontrolsonregional methaneandcarbondioxide ...co2.aos.wisc.edu/~adesai/documents/Desai-AGUFall11-B13J-03.pdf · 1University of Wisconsin-Madison, Center for Climatic Research,

AGU Fall 2011 B13J-‐03 (Desai)

Seasonal controls on regional methane and carbon dioxide exchange observed from a very tall eddy covariance

tower in a wetland-‐rich landscape

Ankur R Desai Atmospheric and Oceanic Sciences University of Wisconsin-‐Madison

5 December 2011


Methane concentraJons conJnue to rise

Source: NOAA ESRL

Source: Park Falls TCCON (P. Wennberg)


Sources and sinks of methane are not well quanJfied

Spahni et al. (2011) Biogeosciences


Wetlands are a primary source of methane emissions in temparate/boreal regions

Buffam et al (2011) Global Change Biology


EvaluaJon of regional fluxes difficult with small towers and chambers

Credit: P. Weishampel Credit: B. Rychter

Source: Cook et al (2008) AGU Poster


Tall towers offer novel approach to esJmaJng regional fluxes

Source: B. Cook Credit: M. Rydzik


Long term CO2 flux record reveals moisture controls on regional flux

Desai et al (2010) JGR-‐G


Long-‐term conJnuous CH4 eddy covariance is now feasible

Credit: M. Rydzik

396 m

122 m

30 m

CO2/H2O flux Picarro G1301-‐f CH4/CO2 (H2O)

122 m

Not shown: Los Gatos for CH4 profile/storage flux LI-‐7000 (NOAA) for CO2 profile/storage


New instrument CO2 and H2O fluxes compare well to exisJng instruments

Picarro Licor-‐In Situ Licor-‐Trailer


Comparison of CH4 and CO2 fluxes reveal stark differences by season

15 Oct 2010-‐ 14 Oct 2011


Large winterJme CH4 emissions influence cumulaJve exchange


Modeled CH4 fluxes for this region do not show these large emissions

Novel approaches to estimating regional CH4 !uxes from a very tall tower Ankur R Desai1,*, Jennifer C Welch1, Bjorn Brooks1, Kristine Jimenez1, Gretchen Keppel-Aleks2, Debra Wunch2, Paul O Wennberg2, Bruce D Cook3, Peter Weishampel4, Jennifer King51University of Wisconsin-Madison, Center for Climatic Research, 2California Institute of Technology, Environmental Science and Engineering, 3NASA Goddard Space Flight Center, 4Northland College, Natural Resources, 5U. California - Santa Barbara, Geography

*Corresponding author contact: Ankur R Desai, Dept of Atmospheric & Oceanic Sciences, 1225 W Dayton St, Madison, WI USA 53706, [email protected], http://!ux.aos.wisc.edu

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IntroductionCan we estimate regional CH4 land surface !ux with:

(a) Column CO2 and CH4 observations from the Total Carbon Column Observatory Network (TCCON) solar spectroscopic FT-IR instrument? (b) Tall eddy covariance !ux tower (WLEF) net ecosystem ex-change (NEE) of CO2 observations?

in a heterogeneous upland-wetland-lake landscape where CH4 !uxes are likely to be signi"cant but poorly constrained?

Observations

MethodsNeglecting entrainment, the time rate of change in atmospheric column should be pro-portional to !ux. Assuming this proportion is the same for CO2 and CH4, we can write a simple equation for NEE CH4:

Daytime averaged column observations of CO2 and CH4 from 2005-2009 in Park Falls, WI USA re!ect global and regional sources and sinks (left).

Total column CH4 observations (red points) were corrected for stratospheric in!uence to estimate troposphere-only CH4 (black points) using HF column (Washenfelder et al., 2003)

Fossil fuel signal was removed by simple linear "t (green line) and gaps "lled with spline inter-polation (blue line) for both CO2 and CH4.

Entrainment can be neglected when averaged over multiple synoptic cycles (Helliker et al., 2004) and by using total column observations. Time derivative of 14-day average CO2 (bottom left) shows pattern that re!ects !ux. Term in bracket above was estimated from slope of NEE to dCO2/dt "t (bottom right), which shows strong correlation.

ResultsEstimated regional CH4 !ux (right, red line) has a seasonal pattern of uptake in winter and emissions in late summer, in contrast to NEE CO2 (blue line).

CH4 !uxes are of similar magnitude to cham-ber observations of CH4 e#ux (green crosses) measured at three wetlands in tower foot-print in 2006-2007, but seasonality is o$set.

Annual CH4 !ux (right, red stars) has high in-terannual variability, alternating from sink to source, but is positively correlated to CO2 !ux interannual variability (blue crosses).

DiscussionSeasonal uptake of CO2 NEE (bottom left, blue line) appears to lag CH4 NEE uptake (red line) by 3-6 months and CH4 maximum e#ux occurs in late summer. While seasonal NEE of CO2 and CH4 are anti-correlated, annual !uxes of CO2 and CH4 are positively correlated. These results imply complex biogeochemical mechanisms occuring at regional scale.

CH4 !ux magnitudes were at lower bounds of those estimated by modi"ed-Bowen ratio technique (bottom right, black line) and nocturnal column accumulation (black dots) from tower GC observations of CH4 and CO2 in 1997 (Werner et al., 2003). Dual peak pattern of CH4 emissions seen in Werner et al. (2003) not apparent in our results.

ConclusionFuture work is needed to test sensitivity of method to assumptions on averaging, fossil fuel estimate, entrainment, linearity of ratio of NEE to column change, di$erence in foot-print between tall tower NEE, column and chamber observations, and observation error.

New measurements of tall tower eddy covariance CH4 initiated in fall 2010 and ongoing model-based upscaling of chamber observations will provide independent estimates of magnitude and pattern of regional methane !ux and applicability of our technique.

Citations: Helliker et al. (2004) J Geophys. Res; Washenfelder et al. (2003) Geophys. Res. Lett.; Werner et al. (2003) Global Change Biol.

Acknowledgments: Analysis and tall tower operations supported by NSF CAREER DEB-0845166 and DOE NICCR Mid-west 050516Z19. Flux tower operations were aided by K. Davis (PSU), J. Thom (UW), J. Ko!er (NOAA), A. Andrews (NOAA), and R. Strand (WI ECB). US TCCON funding is provided by NASA’s Terrestrial Ecology Program, Orbiting Carbon Observatory program, and the DOE/ARM program.. We also acknowledge reprint of "gure from C. Werner.

a) TCCON

b) Tall !ux tower

Photos courtesy of: a) G. Keppel-Aleks, b) B.D. Cook

Desai et al (2011) NACP Mtg. Based on TCCON column observaJons

Werner et al (2003) Based on tall tower flask/GC concentraJon gradient

Spahni et al. (2011) Biogeosciences Modeled (LPJ) zonal seasonal cycles


Flux magnitudes similar to chamber-‐based emissions made in nearby fens and bogs


Similarity seen in diurnal cycles of hourly NEE but CO2/CH4 NEE raJo increases from winter to summer


Environmental controls of CH4 fluxes vary by season

•  Correlated daily CH4 flux to: –  Air temperature –  Incoming PAR –  PrecipitaJon (summer only)

–  NEE CO2 –  ER and GPP –  COSMOS regional soil moisture (summer only)

•  Strongest fits shown on right


Clearly, more invesJgaJon is needed on winterJme CH4 emissions

•  Need to assess flux computaJon, correcJon and gap-‐filling rouJnes for CH4 flux – Small methane fluxes require tests on limits of detecJon, spectral loss

•  SpaJal scale likely has a large influence on observed or modeled flux

•  Chamber flux campaign experiments need to be made in late fall/winter on role of under snow CO2 and CH4 emissions


Thank you!

•  NSF CAREER DEB #0845166 •  WLEF/ Park Falls (US-‐PFa) tall tower research partners: NOAA ESRL (A. Andrews, J. Kofler), USFS NRS (M. Kubiske, D. Baumann), Penn State (K. Davis), Cal Tech (P. Wennberg), COSMOS (M. Zreda), NASA GSFC (B. Cook), WI ECB (J. Ayers) , Ameriflux

•  Desai lab at UW: J. Thom, K. Jimenez, B. Brooks –  hip://flux.aos.wisc.edu –  [email protected] –  608-‐218-‐4208

Documents

Seasonalcontrolsonregional methaneandcarbondioxide ...co2.aos.wisc.edu/~adesai/documents/Desai-AGUFall11-B13J-03.pdf · 1University of Wisconsin-Madison, Center for Climatic Research,