A multi-scale comparison of modeled and observed seasonal methane emissions in northern wetlands

X. Xu; W. J. Riley; C. D. Koven; D. P. Billesbach; R. Y.-W. Chang; R. Commane; E. S. Euskirchen; S. Hartery; Y. Harazono; H. Iwata; K. C. McDonald; C. E. Miller; W. C. Oechel; B. Poulter; N. Raz-Yaseef; C. Sweeney; M. Torn; S. C. Wofsy; Z. Zhang; D. Zona

doi:10.5194/bg-13-5043-2016

Biogeosciences (Sep 2016)

A multi-scale comparison of modeled and observed seasonal methane emissions in northern wetlands

X. Xu,
W. J. Riley,
C. D. Koven,
D. P. Billesbach,
R. Y.-W. Chang,
R. Commane,
E. S. Euskirchen,
S. Hartery,
Y. Harazono,
H. Iwata,
K. C. McDonald,
C. E. Miller,
W. C. Oechel,
B. Poulter,
N. Raz-Yaseef,
C. Sweeney,
M. Torn,
S. C. Wofsy,
Z. Zhang,
D. Zona

Affiliations

X. Xu: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
W. J. Riley: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
C. D. Koven: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
D. P. Billesbach: Biological System Engineering Department, University of Nebraska, Lincoln, Nebraska, USA
R. Y.-W. Chang: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
R. Commane: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
E. S. Euskirchen: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, USA
S. Hartery: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
Y. Harazono: International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, Alaska, USA
H. Iwata: International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, Alaska, USA
K. C. McDonald: Department of Earth and Atmospheric Sciences, CUNY Environmental Crossroads Initiative and NOAA-CREST Institute, The City College of New York, City University of New York, New York, USA
C. E. Miller: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
W. C. Oechel: Global Change Research Group, Department of Biology, San Diego State University, San Diego, California, USA
B. Poulter: Department of Ecology, Montana State University, Bozeman, MT 59717, USA
N. Raz-Yaseef: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
C. Sweeney: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80304, USA
M. Torn: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
S. C. Wofsy: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Z. Zhang: Department of Ecology, Montana State University, Bozeman, MT 59717, USA
D. Zona: Global Change Research Group, Department of Biology, San Diego State University, San Diego, California, USA

DOI: https://doi.org/10.5194/bg-13-5043-2016
Journal volume & issue: Vol. 13, no. 17
pp. 5043 – 5056

Abstract

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Wetlands are the largest global natural methane (CH4) source, and emissions between 50 and 70° N latitude contribute 10–30 % to this source. Predictive capability of land models for northern wetland CH4 emissions is still low due to limited site measurements, strong spatial and temporal variability in emissions, and complex hydrological and biogeochemical dynamics. To explore this issue, we compare wetland CH4 emission predictions from the Community Land Model 4.5 (CLM4.5-BGC) with site- to regional-scale observations. A comparison of the CH4 fluxes with eddy flux data highlighted needed changes to the model's estimate of aerenchyma area, which we implemented and tested. The model modification substantially reduced biases in CH4 emissions when compared with CarbonTracker CH4 predictions. CLM4.5 CH4 emission predictions agree well with growing season (May–September) CarbonTracker Alaskan regional-level CH4 predictions and site-level observations. However, CLM4.5 underestimated CH4 emissions in the cold season (October–April). The monthly atmospheric CH4 mole fraction enhancements due to wetland emissions are also assessed using the Weather Research and Forecasting-Stochastic Time-Inverted Lagrangian Transport (WRF-STILT) model coupled with daily emissions from CLM4.5 and compared with aircraft CH4 mole fraction measurements from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) campaign. Both the tower and aircraft analyses confirm the underestimate of cold-season CH4 emissions by CLM4.5. The greatest uncertainties in predicting the seasonal CH4 cycle are from the wetland extent, cold-season CH4 production and CH4 transport processes. We recommend more cold-season experimental studies in high-latitude systems, which could improve the understanding and parameterization of ecosystem structure and function during this period. Predicted CH4 emissions remain uncertain, but we show here that benchmarking against observations across spatial scales can inform model structural and parameter improvements.

Published in Biogeosciences

ISSN: 1726-4170 (Print); 1726-4189 (Online)
Publisher: Copernicus Publications
Country of publisher: Germany
LCC subjects: Science: Biology (General): Ecology; Science: Biology (General): Life; Science: Geology
Website: http://www.biogeosciences.net

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