Advances in the Eddy Covariance Approach to CH<sub>4</sub> Monitoring Over Two and a Half Decades

Morin, Timothy H.

doi:10.1029/2018jg004796

Cited by 37 publications

(31 citation statements)

References 81 publications

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“…Previous synthesis studies also observed a significant, but weaker, relationship between soil temperature and average CH 4 emissions across sites, explaining <15% of the variation in CH 4 flux in those studies (Olefeldt et al 2013;Yvon-Durocher et al 2014). However, our findings are consistent with numerous site-level studies that report a strong correlation between wetland CH 4 emissions and temperature, with nearly 95% of all EC studies reporting a significant relationship between temperature and CH 4 f lux (Morin 2018). Across sites, Peltola et al (2019) found that the most important predictor in a random forest model used to upscale EC CH 4 emissions across northern latitudes was temperature, again highlighting the importance of temperature in regulating CH 4 emissions within and across sites.…”

Section: Resultssupporting

confidence: 91%

“…More sites in key regions. We expect the number of flux towers measuring CH 4 fluxes will continue to grow (Chu et al 2017;Pastorello et al 2017;Morin 2018), but our compilation of EC CH 4 flux sites highlights key underrepresented regions where future flux towers are needed or where more efforts are needed for existing but nonreporting towers to contribute to FLUXNET (Fig. 1).…”

Section: Ec Flux Data Quality Assessmentmentioning

confidence: 99%

“…There are more than 900 reported active and historical flux tower sites globally and approximately 7,000 site years of data collected (Chu et al 2017). While most of these sites measure CO 2 , water vapor, and energy exchange, the development of new and robust CH 4 sensors has resulted in a rapidly growing number of CH 4 EC measurements (Baldocchi 2014;Morin 2018), primarily in natural and agricultural wetlands (Petrescu et al 2015).…”

mentioning

confidence: 99%

“…EC CH 4 flux measurements became more feasible with advances in sensor development, such as tunable diode laser absorption spectrometers, that allowed researchers to measure previously undetectable trace gas fluxes with higher signal to noise ratios (Rinne et al 2007;McDermitt et al 2011). After these new sensors were commercialized, and low-power, low-maintenance open-path sensors were developed that could be operated by solar panels in remote locations, the number of CH 4 flux tower measurements increased substantially (Baldocchi 2014;Morin 2018). The rapidly growing number of EC CH 4 flux measurements presents new opportunities for FLUXNET-type analyses and syntheses of ecosystem-scale CH 4 flux observations.…”

mentioning

confidence: 99%

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FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

Knox¹,

Jackson²,

Poulter

et al. 2019

Bulletin of the American Meteorological Society

148

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This paper describes the formation of, and initial results for, a new FLUXNET coordination network for ecosystem-scale methane (CH4) measurements at 60 sites globally, organized by the Global Carbon Project in partnership with other initiatives and regional flux tower networks. The objectives of the effort are presented along with an overview of the coverage of eddy covariance (EC) CH4 flux measurements globally, initial results comparing CH4 fluxes across the sites, and future research directions and needs. Annual estimates of net CH4 fluxes across sites ranged from −0.2 ± 0.02 g C m–2 yr–1 for an upland forest site to 114.9 ± 13.4 g C m–2 yr–1 for an estuarine freshwater marsh, with fluxes exceeding 40 g C m–2 yr–1 at multiple sites. Average annual soil and air temperatures were found to be the strongest predictor of annual CH4 flux across wetland sites globally. Water table position was positively correlated with annual CH4 emissions, although only for wetland sites that were not consistently inundated throughout the year. The ratio of annual CH4 fluxes to ecosystem respiration increased significantly with mean site temperature. Uncertainties in annual CH4 estimates due to gap-filling and random errors were on average ±1.6 g C m–2 yr–1 at 95% confidence, with the relative error decreasing exponentially with increasing flux magnitude across sites. Through the analysis and synthesis of a growing EC CH4 flux database, the controls on ecosystem CH4 fluxes can be better understood, used to inform and validate Earth system models, and reconcile differences between land surface model- and atmospheric-based estimates of CH4 emissions.

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Section: Resultssupporting

confidence: 91%

Section: Ec Flux Data Quality Assessmentmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

Knox¹,

Jackson²,

Poulter

et al. 2019

Bulletin of the American Meteorological Society

148

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“…Although a series of biophysical variables (e.g., T air , soil temperature, radiation, WTD, salinity, NEE, GPP, Re, and LE) have been identified as important drivers of F CH4 , their relative significance could vary across different ecosystems and timescales (Morin, 2019). Our results of correlation analysis revealed the importance of a number of key variables (e.g., T air , soil temperature and salinity) in driving F CH4 , which might be confounded by the high collinearity among the drivers (Table 4).…”

Section: Discussionmentioning

confidence: 99%

Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half

Liu

Zhou

Valach

et al. 2020

Global Change Biology

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The role of coastal mangrove wetlands in sequestering atmospheric carbon dioxide (CO 2) and mitigating climate change has received increasing attention in recent years. While recent studies have shown that methane (CH 4) emissions can potentially offset the carbon burial rates in low-salinity coastal wetlands, there is hitherto a paucity of direct and year-round measurements of ecosystem-scale CH 4 flux (F CH4) from mangrove ecosystems. In this study, we examined the temporal variations and biophysical drivers of ecosystem-scale F CH4 in a subtropical estuarine mangrove wetland based on 3 years of eddy covariance measurements. Our results showed that daily mangrove F CH4 reached a peak of over 0.1 g CH 4-C m −2 day −1 during the summertime owing to a combination of high temperature and low salinity, while the wintertime F CH4 was negligible. In this mangrove, the mean annual CH 4 emission was 11.7 ± 0.4 g CH 4-C m-2 year −1 while the annual net ecosystem CO 2 exchange ranged between −891 and −690 g CO 2-C m −2 year −1 , indicating a net cooling effect on climate over decadal to centurial timescales. Meanwhile, we showed that mangrove F CH4 could offset the negative radiative forcing caused by CO 2 uptake by 52% and 24% over a time horizon of 20 and 100 years, respectively, based on the corresponding sustained-flux global warming potentials. Moreover, we found that 87% and 69% of the total variance of daily F CH4 could be explained by the random forest machine learning algorithm and traditional linear regression model, respectively, with soil temperature and salinity being the most dominant controls. This study was the first of its kind to characterize ecosystem-scale F CH4 in a mangrove wetland with longterm eddy covariance measurements. Our findings implied that future environmental changes such as climate warming and increasing river discharge might increase CH 4 emissions and hence reduce the net radiative cooling effect of estuarine mangrove forests.

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Comparing field-scale eddy covariance measurements and crop coefficient estimates of alfalfa evapotranspiration to OpenET model estimates and exploring water budget implications in a dryland environment

Sabiston,

Sabie,

Buenemann

et al. 2024

Irrig Sci

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Remote sensing evapotranspiration (ET) models have the potential to be powerful tools for water planning and management, particularly for agriculture. OpenET is an emerging web-based tool that uses satellite imagery and climate data for calculating six distinct ET models, and an ensemble model of the six models, to provide estimates of actual ET (ETa) which is useful for field-scale irrigation management decisions. Previous studies examining the performance of individual models included in the OpenET platform showed some models used in OpenET consistently predicted lower values of ETa in dryland regions relative to in-situ measurements. The OpenET research team has made modifications to address these isues. There are few studies examining if the modified models included in OpenET sill produce lower values of ETa compared to field values in dryland environments. This study compared satellite-based OpenET estimates of ETa from three alfalfa fields in the Mesilla Valley, New Mexico, USA–one field with measurements of ETa from an eddy covariance tower and two fields with estimated crop evapotranspiration (ETc)–during the 2017 growing season to investigate if OpenET ETa estimates demonstrate an underestimation bias. OpenET ETa estimates were tested against in-situ ETa measurements and ETc estimates using two sample t-tests and Mann-Whitey U tests to determine if there were any significant differences in means between the two groups. Model seasonal percent mean bias error ranged from −33.99 to +11.37%. eeMETRIC and SIMS seasonal estimates were within ±15% of in-situ measurements at any of the three sites and within ±10% of in-situ measurements on average. SSEBop and DisALEXI produced significantly different monthly ETa estimates (p-values < 0.05) when data were extracted using the OpenET field polygons. The results of the small sample of fields suggest the OpenET models may estimate lower values of ETa relative to the field data. Future research should improve the methodology for assessing accuracy of OpenET in small agricultural fields in the western United States.

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Advances in the Eddy Covariance Approach to CH₄ Monitoring Over Two and a Half Decades

Cited by 37 publications

References 81 publications

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half

Comparing field-scale eddy covariance measurements and crop coefficient estimates of alfalfa evapotranspiration to OpenET model estimates and exploring water budget implications in a dryland environment

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Advances in the Eddy Covariance Approach to CH4 Monitoring Over Two and a Half Decades

Cited by 37 publications

References 81 publications

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half

Comparing field-scale eddy covariance measurements and crop coefficient estimates of alfalfa evapotranspiration to OpenET model estimates and exploring water budget implications in a dryland environment

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Advances in the Eddy Covariance Approach to CH₄ Monitoring Over Two and a Half Decades