FLUXNET-CH4: A global, multi-ecosystem dataset and analysis of methane seasonality from freshwater wetlands

Authors: DELWICHE, KYLE - Stanford University; KNOX, SARA - University Of British Columbia; MALHOTRA, AVNI - Stanford University; FLUET-CHOUINARD, ETIENNE - Stanford University; MCNICOL, GAVIN - Stanford University; FERON, SARAH - Stanford University; OUYANG, ZUTAO - Stanford University; PAPALE, DARIO - University Of Tuscia; TROTTA, CARLO - Mediterranean Centre On Climate Change; CANFORA, ELEONORA - Mediterranean Centre On Climate Change; CHEAH, YOU-WEI - Lawrence Berkeley National Laboratory; CHRISTIANSON, DANIELLE - Lawrence Berkeley National Laboratory; ALBERTO, CARMELITA - International Rice Research Institute; ALEKSEYCHIK, PAVEL - Natural Resources Institute Finland (LUKE); AURELA, MIKA - Finnish Meteorological Institute; BALDOCCHI, DENNIS - University Of California; BANSAL, SHEEL - Us Geological Survey (USGS); BILLESBACH, DAVID - University Of Nebraska; BOHRER, GIL - The Ohio State University; BRACHO, ROSVEL - University Of Florida; BUCHMANN, NINA - Institute Of Agricultural Sciences; CAMPBELL, DAVID - University Of Waikato; CELIS, GERARDO - University Of Florida; CHEN, JIQUAN - Michigan State University; CHEN, WEINAN - Chinese Academy Of Sciences; CHU, HOUSEN - Lawrence Berkeley National Laboratory; DALMAGRO, HIGO - Universidade De Cuiaba; DENGEL, SIGRID - Lawrence Berkeley National Laboratory; DESAI, ANKUR - University Of Wisconsin; DETTO, MATTEO - Princeton University; DOLMAN, HAN - Vrije University; EICHLMANN, ELKE - University College Dublin; EUSKIRCHEN, EUGENIE - Institute Of Arctic Biology - Alaska; FAMULARI, DANIELA - Istituto Di Bioscienze E Biorisorse-Uos Portici-cnr; FRIBORG, THOMAS - University Of Copenhagen; FUCHS, KATHRIN - Atmospheric And Environmental Research; GOECKEDE, MATHIAS - Max Planck Institute For Biogeochemistry; GOGO, SEBASTIEN - Université D'Orléans (ORLEANS UNIVERSITY); GONDWE, MANGALISO - University Of Botswana; GOODRICH, JORDAN - University Of Waikato; GOTTSCHALK, PIA - German Research Center For Environmental Health; GRAHAM, SCOTT - Manaaki Whenua Landcare Research; HEIMANN, MARTIN - Max Planck Institute For Biogeochemistry; HELBIG, MANUEL - Universite De Montreal; HELFTER, CAROLE - Centre For Ecology And Hydrology; HEMES, KYLE - University Of California; HIRANO, TAKASHI - Hokkaido University; HOLLINGER, DAVID - Us Forest Service (FS); HORTNAGL, LUKAS - Eth Zurich; IWATA, HIROKI - Shinshu University; JACOTOT, ADRIEN - Université D'Orléans (ORLEANS UNIVERSITY); JANSEN, JOACHIM - Stockholm University; JURASKINKI, GERALD - University Of Rostock; KANG, MINSEOK - National Center For Agrometeorology; KASAK, KUNO - University Of Tartu; KING, JOHN - North Carolina State University; KLATT, JANINA - University Of Applied Sciences; KOEBSCH, FRANZISKA - University Of Rostock; KRAUSS, KEN - Us Geological Survey (USGS); LAI, DERRICK - The Chinese University Of Hong Kong (CUHK); MAMMARELLA, IVAN - University Of Helsinki; MANCA, GIOVANNI - European Commission-Joint Research Centre (JRC); MARCHESINI, LUCA - Fondazione Edmund Mach; MATTHES, JACLYN - Wellesley College; MAXIMON, TROFIM - Reproductive Biology Associates; MERBOLD, LUTZ - International Livestock Research Institute (ILRI) - Kenya; MITRA, BHASKAR - Northern Arizona University; MORIN, TIMOTHY - State University Of New York (SUNY); NEMITZ, EIKO - Centre For Ecology And Hydrology; NILSSON, MATS - Swedish University Of Agricultural Sciences; NIU, SHULI - Chinese Academy Of Sciences; OECHEL, WALTER - San Diego State University; OIKAWA, PATRICIA - California State University; ONO, KEISUKE - National Agriculture And Food Research Organization (NARO), Agricultrual Research Center; PEICHL, MATTHIAS - Swedish University Of Agricultural Sciences; PELTOLA, OLLI - Finnish Meteorological Institute; Reba, Michele; RICHARDSON, ANDREW - Northern Arizona University; RILEY, WILLIAM - Lawrence Berkeley National Laboratory; RUNKLE, BENJAMIN - University Of Arkansas; RYU, YOUNGRYEL - Seoul National University; SACHS, TORSTEN - German Research Center For Environmental Health; SAKABE, AYAKA - Kyoto University; SANCHEZ, CAMILO - University Of California; SCHUUR, EDWARD - Northern Arizona University; SCHAFER, KARINA - Rutgers University; SONNENTAG, OLIVER - Universite De Montreal; SPARKS, JED - Cornell University; STUART-HAENTJENS, ELLEN - Us Geological Survey (USGS); STURTEVANT, COVE - Battelle Memorial Institute; SULLIVAN, RYAN - Argonne National Laboratory; SZUTU, DAPHNE - University Of California; THOM, JONATHAN - University Of Wisconsin; TORN, MARGARET - Lawrence Berkeley National Laboratory; TUITTILA, EEVA-STIINA - University Of Eastern Finland; TURNER, JESSICA - University Of Wisconsin; UEYAMA, MASAHITO - Osaka Prefecture University; VALACH, ALEX - University Of California; VARGAS, RODRIGO - University Of Delaware

Submitted to: Earth System Science Data
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2021
Publication Date: 7/29/2021
Citation: Delwiche, K.B., Knox, S.H., Malhotra, A., Fluet-Chouinard, E., Mcnicol, G., Feron, S., Ouyang, Z., Papale, D., Trotta, C., Canfora, E., Cheah, Y., Christianson, D., Alberto, C., Alekseychik, P., Aurela, M., Baldocchi, D., Bansal, S., Billesbach, D., Bohrer, G., Bracho, R., Buchmann, N., Campbell, D., Celis, G., Chen, J., Chen, W., Chu, H., Dalmagro, H., Dengel, S., Desai, A., Detto, M., Dolman, H., Eichlmann, E., Euskirchen, E., Famulari, D., Friborg, T., Fuchs, K., Goeckede, M., Gogo, S., Gondwe, M., Goodrich, J., Gottschalk, P., Graham, S., Heimann, M., Helbig, M., Helfter, C., Hemes, K., Hirano, T., Hollinger, D., Hortnagl, L., Iwata, H., Jacotot, A., Jansen, J., Juraskinki, G., Kang, M., Kasak, K., King, J., Klatt, J., Koebsch, F., Krauss, K., Lai, D., Mammarella, I., Manca, G., Marchesini, L.B., Matthes, J.H., Maximon, T., Merbold, L., Mitra, B., Morin, T., Nemitz, E., Nilsson, M.B., Niu, S., Oechel, W., Oikawa, P., Ono, K., Peichl, M., Peltola, O., Reba, M.L., Richardson, A., Riley, W., Runkle, B., Ryu, Y., Sachs, T., Sakabe, A., Sanchez, C., Schuur, E.A., Schafer, K.V., Sonnentag, O., Sparks, J.P., Stuart-Haentjens, E., Sturtevant, C., Sullivan, R.C., Szutu, D.J., Thom, J.E., Torn, M., Tuittila, E., Turner, J., Ueyama, M., Valach, A.C., Vargas, R. 2021. FLUXNET-CH4: A global, multi-ecosystem dataset and analysis of methane seasonality from freshwater wetlands. Earth System Science Data. 13(7):3607–3689. https://doi.org/10.5194/essd-13-3607-2021.
DOI: https://doi.org/10.5194/essd-13-3607-2021

Interpretive Summary: Methane is an important greenhouse gas, yet large uncertainties remain in the magnitude and seasonality of these measurements. Measurements of methane with the eddy covariance (EC) technique have many benefits over other approaches, yet challenges remain. The first global dataset of methane measured exclusively collected with EC was gathered together from 81 sites globally and made available. The data includes sites from wetlands (freshwater, brackish and saline), rice paddies, lakes, and uplands. Our results provide seasonality parameters for CH4 modeling, and highlight periods where variability remains unexplained (i.e., seasonality of CH4 peak). The FLUXNET-CH4 dataset provides an open-access resource for CH4 flux synthesis, has a range of applications, and is unique in that it includes coupled measurements of important CH4 drivers such as GPP and temperature. Although FLUXNET-CH4 could certainly be improved by adding more sites and by increasing the number of site-years at existing sites, it is a powerful new resource for diagnosing and understanding the role of terrestrial ecosystems and climate drivers in the global CH4 cycle.

Technical Abstract: Methane (CH4) emissions from natural landscapes constitute roughly half of global CH4 contributions to the atmosphere, yet large uncertainties remain in the absolute magnitude and the seasonality of emission quantities and drivers. Eddy covariance (EC) measurements of CH4 flux are ideal for constraining ecosystem-scale CH4 emissions, including their seasonality, due to quasi-continuous and high temporal resolution of flux measurements, coincident measurements of carbon, water, and energy fluxes, lack of ecosystem disturbance, and increased availability of datasets over the last decade. Here, we 1) describe the newly published dataset, FLUXNET-CH4 Version 1.0, the first global dataset of CH4 EC measurements (available at https://fluxnet.org/data/fluxnet-ch4-community-product/). FLUXNET-CH4 includes half-hourly and daily gap-filled and non gap-filled aggregated CH4 fluxes and meteorological data from 81 sites globally: 44 freshwater wetlands, 6 brackish and saline wetlands, 7 formerly drained ecosystems, 7 rice paddy sites, 2 lakes, and 15 uplands. Then, we 2) evaluate FLUXNET-CH4 representativeness for freshwater wetland coverage globally, because the majority of sites in FLUXNET-CH4 Version 1.0 are freshwater wetlands and because freshwater wetlands are a substantial source of total atmospheric CH4 emissions; and 3) provide the first global estimates of the seasonal variability and predictors of freshwater wetland CH4 fluxes. Our representativeness analysis suggests that the freshwater wetland sites in the dataset cover global wetland bioclimatic attributes (encompassing energy, moisture, and vegetation-related parameters) in arctic, boreal, and temperate regions, but only sparsely cover humid tropical regions. Seasonality metrics of wetland CH4 emissions vary considerably across latitudinal bands. In freshwater wetlands (except those between 20° S to 20° N) the spring onset of elevated CH4 emissions starts three days earlier, and the CH4 emission season lasts 4 days longer, for each degree C increase in mean annual air temperature (CH4 peak is not correlated with mean annual air temperature). On average, the onset of increasing CH4 emissions lags soil warming by one month, with very few sites experiencing increased CH4 emissions prior to the onset of soil warming (for sites above 20° N or below 20° S). In contrast, roughly half of these sites experience the spring onset of rising CH4 emissions prior to the spring increase in gross primary productivity (GPP). The timing of peak summer CH4 emissions does not correlate with the timing for either peak summer temperature or peak GPP. Our results provide seasonality parameters for CH4 modeling, and highlight periods where variability remains unexplained (i.e., seasonality of CH4 peak). The FLUXNET-CH4 dataset provides an open-access resource for CH4 flux synthesis, has a range of applications, and is unique in that it includes coupled measurements of important CH4 drivers such as GPP and temperature. Although FLUXNET-CH4 could certainly be improved by adding more sites in tropical ecosystems and by increasing the number of site-years at existing sites, it is a powerful new resource for diagnosing and understanding the role of terrestrial ecosystems and climate drivers in the global CH4 cycle. All FLUXNET-CH4 data can be downloaded from the links in https://fluxnet.org/data/fluxnet-ch4-community-product/, and a complete list of the 81 individual site data DOIs is provided in Table B2.