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1. GRiMeDB: a comprehensive global database of methane concentrations and fluxes in fluvial ecosystems with supporting physical and chemical information

   https://doi.org/10.6073/pasta/f48cdb77282598052349e969920356ef  

   Stanley, Emily H.; Loken, Luke C.; Casson, Nora J.; Oliver, Samantha K.; Sponseller, Ryan A.; Wallin, Marcus B.; Zhang, Liwei; Rocher-Ros, Gerard (January 2023, Environmental Data Initiative)

   The Global River Methane Database (GriMeDB) is a compilation of measurements of CH4 concentrations and fluxes for flowing water environments derived from publications, reports, data repositories, and other outlets between 1973 and 2021. Assembly of GRiMeDB was motivated by the goal of having a centralized, standardized resource to facilitate further studies of CH4 pattern and process in flowing water systems, upscaling efforts, and identification of tendencies in when, where, and how CH4 has been sampled in streams and rivers across the world. Thus, CH4 data are supported by concurrent observations (as available) of aquatic CO2, N2O, temperature, conductivity, pH, dissolved oxygen, nitrogen, phosphorus, organic carbon, and discharge, along with site data (latitude, longitude, elevation, and [as available]: stream order, elevation, channel slope, catchment size, and codes for distinct or disturbed channel types). GRiMeDB includes over 24,000 records of CH4 concentration and greater than 8,000 flux measurements from over 5,000 unique sites, most of which are resolved to the daily time scale. 

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2. GRiMeDB: the Global River Methane Database of concentrations and fluxes

   https://doi.org/10.5194/essd-15-2879-2023  

   Stanley, Emily H.; Loken, Luke C.; Casson, Nora J.; Oliver, Samantha K.; Sponseller, Ryan A.; Wallin, Marcus B.; Zhang, Liwei; Rocher-Ros, Gerard (January 2023, Earth System Science Data)

   Abstract. Despite their small spatial extent, fluvial ecosystems play a significant role in processing and transporting carbon in aquatic networks, which results in substantial emission of methane (CH4) into the atmosphere. For this reason, considerable effort has been put into identifying patterns and drivers of CH4 concentrations in streams and rivers and estimating fluxes to the atmosphere across broad spatial scales. However, progress toward these ends has been slow because of pronounced spatial and temporal variability of lotic CH4 concentrations and fluxes and by limited data availability across diverse habitats and physicochemical conditions. To address these challenges, we present a comprehensive database of CH4 concentrations and fluxes for fluvial ecosystems along with broadly relevant and concurrent physical and chemical data. The Global River Methane Database (GriMeDB; https://doi.org/10.6073/pasta/f48cdb77282598052349e969920356ef, Stanley et al., 2023) includes 24 024 records of CH4 concentration and 8205 flux measurements from 5029 unique sites derived from publications, reports, data repositories, unpublished data sets, and other outlets that became available between 1973 and 2021. Flux observations are reported as diffusive, ebullitive, and total CH4 fluxes, and GriMeDB also includes 17 655 and 8409 concurrent measurements of concentrations and 4444 and 1521 fluxes for carbon dioxide (CO2) and nitrous oxide (N2O), respectively. Most observations are date-specific (i.e., not site averages), and many are supported by data for 1 or more of 12 physicochemical variables and 6 site variables. Site variables include codes to characterize marginal channel types (e.g., springs, ditches) and/or the presence of human disturbance (e.g., point source inputs, upstream dams). Overall, observations in GRiMeDB encompass the broad range of the climatic, biological, and physical conditions that occur among world river basins, although some geographic gaps remain (arid regions, tropical regions, high-latitude and high-altitude systems). The global median CH4 concentration (0.20 µmol L−1) and diffusive flux (0.44 mmolm-2d-1) in GRiMeDB are lower than estimates from prior site-averaged compilations, although ranges (0 to 456 µmol L−1 and −136 to 4057 mmolm-2d-1) and standard deviations (10.69 and 86.4) are greater for this larger and more temporally resolved database. Available flux data are dominated by diffusive measurements despite the recognized importance of ebullitive and plant-mediated CH4 fluxes. Nonetheless, GriMeDB provides a comprehensive and cohesive resource for examining relationships between CH4 and environmental drivers, estimating the contribution of fluvial ecosystems to CH4 emissions, and contextualizing site-based investigations. 

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3. ABCFlux v2: Arctic–boreal CO ₂ and CH ₄ monthly flux observations and ancillary information across terrestrial and freshwater ecosystems

   https://doi.org/10.5194/essd-2025-585  

   Virkkala, Anna-Maria; Wargowsky, Isabel; Vogt, Judith; Kuhn, McKenzie A; Madaan, Simran; O'Keefe, Richard; Windholz, Tiffany; Arndt, Kyle A; Rogers, Brendan M; Watts, Jennifer D; et al (October 2025, Copernicus Publications)

   Abstract. Measurements of surface-atmosphere carbon dioxide (CO2) and methane (CH4) fluxes have been relatively sparse across the Arctic tundra and boreal biomes, causing significant uncertainties in carbon budget estimates from the region. While the availability of Arctic-boreal carbon flux data has increased substantially over the past decade, the data have remained spread across different repositories, scientific articles, and unpublished sources, making it difficult to leverage. Here we present a new dataset of monthly Arctic-boreal carbon fluxes (ABCFlux v2) across terrestrial (wetlands and uplands) and freshwater (lakes and rivers) ecosystems compiled from previous syntheses including the Arctic-boreal CO2 flux database (ABCFlux v1), the Boreal-Arctic Wetland and Lake Methane Dataset (BAWLD-CH4), and the Global River Methane Database (GRiMeDB). In addition, we consider data from general-purpose (e.g., Zenodo) and flux network repositories, literature, and site principal investigators. The dataset includes surface-atmosphere CO2 fluxes of gross primary production (GPP), ecosystem respiration (Reco), and net ecosystem exchange (NEE), alongside CH4 fluxes. For aquatic ecosystems, we split CH4 fluxes into diffusive and ebullitive flux pathways, and included potential emissions from transient storage in the water column (“storage fluxes”), alongside CO2 and CH4 concentrations dissolved in the surface water. Fluxes are measured through a variety of methods including chamber and eddy covariance techniques alongside bubble traps, ice-surveys, and concentration-based turbulence-driven modelling in aquatic ecosystems. The monthly flux data are reported together with supporting methodological and environmental metadata. The resulting ABCFlux v2 has 23,656 flux site-months, 8,182 concentration site-months, and 199 seasonal observations from 1,024 sites, and includes 55,560 reported fluxes (i.e. sum of GPP, Reco, NEE, and CH4 fluxes) from the years 1984 to 2024. The majority of monthly observations occurred after 1999. Wetlands had the highest number of site-month observations (8,641), followed by boreal forest (6,981), lotic ecosystems (6,275), lentic ecosystems (3,725) and upland tundra (3,308). Measurements of CO2 dominated the dataset across most ecosystem types (25,101) except for lentic ecosystems, where CH4 flux site-months (3,024) were more frequent than CO2 flux site-months (2,858). Overall, ABCFlux v2 includes 158 % more site-months for terrestrial CO2 flux data compared to ABCFlux v1. Integrating and updating BAWLD-CH4 flux data from growing season averages to monthly fluxes resulted in 5,671 site-months of chamber CH4 data compared to 762 site-years. This collaborative initiative, involving contributions from over 260 researchers, provides a comprehensive overview of the current state of the Arctic-boreal carbon flux network and its data, and serves as an important step in reducing uncertainties in Arctic-boreal carbon budgets and in enhancing our understanding of climate feedbacks. The data can be accessed at ORNL DAAC at https://doi.org/10.3334/ORNLDAAC/2448 (Virkkala et al., 2025b). 

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

   https://doi.org/10.5194/essd-13-3607-2021  

   Delwiche, Kyle B.; Knox, Sara Helen; Malhotra, Avni; Fluet-Chouinard, Etienne; McNicol, Gavin; Feron, Sarah; Ouyang, Zutao; Papale, Dario; Trotta, Carlo; Canfora, Eleonora; et al (January 2021, Earth System Science Data)

   null (Ed.)

   Abstract. Methane (CH4) emissions from natural landscapes constituteroughly half of global CH4 contributions to the atmosphere, yet largeuncertainties remain in the absolute magnitude and the seasonality ofemission quantities and drivers. Eddy covariance (EC) measurements ofCH4 flux are ideal for constraining ecosystem-scale CH4emissions due to quasi-continuous and high-temporal-resolution CH4flux measurements, coincident carbon dioxide, water, and energy fluxmeasurements, lack of ecosystem disturbance, and increased availability ofdatasets over the last decade. Here, we (1) describe the newly publisheddataset, FLUXNET-CH4 Version 1.0, the first open-source global dataset ofCH4 EC measurements (available athttps://fluxnet.org/data/fluxnet-ch4-community-product/, last access: 7 April 2021). FLUXNET-CH4includes half-hourly and daily gap-filled and non-gap-filled aggregatedCH4 fluxes and meteorological data from 79 sites globally: 42freshwater wetlands, 6 brackish and saline wetlands, 7 formerly drainedecosystems, 7 rice paddy sites, 2 lakes, and 15 uplands. Then, we (2) evaluate FLUXNET-CH4 representativeness for freshwater wetland coverageglobally because the majority of sites in FLUXNET-CH4 Version 1.0 arefreshwater wetlands which are a substantial source of total atmosphericCH4 emissions; and (3) we provide the first global estimates of theseasonal variability and seasonality predictors of freshwater wetlandCH4 fluxes. Our representativeness analysis suggests that thefreshwater wetland sites in the dataset cover global wetland bioclimaticattributes (encompassing energy, moisture, and vegetation-relatedparameters) in arctic, boreal, and temperate regions but only sparselycover humid tropical regions. Seasonality metrics of wetland CH4emissions vary considerably across latitudinal bands. In freshwater wetlands(except those between 20∘ S to 20∘ N) the spring onsetof elevated CH4 emissions starts 3 d earlier, and the CH4emission season lasts 4 d longer, for each degree Celsius increase in meanannual air temperature. On average, the spring onset of increasing CH4emissions lags behind soil warming by 1 month, with very few sites experiencingincreased CH4 emissions prior to the onset of soil warming. Incontrast, roughly half of these sites experience the spring onset of risingCH4 emissions prior to the spring increase in gross primaryproductivity (GPP). The timing of peak summer CH4 emissions does notcorrelate with the timing for either peak summer temperature or peak GPP.Our results provide seasonality parameters for CH4 modeling andhighlight seasonality metrics that cannot be predicted by temperature or GPP(i.e., seasonality of CH4 peak). FLUXNET-CH4 is a powerful new resourcefor diagnosing and understanding the role of terrestrial ecosystems andclimate drivers in the global CH4 cycle, and future additions of sitesin tropical ecosystems and site years of data collection will provide addedvalue to this database. All seasonality parameters are available athttps://doi.org/10.5281/zenodo.4672601 (Delwiche et al., 2021).Additionally, raw FLUXNET-CH4 data used to extract seasonality parameterscan be downloaded from https://fluxnet.org/data/fluxnet-ch4-community-product/ (last access: 7 April 2021), and a completelist of the 79 individual site data DOIs is provided in Table 2 of this paper. 

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5. Flux chamber measurements of natural geologic methane emissions across the United States

   https://doi.org/10.5281/zenodo.19831233  

   Hall, Kathleen; Weber, Thomas; Ihle, Alexander; Scholer, Margaret; Zhu, Mingzhe; Stock, Marika P; Piao, Haoran; Buursink, Marc; Walter_Anthony, Katey; Kunhardt, Lucy; et al (April 2026, Zenodo)

   Natural geologic methane (CH4) emissions remain one of the most uncertain components of the global atmospheric CH4 budget. These emissions encompass the natural seepage of fossil CH4 from the earth to the atmosphere, including from offshore and onshore gas and oil seeps, diffuse microseepage, mud volcanoes, volcanic vents, and geothermal areas. The large uncertainty in this source stems from a disagreement between bottom-up extrapolation of flux measurements and top-down constraints from ice core 14C measurements. Due to this discrepancy, natural geologic sources could contribute 1-30% of the overall fossil CH4 budget. This large, unresolved uncertainty makes it critical to improve estimates of the magnitude of this source to improve the global budget of CH4, quantification of anthropogenic fossil CH4 emissions, and interpretation of the δ13C-CH4 budget. The largest contribution is thought to be from microseepage or the diffuse emission of CH4 over large areas primarily above hydrocarbon accumulations. However, the current dataset of measurements from microseepage is limited in number, geographic extent, and seepage intensity. Thus, more measurements and regional studies are needed to benchmark new and existing inventories of natural geologic CH4 emissions. To increase the number of CH4 flux measurements of microseepage, this project collected measurements across several hydrocarbon-bearing sedimentary basins across the United States: the Appalachian, Michigan, San Juan, Raton, and Denver-Julesburg basins. These basins ranged from low to high in their predicted level of seepage. Flux measurements were collected such that seepage hotspots were captured and a wide spatial coverage was achieved across the basins. The flux of CH4 from the ground to the atmosphere was measured using closed dynamic flux chambers connected to online, portable greenhouse gas analyzers (a Picarro G4302 and a Los Gatos Research Ultra-Portable Greenhouse Gas Analyzer (CH4/CO2)), which measured CH4 mole fraction. Each site or group of flux measurements (5-10 within ~50 m) was accompanied by measurements of air temperature, barometric pressure, soil temperature, and wind speed. For each measurement, soil moisture was measured and latitude and longitude coordinates were collected with GPS. The dataset includes measurements of both microseepage and miniseepage around seeps. The ~3,300 CH4 fluxes across the 344 sites sampled represent one of the largest datasets collected across the largest geographic extent with a main focus on microseepage.   By using this dataset, the users agree to give fair credit to the dataset authors. This means reaching out to the authors early in the process to discuss whether co-authorship may be appropriate.   This work was funded by NSF Award AGS-2039234 (to VVP and TSW) and the David and Lucille Packard Foundation Fellowship for Science and Engineering (to VVP).   For more information on methods and data interpretation, see: Hall KR, Weber TS, Stock MP, Buursink ML, Piao H, Zhu M, Walter Anthony KM, Petrenko VV. 2026. New measurements indicate that natural geologic methane emissions from microseepage in the Michigan Basin are likely negligible. Elem Sci Anth 14(1): 00058. doi: 10.1525/elementa.2025.00058 Kazemi R, Schlageter W, Hmiel B, Weber TS, Murray LT, Petrenko VV. 2021. Investigating methane emissions from geologic microseepage in Western New York State, United States. Elementa: Science of the Anthropocene 9(1): 00066. doi: 10.1525/elementa.2020.00066 Scholer, M. R., Hall, K. R., Weber, T. S., Buursink, M. L., Zhu, M., Ihle, A. C., Hencmann, D., Smith, A. M., Anthony, K. M. W., and Petrenko, V. V.: Bottom-up characterization of geologic methane emissions in the San Juan Basin in the southwestern USA, Elem Sci Anth, 14, 00061, https://doi.org/10.1525/elementa.2025.00061, 2026. 

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