Luke C. Loken Nora J. Casson Samantha K. Oliver Ryan A. Sponseller Marcus B. Wallin Liwei Zhang Gerard Rocher-Ros Emily H. Stanley 2023 <p><span>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 (</span><span class="inline-formula">CH₄</span><span>) into the atmosphere. For this reason, considerable effort has been put into identifying patterns and drivers of&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;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&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;concentrations and fluxes and by limited data availability across diverse habitats and physicochemical conditions. To address these challenges, we present a comprehensive database of&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;concentrations and fluxes for fluvial ecosystems along with broadly relevant and concurrent physical and chemical data. The Global River Methane Database (GriMeDB;&nbsp;</span><a href="https://doi.org/10.6073/pasta/f48cdb77282598052349e969920356ef" data-mce-href="https://doi.org/10.6073/pasta/f48cdb77282598052349e969920356ef">https://doi.org/10.6073/pasta/f48cdb77282598052349e969920356ef</a><span>, Stanley et al.,&nbsp;2023) includes 24 024 records of&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;concentration and 8205&nbsp;flux measurements from 5029&nbsp;unique sites derived from publications, reports, data repositories, unpublished data sets, and other outlets that became available between 1973 and 2021.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&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;fluxes, and GriMeDB also includes 17 655 and 8409&nbsp;concurrent measurements of concentrations and 4444 and 1521 fluxes for carbon dioxide (</span><span class="inline-formula">CO₂</span><span>) and nitrous oxide (</span><span class="inline-formula">N₂O</span><span>), respectively. Most observations are date-specific (i.e., not site averages), and many are supported by data for&nbsp;1 or more of 12&nbsp;physicochemical variables and 6&nbsp;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&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;concentration (0.20 </span><span class="inline-formula">µmol L⁻¹</span><span>) and diffusive flux (0.44 _{mmol m^-2 d^-1}</span><span>) in GRiMeDB are lower than estimates from prior site-averaged compilations, although ranges (0 to 456 </span><span class="inline-formula">µmol L⁻¹</span><span>&nbsp;and&nbsp;</span><span class="inline-formula">−</span><span>136 to 4057 _{mmol m^-2 d^-1}</span><span>) 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&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;fluxes. Nonetheless, GriMeDB provides a comprehensive and cohesive resource for examining relationships between&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;and environmental drivers, estimating the contribution of fluvial ecosystems to&nbsp;</span><span class="inline-formula">CH₄</span><span>&nbsp;emissions, and contextualizing site-based investigations.</span></p> application/pdf 10.5194/essd-15-2879-2023 en Copernicus Publications GRiMeDB: The Global River Database Methane Database of concentrations and fluxes article