Atmospheric methane is a potent greenhouse gas that plays a major role in controlling the Earth’s climate. The causes of the renewed increase of methane concentration since 2007 are uncertain given the multiple sources and complex biogeochemistry. Here, we present a metadata analysis of methane fluxes from all major natural, impacted and human-made aquatic ecosystems. Our revised bottom-up global aquatic methane emissions combine diffusive, ebullitive and/or plant-mediated fluxes from 15 aquatic ecosystems. We emphasize the high variability of methane fluxes within and between aquatic ecosystems and a positively skewed distribution of empirical data, making global estimates sensitive to statistical assumptions and sampling design. We find aquatic ecosystems contribute (median) 41% or (mean) 53% of total global methane emissions from anthropogenic and natural sources. We show that methane emissions increase from natural to impacted aquatic ecosystems and from coastal to freshwater ecosystems. We argue that aquatic emissions will probably increase due to urbanization, eutrophication and positive climate feedbacks and suggest changes in land-use management as potential mitigation strategies to reduce aquatic methane emissions.
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J.A.R. and B.D.E. were supported by ARC Grants DP160100248 and LP150100519. A.V.B. is a research director at the Fonds National de la Recherche Scientifique (FNRS). C.S. was supported by The Second Tibetan Plateau Scientific Expedition and Research programme grant 2019QZKK0304. J.M. received funding from NASA grant NNX17AK49G. B.P. acknowledges support from the NASA Terrestrial Ecology Program and the Gordon and Betty Moore Foundation (GBMF5439). D.O. was supported by funding from the Campus Alberta Innovates Program (CAIP). Thanks to M. F. Billett, K. McKenzie and M. Wallin for providing additional information for the streams and rivers dataset. Thanks to A. Grinham, L. Gómez-Gener, T. DelSontro, K. Kuhn and K. Delwich for providing ancillary data to the lake and reservoir dataset. We thank P. del Giorgio and Y. Prairie for providing feedback on earlier versions of this work. We thank J.-J. Chen for translating several Chinese papers. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US Government.
The authors declare no competing interests.
Peer review information Nature Geoscience thanks the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editors: Clare Davis; Rebecca Neely.
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Boxplot showing median, lower (Q1), upper (Q3) quartiles and 1.5 times the length of the interquartile range of diffusive methane fluxes in areas with natural gas seeps, estuarine plumes, upwelling areas and the remaining (other) continental shelves. Differences are statistically significant (Kruskal-Wallis test, p<0.0001).
Natural log (ln) transformed methane fluxes over latitudes of all aquatic ecosystems compiled in this study, and individual plots for rivers and streams, lakes, reservoirs, estuaries, coastal wetlands (mangroves, salt marshes, seagrasses), and continental shelves.
Extended Data Fig. 3 Areal methane fluxes from natural and impacted estuaries, mangroves, and salt marshes.
Boxplots showing median, lower (Q1), upper (Q3) quartiles and 1.5 times the length of the interquartile range of methane fluxes from impacted and more natural (low disturbed) estuaries, mangroves and salt marshes. Several sites that could not be classified as ‘impacted’ or ‘natural’ were excluded from this plot.
Extended Data Fig. 4 Areal methane fluxes from eutrophic, mesotrophic and oligotrophic lakes and reservoirs.
Boxplots showing median, lower (Q1), upper (Q3) quartiles and 1.5 times the length of the interquartile range of total (diffusive and ebullitive) methane fluxes from eutrophic, mesotrophic and oligotrophic lakes and reservoirs.
Extended Data Fig. 5 Areal methane fluxes from coastal wetlands and relationships of methane fluxes versus temperature and salinity.
a) Boxplots showing median, lower (Q1), upper (Q3) quartiles and 1.5 times the length of the interquartile range of methane fluxes from salt marshes, mangroves and seagrasses. b) Linear relationships of coastal wetland methane fluxes and temperature (r2 = 0.04, p = 0.07) and salinity (r2 = 0.02, p = 0.1). Salt marsh extreme methane flux values (n = 2) are not shown.
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Rosentreter, J.A., Borges, A.V., Deemer, B.R. et al. Half of global methane emissions come from highly variable aquatic ecosystem sources. Nat. Geosci. 14, 225–230 (2021). https://doi.org/10.1038/s41561-021-00715-2
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