Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems

• Published in: Nature communications 2023-01, Vol.14 (1), p.42-11, Article 42
• Main Authors: Roth, Florian, Broman, Elias, Sun, Xiaole, Bonaglia, Stefano, Nascimento, Francisco, Prytherch, John, Brüchert, Volker, Lundevall Zara, Maysoon, Brunberg, Märta, Geibel, Marc C., Humborg, Christoph, Norkko, Alf
• Format: Article
• Language: English
• Subjects: 38/23; 631/158/47/4113; 704/106/35/823; 704/106/694/682; 704/829/826; Algae; Archaea; Atmosphere; Carbon Dioxide; Carbon dioxide removal; Carbon Sequestration; Carbon sinks; Climate Change; Climate change mitigation; Climate Research; Coastal ecology; Coastal ecosystems; Ecology; Ecosystem; Ecosystems; Ekologi; Emissions; Environmental Sciences; Geochemistry; Geokemi; Habitats; Humanities and Social Sciences; Klimatforskning; Methane; Methanogenic archaea; Microbiology; Mikrobiologi; Miljövetenskap; multidisciplinary; Oceanografi, hydrologi, vattenresurser; Oceanography, Hydrology, Water Resources; Radiative forcing; Science; Science (multidisciplinary); Seaweeds; Sediments; Vegetation; Wetlands
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-35673-9

Coastal ecosystems can efficiently remove carbon dioxide (CO 2 ) from the atmosphere and are thus promoted for nature-based climate change mitigation. Natural methane (CH 4 ) emissions from these ecosystems may counterbalance atmospheric CO 2 uptake. Still, knowledge of mechanisms sustaining such CH 4 emissions and their contribution to net radiative forcing remains scarce for globally prevalent macroalgae, mixed vegetation, and surrounding depositional sediment habitats. Here we show that these habitats emit CH 4 in the range of 0.1 – 2.9 mg CH 4  m −2  d −1 to the atmosphere, revealing in situ CH 4 emissions from macroalgae that were sustained by divergent methanogenic archaea in anoxic microsites. Over an annual cycle, CO 2 -equivalent CH 4 emissions offset 28 and 35% of the carbon sink capacity attributed to atmospheric CO 2 uptake in the macroalgae and mixed vegetation habitats, respectively, and augment net CO 2 release of unvegetated sediments by 57%. Accounting for CH 4 alongside CO 2 sea-air fluxes and identifying the mechanisms controlling these emissions is crucial to constrain the potential of coastal ecosystems as net atmospheric carbon sinks and develop informed climate mitigation strategies. Coastal ecosystems are promoted as nature-based solutions to climate change. Here, the authors show that natural methane emissions across a variety of vegetated and unvegetated coastal habitats can, however, offset one-third of the carbon sink capacity attributed to atmospheric carbon dioxide uptake.