Regulators of coastal wetland methane production and responses to simulated global change

• Published in: Biogeosciences Vol. 14; no. 2; pp. 431 - 446
• Main Authors: Vizza, Carmella, West, William E, Jones, Stuart E, Hart, Julia A, Lamberti, Gary A
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 26.01.2017; Copernicus Publications
• Subjects: Aquatic plants; Atmospheric models; Availability; Bacteria; Budgets; Chemical analysis; Climate change; Coastal aquifers; Coastal effects; Coasts; Computer simulation; Copper; Ecosystems; Emissions; Environmental aspects; Environmental changes; Environmental impact analysis; Fresh water; Freshwater; Greenhouse gases; Incubation period; Inland water environment; Marine ecosystems; Methane; Methane production; Methanogenic bacteria; Methods; Microbial activity; Microorganisms; Organic matter; Productivity; Regulators; Rivers; Saline water intrusion; Salinity; Salinity effects; Salinity gradients; Salt water intrusion; Sea level; Seawater; Seawater intrusion; Sediment; Sediments; Sulfate reduction; Sulfate-reducing bacteria; Sulfates; Sulphate reduction; Water analysis; Wetlands; United States > US; Alaska; Copper River; Gulf of Alaska
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-14-431-2017

Wetlands are the largest natural source of methane (CH4) emissions to the atmosphere, which vary along salinity and productivity gradients. Global change has the potential to reshape these gradients and therefore alter future contributions of wetlands to the global CH4 budget. Our study examined CH4 production along a natural salinity gradient in fully inundated coastal Alaska wetlands. In the laboratory, we incubated natural sediments to compare CH4 production rates between non-tidal freshwater and tidal brackish wetlands, and quantified the abundances of methanogens and sulfate-reducing bacteria in these ecosystems. We also simulated seawater intrusion and enhanced organic matter availability, which we predicted would have contrasting effects on coastal wetland CH4 production. Tidal brackish wetlands produced less CH4 than non-tidal freshwater wetlands probably due to high sulfate availability and generally higher abundances of sulfate-reducing bacteria, whereas non-tidal freshwater wetlands had significantly greater methanogen abundances. Seawater addition experiments with freshwater sediments, however, did not reduce CH4 production, perhaps because the 14-day incubation period was too short to elicit a shift in microbial communities. In contrast, increased organic matter enhanced CH4 production in 75 % of the incubations, but this response depended on the macrophyte species added, with half of the species treatments having no significant effect. Our study suggests that CH4 production in coastal wetlands, and therefore their overall contribution to the global CH4 cycle, will be sensitive to increased organic matter availability and potentially seawater intrusion. To better predict future wetland contributions to the global CH4 budget, future studies and modeling efforts should investigate how multiple global change mechanisms will interact to impact CH4 dynamics.