Patterns of Potential Methanogenesis Along Soil Moisture Gradients Following Drying and Rewetting in Midwestern Prairie Pothole Wetlands
Current models predict more intense rainstorms and extreme drought events in response to global climate change. In wetlands, greater variation in precipitation may increase fluctuation in wetland size, expanding the area of soil exposed to drying/rewetting cycles and periodic inundation. We investigated the potential impact of these changes on rates of methane (CH4) production from wetland soils along a moisture gradient encompassing open water through a zone of seasonal saturation to dry prairie. We used short (2 day) and long term (7 week) anoxic incubations of soils collected along our gradients to assess how soils exposed to varying levels of saturation would respond to drying/rewetting cycles and inundation. In both incubations, permanently-saturated soils showed the highest initial CH4 production potential. Seasonally-saturated (ephemeral) soils, however, generally produced more CH4 after short term drying and rewetting and after several weeks of anoxic incubation. Observed temporal delays in the onset of rapid CH4 production ranged from 5 to 30 days and were longer in ephemeral than in permanently wet soils. In addition, ephemeral soils showed larger increases in rates of CH4 production following temporal delays, suggesting increased CH4 production as wetlands become more hydrologically dynamic.
KeywordsMethanogenesis Temporal lag Ephemeral wetland Anoxic incubation Climate feedback
Funding for this research was provided by the Margaret A. Cargill foundation, St. Olaf College, and NSF DBI-1004817. Thanks go to Dr. Jean Porterfield, Dr. Stephanie Schmidt, Laurel Lynch, Ellen Daugherty, Katie Halvorson, Karl Lapo, Kateri Salk, Laura Nelson, and Holly Rich for discussion of ideas, and assistance in field and laboratory.
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