Top-down control of methane emission and nitrogen cycling by waterfowl.
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Aquatic herbivores impose top-down control on the structure of wetland ecosystems, but the biogeochemical consequences of herbivory on methane (CH4 ) and nitrogen (N) are poorly known. To investigate the top-down effects of waterfowl on wetland biogeochemistry, we implemented exclosure experiments in a major waterfowl overwintering wetland in the southeastern United States over two growing seasons. We found that herbivory inhibited the oxidation of CH4 , leading to a mean increase in emission by 230% over control plots, and prevented nitrification, as indicated by low nitrate availability and undetectable emissions of nitrous oxide. Herbivory reduced belowground biomass of macrophytes, retarding the subsequent spring emergence of aerenchymous stems, effectively starving wetland soils of oxygen necessary for CH4 oxidation and nitrification. The recognition that important populations of aquatic herbivores may influence the capacity for wetlands to emit greenhouse gases and cycle N is particularly salient in the context of climate change and nutrient pollution mitigation goals. For example, our results suggest that (1) annual emissions of 23 Gg CH4 /yr from ~57 000 ha of publicly owned waterfowl impoundments in the southeastern United States could be tripled by overgrazing and that (2) waterfowl impoundments may export as much N as agricultural fields. We discuss potential implications for habitat management in the context of historic wetland loss and waterfowl population recovery.
Published Version (Please cite this version)10.1002/ecy.1640
Publication InfoRichardson, Curtis J; & Winton, RS (2017). Top-down control of methane emission and nitrogen cycling by waterfowl. Ecology, 98(1). pp. 265-277. 10.1002/ecy.1640. Retrieved from http://hdl.handle.net/10161/15699.
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John O. Blackburn Professor
Curtis J. Richardson is Professor of Resource Ecology and founding Director of the Duke University Wetland Center in the Nicholas School of the Environment. Dr. Richardson earned his degrees from the State University of New York and the University of Tennessee. His research interests in applied ecology focus on long-term ecosystem response to large-scale perturbations such as climate change, toxic materials, trace metals, flooding, or nutrient additions. He has specific interests in phosphor