Waterfowl Play Key Role in Wetlands' Methane Emissions And Nitrogen Export

December 6, 2016
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Contact: Tim Lucas 919/613-8084 tdlucas@duke.edu

Note: Scott Winton is available for additional comment at (011) 41-76-296-9474 or scott.winton@gmail.com. Curt Richardson is available at curtr@duke.edu or (919) 613-8006.

DURHAM, N.C. – Wetlands managed as waterfowl refuges are potent emitters of methane – an important greenhouse gas – and can release as much nitrogen into the surrounding environment as agricultural fields, a pair of new Duke University studies find.

But there may be relatively simple way that land managers can reduce these impacts, the studies show.

“Wetlands used as waterfowl impoundments are managed seasonally; managers drain water out to allow seeds to germinate in early spring. Our findings suggest that by tweaking when the water is drained – maybe moving up the drawdown dates by a month or so – you may be able to avoid up to 70 percent of the nitrogen export and roughly 80 percent of the methane emissions, while still providing vital overwintering habitat for the birds,” said Scott Winton, a 2016 doctoral graduate of Duke’s Nicholas School of the Environment, who led the study.

U.S. Fish and Wildlife Service wetland managers have a mandate from the Department of the Interior to mitigate greenhouse gas emissions, Winton noted, “so this approach provides a win-win solution for them and the birds.”

Winton published his novel findings, which are the first to document the top-down control waterfowl exert on nutrient cycling and methane emissions in wetlands, Dec. 5 in the peer-reviewed journal Ecology. He also published related findings on nitrogen cycling in waterfowl impoundments on Sept. 29 in another peer-reviewed journal, Air, Water and Soil Pollution.

Curtis J. Richardson, director of the Duke University Wetland Center and John O. Blackburn Distinguished Professor of Resource Ecology at Duke’s Nicholas School, co-authored the studies. Michelle Moorman of the Fish and Wildlife Service co-authored the Sept 29 paper with Winton and Richardson

To conduct their research, the scientists measured methane emissions and nitrogen export over two growing seasons at eight test plots and eight control plots at Mattamuskeet National Wildlife Refuge in eastern North Carolina, a major overwintering habitat for migratory birds. They used static air chambers to measure greenhouse gases, and collected soil and water samples to measure nitrogen dynamics.

“Methane cycling and nitrogen cycling in wetlands are both oxygen-sensitive processes,” Winton explained. “Plants normally facilitate these processes by moving oxygen into waterlogged wetland soils. This allows microorganisms in the soil to breathe, and consume more methane and transform nitrogen.  

“But when birds eat the wetland plants, this oxygen source is lost. Methane emissions become stronger, and the nitrogen cycle stagnates, leading to more nitrogen runoff when impoundments are eventually drained,” he said.  “Our study suggests that if overgrazing occurred on all 141,000 acres of publicly owned waterfowl impoundments in the Southeast, the amount of methane emitted could triple.”

Moving up the spring drawdown dates in waterfowl impoundments could help mitigate these problems, Winton said, because draining the water earlier would provide oxygen to the soils before methane production could reach its peak potential.

Further studies, conducted at an impoundment-wide scale, will be needed to pinpoint how great the reductions in methane emissions and nitrogen pollution might be, based on various drawdown dates.

Funding for the new studies was provided by the Carolina Bird Club, the Duke University Wetland Center endowment and the Duke University Graduate School.

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CITATIONS: “Top-down Control of Methane Emission and Nitrogen Cycling by Waterfowl,” R. Scott Winton, Curtis J. Richardson. Ecology. Dec. 5, 2016. DOI: 10.1002/ecy.1640.

“Waterfowl Impoundments as Sources of Nitrogen Pollution,” R. Scott Winton, Michelle Moorman, Curtis J. Richardson. Air, Water and Soil Pollution. Sept. 29, 2016. DOI: 10.1007/s11270-016-3082-x.
 

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