Increasing U.S. wetlands by 10% would double nitrogen removal, study finds

Wetlands help to protect against environmental problems such as algal blooms, fish kills and coastal hypoxia. Pictured is the riparian wetland in the boreal forest taiga of Yukon. Photo credit: PiLensPhoto, Adobe Stock.

New computer modeling analysis suggests that prioritizing wetland restoration close to heavily farmed areas may remove up to 40 times more nitrogen than the current approach to wetlands management, which focuses only on achieving “no net loss” of wetland area.

Researchers examined detailed National Wetland Inventory data and nitrogen loads from fertilizer on farm fields throughout the U.S. The model simulations performed by the University of Waterloo in Ontario  and the University of Illinois Chicago suggest that a spatially targeted increase in U.S. wetland area by 10% (or 5.1 million hectares) would double wetland nitrogen removal.

The researchers calculated, for instance, that 868 kilotons of nitrogen from the Mississippi River basin are annually dumped into the Gulf of Mexico. Without wetlands, they estimated the nitrogen load would increase more than 50% to about 1,300 kilotons a year.

Wetlands help to protect against environmental problems such as algal blooms, fish kills and coastal hypoxia.

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“In a warming climate, it is expected that hypoxic zones will grow larger and persist for longer periods, making it of even greater importance to decrease export of excess nutrients from intensively managed landscapes to coastal waters,” the study states.

The researchers also found that wetland restoration in high nitrogen surplus areas has a “strong potential to maximize water quality benefits.”

The cost of the proposed initiative for refocusing wetlands management is estimated at $3.3 billion a year, an amount the researchers describe as feasible given current government spending levels. That is twice the estimated cost of a non-targeted approach and would also require the removal of 2% of total cropland area.

“You get much more bang for your buck if wetland preservation and restoration are targeted,” study co-author and Water Institute member Nandita Basu, told the University of Waterloo. “From a policy perspective, it is dramatically more effective and efficient,” she added.

The study used a recently developed dataset of landscape nitrogen surplus values calculated at a five-kilometre grid scale for the contiguous U.S. to estimate spatially varying inputs to more than 30 million wetlands.

Waterloo engineering PhD student and Collaborative Water Program graduate Danyka Byrnes also contributed to the wetlands study.

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