News Feature | November 19, 2015

Beavers An Unlikely Ally In The War On Algae

Sara Jerome

By Sara Jerome,

Nitrates from agricultural runoff are plaguing waterways across the country. They spur the growth of algae that can be so toxic it endangers drinking water services. Residents in Toledo were unable to use their water for over two days when this problem played out in their taps last year.

As water utilities grapple with how to attack the problem from both a political and technological standpoint, they can use all the allies they can find — including those in the animal kingdom.

A study in the Journal of Environmental Quality shows that beavers help reduce nitrogen levels in vulnerable estuaries. They create ponds that slow the pace of water movement, thus aiding the removal of nitrogen from water.

“Beaver-created ponds and dams, on the rise in the northeastern United States, reshape headwater stream networks from extensive, free-flowing reaches to complexes of ponds, wetlands, and connecting streams,” according to the study.

The study focused on nitrate levels in three beaver ponds in Rhode Island. “Beaver ponds represent a relatively new and substantial sink for watershed N if current beaver populations persist,” the study said. “[Due to] the conditions brought about by the beaver ponds, this process can remove approximately 5 to 45 percent of the nitrogen in the water, depending on the pond and amount of nitrogen present.”

A statement from the American Society of Agronomy explained how the study worked.

The researchers tested the transformative power of the soil by taking sample cores and adding nitrogen to them. These samples, about the size of a large soda bottle, were large enough to incorporate the factors that generate chemical and biological processes that take place in the much larger pond. They were also small enough to be replicated, manageable, and measured for numerous changes.

Researchers added nitrogen to the samples and examined how it changed. “Bacteria in the organic matter and soil were able to transform nitrogen, specifically a form called nitrate, into nitrogen gas, removing it from the system. This is denitrification,” the statement said.

A lead researcher on the study, Julia Lazar, explained the potential policy implications of the findings.

“Most of these beavers are in areas with smaller streams, not big rivers,” she said. “These smaller streams are usually the first to be developed, causing a decrease in beaver populations. So, it may be important to keep these areas from being developed so they can have effects on nitrogen levels downstream.”

Another lead researcher, Arthur Gold at the University of Rhode Island, explained the significance of the findings.

“It’s noteworthy that the beavers have such an impact on improving nitrogen downstream,” Gold said. “We have a species whose population crashed from widespread trapping 150 years ago. With their return they help solve one of the major problems of the 21st century. I don’t want to minimize that. We have to remember that those ponds wouldn’t be there without the beavers.”

For the water industry, the major problem with nitrogen in water is that it is linked to the growth of toxic algae in lakes and rivers. President of the American Water Works Association John Donahue explained this point at a House Energy and Commerce subcommittee hearing on Capitol Hill.

“There is no uncertainty about one critical aspect of the problem: It is always associated with amounts of nitrogen and phosphorus in the water,” Donahue said, per Roll Call. “Although each watershed is unique and has its own mix of nutrient sources, across the nation the most prominent uncontrolled sources of nitrogen and phosphorus are non-point sources — that is, runoff. These sources are at the same time both the hardest to manage and the furthest from being subject to meaningful federal regulatory authority.”

For more on nitrogen removal, visit Water Online’s Nutrient Removal Solutions Center.