A University of Rhode Island study "shows that while agricultural runoff pumps nitrogen into watersheds, beavers returning to some parts of Rhode Island in larger numbers may be helping restore balance in the makeup of these watersheds"..............Researchers found that the ponds created by the Beaver dams slows the flow of nitrates(from agricultural runoff) going downstream with anywhere from 5 to 45% of the nitrates being trapped in the pond, thus helping to prevent toxic algae blooms which often result in massive die-offs of fish and other water-dwelling creatures

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Beaver Dams Control 

Nitrogen

 Flow in Northeastern 

Rivers

By Joshua Rapp Learn

Posted on November 19, 2015

Image Credit: David Smith, licensed by cc 2.0

Beavers may be providing watersheds a service by removing
some of the agricultural nitrogen runoff in northeast rivers.

“There’s a huge concern about the amount of nutrients of our
 lands that get into coastal waters,” said Arthur Gold, a
 professor and chair of the Department of Natural Resources
Science at the University of Rhode Island and coauthor of a
 study published recently in theJournal of Environmental Quality.

Other ongoing research has examined how beavers may be 
used to landscape watersheds and restore ecosystems 
important for a number of other species.Some of these
problems include toxic algae blooms that are affecting marine
 life in coastal areas as well as in the Great Lakes and other
 areas. Other concerns have been raised about the effect of
 excess nitrogen in Dungeness crabs (Metacarcinus magister),
 Gold said — “It’s a big problem.”

Now this study shows that while agricultural runoff pumps
nitrogen into watersheds, beavers returning to some parts
of Rhode Island in larger numbers may be helping restore
balance in the makeup of these watersheds.

Beaver dams turn free-flowing water into ponds, which
 results in more sediment being trapped. Vegetation starts
to increase in these areas due to a larger storage of nutrients.

“As we looked at the sediment or the soil of the beaver ponds
, we realized there’s a lot of organic soil that’s accumulating,”
 Gold said. “There’s this riot of plant life.”

The researchers wanted to see whether these beaver
 ponds have an effect on nitrogen levels in the water, and
conducted an experiment in which they added isotopically
enriched nitrogen into an aquarium with ecosystems similar
 to those of a beaver dam.

“We could see that the gasses that were coming out of the
 pond actually had this nitrogen in it,” Gold said. “Nitrate
 that normally would be moving down the streams has
been intercepted from the pond and has been removed
 and is back up in the atmosphere.”

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He said this is good news, because it meant that through natural processes, the beaver ponds were not
 just capturing the nitrates, but also removing them from
 the system.

They compared the rates at which nitrogen was being
 removed from the aquariums with the estimated density
of beaver ponds in a square mile in southern New England,
 and estimated the beavers were contributing to the
removal of 5 to 45 percent of the nitrogen from the study
 area.

“We were surprised at how high the rates were.”

Lead author Julia Lazar, who conducted the research as
part of her doctoral dissertation, said that many beaver
dams are showing up in smaller streams rather than on
 big rivers, which could hurt beaver numbers since the
streams are typically the first to be developed.

“So, it may be important to keep these areas from being
 developed so they can have effects on nitrogen levels
 downstream.”