Beavers take a chunk out of nitrogen in Northeast rivers

http://www.eurekalert.org/pub_releases/2015-10/asoa-bta102115.php

Public Release: 21-Oct-2015
Beavers take a chunk out of nitrogen in Northeast rivers
Ponds and slower streams created by the rodents serve as nitrogen sinks
American Society of Agronomy

Beavers, once valued for their fur, may soon have more appreciation in the Northeastern United States. There they are helping prevent harmful levels of nitrogen from reaching the area's vulnerable estuaries. By creating ponds that slow down the movement of water, they aid in removing nitrogen from the water.

Nitrogen levels have been increasing in Northeast waters for years. The use of nitrogen fertilizers has risen and urbanization has brought in influences such as septic systems. This nitrogen is released into small streams and ponds and eventually travels to estuaries, where rivers meet the sea.

High levels of nitrogen in these areas stimulate algal blooms. As these organisms die and decompose, oxygen is consumed from bottom waters, creating low oxygen levels that can generate fish kills. While many know of these dead zones in the Gulf of Mexico, they are also becoming a problem for the plentiful estuaries that comprise the coastline of the Northeast U.S.

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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. Thanks to the conditions brought about by the beaver ponds, this process can remove approximately 5-45% of the nitrogen in the water, depending on the pond and amount of nitrogen present.

"I think what was impressive to us was that the rates were so high," Gold explained. "They were high enough and beavers are becoming common enough, so that when we started to scale up we realized that the ponds can make a notable difference in the amount of nitrate that flows from our streams to our estuaries."

The study also found 12% of the nitrogen gases created in the samples were nitrous oxide, a potent greenhouse gas. However, the scientists pointed out that the high amount was likely a result of some unique experimental conditions and these ponds are not likely to release that much of the gas in nature.

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"Most of these beavers are in areas with smaller streams, not big rivers," Lazar 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."

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"It's noteworthy that the beavers have such an impact on improving nitrogen downstream," Gold said. "We have a species whose population crashed from wide-spread 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."