Beaver ponds remove nitrogen pollution from streams
Long-known as beneficial ecosystem engineers, beavers not only build important wetland habitats for plants and animals, but also help reduce the amount of harmful nitrogen downstream of their ponds.
A team of scientists, led by Arthur Gold at the University of Rhode Island, took a close look at how beavers help reduce pollution. The research is important because 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.
Nitrogen in these areas stimulate algal blooms that lead to eutrophication of waters, where low oxygen levels can kill fish. Such dead zones are well-known in other areas, especially in the Gulf of Mexico, but they are also becoming a problem for estuaries along the coastline of the Northeast.
“What motivated us initially to study this process was that we were aware of the fact that beaver ponds were increasing across the Northeast,” Gold said. “We observed in our other studies on nitrogen movement that when a beaver pond was upstream, it would confound our results.”
In their study, the researchers tested the transformative power of the soil by taking sample cores and assessing chemical changes.
“I think what was impressive to us was that the rates were so high,” Gold said. “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 percent 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.
The research has some interesting implications. Julia Lazar, who conducted the work as part of her doctoral dissertation and is now working as an environmental consultant, said it might change the way people think about beavers and their ponds.
“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.”
Gold hopes to study the ponds over a longer period and to study abandoned ponds to see if the nitrogen retaining qualities remain after the beavers are gone.
“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.”