More intense storms are making it harder for freshwater streams and rivers to act as filters for nitrogen pollution, according to a new UNH study.
The research suggests larger storms could cause more harmful runoff to reach coasts and lakes.
Nitrogen comes from lots of things people put in the land – like fertilizer and sewage. Rain and snow wash that pollution into streams and rivers.
But UNH researcher Wil Wollheim says those waterways can usually clean out the nitrogen before it reaches the coast.
“Basically, there are some bacteria in streams and rivers that can breathe with nitrate instead of with oxygen,” he says.
Wollheim’s study looked at the Oyster River watershed, and found it wasn’t as good at removing nitrates after big storms that caused the river to swell.
“There’s just so much more material getting in that there’s not the demand in the water that can remove enough of it to have an impact,” Wollheim says.
Those extra nitrates in the water can cause algae blooms and other problems when they reach lakes and coastal areas, such as Great Bay, which already struggles with nitrogen pollution.
With big storms expected to become more frequent as the climate changes, Wollheim says towns will need to do more to manage stormwater runoff, so rivers have more time to process it.