Re­search con­firms im­por­tance of buf­fers

The Covington News - - Agriculture & Outdoors - By Dun­can Mansfield

KNOXVILLE, Tenn. — Take care of that lit­tle back­yard stream. You could reap the ben­e­fits next time you draw some wa­ter from the tap or go for a swim at the beach.

An ar­ti­cle pub­lished Tues­day in the jour­nal Na­ture de­scribes the crit­i­cal role small streams play in re­mov­ing nitro­gen pol­lu­tion from fer­til­iz­ers, farm an­i­mal waste, sep­tic tanks and fos­sil fu­els be­fore it reaches large reser­voirs and the ocean.

“That stream in your back­yard isn’t it­self play­ing a dom­i­nate role, but when you add up all the small streams in any net­work they are very im­por­tant,” said Pa­trick Mul­hol­land of the Oak Ridge Na­tional Lab­o­ra­tory and Univer­sity of Ten­nessee who was lead au­thor on the study in­volv­ing 31 re­searchers.

To date, most at­ten­tion has been fo­cused on down­stream prob­lems, he said. That’s where ex­cess nitro­gen can lead to an ex­plo­sive growth of mi­cro­scopic al­gae that can kill sea life. Th­ese red tides can be huge. One cov­ered 25,000 square miles off the gulf coast of Florida in 2005.

“Nitro­gen pol­lu­tion is a very big prob­lem and it is grow­ing,” Mul­hol­land said. “The ar­eas are in­creas­ing both in space and in time.”

But ap­par­ently it could be worse. Re­search sug­gests only about a quar­ter of the nitro­gen en­ter­ing wa­ter­ways from farm and city runoff or acid rain reaches oceans and lakes.

“So the ques­tion is, what hap­pens to the rest of that nitro­gen?” Mul­hol­land said. “There has al­ways been this spec­u­la­tion that maybe small streams or stream net­works are the places we should be look­ing as be­ing very im­por­tant to re­tain­ing the nitro­gen.”

To find out, Mul­hol­land and his col­leagues re­leased and tracked an eas­ily trace­able nitro­gen iso­tope, or ni­trate, in 72 streams in North Carolina, Mas­sachusetts, Kansas, Michi­gan, Ore­gon, Ari­zona, New Mex­ico and Puerto Rico. The streams ran past farms, cities and more un­af­fected ar­eas. They ranged in size from 1 to 5 me­ters across.

The re­searchers found that al­gae, fungi and bac­te­ria in the streams will con­sume a lot of the ni­trate through nat­u­ral pro­cesses — ef­fec­tively stor­ing it or re­mov­ing it by con­vert­ing it into harm­less nitro­gen gas.

Small streams, which can make up 80 per­cent of a wa­ter net­work, do a par­tic­u­larly good job of re­mov­ing nitro­gen when there isn’t too much of it, the re­searchers found. Larger streams do a bet­ter job when the nitro­gen reaches mod­er­ate lev­els.

How­ever, when nitro­gen lev­els be­come high “re­moval be­comes in­ef­fec­tive across all stream sizes,” the ar­ti­cle says.

“You can over­load the sys­tem. At some point, it can­not keep up with the added nitro­gen,” Mul­hol­land said.

Then the sys­tem “acts more like a pipe,” he said. “You ba­si­cally trans­port the nitro­gen right down to the (river’s) mouth.”

The study’s be­gin­ning-to-end con­clu­sion was based on ob­ser­va­tions and mod­el­ing on the Lit­tle Ten­nessee River, which flows from North Carolina into Ten­nessee and feeds the Ten­nessee River sys­tem.

“So it is not like we have to pre­serve all our land­scapes and make them pris­tine,” Mul­hol­land said, so long as streams re­main open and buffered from de­vel­op­ment. “We just need to try to pre­serve the in­tegrity of the stream net­work, which is a very im­por­tant fil­ter.

U.S. For­est Ser­vice

A U.S. Forestry Ser­vice worker main­tains a pre­scribed burn in Su­pe­rior Na­tional For­est. Pre­scribed burns can stim­u­late growth of grasses, im­prove ac­cess to wooded ar­eas and re­duce high fuel lev­els that can lead to wild­fires.

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