Study: Streams Vital in Removing Water Pollution

By Eric Beech

 WASHINGTON (Reuters) - Streams play a bigger role than previously thought in removing pollutants before they get to larger waterways, scrubbing as much as half of the excess nitrogen from fertilizer runoff and auto emissions, scientists said on Thursday.  A nationwide study of 12 streams found that the smaller the stream – with its shallow depth and high surface-to-volume ratio -- the more quickly nitrogen was removed, scientists said in the latest edition of the journal Science.  Previously, experts studying pollution focused on larger bodies of water rather than small streams, considering them more like gutters that simply carried nitrogen to lakes, rivers and oceans.  Excess nitrogen can cause ecologically damaging effects in large waterways, including algal blooms, which can kill fish and other aquatic animals. 

 Bruce Peterson of the Marine Biological Laboratory in Woods Hole, Massachusetts, one of the study's 15 co-authors, said the finding could have important implications for land-use policies. He said human efforts to control streams by covering or channeling them have made them less effective at nitrogen removal.  Streams remove nitrogen by providing a habitat for nitrogen-absorbing organisms and by releasing nitrogen from the water into the atmosphere.  ``Small tributary streams in our watersheds, the ones most likely to be plowed under or buried in culverts or destroyed by human activity, have a very important role to play in removing nitrogen from water,'' Peterson said.   ``If we restored and took care of all the small streams on the landscape, our water quality coming down rivers would be greatly improved,'' he said.

 The scientists studied streams in Alaska, Arizona, Kansas, Minnesota, Michigan, New Hampshire, New Mexico, North Carolina, Ohio, Oregon, Puerto Rico and Tennessee.  They dripped trace amounts of ammonium -- a form of nitrogen -- into the streams and measured how much of it was absorbed by plants and animals and how much stayed in the water and was washed downstream. The researchers sampled water, algae and other plant life, bacteria, fungi and insects for six weeks at each site.