Streams remove significant amounts of nitrogen, preventing downstream 'd...( DURHAM N.H. Small streams play a si...)

DURHAM, N.H. Small streams play a significant role in retaining human-generated nitrogen, serving as the kidneys of watersheds by removing nitrogen before it ends up in estuaries and oceans, finds a paper published this week in the journal Nature. University of New Hampshire professor William McDowell and research scientist Jody Potter, both in the department of natural resources, are among the co-authors of the study, led by Patrick Mulholland of the Oak Ridge National Laboratory in Tenn.

The major finding is that streams remove significant amounts of nitrogen thats coming off the landscape, says McDowell, noting that human-generated activities such as agricultural runoff, acid rain, and the human waste stream are major sources of nitrogen. But while this process of denitrification a bacterial process that converts nitrogen to a harmless nitrogen gas -- cleans up waterways, if we overuse it by putting too much nitrogen into the water its not as effective.

Nitrogen removal in streams is important because it reduces the potential for eutrophication the excessive growth of algae and aquatic plants in downstream lakes and coastal marine waters. Eutrophication is linked to problems such as harmful algal blooms and oxygen depletion in places such as the Gulf of Mexico, where the Mississippi River creates a vast dead zone of oxygen depletion with adverse effects on fisheries.

A key finding of the study, titled Stream denitrification across biomes and its response to anthropogenic nitrate loading, is that the effectiveness of streams to remove nitrate was greatest if the streams were not overloaded by nitrogen sources such as fertilizers and wastes from human activities. The largest percentage removal occurred when nitrate entered small healthy streams and traveled throughout the network before reaching larger rivers. As terrestrial ecosystems become increasingly saturated with nitrogen as a result of human activities, the authors cau
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