Scientists show that streams are critical to preservation of oceanic coa...( The plight of the worlds oceans is d...)

The plight of the worlds oceans is dire, according to recent studies, through insults from human-derived activities depopulating and damaging reefs, altering coastlines, and creating pollutants, such as nitrogen runoff from terrestrial watersheds.

A study by 31 aquatic biologists involving 72 stream sites in the United States and Puerto Rico has found that one critical buffer to excess nitrogen run off from agricultural and urban areas turns out to be small streams and rivers. The findings are published March 12 in the journal Nature.

We found that nitrate was filtered from stream water by tiny organisms such as algae, fungi and bacteria, says Patrick Mulholland, lead author of the study and a member of Oak Ridge National Laboratorys Environmental Sciences Division, with a joint appointment at the University of Tennessee. Further, our model showed that the entire stream network is important in removing pollution from stream water.

The study used a rare nitrogen isotope to examine the effects of nitrogen loading in streams. The researchers analyzed its removal relative to the amount of nitrogen present in the stream overall. The results showed that much of the nitrogen was removed by bacteria, in a process called denitrification that releases harmless nitrogen gas to the atmosphere. However, the study also demonstrated that as nitrate loads increase, the efficiency of removal was reduced.

Our study shows that nitrogen loading compromises the ability of streams to retain or transform nitrate, a major pollutant that has been associated with lake and stream eutrophication, groundwater pollution, and coastal dead zones, says Nancy Grimm, an ecologist at Arizona State University who has been involved with the project since the 1980s.

Presently its believed that small streams and rivers remove three-quarters of the excess nitrogen contamination before it reaches the oceans by acting as sinks. However, the researchers f
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