In their study, the scientists added small amounts of an uncommon, non-radioactive isotope of nitrogen N-15 to streams as a nitrate, which is the most prevalent form of nitrogen pollution, Gregory said. By adding the isotope, they were able to measure how far downstream the nitrate traveled, and analyze what processes removed it from the water.
In addition to the 40 to 60 percent taken up by tiny organisms, the researchers found denitrification accounted for about 19 percent of the nitrogen uptake across all the sites. Denitrification takes place through an anaerobic metabolic process that converts the nitrogen to a harmless gas and releases it into the atmosphere.
Slower moving streams with little oxygen have higher rates of denitrification, though they have other pitfalls, including increased risk to fish and humans because of the microbial stew they foster, Gregory pointed out.
The overall amount of denitrification by streams and rivers was lower than what many scientists had anticipated, he said. We had hoped it would be higher. That makes it even more essential to maintain healthy riparian zones so the organisms have the opportunity to process the nitrogen.
Oregon had even lower levels of denitrification than the national average. Johnson said the combination of high-gradient streams, oxygenated water and porous stream beds is not conducive to the denitrification process.
A lot of streams in Oregon have subsurface water flowing beneath the streambed through the gravel, she pointed ou
|Contact: Stan Gregory|
Oregon State University