Friday, March 14, 2008

Nitrogen waste cleaned up by healthy streams

The best way to fight disease is robust good health, and that applies to rivers and bays as well as people. Healthy rivers can shrug off nitrogen pollution, and avoid the dread of eutrophication and resulting dead zones.

Nitrogen runoff kills rivers and bays, creating dead zones by over-fertilizing and using up oxygen. But now there's a new option on the table for solving the problem, healthy rivers. A big new study says healthy rivers can suck up nitrogen and use it as fertilizer for healthy growth of plants and animals, instead of the unhealthy overgrowth of eutrophication. Go healthy rivers!!

This isn't to say that healthy rivers can use up any amount of nitrogen we throw at them. There are limits to how much nitrogen can be consumed even by healthy rivers. But this new finding is important because the value of healthy rivers is largely ignored in efforts to control eutrophication and eliminate dead zones. Instead, the dominant emphasis is on controlling nitrogen runoff, which is important but so far hasn't solved the problem.

Nitrogen waste from fertilizers and sewage is a big problem. The famous Gulf of Mexico dead zone comes from excess fertilizer runoff in the farm belt. The nitrogen fertilizes algae blooms and the algae rot and use up oxygen, killing oysters, fish and most underwater animals.

A gigantic study of rivers and streams from around the US has brought clear consensus on an urgent message: We need healthy stream ecosystems to clean up nitrogen waste.

Healthy stream and river ecosystems consume nitrogen and convert some to animal bodies, while some goes into the atmosphere in bacterial magic called denitrification.

It would be interesting to do a cost/benefit analysis, and I assume that'll be a next step for these scientists. How much does it cost to stop nitrogen runoff at the source, compared to maintaining healthy rivers and consuming the nitrogen in streams and rivers?

3 comments:

Anonymous said...

West coast salmon decline and excess nitrogen pollution more than a little related. One of the generally unrecognized limiting factors for coastal oregon salmon habitat health recovery is likely excess spillover of large amounts of reactive nitrogen species to soils and streams from anthropogenic forest vegetative changes. Percent cedar has been drastically reduced while percent alder has been greatly increased. Nitrogen fixation now often exceeds the ability of the vetetation to buffer the water. Freshwater acidification with accelerated calcium leaching and flushing may be very detrimental to low calcium salmon habitat streams.
Ray Kinney

Wolfman said...

Interesting post, but I couldn't easily grasp from the article what exactly constituted a "healthy" stream. Regardless, I'm all for "healthy" streams and my guess is that they include natural stream flows, chemistry, and natural biological diversity, balance and abundances.

The role of fish in maintaining "healthy" streams, and "healthy" oceans for that matter, is not always fully recognized. For those interested in the role of fish, a paper entitled "Loss of a Harvested Fish Species Disrupts carbon Flow in a Diverse Tropical River" (Taylor et al, 2006; http://www.sciencemag.org/cgi/content/full/313/5788/833) provides an excellent example of this, including a very striking visual image of the change in stream "health", brought about by the exclusion of fish from one side of a stream. In fact, the authors showed that the striking changes in stream "health" demonstrated by their experiment were largely due to the loss of a single fish species that happens to be heavily targeted for harvest in the region.

PS: I would have posted the image, but my limited technical capacity could not grasp how to paste a picture into my response.

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