Rivers, sewage-treatment plants carry nitrogen to Sound

Discharge from sewage-treatment plants and rivers — the end repositories of pollutants rinsing off the land, including stormwater — are major sources of nitrogen pollution, a new state study has found.

Excess nitrogen can be a problem because it feeds algae blooms. When the algae dies, it decomposes and sucks oxygen out of the water that fish and other aquatic life need.

Nitrogen pollution is not a problem everywhere in Puget Sound, but in some areas, where water is shallow and embayments tight, with little water circulation, low levels of dissolved oxygen caused by excess nitrogen can be deadly.

So far scientists have found sewage-treatment-plant pipes contribute 80 to 90 percent of the nitrogen in some parts of Puget Sound during some parts of the year, according to the study.

Rivers, air deposition, sediments, septic systems and even the Pacific Ocean also pump nitrogen into Puget Sound.

The findings, reported by the state Department of Ecology, are just the first part of a long-term study, sampling waters from King to Mason counties. Next will come analysis of how water circulates in Puget Sound, how nitrogen is affecting the water quality and what to do about it.

The places in the study area that don't meet state water-quality standards are Carr, Case and Budd Inlets in south Puget Sound.

But whether or how discharge from rivers and sewage-treatment plants is involved in those low dissolved-oxygen levels is yet to be determined. Scientists need to learn how water circulates in the sound, and how the that, in turn, affects water quality.

Some steps have already been taken to combat nitrogen pollution. The sewage treatment plant in Olympia spent $37 million in 1994 to clean nitrogen from plant effluent from April to October, when sunlight and warmer water temperatures encourage algae growth.

Jan Newton, an expert with the University of Washington on dissolved-oxygen problems in Hood Canal, said the problem with nitrogen isn't how much of it there is, but where it is, and when it's present.

In a fast-flushing body of water with a complex seabed that causes mixing of layers of water, nitrogen is dispersed and mixed in the water column, rather concentrated, and available to feed algae. The time of year also matters. Colder months with less sunlight don't see much algae growth.

How a complex system such as Puget Sound, with its differing depths and circulation patterns can be best managed for water quality is something scientists are still working to figure out.

More study can help target places where the combination of nitrogen loads and local circulation patterns and weather combine to harm aquatic life.

When it's complete in 2010, the study may help target where and how to make smart investments in water-quality improvement, said Duane Fagergren of the Puget Sound Partnership, the new state agency created to protect and restore Puget Sound. Fagergren said.

"If we don't have oxygen, we don't have fish and we don't have shellfish, which naturally filter the water," Fagergren said. "We don't have much of anything."

Lynda V. Mapes: 206-464-2736 or lmapes@seattletimes.com