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Department of Ecology News Release - October 29, 2007
07-324
OLYMPIA - A just-released report by the Department of Ecology (Ecology) draws a connection between winds, water circulation and low dissolved oxygen patterns in South Puget Sound. This information helps Ecology determine where human impacts on low dissolved oxygen are most critical.
The report shows how wind might affect where areas of low dissolved oxygen occur in South Sound, informing all who work to manage the low-oxygen problem in the South Sound.
Fish and aquatic life depend on dissolved oxygen for survival, and can die if there is not enough dissolved oxygen in the water.
"We already know how sensitive South Puget Sound is to low dissolved oxygen and that nutrients from sources like sewage treatment plants, septic tanks and lawn fertilizers contribute to the problem," said Robert Duff, manager of Ecology's environmental assessment program. "Although people can't control the wind, everyone can help protect South Sound's dissolved oxygen. It makes a difference when people cut back on fertilizers, maintain home septic systems, properly dispose of boat sewage, pick up pet waste, and control stormwater runoff from their property."
Low dissolved oxygen is primarily caused by bacterial decomposition of plant and animal matter, which requires oxygen. Excess nutrients added to the water can fuel the problem. Nutrients feed phytoplankton causing algae blooms, and as the tiny organisms die and sink, they decompose, using up vital oxygen in the process. If dissolved oxygen gets too low, fish and other marine animals may suffocate. Anything that discourages mixing of surface-to-deeper water, such as stratification (layering) or slow overall water circulation can worsen dissolved oxygen levels.
Ecology's report is called "Estuarine Flow in the South Basin of Puget Sound and its Effects on Near-Bottom Dissolved Oxygen" by Skip Albertson, Julia Bos, Greg Pelletier and Mindy Roberts.
The report finds that wind patterns determine the net direction of water circulation around Harstine Island. It finds also that circulation patterns influence levels of dissolved oxygen near the bottom of the water.
The tides have a major effect on water movement, sloshing it back and forth. The movement of the water after subtracting out the effects of the tides is called net circulation.
For example, the report finds that winds coming from the north cause the net circulation of water to be in a clockwise circle around Harstine Island.
"A person standing at the shore would never see this clockwise movement because it's a 'two steps forward, one step back' process because of tides," said report co-author Skip Albertson. "We discovered that these northerly winds are better for Budd Inlet's dissolved oxygen, but they are worse for dissolved oxygen in Case and Carr inlets."
The more predominant winds coming from the south, however, cause the water on the surface to move eastwardly at both the north and south ends of Harstine Island rather than encircling the island. This pattern improves dissolved oxygen levels in Case and Carr inlets and worsens dissolved oxygen in Budd Inlet.
Ecology is still investigating why these differences in wind and circulation seem to affect dissolved oxygen.
To help reach these conclusions, Ecology scientists released two simultaneous current meters in Dana and Pickering Passages for several months. The scientists factored in the results from an earlier study in which tens of thousands of surface drift cards were released, then collected and mapped.
Ecology has many other efforts focused on the South Sound. The largest overall study is the South Puget Sound Dissolved Oxygen Study. It is also leading studies to improve water quality in the Budd Inlet-Deschutes River watershed, Oakland Bay, and in Nisqually, Henderson, Eld and Totten inlets.
The Ecology report and short audio PowerPoint synopsis are available online at http://www.ecy.wa.gov/biblio/0703033.html.
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Media contact: Sandy Howard, 360-407-6408; cell 360-791-3177; email srud461@ecy.wa.gov
What you can do to help protect dissolved oxygen in Puget Sound: http://www.ecy.wa.gov/puget_sound/dissolvedO2_help.html
Ecology's environmental assessment program: http://www.ecy.wa.gov/programs/eap/index.html
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.
