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More Information on the Low Dissolved Oxygen Problem

The Problem
In the 2004 Water Quality Assessment, 22 locations in South Puget Sound were deemed impaired due to a lack of dissolved oxygen. Another 43 locations were identified as waters of concern. The locations of greatest concern are Carr, Case, and Budd Inlets. Excess nutrients (nitrogen, specifically) is the main pollutant that causes low dissolved oxygen levels. Human related sources of nitrogen come from both point sources (such as wastewater treatment plants) and nonpoint sources (such as fertilizer use and septic systems).

The state's Water Quality Standards sets the minimum dissolved oxygen criteria for protecting aquatic life. The minimum dissolved oxygen criteria in Puget Sound range from 5.0 milligrams of dissolved oxygen per liter (mg/L) to 7.0 mg/L. As the graphic shows, dissolved oxygen levels in South Puget Sound fall below these minimum criteria. In 2003, dissolved oxygen levels in Budd Inlet were as low as 3.1 mg/L. In Case Inlet they dropped to 2.6 mg/L, and in Carr Inlet they were 4.3 mg/L.

What stage are we at in the study?
We are still in the preliminary data collection and data analysis phase. Earlier work, completed in 2002, found that human activities may affect marine water quality. It also showed that additional data collection was needed. 

Is this study a Total Maximum Daily Load (TMDL)?
No. The intent of this study is to collect data and develop models to determine the effects of nitrogen discharges on dissolved oxygen levels in South Puget Sound. The results of the study will help determine if Ecology needs to do a TMDL. If the study shows that something needs be done to protect dissolved oxygen levels in South Puget Sound, either a TMDL or some other plan of action that will result in clean water will be necessary.

How does this study relate to other studies in Puget Sound?
A number of groups are working on projects to improve Puget Sound. Different models are addressing different issues in the Sound. This South Puget Sound dissolved oxygen study will use a model specifically suited for this purpose. For information on other Puget Sound Marine Environmental Modeling work, please visit http://www.psmem.org/.

What is going on in Hood Canal to address dissolved oxygen issues there? There is a separate study in Hood Canal addressing dissolved oxygen issues there. Some of the issues in Hood Canal are similar to the issues facing South Puget Sound. For more information on the Hood Canal Dissolved Oxygen Project, please visit http://www.hoodcanal.washington.edu.

Why is this study starting now?
About $200 million worth of investments in wastewater treatment plants being planned, designed, or constructed right now in South Puget Sound. As the popultion in the Puget Sound region grows, the capacity of wastewater treatment plants will need to increase. The population in the Puget Sound area is expected to increase from 4.2 million in 2005 to 5.1 million in 2020. That is a 21% increase in the next 15 years and a 51% increase between 1991 and 2020. Every additional person in the region produces about ten pounds of additional nitrogen every year, and much of that nitrogen makes its way to Puget Sound. With this much ongoing work and future expansions. Everyone should know how activities impact dissolved oxygen levels in Puget Sound before it is too late.