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Background Information

April 2005

The Problem

1. The data collected by the University of Washington, Washington Department of Ecology-Puget Sound Ambient Monitoring Program, and most recently by the Hood Canal Salmon Enhancement Group and its citizen volunteers show that Hood Canal’s dissolved oxygen (DO) concentrations are at their lowest as compared to data from the 1950s, 60s, and 90s.

2. Hood Canal has had a history of seasonally low DO concentrations, which have resulted in fish kills that have been documented over the years, including known records from as early as the 1920s.

3. In recent years the low DO condition in Hood Canal has become more widespread. The area of low DO is getting larger, spreading northwards. The periods of low DO last longer. In fact, during 2003-2004 the DO remained low throughout the wintertime, which is normally when concentrations rebound due to annual input of water from the ocean. This pattern was also evident during much of the late 1990s and the 2000s.

4. Hood Canal suffered significant fish kills during both 2002 and 2003. These events affected thousands of juvenile perch (June 2003), and numerous fish and shellfish (fall 2002 and 2003). A more minor fish kill was observed during September 2004. Low oxygen concentrations that can kill or stress marine life were recorded around the time of these fish kills.

5. Threats to the canal resources are threats to treaty-protected resources. The Tribal Treaty, or usual and accustomed, area, is the majority of the Hood Canal basin. The 1855 Treaty of Point No Point pre-dates Washington statehood.

Sources of the Problem

1. Many factors contribute to the low dissolved oxygen problem in Hood Canal. These include: the circulation and flushing of the canal, which is affected by ocean and river waters; the productivity of algae, which is affected by sunlight and nutrient availability; the total carbon load, which can come from both natural and human sources; and the degree of seawater stratification, which is affected by river, ocean, weather conditions, and local processes, and controls vertical mixing.

2. Hood Canal is unique within Puget Sound. The canal is a glacially carved fjord-like basin that is 60 miles long and very deep (600 feet) in some areas. It has an underwater sill, or a shallow area, at its entrance that constricts the water flow. Scientists estimate that it takes several months to over a year for the water in Hood Canal to exchange. In most other parts of Puget Sound this process takes several days or weeks. The dynamics of circulation and mixing of the canal’s waters are complex and add to the conditions that contribute to the low oxygen.

3. People may be affecting the DO concentration in several ways, including altering the river flows and landscapes, adding excess nutrients and carbon to the waters, and stimulating climate change.

4. Another effect on DO may be due to the changes in biota that have developed over the years as native fauna and flora habitat have been altered.

5. With regard to the role of nutrients, it has been established that algal growth in the stratified waters of Hood Canal is limited by the amount of nitrogen available in the water. This means that the more nitrogen available, the more the algae will bloom and grow, as long as sunlight is available. Hood Canal has the highest sensitivity to nutrient additions in all of Puget Sound.

6. Because algal growth is limited by nitrogen in Hood Canal, the addition of extra nitrogen causes more algae, both seaweed and phytoplankton (small microscopic plants). Too much algae can cause aesthetic problems (noxious blooms) and ultimately reduces oxygen concentrations in the canal as the organic material (algae or the products of its consumption) settles out and decomposes. While algae produce oxygen in the surface waters, decomposition of settled material consumes oxygen that would otherwise be available to fish and other organisms in the deeper waters.

7. Many products of human activity contribute nitrogen to Hood Canal, including fertilizers, human sewage, animal manure, and decaying fish carcasses.

8. The United States Geological Survey (USGS) has made an initial nitrogen load estimate for Hood Canal and separately for Lynch Cove based on available data and information. This estimate is for nitrogen entering from river and stream basins including both natural and human related sources, regional ground water, near shore septic systems, the atmosphere, other human sources (e.g., direct point discharges, salmon carcass disposal) and the ocean. NOTE: The estimates are based on literature values and existing information, which include many assumptions, and are subject to change.