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What is dissolved oxygen (DO) anyway?
Every living thing takes up oxygen. Oxygen in water is critical for critters to survive.
 Dissolved oxygen in water can be measured in parts per million (ppm). The air we breathe can also be measured in the same units, although the scale is much different. Imagine the room filled with one million white marbles. The air we breathe is composed of about 21% oxygen… which can be measured as 210,000 ppm. Translated to our imagination, that means over 200,000 out of every million marbles would be blue… representing oxygen. We breathe well with 200,000 blue marbles. Fish, and many other aquatic critters, live in their watery world with the oxygen dissolved in water measured between 5 and 20 ppm. Translated, fish only need 5 blue marbles out of every million marbles to survive. This is one good explanation for why we don’t breathe well under water. Below 5 ppm fish and many other aquatic animals begin to stress, and below 3 ppm many can’t survive.
What‘s the deal about dissolved oxygen (DO) in Hood Canal?
 The levels of dissolved oxygen in the canal are also affected by the geology, bathymetry, slow flushing rates, high stratification, sunlight, nutrient inputs (in the form of all the natural and non-natural stuff) and to some degree, the wind.
The sunny, calm days of summer and early fall have a deceptive effect on the marine waters and activity of the marine critters. The increased sunlight which warms our faces and tans our backs, also is the key for processing the nutrient addition in the canal. All the increased biomass (especially algae) eventual dies, falls to the bottom and becomes part of the decomposition process… using up the little bit of oxygen at the bottom.
 Each year in the late summer and into fall, the DO levels below the surface become lower throughout the canal. Based on bathymetry (especially the southern portions of the canal), certain water areas become extremely low in oxygen and that affects the activity and survivability of the critters living on and near the bottom.
A program to monitor the bottom dwelling critters has revealed that those critters which are mobile, tend to move upward in the water column to escape the low levels of DO. The other critters (anemones, sea cucumber, starfish, and others) which are less mobile, become stressed and may perish. In the fall of 2003, rockfish were observed in the shallows and deepwater shrimp were skittering along the shoreline. Shortly afterwards great numbers of marine critters died because the entire water column was without oxygen.
A water sampling program is continuing to monitor the DO and nutrient levels so that we can all further understand how best to take corrective actions.
How do people fit into the picture?
For a long time (since the retreat of the glaciers 10,000 years ago), Hood Canal has adapted to the dynamics that have naturally influenced the waters and marine life there. When looking at the development and growth of the Hood Canal area it is not surprising to learn that human activities are connected to the dynamics influencing the levels of dissolved oxygen. What’s unclear is the magnitude that things such as lawn and garden fertilizers, effluent from septic systems, stormwater run-off, silviculture/agriculture practices, and disposal of yard waste contribute to the low levels of dissolved oxygen. A scientific study is underway to do just that; to measure and model the role that these different practices play in determining oxygen, relative to other natural processes like effects from the ocean and rivers and sunlight.
Each of us that lives in or visits the watershed, whether upland or along the shoreline, influence the water quality of Hood Canal. Whether you come from near or far, we are each stewards of Hood Canal. Please support the current efforts to understand why the low DO events exist and more importantly, think about what we can do to reduce the impact of our activities that may be part of the problem.
Where can I learn more about the DO issue on Hood Canal?
Hood Canal Dissolved Oxygen Program
www.prism.washington.edu/hcdop
Puget Sound Action Team
www.psat.wa.gov
What can I do to lessen my impact on the low DO events in Hood Canal?
Washington Sea Grant Program
www.wsg.washington.edu
Where can I go to get more involved in the project?
Hood Canal Salmon Enhancement Group
www.hcseg.com
Produced by Dan Hannafious
Edited by Renee Rose
Photos credits:
Hood Canal Salmon Enhancement Group
The NatureMapping Program of Washington
Peter Wiant
Richard Bambans
Washington Department of Fish and Wildlife photo files
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