Despite millions of dollars spent on research in Hood Canal, the precise causes of low-oxygen problems in Southern Hood Canal are still not fully understood, according to a report released this week by the U.S. Environmental Protection Agency and the Washington Department of Ecology.
News articles about the report have created some confusion, and I’ll get to that in a moment.
As I reported in Tuesday’s Kitsap Sun, research has not proven that nitrogen from human sources is responsible for a decline in oxygen levels greater than 0.2 milligrams per liter anywhere in Hood Canal. That number is important, because it is the regulatory threshold for action under the Clean Water Act.
Mindy Roberts, one of the authors of the report, told me that scientists who have worked on the low-oxygen problem have gained an appreciation for Hood Canal’s exceedingly complex physical and biological systems. So far, they have not come to consensus about how much human inputs of nitrogen contribute to the low-oxygen problems in Lower Hood Canal.
The report, which examined the complexity and scientific uncertainty about these systems, seems to have generated some confusion, even among news reporters. I think it is important to understand two fundamental issues:
1. The deep main channel of Hood Canal is almost like a separate body of water from Lower Hood Canal (also called Lynch Cove in some reports). This area is generally defined as the waters between Sisters Point and Belfair. Because Lower Hood Canal does not flush well, low-oxygen conditions there are an ongoing and very serious problem.
2. Fish kills around Hoodsport cannot be equated or even closely correlated with the low-oxygen conditions in Lower Hood Canal. The cause of these fish kills was not well understood a decade ago, but now researchers generally agree that heavy seawater coming in from the ocean pushes up a layer of low-oxygen water. When winds from the south blow away the surface waters, the low-oxygen water rises to the surface, leaving fish no place to go.
I’m not aware that researchers were blaming nitrogen from septic systems for the massive episodic fish kills, as Craig Welch reports in the Seattle Times. At least in recent years, most researchers have understood that this was largely a natural phenomenon and that human sources of nitrogen played a small role, if any, during a fish kill.
The question still being debated is how much (or how little) humans contribute to the low-oxygen level in the water that is pushed to the surface during a fish kill and whether there is a significant flow of low-oxygen water out of Lower Hood Canal, where oxygen conditions are often deadly at the bottom.
The new report, which was reviewed by experts from across the country, concludes that fish kills can be explained fully without considering any human sources of nitrogen. Evidence that low-oxygen water flows out of Lower Hood Canal in the fall is weak, the report says, though it remains a subject of some debate.
“We have not demonstrated that mechanism to their satisfaction,” Jan Newton of the Hood Canal Dissolved Oxygen Program told me in an interview. “We never said it caused the fish kill, only that it can reduce the oxygen level below what it was. In some years, it wouldn’t matter, but in some years it would make it worse.”
A cover letter (PDF 83 kb) to the EPA/Ecology reports includes this:
“While the draft report concludes that although human-caused pollution does not cause or contribute to the fish kills near Hoodsport, our agencies strongly support additional protections to ensure that nitrogen and bacteria loadings from human development are minimized.
“Water quality concerns extend beyond low dissolved oxygen and include bacteria and other pathogens that limit shellfish health. Overall, human impacts to Hood Canal water quality vary from place to place and at different times of year. Hood Canal is a very sensitive water body and people living in the watershed should continue their efforts to minimize human sources of pollution.”
One of the most confounding factors is the large amount of nitrogen born by ocean water that flows along the bottom of Hood Canal. An unresolved but critical questions is: How much of that nitrogen reaches the surface layer, where it can trigger plankton growth in the presence of sunlight?
Plankton growth is a major factor in the decline of oxygen levels, because plankton eventually die and decay, consuming oxygen in the process.
Human sources of nitrogen often enter Hood Canal at the surface, but researchers disagree on how much of the low-oxygen problem can be attributed to heavy seawater that reaches the sunny euphotic zone near the surface.
Here are the principal findings in the EPA/Ecology report, “Review and Synthesis of Available Information to Estimate Human Impacts to Dissolved Oxygen in Hood Canal” (PDF 3.8 mb).
