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Close call, but Hood Canal may escape a major fish kill this fall

With some luck, southern Hood Canal may avoid a major fish kill this year, as we observe extremely low oxygen levels beginning to dissipate.

oxygen

It looks like the fish around Hoodsport dodged a bullet on Friday when south winds pushed the surface layer of oxygenated water to the north, bringing hypoxic waters up from below, according to data from the Ocean Remote Chemical Analyzer (ORCA) buoy near Hoodsport.

University of Washington researchers watching the conditions issued this alert on Friday: “Hypoxic waters have been observed intermittently at the surface at our Hoodsport mooring — in addition to the Twanoh mooring —consistent with the strong southerly winds and upwelling conditions we’ve been seeing over the past few days.”

Seth Book, who monitors the water conditions for the Skokomish Tribe, said he was on vacation last week and did not make his usual rounds to observe potential fish kills. But we have not heard of any reports of dead or dying marine life along the shores of Hood Canal.

The risk of a fish kill is still present, and another strong wind out of the south has the potential to bring more low-oxygen water to the surface. The layers of water and the timing appear similar to last year, when south winds brought deep-water fish — such as ratfish — to the surface, as Seth recorded in a video. See Water Ways, Sept. 1, 2015.

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Each summer, sunny weather brings a growth of phytoplankton that eventually dies, sinks to the bottom and decays, a process that consumes oxygen. The result is extremely low levels of oxygen near the bottom of Hood Canal, a situation that continues until a surge of seawater in late summer or fall pushes in from the Pacific Ocean.

Because of its higher salinity, that seawater comes in along the bottom and pushes up the low-oxygen water, which gets sandwiched between the ocean water and the more oxygenated water near the surface. If the surface layer gets displaced suddenly by the wind, the fish have no place to go to get oxygen. That appeared to be the condition on Friday, but now the middle layer is growing thinner as it mixes with the layers above and below.

Conditions are improving, Seth confirmed, “but the negative side of me still says we have low D.O.” Crabs, shrimp and deep-water fish may be out of the woods for this year, thanks to higher levels of oxygen in the incoming seawater, but mid-level fish are still at risk until the water column equalizes to a greater extent.

In July, areas farther north in Hood Canal, such as Dabob Bay, experienced low-oxygen conditions, which drove a variety of fish to the surface, Seth told me. Of particular interest were thousands of Pacific herring trying to breathe by staying in the upper foot of water along the shore.

“We have dodged something so far this year,” Seth said. “I am hopeful because we are now into September and we can see this intrusion continuing.”

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Low-oxygen scenario following unusual course this year in Hood Canal

Death came early to Hood Canal this year, demonstrating just how odd and unpredictable ocean conditions can be.

Fish kills caused by low-oxygen conditions in southern Hood Canal usually occur in late September or October. That’s when low-oxygen waters near the seabed are pushed upward by an intrusion of heavier water coming in from the Pacific Ocean and creeping along the bottom. Winds out of the south can quickly blow away the surface waters, leaving the fish with no escape.

That’s basically what happened over the past month, as conditions developed about a month earlier than normal. South winds led to reports of fish dying and deep-water animals coming to the surface to get enough oxygen, with the worst conditions occurring on Friday. Check out the video on this page by Seth Book, a biologist with the Skokomish Tribe, who found deep-water ratfish swimming near the surface.

The story of this year’s strange conditions actually begins about a year ago and involves a 1,000-mile-long “blob” of unusually warm ocean water off the West Coast. State Climatologist Nick Bond, who coined the term “blob,” explains its formation in an article in Geophysical Research Letters with a summarized description by Hannah Hickey in UW Today.

The warm, low-density coastal waters related to the blob came into Hood Canal on schedule last fall, but they were not dense enough to flush out the low-oxygen waters, according to University of Washington oceanographer Jan Newton.

Hood Canal entered 2015 with the least-dense waters at depth over the past 10 years. They remained in a hypoxic state, meaning that levels were below 2.5 parts per million. Sea creatures unable to swim away can be unduly stressed and unable to function normally at that level. Conditions worsened into the summer, when the hypoxic layer at Hoodsport grew to about 300 feet thick.

By then, the annual intrusion of deep seawater with somewhat elevated oxygen levels was on its way into Hood Canal, spurred on by upwelling off the coast. This year’s waters are more normal in density, though their arrival is at least a month early. By August 9, the hypoxic layer at Hoodsport was reduced from 300 to 60 feet, pushed upward by the denser water.

It’s always interesting to see this dynamic play out. The layer of extreme low-oxygen water becomes sandwiched between the higher-oxygen water pushing in from the ocean and the surface water, which ordinarily stays oxygenated by winds and incoming streams. Without south winds, the middle low-oxygen layer eventually comes up and mixes into the surface layer.

If south winds come on strong, however, the surface layer is blown to the north, causing the low oxygen water to rise to the surface. Fish, shrimp and other creatures swim upward toward the surface, trying to stay ahead of the rising low-oxygen layer. When the low-oyygen layer reaches the surface, fish may struggle to breathe in the uppermost mixing layer. Unfortunately, the fish have no way of knowing that safer conditions lie down below — beneath the low-oxygen layer and within waters arriving from the ocean.

Jan Newton reported that the low oxygen levels in southern Hood Canal earlier this year were the most extreme measured over the past 10 years. So far, however, the fish kills don’t seem as bad as those in 2003, 2006 and 2010, she said.

The graph below shows how the deep layer coming in from the ocean at 279 feet deep contains more oxygen than the middle layer at 66 feet deep. The surface layer, which normally contains the most oxygen, dipped to extremes several times near the beginning of August and again on Friday, Aug. 28. These data, recorded from a buoy near Hoodsport, are considered unverified.

Graph

Will Hood Canal experience a fish kill this year?

UPDATE, Sept. 26
The Hoodsport monitoring buoy was placed back online yesterday. The dissolved oxygen levels at the surface are much higher now than they were two weeks ago, coming up to about 9 milligrams per liter at a 10-foot depth. But oxygen levels in the middle layer remain about the same — about 2.5 milligrams per liter. And the middle layer still contains less oxygen than levels close to the bottom, which is getting an infusion of heavy seawater from the ocean.

A south wind could still bring low-oxygen waters to the surface, but I don’t believe the levels are low enough to cause a fish kill. Still, the low-oxygen water could force deep-water fish to move upward in the water column. I’m waiting to hear from divers if they are seeing anything unusual, and I’ll let you know if conditions take a turn for the worse.
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Are we about to see one of the infamous fish kills that we have observed in Southern Hood Canal in past years?

I am unable to sound any alarms at this time, but if you live in the Hoodsport-Potlatch area or are scuba diving nearby, you might want to watch for dead fish on the surface, rockfish or shrimp swimming in shallow water, or wolf eels and octopuses acting strangely.

Low 02 9-17

Usually, we can look to the monitoring buoy offshore of Hoodsport to answer questions about whether fish are starving for oxygen. The buoy tells us about dissolved oxygen levels at all depths. I watch this buoy every fall for clues about dangerous conditions, such as when the surface and middle layers of Hood Canal become depleted of oxygen.

Unfortunately, the Hoodsport ORCA buoy has been down for most of the past 10 days. University of Washington technicians are trying to get it back in operation, but it appears to be an Internet/local-network problem at the moment.

As of Sept. 10, the surface layer at 10 feet deep was down to less than 2 milligrams per liter, an alarming level, and conditions were not much better at 66 feet. (See chart.) That means there is a lot of low-oxygen water that could be brought to the surface when we get a wind blowing out of the south. Well, we’ve had some moderate south winds today, and I’m wondering what is happening out there right now.

South winds blow the surface layer away and bring low-oxygen water up from the depths. Fish may come to the surface seeking better conditions, but they may find oxygen levels even worse as they go up — and the fish have no idea that better conditions may lie below.

So far, I have not seen any concerns posted on the Facebook pages of divers who may have gone out recently. Feel free to post a comment to this blog or send me an email (cdunagan@kitsapsun.com) if you see or hear anything that can contribute to the discussion.

A statewide hotline used to report oil spills also will take your calls and alert biologists to reports of dead fish. That number is (800) OILS-911.

With some luck, the UW folks will have the Hoodsport buoy back on line in the next couple days and we’ll see if conditions have improved or gotten worse. For now, we’ll just have to wait. The chart is generated by the Data Explorer at the Northwest Association of Networked Ocean Observing Systems (NANOOS). (Click on “regions” to get to Puget Sound.)

Hood Canal report compiles oxygen studies

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).

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How do we address Hood Canal’s oxygen deficit?

Five years ago, a lot of people were wondering why fish were dying more often in southern Hood Canal during the fall.

Researchers knew that Hood Canal was sensitive to nitrogen. In other words, when nitrogen was introduced to the canal during summer months, nearly all of it was taken up by plankton, which grew into large blooms. When the plankton died, they sank to the bottom, where bacterial decay sucked up the available oxygen.

Beyond that, the questions were numerous: What were the most critical sources of nitrogen affecting the low-oxygen problem? What role does weather and water circulation play? And what can humans do to help the problem — or at least keep it from getting worse.

After a five-year, $4-million study, these questions can be answered with some certainty, as I point out in a story in Sunday’s Kitsap Sun. Now it is time for researchers to convey this information to political leaders and the public, as the Hood Canal Coordinating Council prepares a plan of action.

Scott Brewer, executive director of the HCCC, told me that the eventual plan is likely to include a suite of actions to address nitrogen inputs to the canal, particularly from human sources.
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Fish kill reported in southern Hood Canal

UPDATE: 9-21-2010, 11:35 a.m.

Low-oxygen conditions grew worse overnight. Lots of Hood Canal residents are reporting dead fish and spot prawns on beaches in southern Hood Canal. I’ve posted an update on the Kitsap Sun’s website.

Here are some graphics of the oxycline and time changes, courtesy of Jan Newton.
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