Tag Archives: Southern Hood Canal

Watching the decline of oxygen in Hood Canal

Southern Hood Canal is back to its dirty tricks again, as dissolved oxygen concentrations have dropped to dangerous levels even at the surface. Numerous researchers are watching to see how these conditions play out.

A giant Pacific octopus, which should be hiding, clings to a rock wall Saturday at Sund Rocks Marine Preserve.
Photo by Pat Lynch

The mechanism that causes the oxygen to decline is a little complicated, but it’s pretty well understood. It involves nitrogen, sunlight, plankton, heavy sea water and south winds. See the story I wrote for today’s Kitsap Sun for a brief explanation, or check out a story from April 12, when I described findings from a scientific panel about the sources of nitrogen in the canal.

The graph below shows the oxygen levels at three depths near Hoodsport. As you can see from the blue line, oxygen levels near the surface declined rapidly over the past five days, a period when winds blew out of the south. Levels below 2.5 milligrams per liter are considered highly stressful for sea life.

At Hoodsport, oxygen levels rose at the 10-foot mark starting about midday yesterday. They declined again this morning, starting after midnight. Being close to the surface, oxygen levels in these waters are greatly influenced by winds and waves.

Waters at 66 feet deep stayed low in oxygen but fairly stable, as shown by the green line. Fish tend to swim into shallow waters to avoid those low-oxygen levels. A huge mass of low-oxygen water lies in this mid-range area.

Meanwhile, the low-oxygen waters in the middle layers are being pushed upward by heavy seawater coming in from the ocean. That deep ocean water contains more oxygen than the layer above it, as shown by the red line.

To follow these changes in close to real time, go to the Nanoos website and click on “Click here to view all assets” then on “regions” in the left column and “Puget Sound.” You can get information from most of these buoys. Hoodsport is the closest to the action in southern Hood Canal.

Post to Twitter Tweet This Post

Hood Canal report finds septic systems a problem

An investigation into the causes of low-oxygen conditions in Hood Canal is coming to a close with this week’s release of a final report by the Hood Canal Dissolved Oxygen Program.

The pattern of fall oxygen levels show severely depleted waters from Twanoh State Park to Hoodsport with much better conditions to the north. (Click to enlarge.)
Map courtesy of Hood Canal Dissolved Oxygen Program

I described the report in general terms in a story published in yesterday’s Kitsap Sun. You may read the report for yourself at the HCDOP website.

What the five-year study learned about Hood Canal seems quite impressive. The full report contains extensive discussions about what causes oxygen to decline, the triggering mechanism for fish kills, the inputs of nitrogen that drive the system and much more.

One of the conclusions, which I focused on in my latest story, is that nitrogen from septic systems in Southern Hood Canal appears to be a pivotal factor in fish kills. When the natural decline in oxygen approaches a dangerous range, the added nitrogen from septic systems can tip the balance, causing excessive stress and sometimes death for marine creatures.

According to the report, one cannot easily separate the natural factors from the human factors that create problems in Hood Canal. The long, narrow fjord is flushed slowly compared to most marine systems. Organic carbon and nitrogen, which are the major players in oxygen decline, naturally come in from streams, groundwater and the Pacific Ocean. Numerous human sources, such as septic systems and fertilizers, must be taken into account.

Continue reading →

Post to Twitter Tweet This Post