BREMERTON — Hood Canal researchers are thrilled that a major fish kill did not occur this year — and not just for the sake of the fish.
Oceanographer Jan Newton and numerous other scientists are going into the home stretch in refining a computer model of Hood Canal. The model is designed to describe the physical and biological processes that can mean life or death for sea creatures within the 60-mile-long waterway.
“This year, the oxygen was higher in concentration than certainly last year,” said Newton, associated with the University of Washington’s Applied Physics Laboratory. “That is really a boon to our study, because we can actively research what’s making the difference.”
A series of buoys continually monitors water and atmospheric conditions in various parts of Hood Canal. A fish kill in September of last year allowed the researchers to diagnose conditions before, during and after the event, which resulted in thousands of dead fish, shrimp and even wolf eels.
Differences to study
Two fish kills in 2003, as well as extremely low oxygen conditions in 2002 and 2004, have painted a picture of how fish can be trapped within an area of deadly, low-oxygen waters. Scientists have learned that winds out of the south bring low-oxygen waters up from the depths, leaving marine animals little or no time to escape.
This year, the oxygen concentrations in the water never reached the extremes of recent years and the monitoring buoys recorded the major factors that kept the sea life from experiencing a tragic fate.
“We can calculate the difference,” Newton said, adding that strong south winds this fall did bring low-oxygen waters to the surface but the concentrations were never low enough to be deadly.
Newton talks about three make-or-break issues that seem to determine the oxygen concentrations:
Water circulation: Flows within Hood Canal depend on wind, river currents and ocean conditions. High rates of circulation tend to oxygenate the water at various depths.
Ocean inputs: Sea water comes into Hood Canal along the bottom, bringing in oxygen as well as nutrients and higher salinity. Higher flows of ocean water can boost the oxygen levels in deeper waters.
Organic production: Fewer sunny days this year reduced the growth of phytoplankton, which depend on photosynthesis. When plankton die, they sink to the bottom and decompose, which uses up the available oxygen. Plankton growth can be accelerated with excess nitrogen from human and natural sources, but phytoplankton won’t grow without sunlight.
“It could be that human pollution of nitrogen is OK in a cloudy year but not when the weather is sunny,” Newton said.
Bacteria declines
Dan Hannafious of the Hood Canal Salmon Enhancement Group said higher oxygen levels seem to have reduced the fluffy bacteria growing at the bottom of Lynch Cove outside of Belfair.
“The bacterial mat has dissipated considerably,” Hannafious said. “Now it’s more like polka dots of things across the bottom.”
The bacteria grow under conditions of extremely low oxygen. With higher oxygen levels, they retreat deeper into the sediments where low oxygen conditions prevail.
Newton said the ability to factor in a variety of conditions has improved the computer model of Hood Canal, which is being tested and verified to see if it can replicate known conditions.
The goal is to have the model working well enough by spring to inform the public, legislators and other policymakers what they can do to improve conditions in Hood Canal.
The model is actually three separate computer programs integrated together. The “physical model” accounts for conditions such as currents, temperature, salinity and weather in the body of Hood Canal. The “biological model” accounts for the growth of organisms as one thing eats another in the waterway.
A “terrestrial model” looks at how nutrients, such as nitrogen, flow from the uplands into Hood Canal. Rivers, streams and groundwater calculations from the third model serve as inputs into the other two models.
Question remains
One issue yet to be resolved is how much nitrogen flows out of septic systems at people’s homes. Early in the study, some scientists assumed that septic systems were likely to be the biggest contributor of nitrogen, because most septic systems are not designed to remove nitrogen.
The first phase of a study by UW scientists shows that some actual systems being tested release far more nitrogen than others, Newton said, and it isn’t clear why.
“The second phase is to nail that down to understand what might be influencing … the nitrogen transport,” she said.
The scientists working together as the multiagency Hood Canal Dissolved Oxygen Program have committed to completing a report by next spring, Newton said.
“Our plan is, by May of 2008, to answer the questions that the program was designed to answer,” she said. “We will be able to state what we think the dominant causes of the oxygen variability the low oxygen are. We will then release the information and provide recommendations.”
The model is designed to predict what would happen, for example, if one eliminated all the septic systems in the watershed; replaced nitrogen-producing alders with cedars; or changed the flow in the Skokomish River, the largest single source of nitrogen to Hood Canal.
“We feel very fortunate that the study years have been so different,” Newton said, “because it will allow us to understand how the natural and human factors are controlling the situation.”
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