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Sediment cores from southern Hood Canal expected to reveal historical causes of low oxygen levels

February 2006
Growing concern over the historically low dissolved oxygen concentrations in Hood Canal reached a new peak when three massive fish kills in 2002 and 2003 set back the already low fish populations. Hypoxia (low oxygen) in the deep waters of the fjord-like side basin of Puget Sound is an old problem that appears to be getting worse. Scientists and government officials want to know why and how they can fix the problem. Battelle scientists have begun a two-year project to investigate the hypoxia mystery by delving deep into historical sediments of southern Hood Canal. The project is supported by a $517,000 grant from the National Oceanic and Atmospheric Administration (NOAA), as part of the Coastal Hypoxia Research Program. Occasional fish kills have occurred over the past 50 years, but the recent kills were much larger and were attributed to record lows in dissolved oxygen. The oxygen decline in Hood Canal is strongly suspected to be caused by excess nitrogen from septic systems, fertilizer, and storm runoff. The nitrogen encourages large algae blooms in warm weather. When the algae dies and decays, it uses up dissolved oxygen in the water needed by fish and other life, leaving them to suffocate and die. However, the cause of the oxygen depletion may not be that simple. Hood Canal is unique within Puget Sound-past data collections show that oxygen in southern Hood Canal deep waters is often lower than other areas in Puget Sound. The natural physics and history of the area must be understood before causes can be determined. Key questions in this investigation are-how did the canal's nitrogen burden differ from the past to the present? At what time period did the nitrogen burden begin to increase? What events or changes correlate with the time period of the increased nitrogen? Getting to the Core of the Problem Eric Crecelius, a Battelle marine geochemist working at the Pacific Northwest National Laboratory's Sequim Marine Research Operations (MRO) on the Olympic Peninsula, is the principal investigator for the hypoxia investigation of the Puget Sound and Hood Canal. Crecelius and team began removing "cores" of bottom sediment in southern Hood Canal and Central Puget Sound in September 2005. Some cores captured sediments up to 10 feet deep, representing historic time periods of 100 to 300 years-before logging or European settlement of the area. "This is the first time deep core sampling has been done in southern Hood Canal," said Crecelius. "This study will give us insight into how Hood Canal has functioned in the past from the history accumulated in the cores, and a strong context for why it is functioning the way it is today." "What we're trying to do is construct the history of hypoxia in these basins," said Jill Brandenberger, a Battelle marine research scientist with MRO. "The goal is to say what's happening over the last several hundred years as the area was altered." Tracing Historical Events Battelle has formed partnerships with researchers at other institutions who are experts in their fields for the different tracers they will be looking for in the layers of sediment. The Hood Canal core sediment samples are being age dated and segmented, with portions of each layer shipped to chemists and biologists at collaborating institutions. Crecelius and team will examine the sediments for trace metals, which precipitate and accumulate when oxygen levels are lower; Columbia University in New York will look at isotopes of carbon and nitrogen; Bryn Athyn College near Philadelphia will examine tiny single-celled algae called diatoms; U.S. Geological Survey will search for single-celled creatures with shells called foraminifera; and the University of Washington will study pollens, particularly of alder trees. Plankton is a good indicator of water quality and nutrient conditions. Evidence of different plankton species in the layers of sediment can reveal changes in nutrient levels during specific time periods. Some species of plankton thrive in high levels of nutrients and others in low levels. Diatoms, the skeletons of plankton, are made of silicate and may be the best-preserved markers to indicate the level of biological production at any give time. Researchers may be able to tell if the onset of logging in the 1850s made a difference. Since alder trees grow in the place of clear cut forests, alder pollen will be a marker in the investigation if it shows up in the sediment. Alders are also known to release nitrogen, so if their pollen is found in abundance in the sediments, this may mean that clear cutting forests contributed to hypoxia in Hood Canal. Evidence of major or sudden changes that researchers will be looking for are events such as the diversion of the North Fork of the Skokomish River in the 1920s from its natural flow to trapping the water behind a dam, altering the timing of the historic flows into the Hood Canal. Battelle researchers conducted similar studies using core samples of historic sediments from central Puget Sound. In the Puget Sound sediments, researchers were able to detect that the changeover from use of coal to electricity and the banning of DDT and PCBs had a positive affect on the health of the Sound. The research conducted by other scientists on Chesapeake Bay sediments showed major changes in its plankton indicating that water quality was directly affected by human causes. Researchers were able to detect when large amounts of nitrogen and phosphate began entering the waterway from farms where heavy loads of fertilizer were applied. First results from the Hood Canal hypoxia study are expected around the end of 2006. NOAA's Coastal Hypoxia Research Program expects to use this information to develop advanced techniques for measuring hypoxia in ocean waters, estuaries, and the Great Lakes. Data from this study will be valuable to other teams of Hood Canal investigators, like the group lead by Jan Newton from the University of Washington's School of Oceanography. Newton hopes to develop a computer model that can analyze historical hypoxia data to help explain why the oxygen in Hood Canal waters is decreasing to record lows. Contacts: Eric Crecelius or Charlie Brandt, Resource and Ecosystem Product Line Manager.

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