USGS Washington Water Science Center
|U.S. Department of the Interior
U.S. Geological Survey
Release: June 24, 2002
253-428-3600, ext. 2682
[Note: The report can be viewed on the Web at http://pubs.water.usgs.gov/wri024146.]
Unusually low oxygen readings in the Puyallup River were caused by sensor problems, not poor water quality, according to a cooperative study by the U.S. Geological Survey (USGS), the Puyallup Tribe of Indians, and the Washington State Department of Ecology. Results of the study are released today in a USGS report.
Scientists were puzzled by several readings of low dissolved oxygen in the river during September 2000. The amount of oxygen dissolved in the water is used as a measure of water quality under the Total Maximum Daily Load (TMDL) requirements for the Puyallup River. Several measurements ranged from less than 1 milligram per liter to about 6 milligrams per liter, below the State standard of 8 milligrams per liter.
To find the cause of the low measurements in 2000, scientists from the USGS, the Puyallup Tribe of Indians, and the Washington State Department of Ecology decided to monitor water quality again during 2001.
"Sediment covering the sensors is the most likely cause of the low dissolved-oxygen measurements," said Jim Ebbert, author of the USGS report. "Project scientists discovered the connection when one of the sensors was buried by sediment during the new 2001 sampling and gave us the same kind of low readings. When not covered, the sensor gave readings above the 8-milligrams-per-liter standard."
Scientists also examined other mechanisms that might have potentially caused low dissolved-oxygen measurements. These mechanisms included plant photosynthesis and respiration, release of water from Lake Tapps to the river, and oxidation of minerals in riverbed sediments. Scientists determined that the release of water with low dissolved oxygen from Lake Tapps and plant respiration does lower dissolved oxygen, especially in the White River, which barely met water quality standards. However these mechanisms could not account for the extremely low measurements in the Puyallup River in 2000.
The dissolved-oxygen content of water indicates the biochemical condition of the water. Fish and other aquatic species require relatively high concentrations of dissolved oxygen in order to live.
The report, "Concentrations of Dissolved Oxygen in the Lower Puyallup and White Rivers, Washington, August and September 2000 and 2001" by James C. Ebbert, is published as U.S. Geological Survey Water-Resources Investigations Report 02-4146. Copies of the report are available for reading at the U.S. Geological Survey, 1201 Pacific Avenue, Suite 600, Tacoma, WA 98402. Copies can be purchased from the U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225-0286, telephone 303-202-4200. It can also be viewed on the Web at http://pubs.water.usgs.gov/wri024146.
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