Oregon Water Science Center Hydrologic Studies

Measurement of Sediment Oxygen Demand in Lake Ewauna and Klamath River Downstream from Upper Klamath Lake, Oregon

Background

Sediment oxygen demand (SOD) is the rate at which dissolved oxygen is removed from the water column during the decomposition of organic matter in stream- or lake-bed sediments. In slow moving rivers or those with high levels of organic matter in the bed sediment, SOD can be a major cause of low dissolved oxygen (DO) concentrations in the water column. Low DO concentrations can be detrimental to the survival of aquatic life.

In the early 1990s and in August 1994, the Oregon Department of Environmental Quality (ODEQ) attempted a few SOD measurements in Lake Ewauna (Klamath River mile [RM] 252.3) and in the Klamath River at RM 249.4 and 239.3, downstream from Upper Klamath Lake (map). ODEQ encountered great difficulty in making SOD measurements in this river reach due to environmental conditions and inadequate equipment. The few data that were collected, however, suggest that SOD levels in Lake Ewauna and the Klamath River could be as much 10 times larger than levels measured by USGS in Upper Klamath Lake in 1999 and other stream reaches in Oregon. ODEQ data suggest that SOD is a major factor in the depletion of DO from the water column in this reach of the Klamath River, and they concluded that the measurements should be repeated to improve spatial coverage.

Objectives

Objectives of this study are to provide management agencies with data to:

Determine the magnitude and spatial variability of SOD from Lake Ewauna (RM 252.3) to Klamath RM 239.3

Assess whether SOD levels at different points (i.e. nearshore or midchannel) vary with river depth in each cross section at RM's 252.3, 249.4 and 239.3,

Compare SOD levels in this river reach to levels observed in Upper Klamath Lake in 1999,

Assess associations between SOD levels and bed-sediment particle size and organic carbon content, and

Obtain accurate SOD data that will contribute towards efforts to quantify the oxygen budget in the Klamath River.

Approach

SOD measurements will be made at two to three sites in river cross sections to assess spatial variability and associations with river depth. At each site in a cross section, two to three measurements will be attempted to provide an estimate of the average SOD and a measure of intrasite variability. SOD will be measured with open-bottomed chambers that are seated and sealed on the streambed by SCUBA divers. USGS will provide the SCUBA divers and other water-quality personnel for a 1-week field trip. USGS personnel will be responsible for operating the SOD chambers and water-quality monitors, and for collecting sediment samples. The Bureau of Reclamation will provide boats (up to two boats, if needed) and boat operators, who also will be responsible for maintaining the boats. Samples of surficial bed sediment will be collected by the divers at measurement sites for the determination of ash-free dry weight (a gross measure of organic carbon) and sand fraction (percent of sediment greater than 62 micrometers in diameter). The sediment samples will be sent to the Cascade Volcano Observatory sediment laboratory in Vancouver, Washington, for analysis.

Reports

Doyle, M.C., and Lynch, D.D., 2005, Sediment Oxygen Demand in Lake Ewauna and the Klamath River, Oregon, June 2003: U.S. Geological Survey Sientific Investigations Report 2005-5228, 14 p.

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