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DIEL DISSOLVED OXYGEN MONITORING OF THE SPOKANE RIVER DURING EXTREME LOW FLOW. KOOTENAI COUNTY, IDAHO, 1992
Description:
Diel monitoring of dissolved oxygen and temperature was conducted on an impounded and free-flowing reach of the Spokane River, in north Idaho (17010303) on 2 occasions during an extreme low flow event in water year 1992. The objective was to document excursions from water quality criteria for dissolved oxygen and to provide insight into rates of overnight oxygen uptake or daylight oxygen production for future modeling efforts. Water column temperature and dissolved oxygen were measured on a regular interval for 24 hours at 3 locations in the impounded reach, and at 1 location downstream of Post Falls Dam. The first sample period was characterized by marked stratification, departures from oxygen criteria in the metaliminion, and warm water temperatures. Profiles were significantly different from each other in time and space, largely due to low variability of the data. Generally, water was slightly warmer and contained slightly less oxygen at downstream stations. The run of the river station demonstrated the largest diel change, possibly indicating daytime production of oxygen by attached periphyton. Following a storm event, stratification and criteria violations were not detected during the second sample event. Profiles of temperature and dissolved oxygen were well mixed vertically and the magnitude of the changes were very small. Future water quality modeling efforts can assume that in the impounded reach of the river, a large amount of organic matter is not in the system, and that a large amount of algae or periphyton is not present. Dissolved oxygen criteria violations appear to be infrequent and stratification conditions are fragile. Cochrane, B. 1994. Water Quality Summary Report No. 28. Idaho Department of Health and Welfare, Division of Environmental Quality, Boise, ID. 42 pp.