By Tamara M. Wood, Gregory J. Fuhrer, and Jennifer L. Morace
USGS Water-Resources Investigations Report 96-4079, 57 p., 33 figs., 12 tables.
Water-quality data from 1990 through 1994 were analyzed to determine whether the data support a relation between water quality and lake level in Upper Klamath and Agency Lakes, Oregon. The variables considered included chlorophyll-a, dissolved oxygen, pH, total phosphorus, and water temperature. The timing of the first bloom of Aphanizomenon flos-aquae in the lakes was found to exhibit a relation with May 1 lake level, such that the first bloom was delayed at higher lake levels. The timing of the first bloom also exhibited a relation with the number of degree-days between April 1 and May 15. Because lake level in each year was, to some extent, correlated with the number of degree-days, the relative effects of lake level and number of degree-days on water quality could not be discerned. The frequency of occurrence of high pH values (pH greater than 9.5) in June was found to exhibit a relation with lake level, a direct result of the apparent relation between lake level and the timing of the first bloom (earlier blooms resulted in higher overall pH values in June). Analyses of the relation of frequency of occurrence of low dissolved oxygen concentration (concentration less than 4 mg/L) and total phosphorus concentration with lake level were inconclusive. Water temperature was influenced largely by air temperature; the lakes did not appear to warm or cool more slowly at higher lake levels.
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