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EFFECTS OF TEMPERATURE VARIATION ON CRITICAL STREAM DISSOLVED OXYGEN
Citation:
Eheart, J. AND H. Park. EFFECTS OF TEMPERATURE VARIATION ON CRITICAL STREAM DISSOLVED OXYGEN. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-89/068.
Description:
The classical assumption that the lowest dissolved oxygen (DO) occurs at the highest temperature may not always hold. The DO saturation concentration decreases monotonically with increasing temperature, lowering the DO, but the reaeration coefficient increases monotonically with increasing temperature, tending to raise it. he decay coefficient monotonically increases with increasing temperature, lowering the DO for single discharges but not necessarily for multiple discharges. (Lower decay rates attending lower temperatures could result in low DO at the point where the impact from one discharge meets that of another.) This paper addresses the question of whether DO might under some circumstances worsen with the pattern of discharge that maximizes the derivative of critical dissolved oxygen with respect to temperature is an infinite uniformly distributed load. his suggests that streams receiving a large number of discharges may be more susceptible to DO increaseing with decreasing temperature that streams receiving a small number of discharges. The corresponding maximum value of the derivative is shown to be dC/dT + (C3-C) Ln o mg/L-1 oC-1, where T is the temperature in C, C is the dissolved oxygen standard, C3 is the DO saturation concentration (both in milligrams per liter), and o is the temperature adjustment factoe for the reaeration coefficient. The maximum dericative calue does not depend on the decay coefficient or its temperature adjustment factor. For the maximum reported value of o of 1.047, the maximum derivate value is 0.26273- 0.0028610T + 0.00013371T2 - 0.0000036718T3 - 0.045929C, for which the assumption that DO decreases monotonically with increasing temperature is valid for C greater than about 6 mg/L. owever, this assumption breaks down for values of o just above the range reported in the literature and values of C just below the normally chosen range of 5-6 mg/L.