Geoscience Reference
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Criteria for defining desirable DO concentration often are differentiated as applicable to cold-
water biota, such as trout and their insect prey, and the more low-oxygen-tolerant species of warm-
water ecosystems. Moreover, because of the critical respiratory function of DO in aquatic animals,
criteria often are expressed in terms of the short-term duration and frequency of occurrence of
minimum concentration rather than long-term average concentrations. Studies cited by the U.S.
Environmental Protection Agency (USEPA) of the dependence of freshwater biota on DO suggest
that streams in which the concentration is less than 6.5 mg/L for more than about 20% of the time
generally are not capable of supporting trout or other coldwater fish, and such concentrations could
impair population growth among some warmwater game fish, such as largemouth bass (USEPA,
1986). Streams in which the DO deficit concentration is greater than 4 mg/L for more than 20%
of the time generally cannot support either cold- or warmwater game fish. DO deficit refers to the
difference between the saturation and measured concentrations of DO in a water sample and is a
direct measure of the effects of oxygen-demanding substances on DO in streams.
Major sources of substances that cause depletion of DO in streams are discharges from munici-
pal and industrial wastewater treatment plants; leaks and overflows from sewage lines and septic
tanks; stormwater runoff from agricultural and urban land; and decaying vegetation, including
aquatic plants from the stream itself and detrital terrestrial vegetation. DO is added to stream water
by the process of aeration (waterfalls, riffles) and the photosynthesis of plants.
Dissolved oxygen saturation (DO
sat
) values for various water temperatures can be computed
using the American Society of Civil Engineer's equation (Elmore and Hayes, 1960). This equation
represents saturation values for distilled water (β, 1.0) at sea-level pressure. Even though water
impurities can increase or decrease the saturation level, for most cases β is assumed to be unity,
or 1.0.
DO
sat
= 14.652 - 0.41022
T
+ 0.0079910
T
2
- 0.000077774
T
3
(19.4)
where
DO
sat
= Dissolved oxygen saturation concentration (mg/L).
T
= Water temperature (°C).
■
EXAMPLE 19.3
Problem:
Calculate the DO saturation concentration for water temperatures (
T
) of 0, 10, 20, and
30°C, assuming β = 1.0.
Solution:
At
T
= 0°C,
DO
sat
= 14.652 - 0 + 0 - 0 = 14.652 mg/L
At
T
= 10°C,
DO
sat
= 14.652 - (0.41022 × 10) + (0.0079910 × 10
2
) - (0.000077774 × 10
3
) = 11.27 mg/L
At
T
= 20°C,
DO
sat
= 14.652 - (0.41022 × 20) + (0.0079910 × 20
2
) - (0.000077774 × 20
3
) = 9.02 mg/L
At
T
= 30°C,
DO
sat
= 14.652 - (0.41022 × 30) + (0.0079910 × 30
2
) - (0.000077774 × 30
3
) = 7.44 (mg/L)
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