Environmental Engineering Reference
In-Depth Information
106
molO gO /molO
molC gC/molC
(
32
)
gO
gC
2
2
2
2
r
oca
=
=
267
.
106
(
12
)
or conversely for each gram of carbon produced, 2.67 g of O
2
would be produced.
Production is impacted by the presence of light (Figure 14.8) and by temperature, which varies
over the course of a day as well as over the seasons. Partially as a result, there are often large tem-
poral as well as spatial variations in the distribution of DO.
14.4.4
d
IStrIbutIon
of
o
xyGen
14.4.4.1 Diel Variations
As light variations occur over the course of a day, relatively large diel variations in oxygen con-
centrations may occur. The extent of these variations is a function of a number of environmental
factors, including the rates of productivity and respiration, basin morphometry, wind speed and
direction, depth, and other factors.
Deep dimictic temperate lakes are likely to undergo only moderate diel variations in one or more
physicochemical properties (Hutchinson 1957). In contrast, shallow productive tropical lakes may
show less stratiication and more extreme diel variations in their physicochemical parameters, as
illustrated by diel variations in temperature and DO in Lake Kissimmee, Florida (Dye et al. 1980;
Figures 14.9 and 14.10). As illustrated, temperature stratiication occurs during daylight hours but
it is broken down by nocturnal cooling and wind mixing. Similarly, strong vertical variations in
oxygen occur during daytime hours, but they become mixed during the night.
A somewhat similar pattern in diel variations occurs in deeper southern U.S. reservoirs, such as
Lake Livingston, Texas (Martin 1984). During July, the reservoir is stably stratiied with oxygen
depleted in the hypolimnetic waters (Figure 14.11). During daylight hours and under low wind
0.0
33.0
27.5
32.0
32.5
30.
31.
31.5
29.
30.0
0.5
29.0
28.5
1.0
1.5
28.0
28.0
2.0
27.5
2.5
3.0
900
1315
1700
2100
Time
100
500
900
FIGURE 14.9
Variations in water temperatures at Station 22 of Lake Kissimmee, Florida, July 16-17, 1974.
(From Dye, C.W., Jones, D.A., Ross, L.T., and Gernert, J.L.,
Hydrobiologia
71, 51-60, 1980. With permission.)
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