354
Exercise 29
g.
LCO z = total carbon dioxide, corrected
=a+b+c
which, in this example, is LCO z = 9.43 + 4.52 + 13.10 = 27.04.
h. The oxygen deficit then is calculated and used in the computations of
hypolimnetic COz accumulation. 1\Oz = actual oxygen deficit, i.e., the change
(difference) in Oz concentration observed at any time at that depth, and the
saturation value of that same quantity of water at the temperature and pressure
at spring turnover. The relative areal Oz deficit, calculated by the procedure
discussed earlier in this exercise, is a better measure than the actual oxygen
deficit [cf., Wetzel (1983)] and can be used here when done over the same interval
of time. Using the actual O 2 deficit in this example (Ohle, 1952), the measured
[OzJ =0.56mg/1 at 6.7°C. At spring turnover, the [0 2 ] = 12.27mg/I. Hence,
1\02 = 12.27 - 0.56 = 11.71 mgOz/I. Using the molecular ratio of COz to Oz,
COz/Oz = 44/32 = 1.375, then JCO z = (1\Oz) (1.375), which, in this example, is
JCO z = (11.71) (1.375) = 16.10.
I. The respiratory quotient (RQ) is the ratio of the molecules of CO 2 liberated
during decomposition (respiration) to the molecules of Oz consumed, i.e.,
+ 1\C02/ -1\Oz. An RQ value of 0.85 is a mean value based on a number of
analytical analyses of plant and animal respiration and has been proposed for
use in the hypolimnetic COz accumulation method (Ohle, 1952). This general
value is reasonable for the oxidation of proteins and fats where oxygen is
available as an electron acceptor. When the hypolimnion becomes anaerobic,
however, fermentation by bacteria produces excess CO 2 , a positive CO 2
anomaly, and volatile organic compounds, such as methane, that diffuse out of
the sediments.
Under anaerobic conditions, alternate electron acceptors (e.g., N0 3 -,
S04 2 -), other than molecular Oz, are used [cf., Rich and Wetzel (1978) and Rich
(1983)]. Thus, respiratory quotients would be greater than during aerobic
metabolism. The in situ hypolimnetic RQ values would be expected to vary
seasonally with availability of oxygen and changes in redox gradients. For
example, RQ values of the hypolimnion have been found to vary inversely with
the availability of oxygen and range from less than 1 after spring circulation to
nearly 3 under anoxic conditions of summer stratification (Rich, 1975; 1984).
J. Using an RQ of 0.85 and assuming aerobic hypolimnetic conditions,
In the example being discussed,
y = (11.71)(1.375)(0.85)
= (16.10)(0.85)
= 13.69
k. Then the anaerobic change in CO 2 (total COz at the later date (t 2) minus the sum
of COz at t 1 minus that formed aerobically), 1\CO z, is evaluated by
1\C0 2 = LCO l - Y
which, in the example, 1\CO z = 27.04 - 13.69 = 13.35.
1. This value is then doubled to estimate the equivalent CO 2 under aerobic
Exercise 29
g.
LCO z = total carbon dioxide, corrected
=a+b+c
which, in this example, is LCO z = 9.43 + 4.52 + 13.10 = 27.04.
h. The oxygen deficit then is calculated and used in the computations of
hypolimnetic COz accumulation. 1\Oz = actual oxygen deficit, i.e., the change
(difference) in Oz concentration observed at any time at that depth, and the
saturation value of that same quantity of water at the temperature and pressure
at spring turnover. The relative areal Oz deficit, calculated by the procedure
discussed earlier in this exercise, is a better measure than the actual oxygen
deficit [cf., Wetzel (1983)] and can be used here when done over the same interval
of time. Using the actual O 2 deficit in this example (Ohle, 1952), the measured
[OzJ =0.56mg/1 at 6.7°C. At spring turnover, the [0 2 ] = 12.27mg/I. Hence,
1\02 = 12.27 - 0.56 = 11.71 mgOz/I. Using the molecular ratio of COz to Oz,
COz/Oz = 44/32 = 1.375, then JCO z = (1\Oz) (1.375), which, in this example, is
JCO z = (11.71) (1.375) = 16.10.
I. The respiratory quotient (RQ) is the ratio of the molecules of CO 2 liberated
during decomposition (respiration) to the molecules of Oz consumed, i.e.,
+ 1\C02/ -1\Oz. An RQ value of 0.85 is a mean value based on a number of
analytical analyses of plant and animal respiration and has been proposed for
use in the hypolimnetic COz accumulation method (Ohle, 1952). This general
value is reasonable for the oxidation of proteins and fats where oxygen is
available as an electron acceptor. When the hypolimnion becomes anaerobic,
however, fermentation by bacteria produces excess CO 2 , a positive CO 2
anomaly, and volatile organic compounds, such as methane, that diffuse out of
the sediments.
Under anaerobic conditions, alternate electron acceptors (e.g., N0 3 -,
S04 2 -), other than molecular Oz, are used [cf., Rich and Wetzel (1978) and Rich
(1983)]. Thus, respiratory quotients would be greater than during aerobic
metabolism. The in situ hypolimnetic RQ values would be expected to vary
seasonally with availability of oxygen and changes in redox gradients. For
example, RQ values of the hypolimnion have been found to vary inversely with
the availability of oxygen and range from less than 1 after spring circulation to
nearly 3 under anoxic conditions of summer stratification (Rich, 1975; 1984).
J. Using an RQ of 0.85 and assuming aerobic hypolimnetic conditions,
In the example being discussed,
y = (11.71)(1.375)(0.85)
= (16.10)(0.85)
= 13.69
k. Then the anaerobic change in CO 2 (total COz at the later date (t 2) minus the sum
of COz at t 1 minus that formed aerobically), 1\CO z, is evaluated by
1\C0 2 = LCO l - Y
which, in the example, 1\CO z = 27.04 - 13.69 = 13.35.
1. This value is then doubled to estimate the equivalent CO 2 under aerobic