EXERCISES
Estimates of Whole Lake Metabolism
decomposition:
Z = (L1C0 2 )(2)
In our example, z = (13.35)(2) = 26.70.
m. Then the total hypolimnetic CO 2 accumulation (8) is the sum of z and y:
8=Z+Y
e.g., 8 = 26.70 + 13.69 = 40.39mgC0 2 /1. Then, assuming 30 days/month,
8(30)
8 per month =
.
.
no. of days of stratIficatIOn
355
If, for example, the period of stratification were four months (120 days), then the
total hypolimnetic CO 2 accumulation for the stratified period would be
(40.39)(30)
8 = per month =
120
= 10.1 mgC02/l/month
n. When the CO 2 accumulation is calculated for each stratum of the hypolimnion
and summed for the entire hypolimnion, and this total value is multiplied by the
ratio of the volumes of the hypolimnion to epilimnion, a quantity termed the
relative assimulation intensity can be calculated:
Relative assimilation intensity
= (hYPolimnetic CO2 accumulation) [volume hypolimnion (m 3 ) ]
in mg CO 2 /l/month
volume epilimnion (m 3 )
= mgC02/l/month
If, in our example, the volume of the epilimnion were 7.442 x 10 6 m 3 , and that of
the hypolimnion 4.620 x 10 6 m 3 , then:
R 1 ·
· · 1 · ·
.
(
/
h)(4.620 x 10
6 )
e ahve aSSImI atIOn mtensIty = 10.1 mg CO2 mont 7.442 x 10 6
= 6.3 mg CO 2/l/month for the lake
OPTION 1. FIELD ANALYSES
1. At a suitably stratified lake or well-stratified reservoir, determine the depths of the
epilimnion, metalimnion, and hypolimnion by temperature profiles. Take water samples at as
closely spaced depth intervals as time permits from the upper portion of the hypolimnion to
the sediments.
a. Using appropriate care, collect duplicate dissolved oxygen samples (see Exercise 6).
Chemically fix the oxygen immediately while still in the field.
b. Collect samples of water separately for (i) CO 2 , alkalinity, and pH analyses (Exercise 8);
and (ii) measurement of ammonium ion concentrations (Exercise 7).
2. Perform the analyses of each of the required parameters as soon as possible in the laboratory.