216
Exercise 14
Then,
Total activity
LBI
LB2
DB
5o.-ml samples filtered
Counts per second
(cps)
75.2
74.1
1.3
mg 12C/I available = 12.32
Constant isotopic effect = 1.0.6.
Bottle volume
126ml
132 ml
123 ml
(x)(4.36)(37,o.o.o.) = (12.32) {[ (75.22(125/50.) + (74.1)(131/50.) ]
1.34
2
- [(1.3)(122/50.)] } (10.0.0.)(1.0.6)
(x) = (1.34)(12.32)(187.9o.)(1.o.6)(lo.O~)
(4.36) (3 7,0.0.0.)
(x) = 20..4 mg C/m 3 /time of incubation
Conversion of Volumetric Measurements to Areal
Estimates of Productivity
In comparing aquatic ecosystems, it often is desirable to convert the measured
volumetric productivity values in mg C/m 3 /time at each depth to total productivity
per square meter for a water column extending from the surface to the compensation
depth. This conversion can be done by plotting the values in mg C/m 3 /time against
depth and then integrating the profile generated. Although the integration can be
accomplished by computer analysis, it also can be done with an electronic digitizer
or relatively simply by planimetry (see Exercise 1 and Fig. 1.5). The planimetered
area of the productivity curve is compared proportionally with the planimetered area
of a known standard area of mg/m 3 /time versus depth drawn to the same scale on
the graph. The resulting estimate of productivity is in mg C/m2 of water column/time
of incubation. This value may be converted to mg C/m2/h by dividing by the exact
time in hours of incubation or, more meaningfully, be converted to mg C/m 2 /day by
one of the following methods.
Expansion of Incubation Period to Daily Values
Incubation periods should be limited to 4 to 6 h for a number of reasons [cf.,
Vollenweider and Nauwerck (1961) and Vollenweider (1965)]. This period is long
enough to allow measurement of 14C assimilated but is also sufficiently brief to
minimize errors incurred from longer exposure as a result of bacterial growth on the
walls of the bottles, respiratory recycling of CO 2 , nutrient depletion, and so on. To
be meaningful, however, the results should be expanded to a daily value by correction
factors. Several means are available; all possess disadvantages.
Ideally, productivity measurements should be taken in the euphotic zone at about
4-h increments from darkness to darkness each day for an entire year. Since this rigor
is obviously impractical, estimates can be calculated from data th~t have been
Exercise 14
Then,
Total activity
LBI
LB2
DB
5o.-ml samples filtered
Counts per second
(cps)
75.2
74.1
1.3
mg 12C/I available = 12.32
Constant isotopic effect = 1.0.6.
Bottle volume
126ml
132 ml
123 ml
(x)(4.36)(37,o.o.o.) = (12.32) {[ (75.22(125/50.) + (74.1)(131/50.) ]
1.34
2
- [(1.3)(122/50.)] } (10.0.0.)(1.0.6)
(x) = (1.34)(12.32)(187.9o.)(1.o.6)(lo.O~)
(4.36) (3 7,0.0.0.)
(x) = 20..4 mg C/m 3 /time of incubation
Conversion of Volumetric Measurements to Areal
Estimates of Productivity
In comparing aquatic ecosystems, it often is desirable to convert the measured
volumetric productivity values in mg C/m 3 /time at each depth to total productivity
per square meter for a water column extending from the surface to the compensation
depth. This conversion can be done by plotting the values in mg C/m 3 /time against
depth and then integrating the profile generated. Although the integration can be
accomplished by computer analysis, it also can be done with an electronic digitizer
or relatively simply by planimetry (see Exercise 1 and Fig. 1.5). The planimetered
area of the productivity curve is compared proportionally with the planimetered area
of a known standard area of mg/m 3 /time versus depth drawn to the same scale on
the graph. The resulting estimate of productivity is in mg C/m2 of water column/time
of incubation. This value may be converted to mg C/m2/h by dividing by the exact
time in hours of incubation or, more meaningfully, be converted to mg C/m 2 /day by
one of the following methods.
Expansion of Incubation Period to Daily Values
Incubation periods should be limited to 4 to 6 h for a number of reasons [cf.,
Vollenweider and Nauwerck (1961) and Vollenweider (1965)]. This period is long
enough to allow measurement of 14C assimilated but is also sufficiently brief to
minimize errors incurred from longer exposure as a result of bacterial growth on the
walls of the bottles, respiratory recycling of CO 2 , nutrient depletion, and so on. To
be meaningful, however, the results should be expanded to a daily value by correction
factors. Several means are available; all possess disadvantages.
Ideally, productivity measurements should be taken in the euphotic zone at about
4-h increments from darkness to darkness each day for an entire year. Since this rigor
is obviously impractical, estimates can be calculated from data th~t have been