Primary Productivity of Phytoplankton
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9. Make depth distribution graphical comparisons and calculations of all parameters with the
data.
OPTION 2. LABORATORY ANALYSES WITH CULTURES
1. Using the photoplankton populations provided by your instructor, compare the productivity
of the algae under decreasing light conditions by simultaneous application of the oxygen
and 14C light and dark methods in the laboratory.
2. Perform titrations of the dissolved oxygen concentrations of the initial bottles and of the
alkalinity of the water, and determine the pH and DIC of each series during incubation.
3. Determine the light intensities under the different regimes of incubation.
4. When possible, expose replicate populations to light at different intensities. The light should
be filtered selectively by various absorption materials, e.g., colored celluloid filters as used
in theaters (Caution: Many of such filter materials are water soluble.) Determine the intensity
and spectral characteristics of light under these conditions. When instrumentation for direct
measurements of the light is not available, pieces of the material can be analyzed in a
spectrophotometer (scanning or at a series of wavelengths).
OPTION 3. LABORATORY ANALYSES WITH DATA
1. Using the data provided in Table 14.1, calculate the phytoplanktonic productivity for the
given day by the different methods discussed earlier.
a. Gross and net community productivity and respiration by the oxygen difference
technique.
b. Primary productivity by the 14C method.
c. Plot the data in mg C/m 3 /day, integrate each curve with a digitizer or by planimetry,
and determine the productivity in mg C/m2/day for the water column.
2. Compare the productivity with depth to the temperature profile and to the distribution of
underwater light (Table 14.2).
3. Compare the productivity with depth to the observed distribution of pigment concentrations
(Table 14.3).
4. Using the series of productivity values provided to you in Table 14.4, plot the annual
productivity curve of mg C/m2/day versus time. Integrate the curve by planimetry and
determine the annual mean productivity for this lake in x mg C/m 3 /day.
Questions
1. Assuming a photosynthetic quotient of 1.2, how do the gross and net photosynthetic estimates determined by the oxygen technique compare with the productivity estimate obtained
from the 14C method? Which method do you feel gives the most realistic results? Support
your answer.
2. Under your particular set of conditions in the lake or laboratory, how is the productivity
correlated with light? If surface photoinhibition was observed, how might the population
overcome this problem in a circulating epilimnion?
3. Is the relationship between productivity rates and algal biomass direct? What may underlie
any observed disparities?
4. Using microautoradiography, how might the relationship between total observed productivity of the composite algal community, species activity and growth turnover rates be
clarified?
5. Is the mean rate of photosynthesis measured by the light and dark bottle techniques the
same as the true rate of photosynthesis? Why? Support your answer.
221
9. Make depth distribution graphical comparisons and calculations of all parameters with the
data.
OPTION 2. LABORATORY ANALYSES WITH CULTURES
1. Using the photoplankton populations provided by your instructor, compare the productivity
of the algae under decreasing light conditions by simultaneous application of the oxygen
and 14C light and dark methods in the laboratory.
2. Perform titrations of the dissolved oxygen concentrations of the initial bottles and of the
alkalinity of the water, and determine the pH and DIC of each series during incubation.
3. Determine the light intensities under the different regimes of incubation.
4. When possible, expose replicate populations to light at different intensities. The light should
be filtered selectively by various absorption materials, e.g., colored celluloid filters as used
in theaters (Caution: Many of such filter materials are water soluble.) Determine the intensity
and spectral characteristics of light under these conditions. When instrumentation for direct
measurements of the light is not available, pieces of the material can be analyzed in a
spectrophotometer (scanning or at a series of wavelengths).
OPTION 3. LABORATORY ANALYSES WITH DATA
1. Using the data provided in Table 14.1, calculate the phytoplanktonic productivity for the
given day by the different methods discussed earlier.
a. Gross and net community productivity and respiration by the oxygen difference
technique.
b. Primary productivity by the 14C method.
c. Plot the data in mg C/m 3 /day, integrate each curve with a digitizer or by planimetry,
and determine the productivity in mg C/m2/day for the water column.
2. Compare the productivity with depth to the temperature profile and to the distribution of
underwater light (Table 14.2).
3. Compare the productivity with depth to the observed distribution of pigment concentrations
(Table 14.3).
4. Using the series of productivity values provided to you in Table 14.4, plot the annual
productivity curve of mg C/m2/day versus time. Integrate the curve by planimetry and
determine the annual mean productivity for this lake in x mg C/m 3 /day.
Questions
1. Assuming a photosynthetic quotient of 1.2, how do the gross and net photosynthetic estimates determined by the oxygen technique compare with the productivity estimate obtained
from the 14C method? Which method do you feel gives the most realistic results? Support
your answer.
2. Under your particular set of conditions in the lake or laboratory, how is the productivity
correlated with light? If surface photoinhibition was observed, how might the population
overcome this problem in a circulating epilimnion?
3. Is the relationship between productivity rates and algal biomass direct? What may underlie
any observed disparities?
4. Using microautoradiography, how might the relationship between total observed productivity of the composite algal community, species activity and growth turnover rates be
clarified?
5. Is the mean rate of photosynthesis measured by the light and dark bottle techniques the
same as the true rate of photosynthesis? Why? Support your answer.