Estimates of Whole Lake Metabolism
357
2. Can one assume, on the basis of the results of the laboratory experiments with water
movements (Exercise 3), that the hypolimnetic concentrations of oxygen or CO 2 are
relatively unaffected by the exchange of gases among the water strata? How serious do you
feel this error is in your system? How might the basin morphometry of lakes alter the
magnitude of this error? When a lake has a high relative depth, z" (see Exercise I, p. 11),
how might this error be influenced?
3. If littoral productivities of macrophytic vegetation and sessile algae were large, how would
this organic matter and its decomposition influence the calculated hypolimnetic O 2 deficit or
CO2 accumulation? Where does decomposition of the macrophytic flora and attendant
algae occur? Is some or much of this organic matter transported to the hypolimnion? [See
Godshalk and Wetzel (1977) and Wetzel (1990).J
4. Transport of allochthonous organic matter to lakes occurs both as particulate and as
dissolved organic matter. Which form predominates? How are these materials transformed
during transport? If relatively refractory dissolved organic matter were brought to the lake,
how would its presence and decomposition affect the productivity estimated by the
hypolimnetic change methods?
5. Are the hypolimnetic O 2 deficit and CO 2 accumulation techniques applicable to winter
periods under ice cover? Support your answer. What would be the influence of short renewal
times or water replacement of lakes when these methods are used under winter conditions?
Why?
6. When a significant portion of the autochthonous organic matter is sedimented and interred
permanently in the sediments of the hypolimnion, how would the computations of
productivity by the O 2 deficit and CO2 accumulation methods be affected?
7. If the algae of one lake were dominated by rapidly sedimenting siliceous diatoms and those of
another were dominated by small algae more neutrally buoyant (or possessing buoyancy
mechanisms), how would this difference affect productivity estimates by the two hypolimnetic methods? Why?
8. In the CO 2 accumulation method, if some sulfate or ferric hydroxide in the sediments were
reduced as the redox potential decreases and some bicarbonate was released to the water,
what would be the effect on the productivity estimates?
9. Why are these methods not applicable to meromictic lakes?
10. What is the role of "volatile" ammonium carbonate?
11. Is it better to express the results of the oxygen deficit method on an areal or on a volumetric
basis? Why?
Apparatus and Supplies
1. Boats, anchors, and water sampling devices, e.g., Van Dorn samplers.
2. Thermistor thermometer.
3. Dissolved oxygen:
a. Sample bottles and chemical reagents for oxygen fixation (see Exercise 6, p. 79).
b. Titration apparatus and reagents (see Exercise 6, p. 79).
4. CO2-ammonia analyses:
a. Separate sample bottles for CO 2 , alkalinity, pH, and ammonia.
b. Apparatus and reagents for the determinations of CO 2 and alkalinity (see Exercise 8,
pp. 111-127).
c. pH meter and supplies.
d. Apparatus and reagents for analyses of ammonia (see Exercise 7, pp. 83-84) and a
spectophotometer.
5. Bathymetric maps and planimeter; calculators.
357
2. Can one assume, on the basis of the results of the laboratory experiments with water
movements (Exercise 3), that the hypolimnetic concentrations of oxygen or CO 2 are
relatively unaffected by the exchange of gases among the water strata? How serious do you
feel this error is in your system? How might the basin morphometry of lakes alter the
magnitude of this error? When a lake has a high relative depth, z" (see Exercise I, p. 11),
how might this error be influenced?
3. If littoral productivities of macrophytic vegetation and sessile algae were large, how would
this organic matter and its decomposition influence the calculated hypolimnetic O 2 deficit or
CO2 accumulation? Where does decomposition of the macrophytic flora and attendant
algae occur? Is some or much of this organic matter transported to the hypolimnion? [See
Godshalk and Wetzel (1977) and Wetzel (1990).J
4. Transport of allochthonous organic matter to lakes occurs both as particulate and as
dissolved organic matter. Which form predominates? How are these materials transformed
during transport? If relatively refractory dissolved organic matter were brought to the lake,
how would its presence and decomposition affect the productivity estimated by the
hypolimnetic change methods?
5. Are the hypolimnetic O 2 deficit and CO 2 accumulation techniques applicable to winter
periods under ice cover? Support your answer. What would be the influence of short renewal
times or water replacement of lakes when these methods are used under winter conditions?
Why?
6. When a significant portion of the autochthonous organic matter is sedimented and interred
permanently in the sediments of the hypolimnion, how would the computations of
productivity by the O 2 deficit and CO2 accumulation methods be affected?
7. If the algae of one lake were dominated by rapidly sedimenting siliceous diatoms and those of
another were dominated by small algae more neutrally buoyant (or possessing buoyancy
mechanisms), how would this difference affect productivity estimates by the two hypolimnetic methods? Why?
8. In the CO 2 accumulation method, if some sulfate or ferric hydroxide in the sediments were
reduced as the redox potential decreases and some bicarbonate was released to the water,
what would be the effect on the productivity estimates?
9. Why are these methods not applicable to meromictic lakes?
10. What is the role of "volatile" ammonium carbonate?
11. Is it better to express the results of the oxygen deficit method on an areal or on a volumetric
basis? Why?
Apparatus and Supplies
1. Boats, anchors, and water sampling devices, e.g., Van Dorn samplers.
2. Thermistor thermometer.
3. Dissolved oxygen:
a. Sample bottles and chemical reagents for oxygen fixation (see Exercise 6, p. 79).
b. Titration apparatus and reagents (see Exercise 6, p. 79).
4. CO2-ammonia analyses:
a. Separate sample bottles for CO 2 , alkalinity, pH, and ammonia.
b. Apparatus and reagents for the determinations of CO 2 and alkalinity (see Exercise 8,
pp. 111-127).
c. pH meter and supplies.
d. Apparatus and reagents for analyses of ammonia (see Exercise 7, pp. 83-84) and a
spectophotometer.
5. Bathymetric maps and planimeter; calculators.