1. Depth profile of photosynthesis—how to obtain areal estimate from volumetric
mgC/m3/d
1.0
primary production decreases
at highest light intensity o
1.0 o m
medium light intensity,
highest primary production o o
Low light intensity,
low primary production o

2. The photosynthesis versus irradiance (light intensity) curve

4. A B Comparing the Photosynthethis/irradiance curves among species C
GPP/t
per unit of biomass A B C
Light intensity
10%
25%
50%

5. Assuming that A, B and C are similar in all respects other than their P/I curves, which of these species would you expect to perform best in the well mixed water column of a deep lake (25% light level at 10 m, max depth 100 m)
a) A
b) B
c) C
d) A and B would do equally well
e) A and C would do equally well
GPP/t
per unit of biomass A B C
Light intensity
10%
25%
50%

6. You find that C outperforms both A and B during the summer months but not in the early spring. Assuming that all three species have similar temperature optima and nutrient uptake affinities, which of the following explanations is most plausible?
C is the least palatable species to herbivorous zooplankton
b) B does best at low light intensity, and A does best at high light intensity, but C does best under fluctuating light intensities
c) C has the most eccentric shape
d) a and b are both plausible
e) a and c are both plausible
GPP/t
per unit of biomass A B C
Light intensity
10%
25%
50%

7. Assuming that A and B are equal in all respects other than their P/I curves, under what conditions would you expect B to outperform A?
a) in the epilimnion of a clear stratified lake, (Assume 25% light level at the thermocline)
b) in the well-mixed water column of a deep lake (Assume 25% light level at 10m, max depth 100 m)
c) in the hypolimnion of a clear stratified lake (Assume 25% light level at the thermocline)
d) growing on the substrate near shore in the littoral zone of a clear lake (assume 25 % light level at the outer boundary of the littoral)
e) both a and d
f) both b and c
GPP/t
per unit of biomass A B C
Light intensity
10%
25%
50%

8. In the littoral zone submerged, floating leaved and emergent macrophytes and their epiphytes can be the main primary producers.
Primary productivity in these habitats can be measured either by O2 or CO2 fluxes, or by direct measures of growth of the plants over time—the harvest method.

9. The seasonal dyanamics of the phytoplankton in lakes
Temperature adaptations of different algal groups
Thermal stratification, sinking rates and nutrient dynamics
Food-web interaction—effects of grazing zooplankton
mid-summer low biomass
community shifts to inedible forms

10. Early spring—diatoms dominate--under cold temperatures and low light conditions
plenty of nutrients in the well mixed water column
Summer—lake warms up, thermocline forms diatoms fall out of the mixing layer—low viscosity and low mixing depth
Asterionella the only diatom that can still hang in.
Mid-summer—nutrients lost from mixed layer (sedimentation of algae), warm temperatures favour green algae, and zooplankton herbivory is high favouring fast growing small species eg Chlorella
Late summer—herbivores eliminate edible species, large colonial cyanobacteria dominate eg. Microcystis
Fall—water cooling, thermocline breaks up, mixing depth increases, nutrients increase, diatoms dominate
Winter—low light and cold temp low biomass