1 Name:
Most answers require brief responses: be concise but coherent. Put your name on every page. Point
values for each question are in ( ) next to the question number. Note that longer essay questions are
scattered throughout.
1(2). What is a secchi disc used to measure?
Depth of light penetration in the water column.
2(6). Briefly define the following terms. How are they characterized according to a temperature profile?
Epilimnion
mixed zone; top layer; similar temperature throughout
Metalimnion
transition zone between meta- and hypolimnion; >1 degree change per m in temperature
Hypolimnion
very little mixing; bottom layer of stratified lakes; relatively cold water
3(6). On the first day of class we talked about four different (but complimentary) methods by which to investigate
aquatic systems (and really any ecological system). List at least three of the four methods. Imagine a situation in
which an investigator must decide between two or more methods. What are some limitations or advantages of
each method you have listed?
1. Experiments- don't always reflect interactions on the scale of whole ecosystem; allow for controlled
manipulations
2. Long-term studies- usually can only study one lake at a time; not very useful for someone completing
their degree in three years; allow the study of ecological processes that occur over long time periods
3. Simulation models - they only reflect what you program into them ; they help determine what you
DON'T know when they don't compare well to natural systems
4. Comparative studies - may not be very mechanistic; time for space substitution
4(4). Name at least one mixing process (water movement) that is unlikely to be important to mixing in a lake with a
very small fetch. What might be important?
Unimportant: surface gravity waves, seiches, etc. Important: convection currents, onshore-offshore
currents.
5(6). Why is water such a kick-butt medium? What makes it so useful? (we talked about several unique
properties of water in class) Explain how one of your water characteristics impacts the biota in a lake or stream.
High latent heat content- moderates the aquatic environment
Surface tension- organisms live on or below the surface
Molecular structure: ice is less dense than water slightly warmer so it floats & the whole lake doesn't freeze
Universal solvent- nutrients dissolve in the water so they are available for biological uptake
Aquatic Biology 2002 Exam 1
, 2 Name:
6(2). You were snorkeling in the littoral zone this past summer, and noticed sunlight "dancing" across the
sediments. What properties of light and/or water might cause this?
Reflection off the surface (waves changing the angle of reflection)
Refraction of the light when it enters the water
7(4). If you were a small fish and wanted to be inconspicuous at 10 m depth to avoid predation, what color would
you want to be? Red or blue (circle one). Why?
Red because red light quickly attenuates and so you'd appear grey and inconspicuous!
8(4). Why is it that edible algae may have very high production rates, but never accumulate high biomass?
Because it is being consumed faster than it con accumulate biomass.
9(4). This year it was a particularly windy spring, causing a particularly late onset of stratification in Lake Mendota.
Would you predict summer hypolimnetic temperatures be higher, lower, or the same as usual? Why?
Higher than usual because during the prolonged mixing period all the water in the lake would have
warmed up from 4 oC.
Incident light (%)
01 50 100
Temperature oC
10(2). In the figure to the right, observe that light rapidly goes
0 5 10 15 20
extinct in the shallow surface waters. Briefly explain why 0
warm epilimnetic temperatures extend to a depth of 5 meters.
Light
Temperature
Mixing of the epilimnion 5
Depth (m)
10
15
20
Aquatic Biology 2002 Exam 1
Most answers require brief responses: be concise but coherent. Put your name on every page. Point
values for each question are in ( ) next to the question number. Note that longer essay questions are
scattered throughout.
1(2). What is a secchi disc used to measure?
Depth of light penetration in the water column.
2(6). Briefly define the following terms. How are they characterized according to a temperature profile?
Epilimnion
mixed zone; top layer; similar temperature throughout
Metalimnion
transition zone between meta- and hypolimnion; >1 degree change per m in temperature
Hypolimnion
very little mixing; bottom layer of stratified lakes; relatively cold water
3(6). On the first day of class we talked about four different (but complimentary) methods by which to investigate
aquatic systems (and really any ecological system). List at least three of the four methods. Imagine a situation in
which an investigator must decide between two or more methods. What are some limitations or advantages of
each method you have listed?
1. Experiments- don't always reflect interactions on the scale of whole ecosystem; allow for controlled
manipulations
2. Long-term studies- usually can only study one lake at a time; not very useful for someone completing
their degree in three years; allow the study of ecological processes that occur over long time periods
3. Simulation models - they only reflect what you program into them ; they help determine what you
DON'T know when they don't compare well to natural systems
4. Comparative studies - may not be very mechanistic; time for space substitution
4(4). Name at least one mixing process (water movement) that is unlikely to be important to mixing in a lake with a
very small fetch. What might be important?
Unimportant: surface gravity waves, seiches, etc. Important: convection currents, onshore-offshore
currents.
5(6). Why is water such a kick-butt medium? What makes it so useful? (we talked about several unique
properties of water in class) Explain how one of your water characteristics impacts the biota in a lake or stream.
High latent heat content- moderates the aquatic environment
Surface tension- organisms live on or below the surface
Molecular structure: ice is less dense than water slightly warmer so it floats & the whole lake doesn't freeze
Universal solvent- nutrients dissolve in the water so they are available for biological uptake
Aquatic Biology 2002 Exam 1
, 2 Name:
6(2). You were snorkeling in the littoral zone this past summer, and noticed sunlight "dancing" across the
sediments. What properties of light and/or water might cause this?
Reflection off the surface (waves changing the angle of reflection)
Refraction of the light when it enters the water
7(4). If you were a small fish and wanted to be inconspicuous at 10 m depth to avoid predation, what color would
you want to be? Red or blue (circle one). Why?
Red because red light quickly attenuates and so you'd appear grey and inconspicuous!
8(4). Why is it that edible algae may have very high production rates, but never accumulate high biomass?
Because it is being consumed faster than it con accumulate biomass.
9(4). This year it was a particularly windy spring, causing a particularly late onset of stratification in Lake Mendota.
Would you predict summer hypolimnetic temperatures be higher, lower, or the same as usual? Why?
Higher than usual because during the prolonged mixing period all the water in the lake would have
warmed up from 4 oC.
Incident light (%)
01 50 100
Temperature oC
10(2). In the figure to the right, observe that light rapidly goes
0 5 10 15 20
extinct in the shallow surface waters. Briefly explain why 0
warm epilimnetic temperatures extend to a depth of 5 meters.
Light
Temperature
Mixing of the epilimnion 5
Depth (m)
10
15
20
Aquatic Biology 2002 Exam 1
