Lecture #3

Question 1

At what temp does density effect water?

Answer 1

The maximum density of water is 4 degrees, above/below this it decreases in density

Question 2

At what temperatures is ice less dense than liquid water?

Answer 2

at less than 0 degrees, ice is less dense that water at 4 degrees

Question 3

What does the density of water impact?

Answer 3

This impacts stratification/mixing an also impacts nutrients and organism distributions

Question 4

What is waters surface tension important for? What benefits doe sit give?

Answer 4

It’s important for the flotation and position of organisms and debris, it allows organisms to have nutrients at the surface if they can sit on it

Question 5

How does water viscosity affect the movement of organisms?

Answer 5

Organisms will have adaptations to live in water, as more viscous water is harder to swim in

Question 6

What is more friction water or air?

Answer 6

water has 100x more friction than air

Question 7

How does viscosity affect reduction of supporting tissues?

Answer 7

the aquatic organisms need fewer structutural supports like bones, exoskeletons because viscous water holds them up.

Question 8

How does viscosity affect sedimentation rates?

Answer 8

it effects the rate at which particles will sink, more viscous less sedimentation

Question 9

What happens to viscosity as temperature rises?

Answer 9

it decreases

Question 10

What three things can happen to light when water enters it?

Answer 10

It can be absorbed which causes water to heat
It can be transmitted
Or it can be reflected, which determines the color of the lake

Question 11

What are Photosynthetically active radiation?

Answer 11

Are the wavelengths primary producers are abale to use

Question 12

How does light intensity change with depth?

Answer 12

It decreases logarithmically

Question 13

What is attenuation?

Answer 13

The reduction of force of light, attenuation is faster in more productive water

Question 14

What are eutrophic lakes?

Answer 14

These are highly productive lakes in which the light is attenuated faster because more particles in the lakes scatter and absorb the light faster

Question 15

What are mesotrophic lakes?

Answer 15

These are moderately productive lakes

Question 16

What are oligotrophic lakes?

Answer 16

Lakes with low productivity

Question 17

Explain the eqn Iz= I0e^-klz

Answer 17

check slide 15

Question 18

The attenuation of light divides the lake into which two different zones?

Answer 18

photic (sunlit) zone
aphotic zone

Question 19

What happens to photosynthesis and respiration in the photic zone, in the aphotic zone?

Answer 19

In the photic zone, photosynthesis is greater than respiration
in the aphotic zone, respiration greater than photosynthesis

Question 20

What is the compensation point?

Answer 20

Is the point between photic and aphotic zones where photosynthesis equals respiration, around 1% of light available

Question 21

What is a secchi disk?

Answer 21

It measures light attenuation in water

Question 22

What is the secchi depth?

Answer 22

Is when you drop it until you can’t see it, pull it up until you can, and the midway point is your depth

Question 23

How much surface light is remaining at secchi depth?

Answer 23

10%, the rest has been scattered or absorbed

Question 24

What interaction does lake color depend on?

Answer 24

the interaction between apparent color and real color

Question 25

What is apparent color?

Answer 25

Are wavelengths that are absorbed and scattered back toward the eye, is what the color looks like

Question 26

What is real color?

Answer 26

The color the lake actually is determined by the color of particles, substances, and substrate in the water

Question 27

How does transmittance and absorbance differ amongst oligotrophic, eutrophic, or humic-rich turbid lakes?

Answer 27

oligotrophic lakes- show high transmittance in most of the visible light range, especially blue and green
eutrophic lakes- show low transmittance in blue and red, algae absorbs these
humic rich, turbid lakes- have low transmittance in UV and blue regions due to the humic substances that absorb short wavelengths

Question 28

What is the definition of thermal stratification?

Answer 28

The separation of discrete layers of water of
different temperature in lakes resulting in a change of water
temperature at different depths.

Question 29

Where is the epilimnion, metalimnion, and hypolimnion and thermocline in a thermal profile?

Answer 29

epilimnion, is near the surface and warm
metamilnion is second
hypolimnion is near bottom and colder
thermocline is in metamilnion and is point of highest chnage in water temp

Question 30

Is there movement in a stratified lake?

Answer 30

generally no water movement between the epilimniojn and hypolimnion.

Question 31

What three things cause thermal stratification and how?

Answer 31

Heat absorption from light- at different depths the percentage of surface light changes which influences the temperature profile
Water density- at warmer temps the water density decreases
Wind- causes mixing, can chnage stratification and layers

Question 32

Why do we care about lake stratification?

Answer 32

it effects the distribution of organisms we see such as phyto and zooplankton

Question 33

What is the seasonal sequence of cold lakes?

Answer 33

spring mixing, summer stratification, fall mixing, winter stratification

Question 34

What happens during spring mixing?

Answer 34

Water is isothermal after ice melts, it begins to be mixed by wind then surface waters are heated by solar radiation, this causes the waters to continue to mix

Question 35

What happens during summer stratification?

Answer 35

surface waters heat so wind cannot mix the warmer surface waters with cool water below, mixing occurs only in the epilimnion and then the lake stratifies stably

Question 36

What determines the thermal structure for a lake (6)?

Answer 36

Morphometry
* Topography
* Weather
* Latitude
* Elevation
* Season

Question 37

What occurs during fall mixing?

Answer 37

the epilimnion is cooled to the same temp as the hypolimnion, if cooler is will sink to the bottom and cause mixing, wind mixes the entire lake

Question 38

What occurs during winter stratification?

Answer 38

The surface of the water freezes if the temp of lake falls below 3.9, , if it’s above cool water from surface will sink and mix with less dense water below, if it’s below cool water will freeze at top, once there’s ice there is no more mixing.

Question 39

What are the different thermal classifications of lake types?

Answer 39

Amictic ≡ Never circulates
Meromictic ≡ Incomplete circulation
Holomictic ≡ Circulates fully at least once a year
◦ Dimictic – Circulates twice per year
◦ Monomictic – Circulates once per year
◦ Cold monomictic – Circulates in the summer, ice-covered rest of the year
◦ Warm monomictic – Circulates in the winter
◦ Polymictic – Circulates frequently