Lecture #3 Flashcards
At what temp does density effect water?
The maximum density of water is 4 degrees, above/below this it decreases in density
At what temperatures is ice less dense than liquid water?
at less than 0 degrees, ice is less dense that water at 4 degrees
What does the density of water impact?
This impacts stratification/mixing an also impacts nutrients and organism distributions
What is waters surface tension important for? What benefits doe sit give?
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
How does water viscosity affect the movement of organisms?
Organisms will have adaptations to live in water, as more viscous water is harder to swim in
What is more friction water or air?
water has 100x more friction than air
How does viscosity affect reduction of supporting tissues?
the aquatic organisms need fewer structutural supports like bones, exoskeletons because viscous water holds them up.
How does viscosity affect sedimentation rates?
it effects the rate at which particles will sink, more viscous less sedimentation
What happens to viscosity as temperature rises?
it decreases
What three things can happen to light when water enters it?
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
What are Photosynthetically active radiation?
Are the wavelengths primary producers are abale to use
How does light intensity change with depth?
It decreases logarithmically
What is attenuation?
The reduction of force of light, attenuation is faster in more productive water
What are eutrophic lakes?
These are highly productive lakes in which the light is attenuated faster because more particles in the lakes scatter and absorb the light faster
What are mesotrophic lakes?
These are moderately productive lakes
What are oligotrophic lakes?
Lakes with low productivity
Explain the eqn Iz= I0e^-klz
check slide 15
The attenuation of light divides the lake into which two different zones?
photic (sunlit) zone
aphotic zone
What happens to photosynthesis and respiration in the photic zone, in the aphotic zone?
In the photic zone, photosynthesis is greater than respiration
in the aphotic zone, respiration greater than photosynthesis
What is the compensation point?
Is the point between photic and aphotic zones where photosynthesis equals respiration, around 1% of light available
What is a secchi disk?
It measures light attenuation in water
What is the secchi depth?
Is when you drop it until you can’t see it, pull it up until you can, and the midway point is your depth
How much surface light is remaining at secchi depth?
10%, the rest has been scattered or absorbed
What interaction does lake color depend on?
the interaction between apparent color and real color
What is apparent color?
Are wavelengths that are absorbed and scattered back toward the eye, is what the color looks like
What is real color?
The color the lake actually is determined by the color of particles, substances, and substrate in the water
How does transmittance and absorbance differ amongst oligotrophic, eutrophic, or humic-rich turbid lakes?
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
What is the definition of thermal stratification?
The separation of discrete layers of water of
different temperature in lakes resulting in a change of water
temperature at different depths.
Where is the epilimnion, metalimnion, and hypolimnion and thermocline in a thermal profile?
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
Is there movement in a stratified lake?
generally no water movement between the epilimniojn and hypolimnion.
What three things cause thermal stratification and how?
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
Why do we care about lake stratification?
it effects the distribution of organisms we see such as phyto and zooplankton
What is the seasonal sequence of cold lakes?
spring mixing, summer stratification, fall mixing, winter stratification
What happens during spring mixing?
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
What happens during summer stratification?
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
What determines the thermal structure for a lake (6)?
Morphometry
* Topography
* Weather
* Latitude
* Elevation
* Season
What occurs during fall mixing?
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
What occurs during winter stratification?
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.
What are the different thermal classifications of lake types?
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
