Midterm Flashcards
Distinguish between lotic and lentic fresh water
Lotic - running water
Lentic - standing
Describe the water composition of the earth
Oceans - 97.2%
Ice and glaciers - 2.1% and declining
Surface water <0.02% of that
What are the two different rock types that Manitoban lakes are on
Limestone
Precambrian shield rock
What is the primary difference between limestone lakes and precambrian shield lakes
Precambrian shield lakes are super unproductive. The rock is solid so there are very few dissolved and fewer nutrients solids in those lakes. Things like acid rain can seriously fuck up a lake with no buffer system.
Limestone lakes are more productive with a lot of dissolved solids, so they can take more abuse (pollution and pH change)
Do dissolved substances increase or decrease the density of water?
Increase
What are the factors that affect density of water?
Temperature, pressure, dissolved solids,
The highest density of water is found at ______ degrees Celcius
3.4
Does freezing point go up or down the more dissolved materials there are?
Down
The higher the temperature, the _______ the density change from one degree to the next
Greater
How does density of water effect freshwater fish.
Fish are exposed to more moderate temperature differences throughout the year - with ice only floating on top instead of sinking to the bottom
The viscosity of water is ____x that of air at the same temperature
100x
Surface tension ______ with increasing temperature
Decreases
What external factors affect surface tension and why is that important?
Electrolytes raise surface tension and pollutants (like acids) lower it.
This important because many animals use the surface tension of standing water to walk or lay eggs
What is the nm range for solar radiation
150-3200
What is PAR?
Photosynthetally active radiation - the radiation that can be used by photosynthetic organisms (400-700nm).
Some organisms can photosynthesize out of this range but have special processes to do so
Differentiate between the photic zones of Shoal lake and West Hawk lake
Shoal lake - shallow so photic zone extends to bottom
West hawk lake - deep so photic zone is only top few feet
Why do aquatic macrophytes have a shorter photoperiod than terrestrial ones?
Because when the sun is setting it is as such an extreme angle that almost all light is reflected.
Light over ____nm long does not travel far in water
900
What happens to light when it hits water?
Some light absorbed, some refracted, some continues downward. Light attenuation varies throughout the water column because of the presence of floating substances and algae
Light attenuation is ______ in DISTILLED water
Exponential
What types of lakes are the most clear (highest light attenuation)?
Alpine and crater lakes
Why do deep water algae appear red?
Red light disappears from the water column first so there is not point in trying to absorb it - instead it is reflected and causes colour
What is K= ln Io - ln Iz/Z
Beer-Bouqer law
What is the compensation point?
Point at which respiration = photosynthesis, life barely possible
Why is it better for water to freeze when it is calm?
Because then light can more easily penetrate the ice. If water is flowing when it freezes the ice is “frazzled” and not much light penetrates
Brown peat and bog waters are caused by ______ acids
Humonlimnic
What colour are limestone lakes?
Turqoise/aquamarine
Distinguish between apparent and true colour
Apparent - the way it appears to the eye
True - measured via spectrophotometry of DISTILLED wate
Organisms living in a narrow range of cold temperatures are called _______
Cold stenothermic
Organisms that can readily adapt to temperature change are called
Eurythermic
_______ organisms can only exist at high temperatures
Polythermic
What is a graben lake?
Graben occurs when tectonic shift causes large chunk of earth to fall downwards. This creates a basin. This basin fills with water.
These lakes are very deep with rapidly sloping sides, usually too deep for macrophytes, can be elongated, sometimes have almost perfectly flat bottoms
What are volcanic lakes?
Top blows off volcano and water collects
What is a coulee lake?
Occurs when Laval flows through water basins and cools to form a dam
List the types of glacial lakes (you know this shit)
Moraine-dammed lakes
Kettle lakes
Basins formed by scouring - land depressed so much that ice just collected there (this is how Great Lakes were formed)
What is karst topography and where does it occur?
Caves.
Occur in areas with limestone bedrock
Why do Manitoban waters drain into Hudson Bay?
Because the glaciers during the ice age were thicker/heavier over northern Manitoba so Manitoba is sloped
Has Manitoba always been full of lakes?
No, there have been many warming periods where Manitoba has experienced drought. Lake Winnipeg has even dried up and been overgrown with trees
What are Sub glacial lakes
Permanently covered by ice
How do higher acid concentrations affect heavy metals?
Make them more toxic
How are lagoon lakes formed?
When current from lake deposits so much sediment that it cuts a small part of a lake off from the rest
Where was the first hydro dam in Manitoba?
Point du Bois
Cryogenic lakes are located ________
On permafrost
How are thermokarst lakes formed?
Melting form houses, dumps, railways
What are bog lakes?
Caused by growth of sphagnum moss, which creates acidity and blocks drainage
Hydro dams cause a buildup of mercury in lakes - why is this? What’s the big deal?
Methyl-mercury is often leeched from hydro flooded soils.
Methyl-mercury is so toxic that a tiny amount can kill someone
What are reservoirs?
Man-made lakes
How are saline lakes created?
Often present because rivers terminate. The water has nowhere else to flow so the only removal of water is through evaporation - this leaves salt and other deposits in water
What is Bathymetry?
The study of underwater depth of ocean floors (like scuba maps)
What are the important topographic factors of a lake
Islands, elevation, surface area
Which Manitoban lake used to be known for it’s floating islands and giant leeches?
Sewell
How is the littoral shelf created? Does this exist in precambrian shield lakes? Why or why not?
The littoral shelf is created by waves - which erode the sides of a lake underneath a beach, creating a “littoral shelf” uo on which macrophytes can grow and still be in the photic zone.
No littoral shelf in precambrian shield lakes because the bedrock is too tough to erode
Most of the heat of a lake is absorbed in the top ______
1m
In winter, the lowest level of a lake has a temperature from ____ to _____ degrees Celcius
4 to 6 degrees
How do lakes lose heat?
Radiation to environment, evaporation, conduction
______ is the amount of heat put in a lake over a year
Heat budget
What occurs to the water bodies flowing into Indian Bay when the City of Winnipeg aqueduct pumps water out?
Indian bay loses water so quickly that new water from Shoal Lake and Lake of the Woods must be taken. The top-most layer of water is taken, disrupting any biological communities and causing a lowering in temperature
Above the thermocline is the _______ and below the thermocline is the cooler _______
Epilimnion, hypolimnion
In spring and fall, the epilimnion and hypolimnion are ________ temperatures because ______ occurs
The same, overturning
______ can drive thermocline deeper, or create more than one thermocline
Storms
What is the problem with early fall freezup in a lake?
Animals depend on turnover for oxygen so if the lake freezes over too quickly many fish can die
Describe the thermal regimes of lakes and how they vary season to season
During spring water is mixed and there are no distinct layers. In summer the epilimnion is at it’s deepest, and a lot of algae grows in this layer. There is no mixing, and as a result the hypolimnion can become anoxic because of the sheer amount of dying algae (which are eaten by bacteria that use O2).
In the fall, as temperatures cool, the epilimnion gets smaller and smaller until there is complete mixing.
In the winter a layer of ice covers the lake, followed by a very cold thin layer between 0 and 4 degrees. The rest of the lake is about four degrees, and there is no mixing
Describe a surface seiche
Occurs when very strong winds blow against lake and cause it to slosh back and forth violently - can cause flooding
A _____ consists of layers that do not mix. Describe in detail why this is
Meromictic. Often because of amount of dissolved substances and weight of each in different layers. Can be caused by organisms dying and making the bottom water more dense. Can be caused by photosynthetic organisms producing products that fall to the bottom. Can also be caused by mine tailings, less dense incoming water, or water from springs (crenogenic) containing many dissolved solids may join lake.
_______ lakes overturn constantly
Holomictic
Describe amictic lakes
Do not circulate, permanent ice cover. May be a uniform temperature throughout or may be warmer on bottom due to geothermal heating
Differentiate between cold and warm monomictic lakes
Cold monomictic:
Temperature ever over 4 deegres. Covered in ice in winter, never stratifies, spends all summer mixing and melting
Warm monomictic:
Circulate in winter, stratify in summer, never under 4 degrees.
______ lakes experience regular spring and fall overturns
Dimictic
_____ lakes have irregular circulation. Where are they located
Oligomictic, which are tropical
Describe polymictic lakes
Continuous circulation. Mostly tropical or shallow.
The heat budget of a lake increases the _____ the lake gets
Larger
List the types of arrhythmic water movement
Vertical convection currents
Wind induced currents
Density currents
Turbidity currents
Describe vertical convection currents
Top water cools down from evaporation, wind, etc. and warm water upwells to take it’s place
Describe wind-induced currents
The greater the surface area of the lake, the more significantly wind induced currents are. Water can be piled up on one end of the lake as a seiche. When this happens the undercurrent moves water in the direction of the wind.
Describe Langmuir cells
Wind streaks. Helixes rotate parallel to the wind direction underwater and reverse direction from their adjacent helix. Surface convergent zones occur along line where two helixes are downwelling, and surface divergent zones occur along lines where two helixes are upwelling. These convergent and divergent zones create lines of materials floating on the surface.
Distance of each Langmuir cell will be half the distance between two convergent lines
Describe density currents
River flowing into a lake will find the strata which it’s density requires, and create a current through the lake in that stratum
What occurs when water carries silt load which adds to density
Turbidity currents
Distinguish between laminal flow and turbulent flow
laminar - uniform, parallel, low velocity, small stream diameter (larger streams need current to hardly move to achieve laminar flow), very uncommon
Turbulent - discombobulated, non-parallel, cause eddy effects
Water encounters resistance when it hits water of a different consistency, producing vortices called _______
Eddies
What is helpful about eddies?
Keep sediments moving (prevent too much deposition), maintain plankton in photic zone, transfer heat, move sediments from current to water and vicé versa
Surface waves are ______ water movements
Rhythmic
How are surface waves produced?
When wind hits a water surface, it displaces water which builds up a crest. Water is displaced in an orbital inside the wave crest
What conditions must be present to get white crests on waves?
Ratio of height to wavelength exceeds 1:10. The white crests are the waves toppling over
If the wavelength (λ) is greater than 2πcm the wave is called ________.
If the wavelength (λ) is less than 2πcm the wave is called ________.
Surf occurs when wave height is ______% of λ
Gravity wave, ripple, 77%
What is the fetch of a wave?
Downward distance from shore to cresting wave (AKA distance wind has travelled uninterrupted)
What is undertow?
Breaking waves on shore causing water to flow underneath incoming water. Can drag people down underwater
