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ECOR 9220 > Quiz 2 > Flashcards

Quiz 2 Flashcards

(58 cards)

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1
Q

What is the temperature of maximum density for freshwater?

A

3.98 degrees C

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2
Q

How is saltwater different than freshwater in terms of density? (2)

A

As freshwater cools, it becomes less dense below 4 degrees C

As saltwater cools, it keeps become dense (so why doesn’t it sink?) = salt is excluded from the crystalline hexagonal structure

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3
Q

Why doesn’t the ocean freeze? (3)

A

As salt concentration increases, the freezing point of seawater decreases - salt makes water molecules unable to form ice crystals to freeze the water (eg. Why we put salt on icy sidewalks)

Usually fresh water freezes into hexagonal (6 sided) shape

Salt water forms cubic crystals (4 sided) cubes that leave salt out

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4
Q

What are the density layers of a lake? (4)

A

Epilimnion
Thermocline
Hypolimnion

Lake density variation caused by gravity causes thermal stratification

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5
Q

Circulation patterns (5)

A

Most north and south temperature lakes exhibit a consistent annual cycle of stratification and mixing through

Spring - mixing

Summer - stratification with epilimnion, hypolimnion and thermocline

Fall - mixing

Winter - ice cover and large hypolimnion

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6
Q

What drives lake circulation patterns? (4)

A

Density stratification

Wind energy

Regular periods of energy/heat
gain (spring and summer) and

Regular periods of energy/heat loss (fall and winter)

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7
Q

What kind of lakes are normal north or south temperate lakes? (3)

A

Generally have two periods of complete circulation

Therefore they are Dimictic (mix twice per year)

And Holomictic (mixes completely)

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8
Q

Holomictic

A

Describes a lake that mixes completely

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9
Q

Dimictic

A

Describes a lake that mixes twice per year

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10
Q

Why do lakes stratify in the summer?

A

Because the epilimnion forms and so it can’t be mixed

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11
Q

Normal holomictic dimictic lake temperature with depth (3)

A

In winter, temperature is warmer as depth increases (called inverse stratification)

In spring and fall temperature is constant

In summer, temperature is lower as depth increases

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12
Q

Lakes that don’t “behave” (6)

A 
Warm monomictic 
Cold monomictic
Amictic
Oligomictic
Polymictic
Meromixis
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13
Q

Warm monomictic lakes (4)

A

Temperatures do not go below 4 degrees C

Therefore they don’t freeze

They circulate freely all winter, and stratify thermally from early summer to late fall

Eg. St. Mary Lake on Saltspring Island

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14
Q

Cold monomictic lakes (4)

A

Temperatures never get above 4 degrees celcius

They are all frozen in the winter

They circulate in the late spring/summer/early fall when they are ice-free

Eg. Arctic and high elevation lakes in the Capilano River Watershed

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15
Q

Amictic lakes (2)

A

These lakes are sealed off permanently by ice and do not circulate

They are rare and mainly found in the Antarctic and at high elevations

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16
Q

Oligomictic (4)

A

Oligo means sparse or thin - they rarely circulate and mix only during extreme weather events

These lakes are generally tropical and have temperatures well above 4 degrees celsius

They circulate at irregular intervals during periods of abnormally cold weather (causing sinking) or extreme wind (hurricanes/typhoons)

Usually have a small surface area and/or great depth

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17
Q

Polymictic (4)

A

Poly meaning always mixing (everyday or every few days)

The lakes are usually large in area and only moderate in depth

They are found in equatorial regions

Circulate continually at temperatures near or above 4 degrees celsius

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18
Q

What are the main determinants of circulation patterns in most lakes and how might this change in the future? (3)

A

Elevation and latitude determine the circulation patterns in most lakes

With climate change, cold monomictic lakes might shift to dimictic, and dimictic mike change to warm monomictic lakes as cool temperatures move up altitude or latitude

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19
Q

Meromixes (5)

A

“The wild child”

Mero = rare

They are the opposite of holomictic lakes (“normal” fully mixing lakes)

These lakes do not circulate due to very strong density stratification

Their density is usually determined by the presence of dissolved solids like salinity, and secondarily by temperature

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20
Q

Miromictic lake layers (3)

A

Mixolimnion - upper stratum of the lake that mixes periodically

Chemocline - steep density, temperature, and salinity gradient that separates layers (called chemocline because is related to salinity rather than temperature)

Monimilimnion - permanently stagnant lower layer that is usually anoxic

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21
Q

Monimolimnion (4)

A

Temperature can be several degrees warmer in this layer

Even in the winter under ice cover, the monimolimnion can be over 20 degrees Celsius

Usually anoxic

High is sulphur and can cause purple lakes

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22
Q

The use of meromictic lakes (2)

A

Israel uses meromictic lakes to generate greenhouse gas free heat from solar energy

Island copper pit reclamated from a mine to chemical/heavy metal trapping

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23
Q

Zones of meromictic lake used for heat energy (3)

A

Surface zone - mixed, relatively fresh water

Insulation zone - increasing salt, traps in the storage area

Storage zone - saturated salt water that holds solar energy in the monimolimnion

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24
Q

Why can miromictic lakes be used to generate heat? (2)

Study These Flashcards
A

Solar energy is absorbed at the pond bottom and held there by the insulation layer

The hot water is then pushed out by cold water into a hot engine generating electricity

25
4 categories of meromictic lakes
Crenogenic Ectogenic Endogenic Morphogenic
26
Crenogenic
Result from submerged salt springs that deliver dense water to deep portions of the lake
27
Ectogenic (2)
Results from an external event, such as a tsunami (common form on the coast) that brings salt water into a freshwater lake or freshwater into a saltwater lake Eg. Sakinaw Lake, Nitinat Lake, or Henderson Lake in BC
28
Endogenic (2)
Biogenic meromixes that result from an accumulation of salts released from organic matter in the monimolimnion Eg. Yellow Lake was fixed with a pump that mixes the layers and creates oxygen increasing the abundance of rainbow trout
29
Morphogenic (2)
These lakes are predisposed to become meromictic because of their basin morphometry I.e. small surface area and greater depth - e.g. Colomac Zone 2 Pit Lake
30
Chemoautotrophic (3)
Organisms that are created because they obtain their energy from a chemical reaction Sometimes occur in meromictic lakes and develop bacteria that live in the interface between oxic and anoxic conditions Can turn lakes purpose
31
Why study light in lakes? (4)
Drives photosynthesis and lake metabolism Influences thermal structure Regulates type and metabolism of biota Can damage biota with UV rays
32
What is the dual nature of light? (2)
Energy - heat flux that is measured in energy/time/area Eg. cal/min/cm2 or Joules/min/cm2 Particle - biochemical processes Photons (quanta) Eg. 1 mol photons = 1 Einstein
33
Solar constant
The rate at which radiation reaches the earth’s outer atmosphere
34
Solar energy reflection
Much of the suns solar energy is reflected by the atmosphere, clouds, earth’s surface, and oceans and land
35
Measurement of light in lakes (4)
Measured by PAR = Photosynthetically Active Radiation It is the amount of light available for photosynthesis, which is light in the 400 to 700nm wavelength Units are in umol of photons Waves measured with an underwater photometer
36
Factors affecting light intensity and quality through air (5)
Latitude Solar angle (time of day and season) Altitude Atmospheric transparency - haze, smoke, particles Cloud cover
37
Factors affecting light intensity and quality at the water surface (3)
Angle of light Wave height and foam Ice and snow
38
Absorption of light in water (4)
Light can be absorbed by water through its transformation to heat This occurs in three ways: Through suspended particles Through dissolved particles Through water itself
39
Photic zone and light transmission (5)
1% of surface light transmission is used to define the depth of the photic zone Pure water transmits light at 460nm This is why very clear lakes appear crystal blue As turbidity increases, the peak of maximum transmission shifts to the orange-red part of the spectrum Only blue part of spectrum can reach deep ocean, so that’s why bioluminescent fish produce light at 460nm
40
Light and depth relationship
Light decreases exponentially with depth
41
Extinction coefficient (2)
Refers to how strongly a medium absorbs different wavelengths Absorption is the smallest in water when the wavelength is 480nm
42
Visibility (transparency) (3)
Is the measure of the depth to which you can see in the water Variable between observers and day conditions Can be measured with a secchi disk
43
The secchi disk (2)
Measures both colour and particulates But be consistent in measurements or not very accurate
44
Water movements (3)
Lakes behave like large mechanical oscillators Respond in numerous complex ways to applications of force Are frictionally dampened by viscous forced associated with turbulence
45
Why is it important to understand water movements?
It underlies many restoration activities
46
Convection circulation (4)
Circulation without wind Water is most dense at 4 degrees Celsius and gets less dense as it cools or warms Therefore, as heat is gained (during the day) or lost (at night), movement of lake water is induced by density decrease (warming) or density increase (cooling) This causes rising or sinking of water by convection currents
47
Columnar ice pencils (2)
Can form when sun warms soil and starts to melt edges of lake This begins lake circulation under the ice, which results in dissolved solids leaching back into hexagonal ice crystals forming columns
48
Wind circulation (3)
Lakes are rarely calm and most water movements are initiated by input of wind energy Surface water velocity is about 3% of wind velocity after ~1hr of steady wind Takes up energy from the wind at all size scales
49
Langmuir Circulation (6)
A special type of circulation limited to surface layers Discovered in the 1920s Caused by the Coriolis Force circulating water up and creating “scum line” of debris Alternating rolls of water are at right angles to the wind Wind speeds must exceed about 2 to 3 m per second Downward velocity is ~3X upwards velocity
50
What problems can the coriolis effect cause?
Nutrient dispersal reaching shoreline and creating algal blooms
51
Surface seiche (4)
Is a barotropic (surface wave) which affects the motion of the entire water mass of the lake Wind Set-up is a local rise in water level caused by wind When the wind stops, the periodicity of the vertical movements at the antinodes is a function of the length and depth of the basin Amplitude of vertical oscillation is small
52
Uninodal surface seiche oscillation equation
t = 2L/sqrt(gh) Where: ``` t = time L = length of basin at the surface (m) h = mean depth of the basin g = acceleration of gravity (980.6 cm/sec2) ```
53
Binodal seiche
Are created when pressure is periodically exerted and released in the centre of a lake basin
54
Internal seiche (5)
When a lake is stratified, the layers of differing density oscillate relative to one another Most conspicuous of these is the successive oscillation of the metalimnion (thermocline) Amplitude can much much larger than the displacement of surface seiches (can be up to 40+ meters high) Can be uninodal, binodal, or multinodal Responsible for major fish kills from strong heat mixing and transport
55
Internal seiche equation
t = (2xL)/(sqrt(g(dh-de))/((dh/zh)+(de/ze)) Where: L = length of metalimnion (m) t = periodicity (sec) dh and de = density of hypolimnion and epilimnion (gm/cm3) g = acceleration of gravity (980.6cm/sec2) zh and ze = thickness of hypolimnion and epilimnion (m)
56
Thermal budgets (3)
Temperature of lakes directly influences the physics, chemical reaction rates, and biology of lakes A large body of water yields so much heat to the atmosphere during autumnal cooling that the surrounding land is affected and the first winter frosts are postponed Conversely, in spring, a pager body of water absorbs so much heat that the onset of terrestrial growing season is delayed
57
High thermal capacity of water (2)
Allows for mediation of temperature in lake because heat is being exchanged to and from surround areas This is thanks to hydrogen bonding
58
Heat budget equation (3)
Refers to the amount of heat absorbed by a body of water during a specified amount of time Annual heat budget is the sum of all the other types, and is the total amount of heat that enters a lake from its lowest mean temperature of the year to its highest To calculate the annual heat budget, we calculate the peak mean heat content of the lake and subtract the minimum heat content if the lake V(cm3) x maxtemp(C) - V(cm3) x mintemp(C) —————————— ——————————- Lake area Lake area

ECOR 9220 (11 decks)

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