EXAM 1: Temperature

Where does a lake gain most of its heat?

solar radiation

What kind of solar radiation is mostly absorbed by a lake?

mostly IR and red is absorbed and transformed to heat in the 1st few meters

How do some lakes gain heat?

by in put, runoff, or groundwater temperatures

How do lakes lose most of their heat?

thermal radiation: mainly in the top few centimeters

What are two other ways lakes lose heat?

evaporation

outflow (especially in reserviors)

Where is most heat gain and loss at in a lake?

at the surface

What is the most important thermal implication?

thermal stratification

What is thermal stratification?

layering of water of different temperatures

At what temperature is water at its max density?

4 degrees Celsius

What are the density differences at higher temps compared to lower temps?

at higher temperatures density differences among the temperatures are greater than at lower temperature

What is spring turnover?

in spring, most H2O is roughly 4-8 degrees C and the same density.

-the water mixes well from top to bottom typically via wind action + turbulence

What is the temperature like throughout the water during spring turnover?

homogeneous temperature from top to bottom

As spring progresses, what happens to the surface layers?

they begin to heat rapidly from solar radiation gain.

As the water begins to heat more as spring progresses, what happens?

eventually wind, turbulence, etc, cannot distribute heat throughout the lake as rapidly as it is being gained.

By summer, what occurs?

stratification occurs, which is called summer stratification.

What is the epilimnion?

warmer, less dense, upper layer in summer stratification

What is the hypolimnion?

colder, more dense, lower layer in summer stratification

What is the metalimnion?

area between epilimnion and hypolimnion where the greatest temperature change with depth occurs

When the metalimnion is sharp and distinct, what is this called?

thermocline

What is fall turnover?

surface waters begin to lose heat to the air, which typically happens at night, faster than heat is gained from solar radiation in the day.

What occurs during fall turnover?

cooler, more dense, surface water sinks to the bottom. eventually the epilimnion is similar in temperature (and density) to the hypolimnion. water is homogeneous temperature from top to bottom.

What is another word for winter stratification?

inverse stratification.

What is winter stratification?

eventually the surface cools enough to freeze.

What does inverse stratification mean?

the ice is less dense, but COLDER than the underlying water which is why it is "inverse" stratification

How can summer stratification be easily seen?

by using a "thermal profile"

What is mixis?

lake mixing (turnover)

What is amictic?

no mixing occurs, there is usually a permanent ice cover.

What is meromictic?

partial mixing

What is chemolimnion? What is an example?

chemical layer distinction

-Lake Nyos in Cameroon in 1986 had a limnic erruption

What is holomictic?

more than one complete mixing

What is a dimictic lake? What does it require?

2 periods of mixing per year.

-requires winter inverse stratification (ice cover)

How are holomictic lakes classified?

based upon their mixing frequency

What is a warm monomictic lake? Where does it normally happen?

one period of mixing in the fall/winter

-Typical of southern or warm temperate region lakes

What is a cold monomictic lake?

water is less than 4 degree C with one period of mixing occurring during the summer.

Where do cold monomictic lakes normally occur?

arctic regions, extreme northern temperate regions (think Great Bear Lake)

When does mixing occur in a cold monomictic lake?

mixing occurs when lake surface thaws in the summer

What is a polymictic lake? What are two types?

mixing almost continuously and will mix almost daily.

-Cool polymictic lakes and warm polymictic lakes

What is a cool polymictic lake? Where do these occur?

ice-covered part of the year

-at or slightly above 4 degrees C during the warm season. Stratify briefly in the heat of the day and cool mixed at night

-Occurs in shallows northern temperate lakes

What is a warm polymictic lake? Where does this occur?

Tropical lakes with temperatures greater than 4 degrees C.

-Short periods of heating and weak stratification followed by rapid cooling.

-Winds and convection sufficient to break up stratification.

-Occurs in high altitude tropical lakes.