Chapter 10: Density, Layering, and Lake Mixing

At what temperatre is water most dense at?

4 degrees celsius

What is an isothermal/homiothermal body of water?

A body of water that has a uniform temperature

How does wind mix water and distribute heat?

Wind mixes the upper water layers and distributes the heat downwards

What can you deduce from the following graph?

What is shown is a vertical daylight curve

• Lake B is warm at the surface and gradually gets colder as it increases in depth

• Amount of light piercing the lake decreases with depth as well

what the fuck kind of graph is this

this is a vertical temperature profile showing lake stratification.

• the thermocline is when temp changes in such a short amount of depth

• At the hypolimnion, water becomes more dense and colder

What is the relationship between pressure, temeprature, and maximum density?

pressure lowers the temperature of maximum density.

• A low ratio with tempeature, desnity, and density change means that there was a lot density change, meaning it can take on a gaseous form

What does a high solute concentration do to density?

Temperature of greatest density is depressed

• salt lowers the freezing point of ice

• think of salting roads when there’s ice, it melts the ice faster

• can cause inverse stratification

  • salt

  • biocarbonate

  • calcium

what the fuck kind of graph is this

This is an inverse temperature stratification graph in a saline desert pool

• The solid colored line is temperature, where it is cold at the surface then gets warmer as depth increases

• The broken up light colored line is the density of distilled water, would be the “norm”

What even is stratification?

Lake stratification is when lakes “divide” into different layers (strata) of water with different temperatures

What is the lake stratification during the summer and fall?

During the summer

• Epilimnion

• Metalimnion (thermocline)

• Hypolimnion

(Eat My Hair)

During fall

-Flips over

What is Stability (S)?

the amount of work required to mix a lake to uniform density without adding or subtracting heat.

• Stable occurs bc water has a high heat capacity

What do the peaks of the graph mean? and where can u tell mixing occurred?

• Peaks show how much energy transfer was there during the season

• The biggest peaks show where mixing occurred, as seen with the arrows pointing

What is an Amixis lake?

Always usually permanently covered in ice

lake never mixes

• high latitude

• high elevation

• must be cold all the time to survive

What is a Holomixis lake?

Wind circulation mixes entire lake

• when it overturns, the entire water mass is involved

• Has a lot of subclassifications

  • Oligomixis

  • Monomixis

    • Cold monomixis

    • Warm monomixis

  • Dimixis

  • Polymixis

What is an Oligomictic lake?

Circulation periods are unusual, irregular, and short in duration

There are two types

• Equatorial lakes at low elevations

  • very little seasonal change

• Cold mountain lakes that remain cold but not iced over

  • Lots of seasonal change, ice over in winter

What is a Monomictic lake?

Experience one regular period of mixing per year

• Usually exist where seasonal changes are pronounced

What is a cold monomixis?

One mixing event

• frozen in winter and shielded from wind

• thaws in the summer

  • experiences mixing effects

• common in warm nothern lakes such as in the United States

What is a warm monomixis?

Almost all North Texas lakes are like this

• They circulate in winter and lack ice cover

• located in mid latitude in temperate regions

  • exception: Lake Victoria

    • circulates bc density effects of rainy season

What are Dimictic lakes?

“Di” = two; two mixing periods

• vernal (spring) and autumnal

• stratification occur during warm periods/ turn over

What usually happens during cold dense water in a water mass?

it sinks to the bottom (usually)

What is a seiche?

rocking back and forth motion like wave

• standing wave in an enclosed body of water

By looking at the graph, what months were there water inverse stratification? and what was the temperature at 20m like in July?

Inverse water stratification was seen from November through January, where warm waters were located at the bottom and cold water at the surface.

• In july, the temperature at 15 meters was 6 degrees Celsius

What are polymictic lakes?

“poly” lots of mixing periods or continuously mixed

• influenced through changing conditions thru out day instead of seasonally

• common in shallow bodies of water

• nocturnal cooling occur from evaporation

What are Meromixis lakes?

Lakes circulate at times, but incomplete

• entire water mass DOES NOT participoate

• ottoms remain stagnant and anaerobic

  • bottom layer: Monolimnion

  • upper layer: mixolimnion

  • middle layer: chemocline (rapid chemical change w depth)

What are Biogenic meromixis lakes?

• Very odd and rare; must possess characteristics that prevent mixing and encourage anaerobic respiration

  • Topography and climatology

  • Bacterial growth in deep areas

Anaerobic oxygenation at bottom

What is the Langsee of Austria?

Shallow, surrounded by hills

• goey dark sapropel

• below sapropel, has organic sediments

• cutting trees around the lake= importation of clay which led to meromixis forming 2,000 years ago

what the fuck kind of graph is this

This is dissolved oxygen curve

• arrows points at dichothermic temp curve

• Boxed area is where it is anaerobic

• circled area is where oxygen is expected to be and where biogenic meromixis is at

What is an Ectogenic meromixis?

More common than biogenic meromixis bc no specific conditions

• Almost always because of strong salinity differences

  • Usually in arid areas where water is concentrated by evaporation

what are Crenogenic meromixis lakes?

Happens because of salty inflow of springs from the bottom and surface inflow from streams, rivers, or rainfall.

What is a Dicothermy lake?

Odd temp curves notices that cna be due to

• geothermal sources

• heat produced by bacteria

  • ex) lake Mead and Lake Washington

What is a Mesothermy lake?

• A warm stratum sandwiched between upper and lower colder layers

• Transitory in areas without ice cover

• Can be permanent in areas with ice cover

  • Sometimes caused by weird effects of solar heating through the ice

What is a Poikilothermy?

• Complex temperature curves that have at least one low point and one high point

  • Very rare and transient

What the fuck kind of graph is this?

• Graph A: shows an isothermal curve where is it around 5 ft deep

• Graph B: Shows a middle-layer mesothermal lake

• Graph C: Shows a poikilothermal curve with 2 diff curves

• Graph D: Shows a Dichothermal curve with the first curve showing a warm top layer and the second curve showing an even hotter bottom layer of water mass