L9. Lakes

Question 1

Define lake

Answer 1

hydrological: a body of standing water deeper than 2 meters
biological: a body of standing lentic water with a littoral zone, a photic zone, and a profundal zone (deep water without photosynthesis

Question 2

What a lake origins

Answer 2

• glacial/periglacial lakes
• volcanic/crater lakes
• rift/tectonic lakes (in tectonic rifts)
• Endorheic or aeolian lakes(lakes with no outlet)
• lakes formed by river activity (oxbox lakes, floodplain lakes)
• Thermokarst lakes
  -lagoons

Question 3

What causes disappearance of lakes?

Answer 3

Over long time scales lakes disappear due to sediment deposition (river sediments and accumulation of organic matter)

Question 4

What is global lake distribution

Answer 4

Most lakes are in the northern latitudes
- 60% of lakes are in Canada
- so many small lakes (still important)

Question 5

Why is lake volume important

Answer 5

relates to:
- residence time
- nutrients and pollutants
- carbon budget
- heat budget and mixing patterns
- weather and climate
- biological production
- biodiversity

Question 6

How can you measure lake depth

Answer 6

• Bathymetric surveys (costly and time consuming)
• Gis

Question 7

What are the main hydrologic lake processes

Answer 7

• most lakes have various inputs (P and inflow) and output (E, outflow, and seepage)
• residence time in lakes are usually on the longer time scales (months, years)

Question 8

How does lake stratification work?

Answer 8

Lake stratification is the layering of water due to density differences
- thermal stratification (colder water is denser)
- chemical stratification (typically caused by salt content)

Question 9

How does seasonality impact lake mixing?

Answer 9

Winter: stratification is stable (no wind due to ice)
Spring/fall: turnover starts with inverse temperature gradients at the top (eventually denser water sinks and things mix well)(warmer water in fall)
Summer: strongly divided by the thermocline and mixing due to wind will occur above it

Question 10

What are some properties that affect lake mixing?

Answer 10

• change in temp
• wind
• size and depth
• bathymetry and shape of lake
• inflow and outflow (including groundwater)
• ice cover

Question 11

What are the stratification of a meromictic lake

Answer 11

• epilimion
• metalimmnion
• hypolimnion
• monimolimnion