Lec 9: Lakes I

Question 1

Why do lakes matter? (5)

Answer 1

 Water store
 Fish (food) and biodiversity
 Regulate river flows
 Regulate climate
 cultural and recreational value

Question 2

What percentage of all lakes are in Canada?

Answer 2

62%

Question 3

What are the hydrological and biological definitions of lakes?

Answer 3

• Hydrological definition(s): based on size (depth and width)
   a body of standing water deeper than 2 meters (or 5, or more?)
   a body of water larger than 2 ha (or 5, or more?)
• Biological definition(s): body of standing water with the 5 zones
   a body of standing (lentic) water with a littoral zone (shallow, sloped shore), a photic zone (open water with photosynthetic activity, e.g., algae), and a profundal (benthic, aphotic) zone
  (deep water without photosynthesis)

 a body of standing water with a certain wave dynamic at the shores

Question 4

Name 6 lake origins

Answer 4

1) Glacial/periglacial lakes
* mostly depressions formed
by ice that are filled after glacial retreat (most Canadian lakes)

2) Volcanic/crater lakes
* Inside caldera

3) Rift/tectonic lakes
* In tectonic rifts, can be very deep

4) Endorheic or aeolian lakes
* Aeolian lakes are in depressions caused by wind erosion
* Lakes with no outlet, typically in dry regions

5) Lakes formed by river activity
* E.g., oxbow lakes (formerly part of river meanders), floodplain lakes

6) Many other but rather unique origins
* E.g., land slides damming a river; lagoons; karst sinks (dolines); karst outcrop lakes; waterfall pools; meteorite lakes; beaver dams; …

Question 5

Name 4 types of glacial lakes

Answer 5

• ice-dammed
• bedrock-dammed
• landslide-dammed
• moraine-dammed

Question 6

What are thermokarst lakes?

Answer 6

lakes created by the melting of permafrost, which creates surface depressions that fill with water

Question 7

Which types of lakes are the oldest and deepest?

Answer 7

tectonic lakes

Question 8

What are 5 types of lakes formed by river activity?

Answer 8

► Plunge-pool lakes
* In pools formed by waterfalls

► Lateral lakes
* Tributaries dammed by river
sediments

► Floodplain lakes
* In floodplain depressions

► Oxbow lakes
* Disconnected former
meander loops

► Deltaic lakes
* In river deltas, formed by
sediment damming

Question 9

How do lakes disappear?

Answer 9

Over long time scales, lakes disappear due to sediment deposition
* Influx of river sediments; and/or accumulation of organic matter

more and more nutrients
oligotrophic - mesotrophic - eutrophic - pond/marsh - land

Question 10

How is lake volume measured?

Answer 10

Bathymetric surveys
GIS

Question 11

How much water is estimated to be stored in lakes?

Answer 11

180 000 km3

Question 12

Rank the following in terms of relative storage volume of global lakes (% of the 180 000km3), from biggest to smallest

Answer 12

1) large freshwater lakes (49%)
2) large saltwater lakes (44%)
3) medium lakes
4) small lakes

Question 13

Why is lake volume important? (6)

Answer 13

• determines how much carbon is withheld in the lake
• impacts the weather
• biological production
• biodiversity
• nutrients and pollutants
• residence time