Test 2.1 Lakes

Question 1

What 7 characteristics would you use to describe a lake?

Answer 1

Length
Width or breadth
Depth: max or mean
Shoreline (L)
Volume
Retention or residence time
Light availability

Question 2

How do you calculate residence time?

Answer 2

Volume / mean rate of inflow
or
Mean rate of outflow + evaporation rate

Question 3

How are tectonic lakes formed?

Answer 3

When 2 plates move apart creating a Rift Valley

e.g. Lake Baikal, Siberia, oldest in the world, 1620m deep

Question 4

What are the characteristics of Lake Baikal?

Answer 4

Oldest lake in the world
L=636km
W=80km
L (shoreline)=2100km
D=1620M

3 depressions with total volume of 23,600km^3
>20% world’s surface freshwater
1200 species of animals
1000 species of plants

Question 5

How are glacial lakes formed?

Answer 5

Formed in last ice age

Glacier dredges the bottom of the valley creating a bowl

Or deposited moraine blocks a stream, forming a lake

Kettle lakes formed by melting ice blocks

Question 6

How are thermokarst lakes formed?

Answer 6

Permafrost thawing to create shallow surface tundra lakes

Question 7

How are oxbow lakes formed?

Answer 7

Large meanders in rivers join up and cut off the old river path

Question 8

Reasons for building man made lakes?

Answer 8

Hydro power e.g. Lake Powell, Hoover Dam

Water supply/ flood storage

Question 9

Meaning of Lotic

Answer 9

Flowing - rivers

Question 10

Meaning of Lentic

Answer 10

Standing - lakes

Question 11

What variables are significant in lakes?

Answer 11

Depth for:

• Light penetration
• Temperature regime

Distinct seasonal patterns in temperature & water chemistry

Current velocity less significant

Autochtonous production more important than allochthonous production

Question 12

What is lake temperature stratification?

Answer 12

Summer air temperatures warming the upper layers of lakes separates the upper layer of water from the lower colder layer.

Question 13

What is the name of the upper warmer surface layer of a lake?

Answer 13

Epilimnion - well oxygenated

Question 14

What is the name of the deeper cooler layer of a lake?

Answer 14

Hypolimnion - oxygen depleted

Question 15

What is the name of the distinct separation of layers between upper warmer water and deeper cooler water?

Answer 15

Thermocline

Question 16

Why is the separation of water layers important?

Answer 16

In summer they can become separated:

Stops oxygen moving from surface to deeper layers- depleted
Prevents nutrients from lower layers reaching the upper layers- depleted

In cold regions the temperature of layers is the opposite

Mixing occurs in spring and autumn

Question 17

Definition of Holomictic lakes

Answer 17

mixed all year. Never form epilimnion or thermocline

Question 18

Definition of Monomictic

Answer 18

Lakes that mix once per year

Question 19

Definition of warm Monomictic

Answer 19

Lakes that stratify in summer, mixed in winter

Question 20

Definition of Dimictic

Answer 20

Lakes that stratify in both winter and summer, mix in autumn and spring

Question 21

Definition of Meromictic

Answer 21

Lakes that never mix

Question 22

How does warmer waters affect deepwater fish species and oxygen levels?

Answer 22

Lake stratification creates a greater contrast between the two layers, reducing the oxygen mixing to the deepest parts therefore fish cannot survive

Question 23

What are the limiting factors for producers in lakes?

Answer 23

Nutrients: phosphorus & nitrogen

Light: Transparency (turbidity and colour) determines light

Question 24

What interferes with light penetration?

Answer 24

Colour- (dissolved substances)
coloured lakes less productive

Turbidity- suspended particles
plankton will also limit light reaching bed

Question 25

What do you use to measure nutrients and light penetration?

Answer 25

Van Dorn sampler (tube) Secchi disc for transparency- measure how deep before not visible

Question 26

What is an Oligotrophic lake?

Answer 26

- Nutrient poor - Low productivity - High transparency in epilimnion - High dissolved oxygen in hypolimnion

Question 27

What is a Mesotrophic lake?

Answer 27

middle rich?.?.?

Question 28

What is a Eutrophic lake?

Answer 28

- Nutrient rich - High productivity - Low transparency in the epilimnion - Low dissolved oxygen in the hypolimnion

Question 29

What is benthic algae?

Answer 29

Algae on the lake bed

Question 30

What is planktonic algae?

Answer 30

Algae living in the open water e.g. diatoms

Question 31

What are macrophytes?

Answer 31

Rooted aquatic plants e.g. Litorella 'shore weed'

Question 32

What are zooplankton?

Answer 32

Microscopic animals feeding on phytoplankton and other zooplankton

Question 33

What are phytoplankton?

Answer 33

Some are filamentous algae | Some diatoms- single cells or in colonies (require silica)

Question 34

Name some consumers

Answer 34

Mayfly Chironomidae Pond snail Freshwater limpet

Question 35

Name some predators

Answer 35

Waterfleas Phantom midge larva Roach fish

Question 36

What are keystone species. Give examples

Answer 36

Species that have particular importance within a community Gwyniad fish Perch and Ruffe fish

Question 37

Give an example of a dominant lake species

Answer 37

Chronomidae

Question 38

What are the winter patterns of phytoplankton?

Answer 38

Lake is well mixed but plankton abundance low, limited by light and temperature

Question 39

What are the spring patterns of phytoplankton?

Answer 39

Plankton increase and use up nutrients

Question 40

What are the summer patterns of phytoplankton?

Answer 40

Lower plankton abundance, limited by nutrients

Question 41

What are the autumn patterns of phytoplankton?

Answer 41

- First storms - Mixing - Thermocline breaks up - Plankton exploit newly available nutrients

Question 42

What is the adaptation of water scorpions

Answer 42

Breathing tubes

Question 43

What is the adaptation of Phantom midge larvae

Answer 43

Buoyancy

Question 44

What is the adaptation of Water Measurer

Answer 44

Long legs to walk on water

Question 45

What is the adaptation of Water Boatmen

Answer 45

Traps air

Question 46

What is the adaptation of Chironomidae

Answer 46

Haemoglobin type pigment

Question 47

What is the Euphotic depth?

Answer 47

Depth where photosynthesis is possible - limits phytoplankton depth - limits growth of rooted plants and benthic algae

Question 48

What is the Littoral zone?

Answer 48

Lake bed where plants can grow

Question 49

What is the Profundal zone?

Answer 49

Lake bed where there is no plant growth