Lake and Rivers

Question 1

What are the different ways in which lakes can form?

Answer 1

Retreating glaciers forming basins 
Slit deposition or cut-off meanders in rivers 
Sinking volcanoes 
Extinct volcano crates 
Landslides 
Man-made reservoirs

Question 2

What are the different zones of water column?

Answer 2

Epi= Surface layer 
Meta= Middle layer 
Hypo= Bottom layer

Question 3

What happens to temperatures to lakes?

Answer 3

Water has high specific heat capacity= Slow warming and cooling of surface
Seasonal stratification of temperature= Separation of the water into 3 layers, change in temperature at different depths

Cold water is denser than warm water

Question 4

What happens to the lake stratification during summer?

Answer 4

Surface water becomes heated, becomes lighter= Floats on cold water below

Thermal barrier

Little mixing

Steep temperature decline= Thermocline= Lowest temperature is the shallowest

Question 5

What happens in the autumn?

Answer 5

Air temperature falls= Surface water loses heat= Metalimnion sinks (middle becomes denser) while the top layer (epi) increases to whole lake

One temperature

Mixing

Question 6

What happens in winter?

Answer 6

Surface water cools= Becomes lighter on surface, Wind
IF no ice= High mixing
IF ice= Water immediately below ice warms= increases density?= Drops to bottom

High temperature at bottom , Inverse stratification= Lowest temperature becomes the deepest

Question 7

What happens during Spring?

Answer 7

Ice melts, surface water drops
Mixing of water
All becomes 4 degrees celsius= Wind mixes easily
If above 4 degrees celsius= Summer stratification

Question 8

What happens to the oxygen in lakes?

Answer 8

Cold water= Holds more oxygen than warm

Oxygen Into lake: Atmosphere, mixing, photosynthesis
Oxygen out of rivers: Increased temperature, increased respiration, aerobic decomposition

In summer: Lake becomes stratified, decomposition of bottom sediments is aerobic = Uses up oxygen, becomes hypoxic or anoxic

Hypoxic= Little oxygen 
Anoxic= No oxygen 

However there are exceptions: Good oxygen content throughout summer in deep oligotrophic lakes as there is little demand for oxygen + clear lakes= Light below thermocline (temperature gradient) so photosynthesis can take place

Spring and autumn: Water re-circulates= O2 replenished in deep water

Winter: No ice, plentiful oxygen= Less bacterial decomposition= Cold water holds more O2

Question 9

What are the different zonation of organisms?

Answer 9

• Pelagic: open water
• Littoral: high water level to euphotic depth (with light)
• Profundal: zone below euphotic depth (no light)
• Benthic: bottom – all depths

Question 10

What is the productivity like in lakes?

Answer 10

Autochthonous: Something that comes from the lake itself
Autochthonous input of organic material tends to dominate
Types of primary productivity depends on lake morphology
Primary productivity: The rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances

If you have: High pelagic/littoral ratio= Deep, open lake= Pelagic phytoplankton= Low productivity

If you have: Low pelagic/littoral ratio= Shallow lakes, extensive bays= Dominated by macrophytes= Large attached plants and algae= High productivity

Phytoplankton seasonality: Spring blooms in temperate lakes due to mixing= Depletion of nutrients in summer due to stratification leading to drop in phytoplankton populations. Autumn= May get smaller peak due to mixing

Question 11

What is the plant community like in lakes?

Answer 11

Zonation in the littoral:
-Submerged, emergent floating vascular plants
Often no vascular plants below 10-15m= due to insufficient light penetration

Question 12

What is the animal community like in littoral waters (moving water)? If you really care, look this up because I have no idea what this is

Answer 12

Rivers
1) Upper shore= More wave action and larger stones/ gravel= Agal protists and bacteria attached to rocks, caddis fly larvae, motile scrapers, mayfly and stonefly nymphs

Lower shore: Less wave action= Finer sediment= Bacteria and protozoans, invertebrates such as mayfly and stonefly again.

Pelagic= Zooplankton= Some independent movement
Profoundal (deeper waters) = Relatively simple community, if enough oxygen also invertebrates and fish. Low oxygen= bloodworms

Question 13

What are the different properties of littoral benthos (well lit, open surface waters) compared to profundal benthos (deep zone)

Answer 13

Heterogeneity:
L: Heterogenous
P: Homogenous

Temperature
L: Warm
P: Cold

Oxygen
L: Plenty
P: Little

Food
L: Intrinsic food
P: No intrinsic food

Microhabitats
L: Many
P: Few

Species richness
L: High
P: Low

Food web complexity
L: High
P: Low

Primary consumers
L: Many insect larvae and molluscs
P: Bloodworm (Chironomous), Phantom midge (Chaoborus), Pea clams (Pisidium)
Carnivores
L: Fishes, leeches, insect larvae

Question 14

What are catchments?

Answer 14

Dendritic structures (tree-like) with lower and higher order channels

Some areas are braided (intertwining channels that split/join) or meandering

Question 15

What does velocity and substrate of rivers depend on?

Answer 15

Velocity of river dependent on size, shape, gradient of channel, roughness of bottom, depth, precipitation

Substrate type dependent on velocity; higher velocity – moves bottom stones , removes larger stones; lower velocity – water does not carry as much sediment, silt deposition

Question 16

What are some properties of the upper catchment of rivers?

Answer 16

1) Small erosive streams
2) Steepest= Bedrock or boulders
3) Less steep= Shallow riffles gravel and cobble and have deeper pools sand and gravel

Question 17

What are some properties of the middle catchment?

Answer 17

Large channels= Intermediate gradient riffles with smaller particles

Question 18

What are some properties of the lower catchment?

Answer 18

Slower current= Nearly all deposited, high flow and winding channel

Question 19

What adaptations do animals living in rivers need to have?

Answer 19

1) Attachment= Or risk of stranding, can be attached to organisms underneath e.g. sponges
2) Streamlining= e.g. flattened body of mayfly nymph
3) Other adaptations of fish body shape= Broad flat head of bullhead, Rapid water= Needs to swim well

Question 20

What is the river continuum concept?

Answer 20

It is a model for classifying and describing flower water, in addition to the classification of individual sections of waters after the occurrence of indicator organisms

Based on concept of dynamic equilibrium= Balance between physical parameters as well as biological factors

It helps to explain living communities and their sequence in individual sections of water

Continuous differences of properties within the river are dependent on the specific composition of organisms in the different sections of the water.

Proportion of 4 major food types changes:
Shredders: Organisms that feed off coarse particular organic material= Tiny things, examples of shredders: Mayfly
Longitudinal continuum upstream to downstream e.g. higher proportion of shredders upstream= Break up larger material such as leaves

Collectors: Use traps and other features to filter and catch organic matter, smaller particles than shredders
Example: Fly larvae
High proportion midstream= light levels higher

Also have grazers and predators

RCC: Proportions of shredders/collectors/grazers/predators changing upstreams to downstreams

Question 21

What are the different types of connectivity?

Answer 21

Longitudinal: (Up vs downstream)= Primary importance
Vertical: Spring and rainwater
Lateral: Floodplains, flood pulse concept, lowland rivers which are important for nutrients

Mountain headwater= Longitudinal connectivity most important