Lake and Rivers Flashcards
What are the different ways in which lakes can form?
Retreating glaciers forming basins Slit deposition or cut-off meanders in rivers Sinking volcanoes Extinct volcano crates Landslides Man-made reservoirs
What are the different zones of water column?
Epi= Surface layer Meta= Middle layer Hypo= Bottom layer
What happens to temperatures to lakes?
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
What happens to the lake stratification during summer?
Surface water becomes heated, becomes lighter= Floats on cold water below
Thermal barrier
Little mixing
Steep temperature decline= Thermocline= Lowest temperature is the shallowest
What happens in the autumn?
Air temperature falls= Surface water loses heat= Metalimnion sinks (middle becomes denser) while the top layer (epi) increases to whole lake
One temperature
Mixing
What happens in winter?
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
What happens during Spring?
Ice melts, surface water drops
Mixing of water
All becomes 4 degrees celsius= Wind mixes easily
If above 4 degrees celsius= Summer stratification
What happens to the oxygen in lakes?
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
What are the different zonation of organisms?
- Pelagic: open water
- Littoral: high water level to euphotic depth (with light)
- Profundal: zone below euphotic depth (no light)
- Benthic: bottom – all depths
What is the productivity like in lakes?
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
What is the plant community like in lakes?
Zonation in the littoral:
-Submerged, emergent floating vascular plants
Often no vascular plants below 10-15m= due to insufficient light penetration
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
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
What are the different properties of littoral benthos (well lit, open surface waters) compared to profundal benthos (deep zone)
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
What are catchments?
Dendritic structures (tree-like) with lower and higher order channels
Some areas are braided (intertwining channels that split/join) or meandering
What does velocity and substrate of rivers depend on?
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
What are some properties of the upper catchment of rivers?
1) Small erosive streams
2) Steepest= Bedrock or boulders
3) Less steep= Shallow riffles gravel and cobble and have deeper pools sand and gravel
What are some properties of the middle catchment?
Large channels= Intermediate gradient riffles with smaller particles
What are some properties of the lower catchment?
Slower current= Nearly all deposited, high flow and winding channel
What adaptations do animals living in rivers need to have?
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
What is the river continuum concept?
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
What are the different types of connectivity?
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
