Lake Ecosystems Flashcards
What are the main factors that impact lake biota?
-Light
-Temperature
-Dissolved Oxygen
-Nutrient Bioavailability
What % of energy is absorbed in the first 1m in a lake?
50% of light energy
What takes place in the photic zone?
Photosynthesis + respiration
What takes place in the aphotic zone?
Respiration only
What affects light absorption?
-Water clarity
-Wave type
-Dissolved & suspended material
How does light absorption affect photosynthesis?
Constrains algal and macrophyte primary production in the littoral zone
Why is light absorption so important?
-Heating the waterbody
-Stratification
-Characteristic colour to lakes (blue, green)
-Affects organisms that are sensitive to light (the movement and migration of zooplankton & fish)
What is the max depth that photosynthesis can occur?
In the aphotic zone
What determines water temperature in a lentic environment?
Heating, cooling and movement of heat through the water determines water temperature
Why is water temperature important?
-Controls the rates of biological activity (activity, behaviour, metabolic rate
What are eurytherns?
Fish that can tolerate a wide range of temperatures ( cyprinids ie. carps and minnows)
What are stenotherms?
Fish that have a narrow temperature range (salmonids)
Why are fish classified as cold and warm water species?
This is due to different species having different optimum temperature range which a fish spp. can survive and reproduce
When do carp spawn?
Mid -July
Like slow, warm vegetated waters
When do trout spawn?
November to January
Like cool, clear waters with gravel substrates
What are some biotic adaptations to changing temperatures?
-Acclimatization
-Resting stages
-Temperature Induced-hatching
-Behavioural thermoregulation
Describe acclimatisation
-When an organism can acclimatise to changing temperature regime
-Chlorella spp. show max growth rates at 20, 26 and 36 degrees
-Can get used to a range of 16 degrees
Describe resting stages
-Formed by organisms under sub-optimal temperature conditions
-Plankton form thick-walled cyst that are morphologically different from vegetative cells
-Functions as a time-dispersal system, allowing rapid recolonisation after unfavourable environmental conditions
Describe temperature induced-hatching
-Rutilis rutilis (roach) eggs do not hatch at same time of year
-Hatching dependent on accumulated temperature on days preceding hatching
-Eggs hatch after fixed degree-day threshold
-Availability of food and the activity of predators are also dependent on temperature
Describe behavioural thermoregulation
-Diel vertical migration displayed by plankton and fish
-Spend their days in cold hypolimnion
-Move up to warmer epilimnion only during the night
What is a key process in cold temperature lakes?
Seasonal thermal stratification
`What happens in lakes during spring (thermocline)?
-Weak solar radiation
-Degree of vertical mixing
-Oxygen saturation levels >100%
-Well mixed nutrients- bioavailable
What happens during the summer in lakes? (thermocline)?
-Thermal stratification occurs
-Solar radiation and density
-Split into the epilimnion, thermocline and hypolimnion
-Atmospheric O2 (Epilimnion)
-Anoxic (Hypolimnion)
-Storage of nutrients in hypolimnion
What happens during the autumn in lakes (thermocline)?
-Autumn turnover
-Degree of vertical mixing
-Oxygen saturation >100%
-Well mixed nutrients = bioavailable
