Test 2.1 Lakes Flashcards
What 7 characteristics would you use to describe a lake?
Length Width or breadth Depth: max or mean Shoreline (L) Volume Retention or residence time Light availability
How do you calculate residence time?
Volume / mean rate of inflow
or
Mean rate of outflow + evaporation rate
How are tectonic lakes formed?
When 2 plates move apart creating a Rift Valley
e.g. Lake Baikal, Siberia, oldest in the world, 1620m deep
What are the characteristics of Lake Baikal?
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
How are glacial lakes formed?
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
How are thermokarst lakes formed?
Permafrost thawing to create shallow surface tundra lakes
How are oxbow lakes formed?
Large meanders in rivers join up and cut off the old river path
Reasons for building man made lakes?
Hydro power e.g. Lake Powell, Hoover Dam
Water supply/ flood storage
Meaning of Lotic
Flowing - rivers
Meaning of Lentic
Standing - lakes
What variables are significant in lakes?
Depth for:
- Light penetration
- Temperature regime
Distinct seasonal patterns in temperature & water chemistry
Current velocity less significant
Autochtonous production more important than allochthonous production
What is lake temperature stratification?
Summer air temperatures warming the upper layers of lakes separates the upper layer of water from the lower colder layer.
What is the name of the upper warmer surface layer of a lake?
Epilimnion - well oxygenated
What is the name of the deeper cooler layer of a lake?
Hypolimnion - oxygen depleted
What is the name of the distinct separation of layers between upper warmer water and deeper cooler water?
Thermocline
Why is the separation of water layers important?
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
Definition of Holomictic lakes
mixed all year. Never form epilimnion or thermocline
Definition of Monomictic
Lakes that mix once per year
Definition of warm Monomictic
Lakes that stratify in summer, mixed in winter
Definition of Dimictic
Lakes that stratify in both winter and summer, mix in autumn and spring
Definition of Meromictic
Lakes that never mix
How does warmer waters affect deepwater fish species and oxygen levels?
Lake stratification creates a greater contrast between the two layers, reducing the oxygen mixing to the deepest parts therefore fish cannot survive
What are the limiting factors for producers in lakes?
Nutrients: phosphorus & nitrogen
Light: Transparency (turbidity and colour) determines light
What interferes with light penetration?
Colour- (dissolved substances)
coloured lakes less productive
Turbidity- suspended particles
plankton will also limit light reaching bed
What do you use to measure nutrients and light penetration?
Van Dorn sampler (tube)
Secchi disc for transparency- measure how deep before not visible
What is an Oligotrophic lake?
- Nutrient poor
- Low productivity
- High transparency in epilimnion
- High dissolved oxygen in hypolimnion
What is a Mesotrophic lake?
middle rich?.?.?
What is a Eutrophic lake?
- Nutrient rich
- High productivity
- Low transparency in the epilimnion
- Low dissolved oxygen in the hypolimnion
What is benthic algae?
Algae on the lake bed
What is planktonic algae?
Algae living in the open water e.g. diatoms
What are macrophytes?
Rooted aquatic plants e.g. Litorella ‘shore weed’
What are zooplankton?
Microscopic animals feeding on phytoplankton and other zooplankton
What are phytoplankton?
Some are filamentous algae
Some diatoms- single cells or in colonies (require silica)
Name some consumers
Mayfly
Chironomidae
Pond snail
Freshwater limpet
Name some predators
Waterfleas
Phantom midge larva
Roach fish
What are keystone species. Give examples
Species that have particular importance within a community
Gwyniad fish
Perch and Ruffe fish
Give an example of a dominant lake species
Chronomidae
What are the winter patterns of phytoplankton?
Lake is well mixed but plankton abundance low, limited by light and temperature
What are the spring patterns of phytoplankton?
Plankton increase and use up nutrients
What are the summer patterns of phytoplankton?
Lower plankton abundance, limited by nutrients
What are the autumn patterns of phytoplankton?
- First storms
- Mixing
- Thermocline breaks up
- Plankton exploit newly available nutrients
What is the adaptation of water scorpions
Breathing tubes
What is the adaptation of Phantom midge larvae
Buoyancy
What is the adaptation of Water Measurer
Long legs to walk on water
What is the adaptation of Water Boatmen
Traps air
What is the adaptation of Chironomidae
Haemoglobin type pigment
What is the Euphotic depth?
Depth where photosynthesis is possible
- limits phytoplankton depth
- limits growth of rooted plants and benthic algae
What is the Littoral zone?
Lake bed where plants can grow
What is the Profundal zone?
Lake bed where there is no plant growth
