Test 2.1 Freshwater Ecosystems Flashcards
Key 8 physical and chemical properties of freshwater ecosystems include:
- Density, viscosity
- Flow, velocity and depth
- Light
- Temperature
- Dissolved Oxygen
- Carbon dioxide
- pH
- Nutrients
% Proportion of ocean water of all water
around 97%
% Proportion of freshwater of all water
around 3%
2.15% of which is glaciers
6 physical challenges of living in freshwaters?
Physical medium of water Buoyancy Density Viscosity Temperature Salinity
What is viscosity?
The resistance of a fluid to shear stress - ‘thickness’ or ‘drag’
What is Reynold’s number?
Ratio of inertial forces (opposing current forces) to viscous forces ‘roughness’
What increases roughness/ Reynold’s number?
Size and velocity
Water properties important for large objects?
Pressure
Water properties important for medium objects?
Pressure and drag
Water properties important for small objects?
Drag and viscosity
Increase in discharge and flow down the hydrological system due to?
Why are the proportions important?
Greater amount of inputs: Direct runoff Ice melt Groundwater etc.
Temperature and nutrient levels are due to where its from- affects organisms present
What are Lotic systems?
Flowing systems - rivers
What are Lentic systems?
Standing systems - Lakes
Why is flow important in freshwater ecosystems?
Organisms are adapted to velocity and shear stress
Provides nutrients
List hydraulic variables
Velocity
Shear stress
Water depth- more important in lakes
Why is depth more important in lakes?
Temperature- Deep lakes with limited flow proceed strong patterns, effects nutrients
Light- source of energy for organisms
What determines the temperature of water? (6 reasons)
Origin & inputs- groundwater, glacier e.g.
Air temperature
Season
Time of day
Water depth and discharge
Substrate and amount of turbulence (mixing)
Hyporheic zone meaning
Below the river bed zone containing water
Exchange of groundwater to surface water- affects temperature
Why is water temperature less variable than air temperature?
Due to water’s high specific heat capacity
What are the two forms of ice found in rivers?
Frazil ice- mobile first particles that form on the surface of the water
Anchor ice- Ice frozen in solid connection with the banks, spreads across the rest of the river surface
What is the coolest source in order:
Surface run off
Glacial
Karstic - what is it?
Average coolest temperature:
- Glacial
- Karstic (high proportion from groundwater & most stable)
- Surface run off snow melt (most variable)
How does variability and average water temperature vary downstream?
Average temp increases as you go downstream
Variability is greatest in smaller streams
Larger rivers are more stable due to greater size and buffering capacity
How does topography and vegetation affect water temperature?
Cooling effect due to shading and evapotranspiration
What is the long term trend of average temperature in large rivers (Mississippi; Trent)
What are the causes?
Increased even though air temperature recorded was 2.2 degrees cooler.
Mississippi: Warming due to industrial warm effluents.
Trent: Cooling due to closed coal power stations no longer produce water effluent for cooling
How does temperature effect Salmon?
Salmon develop in warmer conditions. Very warm conditions can be damaging.
How does temperature effect Mayflies?
Speed of development and timing of hatching is temperature dependent. Fast summer generation, slow winter generation
Definition of Univoltine & bivoltine?
Univoltine: Single generation period per year
Bivoltine: 2 generations per year
Often in tropical rivers there are more multivoltine species
What effects dissolved oxygen in river water?
Increase:
Photosynthesis
Turbulence
Decrease:
Respiration (decomposers - microorganism’s)
How does temperature affect oxygen levels?
High temperature results in lower oxygen
How does altitude affect oxygen level?
Water at sea levels can hold more oxygen than at altitude
What is the ecological significance of dissolved oxygen in salmon, trout and tench?
Salmon and trout need high levels of oxygen
Tench more tolerant of lower oxygen levels
What concentration of oxygen is required for salmon eggs to survive and develop?
5mg/L
How are invertebrate species adapted to low oxygen levels?
Gills on body
High haemoglobin content
Caddis have gills along body, can create current to bring o2 to gills
How does pollution affect dissolved oxygen?
Organic sewage broken down using respiration & therefore oxygen.
Hows does carbon dioxide affect water quality?
Dissolves to form carbonic acid - disassociation reduces to produce hydrogen ions - raises pH
How does temperature affect CO2 levels?
Higher temperature means higher CO2 levels
How does limestone & chalk affect buffering capacity?
Rich in natural carbonates and bicarbonates, buffered against acidity due to high pH
How many microequivalents per litre are required for a residual buffering capacity?
120me/L and above
What are the changes of alkalinity in a diurnal pattern?
Low natural alkalinity with vegetation present tend to find pH rises in afternoon with increase in photosynthesis
List essential nutrients for plant growth
Main:
Nitrogen
Phosphorus
Other: Calcium Iron Manganese Magnesium Potassium Silica Sodium
Where does nitrogen come from in a river?
Atmospheric nitrogen fixed by nitrogen fixing microorganisms into ammonium
Decomposition of organisms. Ammonium then through nitrification to nitrite to nitrate
Where does phosphorus come from in a river?
Taken up in plants, consumed by animals, broken down and released by bacteria into inorganic phosphorus.
Closed cyclic system
Name the globally most important limiting element
Phosphorus
Sometimes silica
What is the natural ratio of N:P?
N:P
16:1
What its the effect of nitrogen and phosphorus pollution?
Pollution raising nitrogen no significant effect
Pollution raising phosphorus where there is abundant nitrogen has significant effects
