L1 - Properties of water and aquatic environments Flashcards
Where most is freshwater found? where is it most accessible?
- Most freshwater is frozen or underground
- Most accessible is in lakes (0.0007% of total water)
What % of landcover does freshwater habitats make up?
2%
Why are marine ecosystems important?
Freshwater habitats are really critical for a large biodiversity on earth.
They provide a water source for terrestrial organisms.
Freshwater links with terrestrial and marine ecosystems for nutrient and energy flows
Ecosystem services and cultural importance for humans.
How much of the Earth’s surface do marine habitats take up?
About 71%
How much of our atmosphere’s oxygen does marine phytoplankton produce?
50%-80%
* one genus of cyanobacteria (Prochlorococcus) generates ~20%
What are the 8 attributes of aquatic environments?
salinity
physical structure
flow
mixing
temperature
oxygen
nutrients
light.
What is salinity?
The amount of dissolved ions in water.
*Salt is primarily (but not only) sodium and chloride ions
What is the salinity of most rivers and lakes (freshwater)?
0 - 0.5
What is the salinity of Estuaries (brackish water)?
0.5-30
e.g. Thames River, Baltic Sea
What is the salinity of oceans (saline water?
30-38
e.g. Morecambe Bay, Atlantic and Pacific Oceans
What is the salinity of Saline lakes (Hypersaline water)?
38-440
e.g. Dead Sea, Don Juan Pond (Antarctica)
What are the 2 features of the physical structure of a body of water?
Lotic = running water (rivers and streams)
Lentic = standing water (lakes, ponds, and wetlands)
Explain what Lotic Bodies are?
no strict definition for river vs stream, Rivers are generally “large” streams, Classified by their order or Strahler number (bigger = bigger*) → The Amazon is 12th order → 80% of streams and rivers are 1st or 2nd order (within a given river system)
Explain what lentic bodies are
Ponds must be shallow AND small, Lakes can be deep OR large (or both), Wetlands are shallow and have >30% emergent vegetation cover
What are the zones in aquatic habitats and their meanings (marine and freshwater)?
Littoral zone: shallows near the shore edge, often has vegetation
Pelagic zone: Open water in the middle of a water body
Benthic zone: near the bottom sediments
How is flow in rivers measured?
Velocity (in meters per second)
Discharge (in cubic meters per second)
*having a bi-directional relationship between flow and structure
*flow can be very turbulent
Explain the flow regimes in rivers
Driven by seasonal patterns of snowmelt, rainfall, and evaporation
Categorised by average flows, ignoring short-term variation from storms
Most UK river regimes are primarily driven by seasonal evaporation
Explain vertical stratification (mixing)
Vertical stratification - occurs in deep lakes (>3m): → distinct layers at different depths, during some parts of the year. → Layers form because kinetic energy from the wind is limited in how deep it can mix water
How is vertical stratification maintained?
By differences in the density of water
What are mixing regimes in lakes categorized by?
the frequency of stratification and ‘turnover’ (i.e. mixing)
What is the most common mixing regime?
Dimictic
Explain Dimictic (mixing regime)
Mixing pattern - 2x per year
Typical habitat - most temperate lakes (mix in spring and fall)
What happens once vertical stratification is established (mixing)?
it can create gradients in other characteristics like oxygen and nutrients (and these may become trapped within specific layers)
Water has a higher heat capacity than air, what does this mean and what is the result?
Takes more energy to heat up
Can store lots of heat, which means it cools slowly
Result: aquatic environments are generally more thermally stable and insulated from temperature extremes
What are the 3 layers of thermal stratification?
→ Top: epilimnion (warm)
→ Middle: metalimnion
→ Bottom: hypolimnion (cold)
What is thermocline and where is it located?
Depth where temperature change is steepest
Located within the metalimnion (terms often used interchangeably)
Which organisms experience multiple different temperatures?? (Temperature depends on depth)
Organisms which move vertically
*temperature is one of many factors an organism must balance when choosing their habitat
Why does ice float?
Because it is less dense than water by ~9%
What does floating ice create on lake surfaces and why?
Ice creates an insulating layer on lakes
- keeps the lake from completely freezing, allowing organisms to (overwinter) be at the bottom in the densest layers where it is warmer (about 4 degrees)
Why is breathing underwater hard?
There is less oxygen
Diffusion is slower (by about 8000x)
How does oxygen get in the water (2 ways)?
Diffusion from atmosphere
Photosynthesis
*Once in the water, O2 can move within a layer via mixing by the wind
What is oxygen solubility?
The maximum amount of O2 that water can hold
Explain how oxygen solubility varies with abiotic factors? (increase, decrease)
Decreases: Temperature, Salinity
Increases: Air/water pressure
What is hypoxia, and how does this affect microbial activity?
Depletion of oxygen (low level)
- If a hypoxic zone is small, mobile organisms can avoid it
- Large dead zones can lead to fish kills
What are the 3 major nutrients in all ecosystems?
Carbon, Nitrogen, Phosphorus
What do nutrient levels within water body’s depend on?
Catchment
*nutrient supply in the run-off depends on the catchment size, its soil, and the land type and use.
what is light availability within aquatic ecosystems important for?
photosynthesis, and predator-prey interactions
Explain how light attenuation depends on water quality
Turbidity = level of light blocked by suspended particulate matter:
→ Algae
→ Sediment
Dissolved organic carbon (DOC) is brown and absorbs light:
→ Molecules leached from decomposing soil and plant matter in the catchment
What is light availability estimated by?
secchi depth
*it works where you lower it until you can’t see the pattern anymore?
What is a potential issue with secchi depth?
It only works properly with clear water, as it measures depth better.
e.g. due to algae, suspended sediment and dissolved organic carbon (DOC)
How often do bodies of water such as lakes ‘mix’?
Twice a year.
Once in the fall, and once in the spring
What does secchi depth tell us when looking at water depth?
The deeper the secchi can be seen, the fewer nutrients the water has.
The shallower the secchi can be seen, there are more nutrients in the water
