L1 - Properties of water and aquatic environments

Question 1

Where most is freshwater found? where is it most accessible?

Answer 1

• Most freshwater is frozen or underground
• Most accessible is in lakes (0.0007% of total water)

Question 2

What % of landcover does freshwater habitats make up?

Answer 2

2%

Question 3

Why are marine ecosystems important?

Answer 3

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.

Question 4

How much of the Earth’s surface do marine habitats take up?

Answer 4

About 71%

Question 5

How much of our atmosphere’s oxygen does marine phytoplankton produce?

Answer 5

50%-80%
* one genus of cyanobacteria (Prochlorococcus) generates ~20%

Question 6

What are the 8 attributes of aquatic environments?

Answer 6

salinity
physical structure
flow
mixing
temperature
oxygen
nutrients
light.

Question 7

What is salinity?

Answer 7

The amount of dissolved ions in water.
*Salt is primarily (but not only) sodium and chloride ions

Question 8

What is the salinity of most rivers and lakes (freshwater)?

Answer 8

0 - 0.5

Question 9

What is the salinity of Estuaries (brackish water)?

Answer 9

0.5-30
e.g. Thames River, Baltic Sea

Question 10

What is the salinity of oceans (saline water?

Answer 10

30-38
e.g. Morecambe Bay, Atlantic and Pacific Oceans

Question 11

What is the salinity of Saline lakes (Hypersaline water)?

Answer 11

38-440
e.g. Dead Sea, Don Juan Pond (Antarctica)

Question 12

What are the 2 features of the physical structure of a body of water?

Answer 12

Lotic = running water (rivers and streams)
Lentic = standing water (lakes, ponds, and wetlands)

Question 13

Explain what Lotic Bodies are?

Answer 13

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)

Question 14

Explain what lentic bodies are

Answer 14

Ponds must be shallow AND small, Lakes can be deep OR large (or both), Wetlands are shallow and have >30% emergent vegetation cover

Question 15

What are the zones in aquatic habitats and their meanings (marine and freshwater)?

Answer 15

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

Question 16

How is flow in rivers measured?

Answer 16

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

Question 17

Explain the flow regimes in rivers

Answer 17

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

Question 18

Explain vertical stratification (mixing)

Answer 18

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

Question 19

How is vertical stratification maintained?

Answer 19

By differences in the density of water

Question 20

What are mixing regimes in lakes categorized by?

Answer 20

the frequency of stratification and ‘turnover’ (i.e. mixing)

Question 21

What is the most common mixing regime?

Answer 21

Dimictic

Question 22

Explain Dimictic (mixing regime)

Answer 22

Mixing pattern - 2x per year
Typical habitat - most temperate lakes (mix in spring and fall)

Question 23

What happens once vertical stratification is established (mixing)?

Answer 23

it can create gradients in other characteristics like oxygen and nutrients (and these may become trapped within specific layers)

Question 24

Water has a higher heat capacity than air, what does this mean and what is the result?

Answer 24

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

Question 25

What are the 3 layers of thermal stratification?

Answer 25

→ Top: epilimnion (warm)
→ Middle: metalimnion
→ Bottom: hypolimnion (cold)

Question 26

What is thermocline and where is it located?

Answer 26

Depth where temperature change is steepest
Located within the metalimnion (terms often used interchangeably)

Question 27

Which organisms experience multiple different temperatures?? (Temperature depends on depth)

Answer 27

Organisms which move vertically
*temperature is one of many factors an organism must balance when choosing their habitat

Question 28

Why does ice float?

Answer 28

Because it is less dense than water by ~9%

Question 29

What does floating ice create on lake surfaces and why?

Answer 29

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)

Question 30

Why is breathing underwater hard?

Answer 30

There is less oxygen
Diffusion is slower (by about 8000x)

Question 31

How does oxygen get in the water (2 ways)?

Answer 31

Diffusion from atmosphere
Photosynthesis
*Once in the water, O2 can move within a layer via mixing by the wind

Question 32

What is oxygen solubility?

Answer 32

The maximum amount of O2 that water can hold

Question 33

Explain how oxygen solubility varies with abiotic factors? (increase, decrease)

Answer 33

Decreases: Temperature, Salinity
Increases: Air/water pressure

Question 34

What is hypoxia, and how does this affect microbial activity?

Answer 34

Depletion of oxygen (low level)
- If a hypoxic zone is small, mobile organisms can avoid it
- Large dead zones can lead to fish kills

Question 35

What are the 3 major nutrients in all ecosystems?

Answer 35

Carbon, Nitrogen, Phosphorus

Question 36

What do nutrient levels within water body’s depend on?

Answer 36

Catchment
*nutrient supply in the run-off depends on the catchment size, its soil, and the land type and use.

Question 37

what is light availability within aquatic ecosystems important for?

Answer 37

photosynthesis, and predator-prey interactions

Question 38

Explain how light attenuation depends on water quality

Answer 38

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

Question 39

What is light availability estimated by?

Answer 39

secchi depth
*it works where you lower it until you can’t see the pattern anymore?

Question 40

What is a potential issue with secchi depth?

Answer 40

It only works properly with clear water, as it measures depth better.
e.g. due to algae, suspended sediment and dissolved organic carbon (DOC)