18. The Hydrosphere

Question 1

What is the hydrosphere composed of? 5

Answer 1

1. 97.5% sea water, icl estuaries 2. 2.24% glaciers 3. 0.009% standing/lentic water 4. 0.001% running/lotic water 5. lack of water impacts water security and availability, so has economic and also ecologicial impacts

Question 2

Why are freshwaters important to the biosphere? 3

Answer 2

1. Movement of water between and within ecosystems 2. Transport of natural substances including nutrients 3. Water is provided for the terrestrial system

Question 3

Why is freshwater important to humans? 3

Answer 3

1. transport 2. irrigation 3. waste disposal

Question 4

What are the types of non-marine water environment? 6

Answer 4

Question 5

What are the major biological communities that live in freshwaters composed of? 5

Answer 5

—

—1. Plankton – floating and movement depend on currents. less in running water as washed away- can’t move against current

—2. Epibenthos – attached or clinging to mcro/macroplants

3. —Nekton – swimming and able to navigate at will ie. fish

—4. Benthos - attached or living on/in bottom sediments

—5. Neuston - resting or swimming at surface due to surface tension

Question 6

What are shredders? 2

Answer 6

1. Shred food material eg. dead leaves
2. incl Trichoptera (caddis flies), Amphipoda (Gammaridae), Isopoda (Asellidae) Decapoda (various families of crayfish)

Question 7

What are grazers in the water? 2

Answer 7

1. graze on algae etc that is on stones and the like
2. incl Ephemeroptera (mayflies), Gastropod molluscs

Question 8

What are collectors in the water? 3

Answer 8

1. collect bits of food eg, parts that have been shredded by shredders
2. Those in the water column incl Diptera, Trichoptera
3. those on sediment incl. oligochaeta, diptera and bivalve molluscs

Question 9

What are predators in the water? 2

Answer 9

1. May eat directly, may suck blood
2. incl Hirudinea (leeches) Trichoptera, Plectoptera (stoneflies), Odonata (dragon/damsel flies), Coleoptera (beetles)

Question 10

How do freshwater ecosystems form a continua? 6

Answer 10

—1. Different organisms occur in different reaches (‘stretches’), river communities grade into one another - ‘river continuum’

2. Results in changes in energy transfer

—3. shredders/grazers -> collectors of coarse particulates (from above)/grazers -> collectors of fine particulates (as river slows down so larger particles are eroded)

—4. Energy: allochthonous (from outside eg. leaf fall) and autochthonous material (aqueous primary production eg. moss, epibenthic algae)

——5. Slow-flowing deep river behaves more like a lake – ‘linear lake’.

6. get stratificiation

Question 11

What is stratification? 7

Answer 11

—1. Thermal stratification common in deep (>5 m) lakes

2. —Oxygen depletion due to reduced re-aeration from the atmosphere
3. —Rivers too fast flowing and shallow for stratification
4. —However, stratification can occur in slow-flowing deep rivers
5. The surface layer, the epilimnion, is warmer, therefore less dense, so creates a distinct layer
6. The cooler layer is the lower hypolimnion
7. dissolved o2 decreases getting deeper into this, as o2 can’t penetrate and is not replenished when used

Question 12

What is the significance of the temperature of water? 1

Answer 12

1. It is in lquid form all year round

Question 13

What is the significance of the density of water? 5

Answer 13

1. Similarity in density of water and aquatic biota limits the rate of passive sinking (sedimentation)
2. allows shells and bouyant organisms to keep position
3. Density lower above and below 4 degrees C
4. Allows ice to be less dense than water - important as sinking would freeze substrate so no burrowing/feedind
5. Above 4deg C: surface warming - thermal stratification in standing and slow moving running waters

Question 14

What is the significance of the high absoloute viscosity of water? 3

Answer 14

1. High viscosity limits:
2. mixing of water (slower)
3. sedimentation of biota

Question 15

What is the significance of the low thermal conductivity and high specific heat capacity of water? 3

Answer 15

1. slow response to change in air temperature
2. So organisms don’t have to adapt to sudden temperature changes
3. localised surface heating and hence stratification

Question 16

What is the significance of the high dielectric constant of water? 3

Answer 16

1. Determines the ability of ions of opposite charge to stay in solution - thus form wide range of solutions
2. allows facilitation of biochemical processes
3. central to all life

Question 17

What is the significance of the high surface tension of water? 4

Answer 17

Allows invertebrates to attach to the water surface – above (neuston) and below

2. can take advnatage of this
3. eg. pond skater/G. Hucustris on top
4. Mosquito larvae of Culex genera suspend below surface and has a respiratory tube that sticks out of surface

Question 18

What is the significance of the low light absorption and scattering in water? 5

Answer 18

1. Low light absorption and scattering: high light penetration
2. but light only penetrates to a certain depth
3. Particulates eg. pollution or natural like phytoplankton are self shading in the water column, and will reduce transparency
4. resulting blooms can shift community structure
5. Penetration of light is wavelength-dependent.

Question 19

Water has quite a low solubility of oxygen - what is the significance of this? 6

Answer 19

1. Dissolved oxygen (DO) often limiting to biota particular at high temperature.
2. Oxygen be limiting in stratified waters due to lack of transfer to the lower layer (hypolimnion).
3. Plant respiration can deplete oxygen levels in night resulting in diurnal variations
4. o2 dissolving in water is temperature dependent
5. low o2 content can be limiting in some organisms eg. some fish, like salmon, can’t survive in low o2 levels so only live in cooler water
6. layering of microorganisms means oxygen can be depleted easily