Lec 20: Stressors on Freshwater Ecosystems

Question 1

why are freshwater environments important?

Answer 1

they contain more relative species richness than terrestrial and marine when compared to their actual surface area ( less than 1%) these species are also the most endangered of extinction

Question 2

why are there so many species in North America?

Answer 2

we have diverse freshwater sources

Question 3

do we over or under-estimate extinction rates?

Answer 3

we often underestimate extinctions

Question 4

what is the natural extinction rate for freshwater fishes?

Answer 4

1 extinction per 3 million fish per year

Question 5

what are the 4 stressors linked to physical habitat alteration

Answer 5

1. River channelization
2. River impoundment
3. Water removal & diversion
4. watershed alteration

Question 6

River channelization

Answer 6

Reduced habitat complexity: Reduced diversity favoring generalist species

Question 7

River impoundment

Answer 7

Habitat fragmentation: loss of natural flow variability, altered water quality

Question 8

water removal & diversion

Answer 8

altered flow regimes, loss of habitat

Question 9

watershed alteration

Answer 9

altered nutrient inputs: flash floods increased delivery of sediments & contaminants; facilitation of invasion

Question 10

what are the 3 stressors linked to contaminants

Answer 10

1. organic pollution (nutrient enrichment from agriculture, domestic sewage)
2. toxins (PCBs, heavy metals from mining, salts)
3. acidification (from fossil fuels)

Question 11

organic pollution

Answer 11

increased productivity, algal blooms, altered water quality

Question 12

toxins

Answer 12

food chain effects through biomagnification, loss of sensitive species

Question 13

water acidification

Answer 13

altered water quality, (low calcium, pH) , molluscs, crustaceans most heavily impacted

Question 14

how are burning fossil fuels linked to water acidification?

Answer 14

burning fossil fuels releases SO2 and NO which react with water in the atmosphere to produce acids

Question 15

2 stressors linked to climate change

Answer 15

1. Temperature changes
2. Precipitation changes

Question 16

Temperature changes

Answer 16

Altered evapotranspiration & flow regimes; altered water quality; species range shifts

Question 17

Precipitation changes

Answer 17

Altered flow regimes (greater extremes (flash floods))

Question 18

what are the stressors to biological invasion (5)

Answer 18

1. predation
2. competition
3. Hybridization
4. Habitat modification
5. Disease transfer

Question 19

Effects of biological invasion on local scale

Answer 19

reduced native populations; net gain( short term) or loss of species richness

Question 20

Effects of biological invasion on global scale

Answer 20

loss of species richness; increased biotic homogenization

Question 21

upstream impacts of large dams

Answer 21

flowing waters converted to still water

habitat quality shifts: O2 decreases, Turbidity increases, sedimentation increases, Temperature stratification

Question 22

at the dam impacts of large dams

Answer 22

Fish migration is blocked
fish may be cut up in the turbines

Question 23

downstream of the dam impacts of large dams

Answer 23

• altered flow regime
• reduced water temperature
• scouring of stream bed immediately below dam
• siltation of stream bed further downstream

Question 24

impacts of reservoir formation

Answer 24

• shrinkage of terrestrial habitat (ex: loss of territory for large animals)
• release of GHG globally
• release of methyl-mercury into foodwebs