Lecture 20: Stressors on Freshwater Ecosystems

Question 1

Which environment has the highest species richness (relative to size)

Answer 1

Freshwater (specifically north american fresh water - 12% of all known freshwater fish)

Question 2

Ex: given that 35/297 species of fw mussels went extinct between 1900-1999, what is the extinction rate?

Answer 2

r = 1-p^(1/n) and given 10 decades:
r = 1-(35/297)^(1/10) = 1.2% loss per decade

Question 3

How long do species tend to last in fossils?

Answer 3

1-10 million years

Question 4

Ex: if in the last 100 years, 40 of 1061 species have gone extinct, how many extinctions happen per million species per year?

Answer 4

(40 extinctions)
————————————– * 1 million
(1061 species * 100 years)
= 377 extinctions/million species/year

Question 5

Which north american fauna are expected to face most % species loss per decade?

Answer 5

freshwater animals

Question 6

What are the causes of freshwater fish extinctions?

Answer 6

• Physical habitat alteration
• invasions
• pollutions
• hybridization
• overharvesting

Question 7

What are the types of physical habitat alterations and their effects?

Answer 7

1. river channelization (altering shape of rivers to allow ships to pass) –> causes reduced habitat complexity favouring species that can survive in wider range of habitats
2. river impoundment (creating dams) –> causes habitat fragmentation and loss of natural flow variability and water quality

Question 8

What are the environmental impacts upstream of a dam?

Answer 8

moving water has particles in suspensions –> dams cause still water upstream and sediments sink in still water which depletes oxygen due to decomposition of these sediments.

still water also causes temperature stratification (temp layers) which changes oxygen concentration and affects living species

Question 9

What are the environmental at a dam?

Answer 9

Fish/marine animal migration is blocked and fish can get cut up by turbines (if its a hydroelectric dam)

Question 10

What are the environmental impacts downstream of a dam?

Answer 10

• altered flow regime
• reduced water temp
• scouring of stream bed immediately below dam (due to high pressure water)
• siltation (sediments sinking) where pressure is reduced further downstream

Question 11

What are other impacts of large dams (reservoir formation)?

Answer 11

• shrinkage of terrestrial habitat (loss of territory for large land mammals)
• release of GHGs (anaerobic decomp = methanation)
• release of methyl-mercury to foodwebs

Question 12

What are types of contaminants in freshwater?

Answer 12

• organic pollution (domestic sewage, fertilizer runoff…) causes algal blooms or altered water quality
• toxins (heavy metals, road salt) cause loss of sensitive species and affect food webs
• acidification (from fossil fuels) causes altered water quality impacting molluscs & crustaceans

Question 13

How do fossil fuels cause acidification?

Answer 13

Burning fossil fuels produces SO2 and HOx which react with water in the atmosphere to produce acids

Question 14

What climate stressors affect freshwater?

Answer 14

• temp changes causes altered evapotranspiration, altered water quality and species shifts
• precipitation changes cause extreme flow regimes (droughts and flooding)

Question 15

What are the ways that biological invasions that affect FW?

Answer 15

• predation (prey & predator)
• competition
• hybridization
• habitat modification
• disease transfer

Question 16

What are the ecological consequences of extinction?

Answer 16

1. extinctions reduce ecosystem functioning and efficiency (diverse species use resources more efficiently and facilitate each other)
2. diverse species is insurance in a fluctuation environment (species function optimally at different parameters –> diversity ensure that “jobs” are performed under varying conditions