Lec 20: Stressors on Freshwater Ecosystems Flashcards
why are freshwater environments important?
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
why are there so many species in North America?
we have diverse freshwater sources
do we over or under-estimate extinction rates?
we often underestimate extinctions
what is the natural extinction rate for freshwater fishes?
1 extinction per 3 million fish per year
what are the 4 stressors linked to physical habitat alteration
- River channelization
- River impoundment
- Water removal & diversion
- watershed alteration
River channelization
Reduced habitat complexity: Reduced diversity favoring generalist species
River impoundment
Habitat fragmentation: loss of natural flow variability, altered water quality
water removal & diversion
altered flow regimes, loss of habitat
watershed alteration
altered nutrient inputs: flash floods increased delivery of sediments & contaminants; facilitation of invasion
what are the 3 stressors linked to contaminants
- organic pollution (nutrient enrichment from agriculture, domestic sewage)
- toxins (PCBs, heavy metals from mining, salts)
- acidification (from fossil fuels)
organic pollution
increased productivity, algal blooms, altered water quality
toxins
food chain effects through biomagnification, loss of sensitive species
water acidification
altered water quality, (low calcium, pH) , molluscs, crustaceans most heavily impacted
how are burning fossil fuels linked to water acidification?
burning fossil fuels releases SO2 and NO which react with water in the atmosphere to produce acids
2 stressors linked to climate change
- Temperature changes
- Precipitation changes
Temperature changes
Altered evapotranspiration & flow regimes; altered water quality; species range shifts
Precipitation changes
Altered flow regimes (greater extremes (flash floods))
what are the stressors to biological invasion (5)
- predation
- competition
- Hybridization
- Habitat modification
- Disease transfer
Effects of biological invasion on local scale
reduced native populations; net gain( short term) or loss of species richness
Effects of biological invasion on global scale
loss of species richness; increased biotic homogenization
upstream impacts of large dams
flowing waters converted to still water
habitat quality shifts: O2 decreases, Turbidity increases, sedimentation increases, Temperature stratification
at the dam impacts of large dams
Fish migration is blocked
fish may be cut up in the turbines
downstream of the dam impacts of large dams
- altered flow regime
- reduced water temperature
- scouring of stream bed immediately below dam
- siltation of stream bed further downstream
impacts of reservoir formation
- shrinkage of terrestrial habitat (ex: loss of territory for large animals)
- release of GHG globally
- release of methyl-mercury into foodwebs
