Test 2.3 Impacts of Altered Flows Flashcards
How do droughts affect river organisms
Reduced depth & wetted area:
- reduction of living space; crowding; competition
e. g. territory for fish
-Change in proportional habitat composition- loss/ gain of wetted lands
With regard to altered flows name some threats to freshwater systems
Demand for water & energy
- reduced flows
- impoundments
Demand for space
- Channelization
- Flood protection
Land use changes; agriculture, forestry, industry
Pollution
Exploitation of species
Introduction of non native species
Climate change
Describe a common natural flow regime in the northern hemisphere
Lowest flows in summer
Higher flows & floods in autumn & spring
If the river freezes in winter then the greatest floods may be here
Describe a common natural flow regime in the Southern hemisphere
Highest flows in winter period lowest in summer, but over different months
Why are small increases of flows or freshets important for ecology
First increases in flow and end of season: trigger migration of fish upstream
What are the ecological impacts of winter high flow floods?
Reshaping the channel
Moving sediment
Depositing sediment onto floodplain
Meaning of drought
Extreme low flow events resulting from lack of rainfall
What affects the ecological impacts of drought?
Duration
-weeks-years
Timing (season)
-life cycles, spawning
River type
- naturally stable flow regime or naturally variable?
Frequency
- predictability
Management practices
-abstraction, regulation, lands change, channelisation, macrophyte management
Definition of disturbance
A desecrate event in time that lies outside a predictable range for the system
What is a supra-seasonal drought?
Water levels gradually decrease summer after summer
Name an example of a famous UK drought
River Severn :
1976, quite a dry winter
1989-1993: 89 was a dry summer
How does groundwater affect river regime?
Groundwater fed rivers are more stable with a smaller variability of water levels
What defines a ‘Summer Low Flow’ (qL)
The lowest average of seven consecutive Daily Mean Flows
What defines a ‘Standard Summer Low Flow’ or ‘standard dry-weather flow’
The lowest qL occurring every two out of three years
What defines more severe low flows
Defined by frequency e.g.
qL20= lowest qL recorded on average once every 20 years
What does Q100 mean in terms of flooding?
A 100 year flood
With regard to droughts how does reduced current velocity affect river organisms?
Problems with respiration, locomotion, drift, food availability
With regard to droughts how does siltation of substrate/deposition of organic matter affect river organisms?
- Loss of interstitial ‘living space’
- Smothering effects
- Clogging of spawning gravels
- Increased food supply for detritivores
- Increased colonisation by marginal plants
With regard to droughts how does concentration of nutrients/pollutants affect river organisms?
- Toxic effects
- Increased algal production; smothering of macrophytes
With regard to droughts how does increased water temperature / temperature variability affect river organisms?
-Problems with respiration esp in spawning areas
changes in growth and development rates
With regard to droughts how does increased light penetration affect river organisms?
Increased algal production: smothering of macrophytes
How do invertebrates adapt to drought biologically?
Breathing atmospheric oxygen: Coleoptera
Utilising low dissolved oxygen: Chironomidae
Adapted gills or respiratory behaviour: mayflies
How do invertebrates adapt to drought behaviourally?
Survive in damp substrate/wood
Aestivation: hibernation for hot dry period e.g. beetles, shelled molluscs
Move into hyporheic zone
Move to nearby permanent water bodies
Not being there
How does drought affect fish?
Lack of O2 due to increased temp may follow increase and decay of plants
Severest effect on 0+ 1+ aged fish. Bigger = more tolerant
Spawning: salmon fish need clean gravel and oxygenated water
How does drought affect macrophytes?
Positive correlation with growth & drought
Low water levels = grazing e.g. swans
How does drought affect algae?
Increased under low, warm flows. Grown rapidly; smothers other plants e.g. water Crowfoot
How does drought affect diatoms?
Good indicator of local drought conditions
Positive response to light, nutrients, substrate stability
What proportion of the worlds rivers are regulated
2/3
Approx 15% of total annual runoff globally held back
Roughly how many dams are there worldwide over 15m?
57,000
22,000 of which in China
Over 300 giant dams (>150m)
Largest dam is >300m high: Jinping-1 Dam, China
