Test 2.3 Impacts of Altered Flows

Question 1

How do droughts affect river organisms

Answer 1

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

Question 2

With regard to altered flows name some threats to freshwater systems

Answer 2

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

Question 3

Describe a common natural flow regime in the northern hemisphere

Answer 3

Lowest flows in summer
Higher flows & floods in autumn & spring

If the river freezes in winter then the greatest floods may be here

Question 4

Describe a common natural flow regime in the Southern hemisphere

Answer 4

Highest flows in winter period lowest in summer, but over different months

Question 5

Why are small increases of flows or freshets important for ecology

Answer 5

First increases in flow and end of season: trigger migration of fish upstream

Question 6

What are the ecological impacts of winter high flow floods?

Answer 6

Reshaping the channel

Moving sediment

Depositing sediment onto floodplain

Question 7

Meaning of drought

Answer 7

Extreme low flow events resulting from lack of rainfall

Question 8

What affects the ecological impacts of drought?

Answer 8

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

Question 9

Definition of disturbance

Answer 9

A desecrate event in time that lies outside a predictable range for the system

Question 10

What is a supra-seasonal drought?

Answer 10

Water levels gradually decrease summer after summer

Question 11

Name an example of a famous UK drought

Answer 11

River Severn :
1976, quite a dry winter

1989-1993: 89 was a dry summer

Question 12

How does groundwater affect river regime?

Answer 12

Groundwater fed rivers are more stable with a smaller variability of water levels

Question 13

What defines a ‘Summer Low Flow’ (qL)

Answer 13

The lowest average of seven consecutive Daily Mean Flows

Question 14

What defines a ‘Standard Summer Low Flow’ or ‘standard dry-weather flow’

Answer 14

The lowest qL occurring every two out of three years

Question 15

What defines more severe low flows

Answer 15

Defined by frequency e.g.

qL20= lowest qL recorded on average once every 20 years

Question 16

What does Q100 mean in terms of flooding?

Answer 16

A 100 year flood

Question 17

With regard to droughts how does reduced current velocity affect river organisms?

Answer 17

Problems with respiration, locomotion, drift, food availability

Question 18

With regard to droughts how does siltation of substrate/deposition of organic matter affect river organisms?

Answer 18

• Loss of interstitial ‘living space’
• Smothering effects
• Clogging of spawning gravels
• Increased food supply for detritivores
• Increased colonisation by marginal plants

Question 19

With regard to droughts how does concentration of nutrients/pollutants affect river organisms?

Answer 19

• Toxic effects

- Increased algal production; smothering of macrophytes

Question 20

With regard to droughts how does increased water temperature / temperature variability affect river organisms?

Answer 20

-Problems with respiration esp in spawning areas

changes in growth and development rates

Question 21

With regard to droughts how does increased light penetration affect river organisms?

Answer 21

Increased algal production: smothering of macrophytes

Question 22

How do invertebrates adapt to drought biologically?

Answer 22

Breathing atmospheric oxygen: Coleoptera

Utilising low dissolved oxygen: Chironomidae

Adapted gills or respiratory behaviour: mayflies

Question 23

How do invertebrates adapt to drought behaviourally?

Answer 23

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

Question 24

How does drought affect fish?

Answer 24

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

Question 25

How does drought affect macrophytes?

Answer 25

Positive correlation with growth & drought

Low water levels = grazing e.g. swans

Question 26

How does drought affect algae?

Answer 26

Increased under low, warm flows. Grown rapidly; smothers other plants e.g. water Crowfoot

Question 27

How does drought affect diatoms?

Answer 27

Good indicator of local drought conditions

Positive response to light, nutrients, substrate stability

Question 28

What proportion of the worlds rivers are regulated

Answer 28

2/3

Approx 15% of total annual runoff globally held back

Question 29

Roughly how many dams are there worldwide over 15m?

Answer 29

57,000

22,000 of which in China

Over 300 giant dams (>150m)

Largest dam is >300m high: Jinping-1 Dam, China