Transcript NEW METHODS FOR DETERMINING ENVIRONMENTAL FLOWS …

THE FLOW STRESSOR-RESPONSE
METHOD
Jay O’Keeffe,
WWF Professor of Freshwater Ecosystems,
Department of Environmental Resources
South African rivers
•
•
•
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Semi-arid
Flashy
Unpredictable
Highly variable
• Incised channels
• Few with floodplains
• No/few commercial
fish
DEFINITIONS OF STRESS
Begon, Harper and Townsend (1996):
Physics has a strict definition of a force
per unit area and producing strain in
the body to which the force is applied.
Biology has a wide variety of meanings ....
The word is often used confusingly in two
senses, both to describe force and the
condition induced in the organism by the
force – a confusion of stimulus and response.
DEFINITIONS OF STRESS
r, Gath and Mayou (1990):
First it is applied to events or Situations .... that
may have an adverse effect on someone,
second, it is applied to the adverse effects that
are induced.
The first set of factors can usefully be called
stressors
The effect on the person can usefully be called
the stress reaction
There are lots of different types of stress
Stresses due to:
Flow,
Water quality,
Temperature, Predation,
Competition,
etc. etc.
In this method, we are dealing initially with
stresses caused by low flows. We will also
investigate the quite different stresses caused by
high flows to see if the method can usefully be
extended to deal with these.
OUR DEFINITION
The term stress is used ...... to denote the
discomfort/damage/reduction suffered by the flow-dependent
biota/habitats as discharges are reduced. Natural flow
regimes normally include low flow episodes which cause
stress to elements of the system (equivalent to components of
the natural disturbance regime sensu Townsend, 1989).
Stress is therefore seen as a requirement for the maintenance
of the natural dynamic mosaic of habitat/species assemblages
through space and time, and the severity of stress likely to be
caused by any modified flow regime is judged by how much
it is increased or decreased from natural levels.
THE CONCEPT OF LOW-FLOW
STRESS
• River processes, functions and components
are best adapted to their natural flow regime
• The flow regime is a main driver of the
ecological disturbance regime, which drives
much of the biodiversity of a system
• Natural biodiversity = Ecosystem goods
and services, and stability and resilience of
ecosystems
BUT
• People need the water resources
• By reducing the flow, they increase the lowflow disturbances in the system
• Natural biodiversity, goods and services,
stability and resilience are reduced (its
ecological health is reduced)
• The ecological risk to the system is increased,
it becomes an increasingly stressed system
• We use fish/inverts/veg/sediment processes as
indicators of the overall stress in the system
SOMETIMES
• The low flows are increased (IBT’s, return flows)
• Natural low-flow disturbances in such systems are
decreased, and stress is removed
• Habitat diversity in time and space is decreased
• Some species are advantaged to the detriment of
others
• Biodiversity etc is decreased.
USE FOR THIS METHOD
• Stressors (decreased flow, reduced habitat), cause
stress responses (reduced abundance, increased
risk, death)
• Both biotic and abiotic components can be
stressed, as can the whole system
• Natural stress levels will vary from system to
system (temporary streams will have much higher
natural stress levels than permanent streams)
• The desirability (or otherwise) of stresses in a
system can only be judged in relation to the
natural (or reference) stress regime
Assessing increased and decreased stress
S
t
r
e
s
s
Decreased
Flow (C)
Natural (A)
Inc. Flow (C)
% Duration
HYDRAULIC ASSUMPTION
The structure and resultant hydraulic
complexity of most natural river
channels ensures that, when there are
areas of fast deep flow, there will also
be areas of other hydraulic habitats (eg
fast shallow, slow shallow, slow deep
and no flow) – and therefore
conditions suitable for a variety of
species
A Generic Stress Index
• An index of 0 to 10 where 0 indicates no stress,
•
•
•
•
and 10 the highest level of stress
Stressors: Flow-related hydraulics and habitat
Biological responses: Reduced abundance (1 to 3),
increasing risk to critical life stages (4 to 6), and
disappearance of populations (7 to 10)
Flow-related hydraulics: Velocity, depth and
wetted perimeter
Habitat: Quantity and quality (the diversity and
connectivity of habitat types)
Site specific
discharge
(m3s-1)
5Biological
1Stressors
2,3Flow-related
hydraulics
4Physical
habitat
Very fast
Very deep
Very wide WP
In excess
Very high quality
Fast
Deep
Wide WP
Plentiful
High quality
Fast
Deep
Wide WP, slightly
reduced
Critical habitat
sufficient
Quality slightly
reduced
Moderate velocity
Fairly deep
WP slightly/ moderately
reduced
Reduced critical
habitat
Reduced critical
quality
Moderate velocity
Some deep areas
WP moderately reduced
Critical habitat
limited
Moderate quality
Moderate/slow velocity
Few deep areas
WP moderately/very
reduced
Critical habitat
very reduced
Moderate/low
quality
Moderate/slow velocity
No deep areas
Narrow WP
Critical habitat
residual
Low quality
Slow
Shallow
Narrow WP
No critical habitat
Other habitats
moderate quality
Slow
Trickle
Very narrow WP
No flow
No surface water
responses of target organism(s)
Stress
Index
Abundance
Aquatic Life Stages
8Persistence
0
Very abundant
All 7healthy
Yes
1
Abundant
All healthy
Yes
2
Slight reduction for
6sensitive rheophilic
spp
All healthy in some
areas
Yes
3
Reduction for all
6rheophilic species
All healthy in limited
areas
Yes
4
Further reduction for
all rheophilic species
All 7viable in limited
areas, critical lifestages of some
sensitive rheophilic
species at risk
Yes
5
Limited populations
of all rheophilic
species
Critical life-stages of
sensitive rheophilic
species at risk or
non-viable
Yes
6
Sensitive rheophilic
species rare
Critical life-stages of
sensitive rheophilic
species non-viable,
and at risk for some
less sensitive species
In the short-term
7
Most rheophilic
species rare
Most sensitive
rheophilic species
disappear
Flowing water
habitats residual
Low quality
All life-stages of
sensitive rheophilic
species at risk or nonviable
8
All life-stages of most
rheophilic species at
risk or non-viable
Many rheophilic
species disappear
Standing water
habitats only
Very low quality
Remnant populations
of some rheophilic
species
9
Mostly pool dwellers
All life-stages of most
rheophilic species
non- viable
Most or all
rheophilic species
disappear
10
Only specialists
persist
Virtually no
development
Only specialists
persist
Only hyporheic
refugia
COMPONENT
PES
TRAJ
LONG
TERM
(20 Y)
WATER
QUALITY
B
0
B
GEOMORPH
D
-
D/E
RIPARIAN
VEGETATION
C
-
C/D
ERC
EIS
M
O
D
E
R
A
T
E
B
D
C
SI
FISH
C
AQUATIC
INVERTS
B/C
ECOSTATUS
C
0
0
-
C
B/C
C
M
O
D
E
R
A
T
E
C
B/C
C
The process for applying the
FS/R method
• Select a site, survey and model hydraulic
•
•
•
•
characteristics
Specialists apply the stress index to the site, in relation
to selected species/groups, to develop stress curves
The hydrologist converts the resulting critical stress
curve to stress time series for flow scenarios
Analyse the stress profile of each scenario in terms of
the magnitude, frequency and duration of different
stresses
Assess the severity of each stress profile in relation to
the natural stress profile
AN EXAMPLE OF A SITE SPECIFIC STRESS
INDEX FOR INVERTEBRATES
Flow
rate
(m33/s)
Stress
Res ponse
4
0
Average velocities > 0.6 m/s, and average depth > 0.4m provides abundant fast
deep and fas t shallow habitat for rheophilic species (such as s imuliids and
hydropsydhids.
3.8
1
Average velocity 0.61 m/s, average depth still > 0.4m. Abundance of critical
habitats is s lightly reduced, but all species are still abundant.
0.3
3
Average velocity 0.2 m/s (therefore ma ximum velocity approximately 0.4 to 0.5
m/s ). Average depth 0.17m, maximum 0.4m. Still some critical habitat, but
rheophilic species abundance much reduced.
0.13
5
Average velocity 0.12 m/s (therefore maximum velocity 0.2 to 0.3 m/s). Average
depth 0.14m, maximum 0.34m. Wetted perimeter 9m - marginal vegetation
habitats only just in the water. Rheophilic species confined to very small areas,
egg and early larval stage probably non-viable.
0.03
7
Average velocity 0.05 m/s (maximum approximately 0.1 m/s ). Average depth
0.12m, ma ximum depth 0.28m. Wetted perimeter 6.4m, no longer in marginal
habitats. Loss of all critical flowing habitat, only remnant areas for short-term
survival of hardy rheophilic species .
0.01
8
Average velocity 0.01 m/s, only s low trickles and s tanding water habitats remain.
All rheophilic species will disappear if this flow condition pers ists.
0
9
Standing water only
Note:
Stresses of 2, 4 and 6 have not been specifically motivated, and are simply extrapolations of the
adjacent stress motivations.
Blyde River
100
10
1
0.1
0.01
0.001
0
Barbus
2
Cpre
4
6
Stress
Inv
8
Rip Veg
10
Total
Black = Natural, Red = Recommended, Blue = Present day
Blyde River spell analysis (Stress = 1.5)
White = natural, Red = recommended, Blue = Present day
V ar 1
V ar 2
V ar 3
V ar 4
V ar 5
In t e g r a t e
10
9
8
Fish
7
6
Fish and
inverts
5
4
3
Fish
2
1
Rip Veg
0
1
F lo w
2
( m ^ 3 /s )
F dep Inverts wet
F dep Inverts dry
Reference
B
C
Reference
D
B
C
D
10
9
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
10
20
30
40
50
60
70
% Time Equalled or Exceeded
80
90
100
10
20
30
40
50
60
70
% Time Equalled or Exceeded
80
90
100
OBJECTIVES HIERARCHY
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•
•
•
Overall objective (Ecological category A to D)
General flow objectives
Component objectives
Target species objectives
+ Descriptions of conditions for classes below and
above the objective category
EXAMPLE OBJECTIVES
(e.g. to maintain Category B)
• Maintain perennial flow
• Summer flows > winter flows
• Av. velocity > 0.1 m/s at all times for target fish (stress
never > 6)
• Sufficient depth (30 cm) to allow target fish to feed and
breed 85% of time in summer (stress < 1 for 42.5% of time)
• Av. velocity > 0.3 m/sec for 80% of time, to ensure
Trichoptera habitat (stress < 3 for 80% of time)
• Wetted perimeter in reeds for 60% of summer to provide
marginal habitats (stress < 0.8 for 30% of time)
Application of objectives to define
ecological category B
Fish:
Stress never >6
10
S
t
r
e
s
s
Inverts:
Stress <3
80% time
8
Fish:
Stress <1
42.5 % time
6
Riparian veg:
Stress <0.8
30% time
4
2
0
0
10
20
30
40
50
60
70
% Time Exceeded
80
90
100
Application of objectives to define
ecological category B
Fish:
Stress never >6
10
S
t
r
e
s
s
Inverts:
Stress <3
80% time
8
Fish:
Stress <1
42.5 % time
6
Riparian veg:
Stress <0.8
30% time
4
2
B
0
0
10
20
30
40
50
60
70
% Time Exceeded
80
90
100
Application of objectives to define
ecological category B
Fish:
Stress never >6
10
S
t
r
e
s
s
Fish:
Stress <1
42.5 % time
Inverts:
Stress <3
80% time
8
6
Riparian veg:
Stress <0.8
30% time
4
2
D
B
0
0
10
20
30
C
40
50
60
70
% Time Exceeded
80
90
100
Thukela IFR4 Based on dry season flows
B
B/C
ADVANTAGES OF THE FS-R METHOD
• Biological responses treated as a continuum rather than
as thresholds
• Analysis includes frequency and duration as well as
magnitude
• Links between flow and biological responses are
explicit
• Analysis of any number of flow regimes is possible and
repeatable
• The natural stress profile provides a reference condition
FURTHER DEVELOPMENTS
• Apply method to high flows
• Parallel development of FS-R method for
water quality
• Refinement of stress index
• Analysis and comparison of stress profiles
• Regionalised stress/response relationships
REFERENCE:
O’KEEFFE J H, HUGHES D A AND THARME R E (2002)
Linking ecological responses to altered flows, for use in
environmental flow assessments: The Flow Stressor-Response
method.
Proceedings of the International Association of Theoretical and
Applied Limnology, 28:84-92.