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Assessing Ecological Condition: Overview of DWS EcoStatus System for Rivers
Mandy Driver
with input from Jeanne Nel & Neels Kleynhans
Overview
• DWS Ecological Categories
• Early days: River Health Programme
• National assessments of condition of rivers
– Present Ecological State 1999
– Present Ecological State 2011 – EcoStatus method
• Latest: River EcoStatus Monitoring Programme
DWS Ecological Categories
A: Natural
B: Largely natural,
with few
modifications
C: Moderately
modified
D: Largely modified
E: Seriously modified
F: Critically modified
DWS Ecological Categories
A: Natural Unmodified, natural
B: Largely natural,
with few
modifications
A small change in natural habitats and biota may have
taken place but the ecosystem functions are essentially
unchanged
C: Moderately
modified
A loss and change of natural habitat and biota have
occurred but the basic ecosystem functions are still
predominantly unchanged
D: Largely modified A large loss of natural habitat, biota and basic
ecosystem functions have occurred
E: Seriously modified The loss of natural habitat, biota and basic ecosystem
functions are extensive
F: Critically modified
Modifications have reached a critical level and the
system has been modified completely with an almost
complete loss of natural habitat and biota. In the worst
instances the basic ecosystem functions have been
destroyed and the changes are irreversible.
Summary
classes
Our detailed
classes DWS Ecological categories Score
Good
Natural A: Natural 90-100
Near-natural B: Largely natural, with
few modifications 80-89
Fair Moderately
modified C: Moderately modified 60-79
Poor
Heavily modified D: Largely modified 40-59
Severely modified E: Seriously modified 20-39
Irreversibly
modified F: Critically modified 0-19
Lost Outright loss
River Health Programme
• Initiated mid-1990s, before National Water Act of 1998
• General aim: monitoring of aquatic biota as indicators of the ecological condition/integrity
Natural Human activity has caused no or minimal changes to the historically
natural structure and functioning of biological communities … and
their habitats
Moderately used/
impacted
Resource conditions are slightly to moderately altered from the
Natural class due to impact of human activity and water use
Heavily used/ impacted Resource conditions are significantly changed from the Natural class
due to impact of human activity and water use, but are nonetheless
ecologically sustainable
Unacceptably
degraded
Due to over-exploitation, water resources are in a state that is
ecologically unsustainable
South African
Scoring System
(SASS)
Fish Communities Aquatic invertebrates
Fish Assemblage
Integrity Index
(FAII)
Riparian vegetation
Riparian vegetation
index
(RVI)
River Health Programme approach
River Health Programme outputs
• Successful in involving stakeholder groups
• Booklets, posters, etc attracted the interest of various other groups
River Health Programme • Focus on aquatic biota as indicators of the ecological
condition
• BUT relationship between stressors and biological responses is seldom clear or well established for South African biota
• AND not aligned with requirements in the NWA – Ecological Reserve Requirements
– Classification System for water resources
– Resource Quality Objectives (RQOs)
• Result: RHP information not suitable for resource management / informing management decisions
Present Ecological State (PES) 1999
• Urgent need for a national assessment of river condition to inform national water planning processes
• Main rivers in quaternary catchments (linked with hydrological models)
• Desktop assessment by experts – several workshops over several months in 1998/1999 – very rapid
• Intended for broad-scale use not site-level decisions
Quaternary and sub-quaternary catchments
• Quaternaries Average size ~650 km2
• Sub-quaternaries 8547 Average size ~170 km2
reaches…..process segments…..pattern
Can be as long as the
Orange River
Sub-quaternaries
River reaches within catchments
River network topology
Quaternary mainstem
Tributaries
PES 1999 based on 6 attributes / characteristics
• Attributes:
– Flow (e.g. quantity, timing, velocity)
– Inundation (dams, weirs, other obstructions in the channel)
– Water quality
– Stream bed condition
– Riparian or stream bank condition
– Introduced in-stream biota
• For each attribute:
– Extent of modification from natural was assessed
– Based on data and expert knowledge, with a confidence rating
• flow,
• inundation
• water quality
• stream bed condition
• introduced instream biota
• riparian or stream bank condition
Present Ecological State 1999 (quaternary mainstems)
Present Ecological State 2011
• Sub-quaternary scale – main rivers and tributaries
• Based on 6 factors:
– Hydrology
– Geomorphology
– Physico-chemical (water quality)
– Fish
– Macro-invertebrates
– Riparian vegetation
• Combined to give EcoStatus
FISHAQUATIC
INVERTEBRATES
RIPARIAN
VEGETATIONFISH
AQUATIC
INVERTEBRATES
RIPARIAN
VEGETATION
HABITAT ATTRIBUTES: INSTREAM AND RIPARIAN
WATER COLUMN:
PHYSICO-
CHEMICAL
HYDROLOGY GEOMORPHOLOGY
WATER COLUMN:
PHYSICO-
CHEMICAL
HYDROLOGY GEOMORPHOLOGY
LAND USECATCHMENT AND
ATMOSPHERE
SYSTEM DRIVERS
HABITAT
BIOLOGICAL
RESPONSES
EC
OR
EG
ION
AL R
EF
ER
NC
ES
Kleynhans & Louw 2007
6 indicators for assessing river ecological condition
1. Hydrological Driver Assessment Index (HAI)
2. Geomorphology Driver Assessment Index (GAI)
3. Physico-chemical Driver Assessment Index (PAI)
4. Fish Response Assessment Index (FRAI)
5. Macro Invertebrate Response Assessment Index (MIRAI)
6. Riparian Vegetation Response Assessment Index (VEGRAI)
drivers
responses
COMPONENTS Desktop Level 1 Level 2 Level 3 Level 4
DRIVER
Geomorphology
QHI IHI (instream
and riparian)
IHI (instream
and riparian)
IHI (instream
and riparian) en
GAI 3
GAI 4
Water quality PAI
Hydrology HAI
RESPONSES
Fish Rating Rating
None FRAI FRAI
Invertebrates MIRAI MIRAI MIRAI
INSTREAM
Combination of
fish, invert
ratings and QHI
Combination of
fish, invert
ratings and IHI
Combination of
fish rating and
MIRAI and IHI
FRAI & MIRAI
& confidence
FRAI & MIRAI
& confidence
Riparian
vegetation
Rating Rating Rating VEGRAI 3 VEGRAI 4
ECOSTATUS
EcoStatus
Combination of
Instream (2/3)
and riparian
vegetation (1/3)
Combination of
Instream (2/3)
and riparian
vegetation (1/3)
Combination of
Instream (2/3)
and riparian
vegetation (1/3)
Combination of Instream &
VEGRAI. Confidence and
weights included
Levels of EcoStatus assessment – depending on available data
Kleynhans & Louw 2007
Example of an EcoStatus summary
C/DINSTREAM
DRIPARIAN
VEGETATION
DECOSTATUS
DAQUATIC
INVERTEBRATES
CFISH
Component
EC
Response
components
B/CWATER QUALITY
EGEOMORPHOLOGY
EHYDROLOGY
Component
EC
Driver
Components
C/DINSTREAM
DRIPARIAN
VEGETATION
DECOSTATUS
DAQUATIC
INVERTEBRATES
CFISH
Component
EC
Response
components
B/CWATER QUALITY
EGEOMORPHOLOGY
EHYDROLOGY
Component
EC
Driver
Components
Biota (responses) may be in a better or worse state than the drivers, depending on how responsive/resilient they are
ABCDEF
Present Ecological State 2011 (sub-quaternary scale)
PES 1999 + modelled AB tribs
In order to develop a trend…
ABCDEF
PES 1999 – mainstems only
Modelled condition of tributaries in 1999 based on land cover – proportion of natural vegetation within each sub-catchment
0
10
20
30
40
50
60
1999 2011
% r
iver
len
gth
%AB
%C
%DEF
0
10
20
30
40
50
60
1999 2011
% r
iver
len
gth
AB
C
DEF
Mainstems only
Mainstems & tributaries
Fewer mainstem rivers in AB condition AB decline is not as dramatic in mainstem rivers
Comparison of factors used for PES 1999 and 2011
• Flow
• Inundation
• Water quality
• Stream bed condition
• Riparian condition
• Introduced in-stream biota
• Hydrology
• Geomorphology
• Physico-chemical
• Fish
• Macro-invertebrates
• Riparian vegetation
• PES 1999 and 2011 – extremely valuable national datasets
• Currently no plan to do a third national assessment of river condition
River EcoStatus Monitoring Programme
• Recently underway – revitalising the River Health Programme
• Now aligned with EcoStatus approach
• New method: Rapid Habitat Assessment Model (RHAM)
– aimed at Ecological Water Requirement monitoring
– DWS running training courses in RHAM
