Assessing Ecological Condition: Overview of DWS EcoStatus System for Rivers

Transcription

1 Assessing Ecological Condition: Overview of DWS EcoStatus System for Rivers Mandy Driver with input from Jeanne Nel & Neels Kleynhans

2 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

3 DWS Ecological Categories A: Natural B: Largely natural, with few modifications C: Moderately modified D: Largely modified E: Seriously modified F: Critically modified

4 DWS Ecological Categories A: Natural Unmodified, natural B: Largely natural, with few modifications C: Moderately modified D: Largely modified E: Seriously modified F: Critically modified A small change in natural habitats and biota may have taken place but the ecosystem functions are essentially unchanged A loss and change of natural habitat and biota have occurred but the basic ecosystem functions are still predominantly unchanged A large loss of natural habitat, biota and basic ecosystem functions have occurred The loss of natural habitat, biota and basic ecosystem functions are extensive 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.

5 Summary classes Our detailed classes DWS Ecological categories Score Good Fair Natural A: Natural Near-natural Moderately modified B: Largely natural, with few modifications C: Moderately modified Heavily modified D: Largely modified Poor Lost Severely modified E: Seriously modified Irreversibly modified Outright loss F: Critically modified 0-19

6 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

7 River Health Programme approach Natural Moderately used/ impacted Heavily used/ impacted Unacceptably degraded Human activity has caused no or minimal changes to the historically natural structure and functioning of biological communities and their habitats Resource conditions are slightly to moderately altered from the Natural class due to impact of human activity and water use Resource conditions are significantly changed from the Natural class due to impact of human activity and water use, but are nonetheless ecologically sustainable Due to over-exploitation, water resources are in a state that is ecologically unsustainable Aquatic invertebrates South African Scoring System (SASS) Fish Communities Fish Assemblage Integrity Index (FAII) Riparian vegetation Riparian vegetation index (RVI)

8 River Health Programme outputs Successful in involving stakeholder groups Booklets, posters, etc attracted the interest of various other groups

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10 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

11 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

12 Quaternary and sub-quaternary catchments Quaternaries Average size ~650 km 2 Sub-quaternaries 8547 Average size ~170 km 2

13 River reaches within catchments Quaternary mainstem Can be as long as the Orange River Tributaries reaches..process River network topology segments..pattern Sub-quaternaries

14 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

15 Present Ecological State 1999 (quaternary mainstems) flow, inundation water quality stream bed condition introduced instream biota riparian or stream bank condition

16 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

17 ECOREGIONAL REFERNCES LAND USE CATCHMENT AND ATMOSPHERE SYSTEM DRIVERS WATER COLUMN: PHYSICO- CHEMICAL HYDROLOGY GEOMORPHOLOGY HABITAT HABITAT ATTRIBUTES: INSTREAM AND RIPARIAN FISH AQUATIC INVERTEBRATES RIPARIAN VEGETATION BIOLOGICAL RESPONSES Kleynhans & Louw 2007

18 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

19 Levels of EcoStatus assessment depending on available data COMPONENTS Desktop Level 1 Level 2 Level 3 Level 4 DRIVER Geomorphology Water quality Hydrology QHI IHI (instream and riparian) IHI (instream and riparian) IHI (instream and riparian) en GAI 3 GAI 4 PAI HAI RESPONSES Fish None FRAI FRAI Rating Rating Invertebrates MIRAI MIRAI MIRAI INSTREAM Riparian vegetation EcoStatus 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 Rating Rating Rating VEGRAI 3 VEGRAI 4 Combination of Instream (2/3) and riparian vegetation (1/3) Combination of Instream (2/3) and riparian vegetation (1/3) ECOSTATUS Combination of Instream (2/3) and riparian vegetation (1/3) Combination of Instream & VEGRAI. Confidence and weights included Kleynhans & Louw 2007

20 Example of an EcoStatus summary Driver Components HYDROLOGY GEOMORPHOLOGY Component EC E E Biota (responses) may be in a better or worse state than the drivers, depending on how responsive/resilient they are WATER QUALITY Response components FISH AQUATIC INVERTEBRATES INSTREAM RIPARIAN VEGETATION ECOSTATUS B/C Component EC C D C/D D D

21 Present Ecological State 2011 (sub-quaternary scale) AB C DEF

22 In order to develop a trend PES 1999 mainstems only PES modelled AB tribs AB C DEF Modelled condition of tributaries in 1999 based on land cover proportion of natural vegetation within each sub-catchment

23 % river length % river length 60 Mainstems only AB C DEF Mainstems & tributaries %AB Fewer mainstem rivers in AB condition %C %DEF AB decline is not as dramatic in mainstem rivers

24 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

25 PES 1999 and 2011 extremely valuable national datasets Currently no plan to do a third national assessment of river condition

26 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