Identifying key environmental assets, key ecosystem functions, the productive base and key environmental outcomes
The Water Act defines the ESLT as the level at which water can be taken from a water resource which, if exceeded, would compromise:
- key environmental assets of the water resource; or
- key ecosystem functions of the water resource; or
- the productive base of the water resource; or
- key environmental outcomes for the water resource.
In determining an ESLT, an important step has been for MDBA to decide on definitions for each of these elements (note the Water Act further defines environmental assets and environmental outcomes - it does not define which of these should be considered key - and it does not provide definitions of ecosystem functions or productive base). The processes developed by MDBA to do this are described below and in Section 5, with further detail in Appendix A.
4.1 Key environmental assets
The Water Act defines environmental assets as including water-dependent ecosystems, ecosystem services, and sites with ecological significance.
MDBA selected five criteria (with accompanying achievement indicators) to assess environmental assets within the Basin, and determine which of these would be considered key (see further details in Appendix A). The criteria were developed based on international obligations and in broad alignment with the National Framework and Guidance for Describing the Ecological Character of Australian Ramsar Wetlands (Department of the Environment, Water, Heritage and the Arts 2008) and the draft criteria for identifying High Conservation Value Aquatic Ecosystems (SKM 2007)
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Criterion 1:
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The water-dependent ecosystem is formally recognised in, and/or is capable of supporting species listed in, international agreements; and/or
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Criterion 2:
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The water-dependent ecosystem is natural or near-natural, rare or unique; and/or
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Criterion 3:
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The water-dependent ecosystem provides vital habitat; and/or
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Criterion 4:
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The water-dependent ecosystem supports Commonwealth, State or Territory listed threatened species and/or ecological communities; and/or
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Criterion 5:
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The water-dependent ecosystem supports or is capable of supporting significant biodiversity.
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MDBA also considered the ability to manage and deliver water to assets, in determining which would be considered key. Some assets are not connected to the main rivers and water resources of the Basin, and obtain water from local runoff or other processes. These assets are outside of the MDBA's ability to manage or influence, and are not considered key. There are also floodplain and wetland assets that require very high flows to inundate. These flows occur as unregulated events in response to extensive rainfall. Assets that require unregulated flows that cannot be managed are also not considered key. In these two situations, flows that sustain these assets will not be affected by the Basin Plan and will continue to occur through existing processes.
In addition to determining criteria for key environmental assets (including delivery constraints), MDBA has also undertaken some preliminary work to commence the development of a key environmental asset inventory. This process will be further developed in the future through the implementation of the Environmental Watering Plan, as set out in the Legislative Instrument, in partnership with State agencies, the Commonwealth Environmental Water Holder, and other stakeholders.
There are estimated to be in the order of 30,000 wetlands and many thousands of kilometres of rivers and streams in the Basin. There is not currently a comprehensive list or inventory of these environmental assets across the Basin for use in the determination of key environmental assets. Therefore, identifying all environmental assets in the Basin as a 'pool' from which key environmental assets can be assessed and selected is not currently feasible. Further work would be required to enable this to occur.
For the purpose of developing the preliminary asset inventory, environmental assets with known values were compiled as potential key environmental assets. This list of potential key environmental assets was compiled using existing international, Commonwealth and State/Territory sources including (but not limited to):
- Declared Ramsar Wetlands;
- Wetlands listed on the Directory of Important Wetlands of Australia;
- High Conservation Value Aquatic Ecosystem sites;
- Icon Sites established under The Living Murray Initiative;
- Published and unpublished literature e.g. jurisdiction management plans; and
- Spatial databases e.g. the EPBC Act 1999 threatened species spatial layer.
Each of the potential key environmental assets identified was then assessed against the criteria.
Thousands of environmental assets were initially listed. However for many of these, only limited information was available to assess against the criteria. A basic assessment of these assets was undertaken and, if an asset met the achievement indicators for at least one of the five criteria, it was selected as a key environmental asset.
One major challenge faced by MDBA was determining which assets can be actively managed, and which assets are either disconnected from the main water resources or require large unregulated flows. Conceptually there is good understanding of these issues, but currently there is no detailed mapping to define the zone of potential environmental water management in the Basin. This means it is currently not feasible to 'filter' the assets to determine those that can be actively managed. This would require further investment in floodplain inundation mapping, hydrologic modelling and understanding of the flow delivery constraints, including the combined effects of multiple constraints in upstream tributaries on downstream flows.
Notwithstanding these issues, it is clear that the Basin contains a large number (potentially thousands) of key environmental assets. The preliminary inventory identified more than 2400 named key environmental assets and up to twice as many more unnamed assets. MDBA acknowledges the uncertainties associated with this work and does not consider this work provides a robust inventory of key environmental assets in the Basin. Considerable further research and knowledge gathering is required, coordinated through the Environmental Watering Plan process, to resolve the issues identified above.
It is also clear from the assessments that the current level of knowledge and information is insufficient to enable the environmental water requirements for many key environmental assets to be determined. Consequently MDBA has developed and applied the indicator site approach, described in Section 5.
4.2 Key ecosystem functions
The Water Act does not define ecosystem functions, so MDBA has utilised the following definition:
Processes that occur between organisms and their environment, within and between populations and communities, and within river systems - including interactions between the living and non-living environment which lead onto dynamics and change in the ecosystem (adapted from Gigney et al. 2010).
There is good understanding within the scientific literature and community regarding the importance of ecosystem functions in achieving environmental objectives and outcomes. There is also a good conceptual understanding of the interplay between ecosystem functions and the health of key environmental assets and populations of plants and animals. There are different approaches to describing ecosystem functions (ecological and geomorphic approaches) and the current knowledge base does not enable ecosystem functions to be explicitly mapped or quantified across the Basin.
With the limited knowledge base (and associated uncertainties) in mind, MDBA developed an interim list of key ecosystem functions to inform the ESLT. These were identified from a review of available scientific literature. Three criteria were applied to determine which of these functions were considered to be key (see Appendix A). This resulted in an identification of the following 14, Basin-wide, key ecosystem functions (Alluvium, 2010):
- Disturbance through cease-to-flow periods;
- Disturbance and wetting through bankfull and overbank flows;
- Provide wetted habitat diversity in pool environments;
- Provide wetted habitat in riffle and run environments;
- Provide appropriate wetted habitat heterogeneity within a reach ;
- Provide in-channel habitat features within a reach;
- Organic and inorganic sediment delivery to downstream reaches;
- Sediment delivery to and from floodplains;
- Dilute carbon and nutrients from litter and soil on receding flows from floodplains;
- Dispersal of aquatic communities;
- Recolonisation of aquatic fauna and flora communities;
- Migration to fulfil requirements of life- history stages;
- Instream primary production by periphyton, phytoplankton and biofilms; and
- Foraging of aquatic species.
MDBA also considered how to determine the environmental water requirements for each of these key ecosystem functions. This followed the process of first identifying the flow regime components required to support each key ecosystem function, and then developing ways (metrics or indicators) to measure and set target values for those flows. This process is set out in Alluvium (2010).
4.3 The productive base
The Water Act does not define the productive base, so the MDBA has used advice drawn from Reid-Piko et al. (2010) which found that productive base is not widely employed or well-supported concept in the literature. Taken broadly it equates to ensuring that ecosystem services are supported. Ecosystem services are the benefits that humans obtain from ecosystems. They can be divided into provisioning, regulating, supporting and cultural services. Ecosystem services are influenced by ecosystem conditions and ecosystem processes. In determining the ESLT, Reid-Pike et al. (2010) conclude that there would be little to be gained by separately distinguish ecosystem services from the productive base and they should be treated synonymously.
Ecosystem services as a concept is still in development, and current empirical evidence on environmental water quantities needed to support ecosystem services is relatively immature. The relationship between biodiversity and ecosystem services is not sufficiently understood; scale inconsistencies remain unresolved and establishing robust measures for calculating human value and then disaggregating it to the ecosystem service level is a developing field Reid-Pike et al. (2010). In determining the surface water ESLT, MDBA considers that by providing environmental water for key ecosystem functions and key environmental assets, productive base water requirements will also be supported (see Appendix A for further details). Further research and experience in the management of environmental water through adaptive management processes will continue to inform the establishment of environmental water for ecosystem services and thus productive base.
4.4 Key environmental outcomes
The Water Act definesenvironmental outcomes to include ecosystem function, biodiversity, water quality and water resource health. Key environmental outcomes expected from the ESLT for ecosystem functions and biodiversity are set out in Section 9. Key environmental outcomes for water quality and water resource health are incorporated in the Basin Plan Water Quality and Salinity Management Plan.
4.5 Key issues and way forward
Through the processes outlined above, MDBA made determinations on the definitions for key environmental assets, key ecosystem functions, the productive base and key environmental outcomes, and gathered a considerable knowledge base surrounding these features. Very early in this process it became apparent that, due to the knowledge gaps identified above, and the very large number of potential key environmental assets, it would not be possible to determine the environmental water needs for each of these components in turn, and then combine them to inform an ESLT.
Consequently another approach was required to determine the ESLT, based on the currently available information. This approach would also need to be applicable with the existing river system modelling platform. The approach chosen by MDBA to inform the ESLT is often referred to as the hydrologic indicator site (or indicator site) method. This method is described in the next section of the report.
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