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Assessing river condition

Without improvements in river and catchment management, existing uses of and benefits obtained from Australia's rivers will not be sustainable. The assessment of river condition provides a baseline data set from which river managers can gauge improvements in the future.

The assessment incorporates a range of attributes that indicate key ecological processes at the river reach and basin levels. Rivers in near natural condition serve as a reference against which condition of other rivers can be assessed.

Natural resource management requires information measured at an appropriate scale to:

• assist policy development;
• support investment decisions;
• evaluate program and policy performance; and
• direct resource allocation priorities.

Clients for this information include Commonwealth, State/Territory and local governments, rural industries, the community, and other government and non-government organisations.

Key river management issues include:

• loss of riparian vegetation;
• intensity of land use;
• increased sedimentation;
• increased nutrient loads; and
• altered hydrology.

A national protocol has been developed by the Audit for reporting river condition. This protocol provides for the incorporation of results from river assessments at the State/Territory or regional level and strengthens the overall results of the river assessment. The best available information can be incorporated from the State/Territory, regional and local levels, without compromising the role of the national assessment. Results using the national protocol are available from the Australian Natural Resources Atlas.

Methods

The river assessment is based on the premise that:

• ecological integrity is the fundamental measure of river condition; and
• aquatic biota demonstrate an ecological response to changes in physical and chemical features of their environment.

Catchment activities, including land uses, can affect riverine habitat (riparian vegetation, snags and channel geomorphology) and instream water conditions. Riverine habitat, and structures (e.g. dams, weirs and levees) in turn affect biota (aquatic vegetation, invertebrates, fish and waterfowl). The assessment approach is therefore founded in our understanding of the links between catchments, riverine habitats and aquatic biota.

A detailed description of the methods is available in the project report and covers:

• definition of reach network;
• aggregation (i.e. aggregating measures for a group of reaches to provide a measure for a basin);
• integration (e.g. reach-scale subindices integrated to create the environment index for a reach);
• justification and descriptions of condition classes;
• calculations, modelling and validation of subindex scores; and
• river sediment budget methods.

Indices of river condition

The river assessment calculates an index of condition for key measures affecting river condition (Figure 35). Aquatic biota are considered to be the key measure of environmental condition. Environmental variables are important measures and drivers. It is important to measure both aquatic biota and environmental variables, because:

• assessing only biota may tell us that the biota is impaired but not why;
• there may be a time lag between environmental disturbance and biotic response, so measures of environmental changes can provide an early warning; and
• a biotic response in the absence of any environmental indication may suggest that there is an environmental component that needs to be monitored (e.g. a particular toxicant).

The assessment is reported using an aquatic biota index (macro-invertebrate), based on AUSRIVAS (Australian River Assessment System) macro-invertebrate data collected under the National River Health Program and an environment index that combines the:

• catchment disturbance subindex;
• riverine habitat subindex;
• hydrological disturbance subindex; and
• nutrient and suspended sediment load subindex.

The aquatic biota index should include other biotic indicators in addition to macro-invertebrates since:

• macro-invertebrates may not be sensitive to all forms of river modification;
• other biota may show up effects at larger or smaller time and spatial scales; and
• effects shown by more than one kind of biota strengthen conclusions and may enable insights into ecosystem effects.

Assessment philosophy is based on departure from reference - or pre-European settlement conditions. It is hard to find pristine rivers in the assessment area with which to compare test sites, especially for lowland rivers surrounded by extensive agricultural development. Reference conditions were therefore set by using a combination of:

• minimally disturbed sites;
• historical data;
• modelling of past conditions; and
• professional judgement (Table 9).

Table 9: River assessment indices and their reference conditions.

	Reference condition
Aquatic biota index (macro-invertebrates)
The aquatic biota index represents the response of macro-invertebrates to changes in the environment. The index is based on extensive national sampling of aquatic macro-invertebrates collected by State/Territory agencies under the National River Health Program. Data were collected and analysed using the standardised AUSRIVAS methods (Coysh et al. 2000, Simpson & Norris 2000). Approximately 6000 sites have been sampled throughout Australia; at most sites two habitats have been assessed, with many being re-assessed four to six times since 1996. AUSRIVAS models assess biological condition by comparing the kinds of aquatic invertebrates observed at sites of unknown condition (test sites) with the biota predicted to occur in reference sites. The ratio of the number of observed taxa to expected is the basis of the index.	Comparison with biota at a near pristine or minimally modified site
Environment index
The environment index brings together the cumulative effects of catchment-scale features and local features including habitat, hydrology, and nutrients and suspended sediment loads.	Comparison with a completely undeveloped catchment (pre-European settlement conditions)
The catchment disturbance subindex focuses on anthropogenic changes to land surfaces that influence rivers. The Agricultural Land Cover Change data set (Kitchin & Barson 1998) was used to provide a measure of recent change in land use over time. Included in the data set is a measure of the loss of woody vegetation over the period 1990-1995. Infrastructure information is not included in the land use coverage, so the Wild Rivers data set (Stein et al. 1997) was used for this information.
The habitat subindex uses measures of sediment inputs, riparian vegetation clearing and connectivity (dams, weirs, levee banks) to assess the state of local habitat and its probable ability to support aquatic life.
Bed condition
The bedload model calculates the mean annual historical deposition of bedload in river reaches as a result of supply of sediment from bank erosion and gully erosion upstream. This volume of deposition is expressed as a total bed accumulation of sand and gravel over historical times (measured in metres).	Comparison with a stable bed of no net accumulation or degradation at century time scale
Riparian vegetation
Riparian vegetation is calculated by estimating the extent of tree cover in the riparian zone within 100 m of the river bank using satellite imagery. The Agricultural Land Cover Change data set (Kitchin & Barson 1998) was used to calculate an assessment of riparian extent. This data set has information on the distribution of broad structural categories of vegetation at a scale fine enough to be useful for assessing riparian extent in a majority of situations. The data set covers much of Australia, and the land cover component is relatively current (1995).	Comparison with riparian vegetation coverage assumed to have existed under pre-European settlement conditions
Connectivity
There are two important components of connectivity: upstream-downstream connectivity (longitudinal) and connectivity with the floodplain (lateral). The former is important for the migration and breeding of many fish species, the latter for movement of water, biota and material across the floodplain. Connectivity was calculated from the Wild Rivers data set (Stein et al. 1997) and data on impoundments and levees.	Comparison with a no-dam, no-levee regime (pre-European settlement conditions)
The hydrological disturbance subindex assesses the change to flow regimes that typically result from river regulation and/or substantial flow diversion or extraction. The hydrological disturbance subindex is based on comparisons of the current flow regime to the natural or pre-European settlement flow regime. The key aspects of flow regime change included are: changes in total flow volumes using a mean annual flow index; changes in flow regime variability using a monthly flow-duration curve difference index (a measure of flood frequency); and changes in the seasonal pattern of flows using a seasonal periodicity index to assess changes to the seasonal timing of high and low flows, and a seasonal amplitude index to assess changes in the magnitudes of seasonal highs and lows. Values were assigned to: regulated reaches with observed and/or modelled monthly data to describe both the current and natural flow regimes, and unregulated reaches in river basins where existing total annual extractions are less than 0.5% of the basin mean annual flow. No extraction data were available at the reach scale, and so unregulated reaches in basins with higher levels of extraction could not be reliably assessed.	All subindices were compared with modelled pre-European settlement flow regimes, which generally do not account for changes in run-off associated with land clearing.
The nutrient and suspended sediment load subindex considers the effects of long-term changes in suspended sediment and total nutrient loads, and the effects of short-term changes in toxicant levels. The subindex is primarily a comparison between existing and natural average annual loads of nutrients and suspended sediments, using modelled data. The modelled sediment and nutrient loads compare well with load estimates based on measured water quality and flow data. However, they cannot be directly compared to water quality assessments based on exceedance of guideline threshold values. This is because the relative increases over natural conditions implied by the thresholds in exceedance guidelines do not correspond to the relative increases over natural conditions used to define sediment and nutrient load assessment categories. Water quality measurements are also typically biased towards low flow conditions and do not necessarily correlate well with total loads.	Comparison with nutrient and sediment transport modelled present and  pre-European settlement regimes

Reporting bands

In the classifications that have been used, individual reach scores have been aggregated into descriptive condition bands on a linear gradient between 0 and 1 to simplify Australia-wide reporting (Table 10, Figure 36).

Table 10: River condition assessment classification.

Aquatic biota index (macro-invertebrates)
Reference condition	stream macro-invertebrates are similar in type to those at reference sites
Significantly impaired	between 20% and 50% of the expected macro-invertebrate families have been lost
Severely impaired	between 50% and 80% of the expected macro-invertebrate families have been lost
Extremely impaired	between 80% and 100% of the expected macro-invertebrate families have been lost
Environment index
Largely unmodified	minimal disturbance from catchment land uses such as conservation, forestry, low levels of grazing or cropping limited changes to the hydrological regime limited changes to the habitat (e.g. riparian vegetation reasonably intact, no dams or levees and very little sediment deposition) loads of suspended sediment, total nitrogen and total phosphorus close to natural
Moderately modified	catchment dominated by land uses that disturb the river to some extent (e.g. dryland cropping and grazing) some changes to the hydrological regime as a result of impoundments or abstraction some changes to habitat (e.g. riparian vegetation reduced to 50-75% original coverage, dams upstream but not in the reach, and some sediment deposition) loads of suspended sediment, total nitrogen and total phosphorus above natural
Substantially modified	catchment land uses, such as intensive cropping and irrigation, cause moderate to severe disturbance substantial changes to the hydrological regime as a result of impoundments or abstractions substantial changes to the habitat including loss of 50-75% riparian vegetation, connectivity affected by nearby dams or levees, and substantial sediment deposition moderate to high loads of suspended sediment, total nitrogen and total phosphorus
Extensively modified	catchment land uses, such as intensive agriculture or urbanisation, cause significant disturbance to streams significant changes to the hydrological regime (e.g. large reductions in flow and changes in the seasonality of flow events) extensive changes to the habitat, including loss of riparian vegetation, loss of connectivity and extensive sediment deposition high loads of suspended sediment, total nitrogen and total phosphorus

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