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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Water - Appendix 5. Surface Water Quality Assessment
Water quality guidelines
Water quality guidelines provide a means to assess the capacity of surface waters to meet ecological, social and economic requirements. Specific guidelines have been established for indicators that reflect the water quality requirements for:
- protection of aquatic ecosystems;
- agricultural water;
- recreation and aesthetics; and
- drinking water.
In Australia, national water quality guidelines established by the Australian and New Zealand Environment and Conservation Council (ANZECC 1992, ANZECC in press) are supplemented by State and regional guidelines established to meet specific water quality management objectives.
Use of site or waterway-specific guidelines is recommended by ANZECC (in press) in recognition of the extreme natural variation in Australian waterways and the differing levels of protection afforded to waterways with varying levels of development and catchment modification. For the Audit assessment of surface water quality, State and Territory water quality guidelines (see table below) were used to compile the national overview. Where States or Territories did not have established guidelines for particular water quality variables National Guidelines ANZECC (1992) were used as the default.
Meeting guidelines
For the Audit assessment of water quality, individual monitoring sites were classified as ?good?, ?fair? or ?poor? for each variable based on whether established guidelines (see below) were exceeded. Generally a good classification was achieved where water quality was within established guidelines for a greater period of time while a poor classification resulted where water quality did not fall within the guidelines for a greater period of time. A range of statistical measures including median, ninetieth percentile, and percent time exceedance were used by States and Territories for this determination dependent upon the variable concerned and whether the analysis was based on assessing acute (short-term extreme event) or chronic (long-term sustained event) water quality impacts.
Basin summaries
To be able to build an overview of State and national water quality it was necessary to aggregate water quality results from individual sites to whole river basins. To do this an ?upstream area weighting? method was used. Results obtained by an individual monitoring station are multiplied by the amount of catchment area that it samples. Weighted results from individual monitoring stations allows an entire reporting area (i.e. a basin) to be characterised in terms of the percentage of area classified as good, fair or poor, or in terms of the area undergoing increasing or decreasing trends for a particular water quality variable.
This method was supported and adopted by State and Territory agencies when compiling the national assessment and can be rationalised in terms of the way water quality interacts within a basin. The potential for error generation was recognised. Generally when monitoring coverage is limited the opportunity for bias in the characterisation of basin water quality becomes an issue. This may lead to the underestimation of the extent of a water quality issue where monitoring stations are not placed within impacted areas, or alternatively overestimation where in the absence of upstream monitoring stations, results obtained by impacted lowland sites are used to characterise the upper basin.
Detecting trends
Detecting trends in surface water quality is complicated by seasonal climatic variation and the influence of stream flows on the observed concentrations of water contaminants. For these reasons a long term (~10 year) dataset containing relatively frequently collected water quality samples (monthly as a minimum) and concurrently collected flow data are required to support trend assessments. A range of statistical analyses were used by States and Territories to report on water quality trends, dependent upon the nature of the monitoring (i.e., flow based versus regular sampling) and quality of the data (i.e., the method?s ability to accommodate missing data values). All used methods that accounted for seasonality and stream flow influences (ASoE & Audit, in prep.).
The significance of observed trends were assessed statistically. Significant trends were reported in terms of their magnitude (i.e., how much change per annum) and their direction i.e. whether they were increasing or decreasing. Results that indicated no trends were also reported.
The web based Australian Natural Resources Atlas provides a reporting capacity to interrogate data down to an individual monitoring site scale.
Full discussion of the methods used for water quality exceedance and trend assessment are presented in A review of Australia?s surface water quality (ASoE & Audit, in prep.).
To compile an overview of surface water salinity guideline exceedances within Australia?s river basins, the following definitions were used:
- ?major? issues occurred where guideline exceedances were calculated to occupy greater than a third (33%) of a basin area;
- ?significant? issues occurred where guideline exceedances were calculated to occupy greater than 5% but less than 33% of a basin area;
- ?not significant? issues occurred where monitoring coverage was greater than 50% of a basin area; and observed guideline exceedances represented less than 5% of a basin area.
- ?undetermined? issues occurred where monitoring coverage was less than 50% of a basin area; and observed guideline exceedances represented less than 5% of a basin area.
Table A7. State and Territory water quality guidelines.
| Units | Method | Good | Fair | Poor | |
|---|---|---|---|---|---|
| Salinity | |||||
| New South Wales | (µS/cm) | median | <500 | 500 - 1500 | >1500 |
| Victoria | (µS/cm) | median1 | <500 | 500 - 1500 | >1500 |
| Queensland | (µS/cm) | mean | <500 | 500 - 1500 | >1500 |
| South Australia | (µS/cm) | 90th percentile | <1000 | 1 000 - 2000 | >2000 |
| South Australia (modified) | (µS/cm) | median | <800 | 800 - 1500 | >1500 |
| Western Australia | (TDS mg/L) | median | <1000 | 1 000 - 5000 | >5000 |
| Australian Capital Territory | (µS/cm) | median | <800 | 800 - 1100 | >1100 |
| Turbidity | |||||
| New South Wales | (NTU) | median | <5 | 5-50 | >50 |
| Victoria1 | (NTU) | median | <5 | 5-50 | >50 |
| Queensland | (NTU) | median | <5 | 5-50 | >50 |
| South Australia | (NTU) | 90th percentile | <20 | 20-50 | >50 |
| Western Australia | (TSS mg/L) | median | <10 | 10-30 | >30 |
| Australian Capital Territory | (NTU) | median | <10 | 10-15 | >15 |
| Total nitrogen | |||||
| New South Wales2 | (mg/L) | median | <0.1 | 0.1-0.75 | >0.75 |
| Victoria1 | (mg/L) | median | <0.35 | 0.35-0.5 | >0.5 |
| Queensland | (mg/L) | median | <0.375 | 0.375-0.75 | >0.75 |
| South Australia | (mg/L) | 90th percentile | <1 | 1-10 | > 10 |
| South Australia (modified) | (mg/L) | modified median | <0.6 | 0.6-5 | > 5 |
| Western Australia | (mg/L) | median | <1.0 | 1.0-3.0 | >3.0 |
| Australian Capital Territory2 | (mg/L) | median | <0.1 | 0.1-0.75 | >0.75 |
| Total phosphorus | |||||
| New South Wales | (mg/L) | median | <0.02 | 0.02-0.05 | >0.05 |
| Victoria1 | (mg/L | median | <0.025 | 0.025-0.05 | >0.05 |
| Queensland | (mg/L) | median | <0.05 | 0.05-0.10 | >0.10 |
| South Australia | (mg/L) | 90th percentile | <0.10 | 0.1-1.0 | > 1 |
| South Australia | (mg/L) | modified median | <0.05 | 0.05-0.5 | >0.5 |
| (modified) | |||||
| Western Australia | (mg/L) | median | <0.10 | 0.10-0.30 | >0.30 |
| Australian Capital Territory | (mg/L) | median | <0.08 | 0.08-0.10 | >0.10 |
| pH | |||||
| New South Wales | n/a | n/a | n/a | ||
| Victoria1 | pH | % of months outside range 6.5-8.5 | <10% | 10-25% | >25% |
| Queensland | pH | % of months outside range 6.5-9 | <10% | 10-25% | >25% |
| South Australia | pH | median | 6.5-9 | n/a | <6.5 or >9 |
| Western Australia | pH | % of months outside range 6.6-8.8 | <10% | 11-25% | >25% |
| Australian Capital Territory | pH | median | 6.5-8.5 | 6-6.5 or 8.5-9 | <6 or >9 |
1 Catchment-specific guidelines and classification schemes exist for some Victorian catchments (under State environmental protection policies).
n/a not available
Table of Contents for the Australian Water Resources Assessment 2000
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