Australian Natural Resources Atlas

Natural Resource Topics

Water resources - Quality - Queensland

Location map of Basin Brisbane River

Basin: Brisbane River

Surface water quality in Brisbane River

Copyright Context map of Basin Brisbane River

Attributes for which exceedance analyses could be determined:

Salinity, pH, Total Phosphorus, Total Nitrogen, Turbidity

Attributes for which trend analyses could be determined:

Salinity, pH, Total Phosphorus, Turbidity

The Brisbane River basin is located in the South East corner of the North East Coast Drainage Division where approximately 80% of Queensland's human population resides. Several urban centres, including Brisbane City, are located in this basin. The basin is characterised by flat coastal plains, steep ranges and variable but high intensity rainfall. Streams in the region start as fast flowing streams in the ranges and become larger but still moderately flowing rivers on the coastal plain. The basin also contains several impoundments to serve the large urban centres. Land use is diverse in the basin. It includes major urban areas along the coast, some intensive agriculture, grazing, mining and forested areas in the ranges. Due to population pressures, a large proportion of the basin has been fully developed. At present, the Brisbane River Basin, particularly in and around the urban centre of Brisbane, is experiencing rapid growth and development and this is invariably placing greater pressure on it's water resources.

Data for the exceedance analysis were collected from twenty sites, which are located in the Brisbane and Bremer Rivers, and Warrill, Lockyer, Oxley and Moggill Creeks. Together, these sites represent approximately 65% of the basin. For the trend analysis, data were collected from two sites, located in the Brisbane River and Lockyer Creek, representing 60% of the basin.

Surface water salinities were found to be suitable for aquatic ecosystem protection (ANZECC 1992), drinking water (NHRMC 1996) and agricultural use (Gill 1986) at all of the monitored sites. These levels are not rising in the Brisbane and Bremer Rivers.

The exceedance analysis indicated that turbidity levels at all of the monitored sites exceeded NHMRC (1996) guidelines for drinking water. However, turbidity levels in the upper reaches of the Brisbane River, and in Bremer River and Moggill Creek, remained within ANZECC (1992) guidelines for aquatic ecosystem protection and these levels were not found to be increasing. Oxley Creek, on the other hand, exhibited extremely high levels of turbidity, rendering the water unsuitable for aquatic ecosystem protection (ANZECC 1992). This can be attributed to the extensive clearing of native vegetation for urban, industrial and agricultural development that takes place in the area as well as from industrial, stormwater and sewerage effluent discharges.

pH levels are within ANZECC (1992) and NHMRC (1996) targets throughout the monitored catchment. However, although still within (1992) and NHMRC (1996) guidelines, the trend analysis indicated that the upper reaches of the Brisbane River are becoming increasingly alkaline. Reasons for this are currently unknown and require further investigation.

TN and TP levels are extremely high in the lower reaches of Oxley Creek and this may be partly related to the sewerage treatment plant located upstream from these sites. The high TP values can also be associated with the high levels of suspended particulates that occur throughout these waters. High TN and TP levels were also found in the lower reaches of the Bremer River where land-use is primarily agriculture, and where fertiliser is most likely applied.

Faecal coliform concentration data were only available from two sites, which are located in the lower reaches of Oxley Creek. These data indicated that Oxley Creek's faecal coliform concentrations are extremely high, rendering the water unsuitable for both primary and secondary contact activities (NHMRC 1996). This may be partly related to treated sewerage discharge into Oxley Creek although urban stormwater discharges and terrestrial runoff are also likely to elevate the creek's bacterial levels.

Monitoring StationSalinity - Electrical conductivityTotal nitrogen Total phosphorus Turbidity pHBlue Green Algae
ExceedTrendExceedTrendExceedTrendExceedTrendExceedTrendExceedTrend
1432063No DataNo DataNo DataNo DataGoodNo DataNo DataNo DataNo DataNo DataNo DataNo Data
143001CGoodNo TrendNo DataNo DataGoodNo DataGoodNo TrendGoodIncreasing TrendNo DataNo Data
14331001050GoodNo DataNo DataNo DataNo DataNo DataPoorNo DataGoodNo DataNo DataNo Data
14331001270GoodNo DataGoodNo DataGoodNo DataPoorNo DataGoodNo DataNo DataNo Data
14331000930GoodNo DataNo DataNo DataNo DataNo DataPoorNo DataGoodNo DataNo DataNo Data
14331000840GoodNo DataNo DataNo DataNo DataNo DataPoorNo DataGoodNo DataNo DataNo Data
14331000790GoodNo DataGoodNo DataGoodNo DataPoorNo DataGoodNo DataNo DataNo Data
14331000530GoodNo DataGoodNo DataGoodNo DataPoorNo DataGoodNo DataNo DataNo Data
14331000270GoodNo DataGoodNo DataGoodNo DataPoorNo DataGoodNo DataNo DataNo Data
143203CGoodNo TrendNo DataNo DataNo DataNo DataNo DataNo TrendNo DataNo TrendNo DataNo Data
14320000920GoodNo DataNo DataNo DataNo DataNo DataPoorNo DataGoodNo DataNo DataNo Data
14320001110GoodNo DataPoorNo DataPoorNo DataPoorNo DataFairNo DataNo DataNo Data
14320001370GoodNo DataNo DataNo DataNo DataNo DataPoorNo DataGoodNo DataNo DataNo Data
14320001600GoodNo DataNo DataNo DataNo DataNo DataPoorNo DataGoodNo DataNo DataNo Data
1432070No DataNo DataNo DataNo DataFairNo DataNo DataNo DataNo DataNo DataNo DataNo Data
14320002110GoodNo DataFairNo DataGoodNo DataPoorNo DataGoodNo DataNo DataNo Data
1432066No DataNo DataNo DataNo DataPoorNo DataNo DataNo DataNo DataNo DataNo DataNo Data
14320002890GoodNo DataFairNo DataGoodNo DataPoorNo DataGoodNo DataNo DataNo Data
1431057GoodNo DataNo DataNo DataGoodNo DataPoorNo DataGoodNo DataNo DataNo Data
14346003720GoodNo DataPoorNo DataPoorNo DataPoorNo DataGoodNo DataNo DataNo Data

Select a station name in the table above to view a detailed station report.

Monitoring Water Quality Guideline exceedances and trends

Exceedance Classification

For the Audit assessment of surface water quality, individual monitoring sites were classified as good, fair or poor for each variable based on whether State and Territory water quality guidelines (see below) were exceeded. Generally a 'good' classification was achieved where water quality was within 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 the median, 90th percentile, and % time exceedance, were used by States and Territories for this determination dependent upon the variable and whether the analysis was based on assessing acute (short term extreme event) or chronic (long term sustained event) water quality impacts. 'Fair' water quality describes situations intermediate between good and poor. Full discussion of the methods used for water quality exceedance and trend assessment are presented in the Water Quality Technical Report (see link to technical report).

Water quality 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) data set containing relatively frequently collected water quality samples (monthly as a minimum) and concurrent 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 (see link to technical report).

The significance of observed trends were assessed statistically to ensure they were not the result of random variation. 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.

Result Aggregation

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 river basins. To do this an 'upstream area weighting' method was used. Results obtained from a monitoring station were multiplied by the amount of catchment area that it samples. Weighted results from individual monitoring stations allows a river 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. Results per basin are presented graphically as colored pie charts.

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. Nevertheless, the potential for error generation was recognised, particularly when monitoring station coverage across the basin is limited, the opportunity for bias in the characterisation of basin water quality increases. 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.

The Water resources - Quality - Queensland's reporting capacity to interrogate data down to an individual monitoring site scale provides the opportunity for basin wide aggregations presented elsewhere to be further examined.

Note: some attribute information may not be available for some areas

Trend Legend

Trend chart legend

Exceedance Legend

Exceedance chart legend

Salinity

Trend

Chart of Salinity - trend

Salinity describes the salt concentration in water. It is usually measured in terms of the ability of water to conduct an electrical current (electrical conductivity EC) in units of micro siemens per cubic centimetre (m Scm-1). EC is an appropriate indicator of salinity, as it is proportional to the concentration of total dissolved salts and is easily measured in the field or by later laboratory analysis. Salinity is also sometimes measured directly (as is the case in Western Australia) in terms of total dissolved salts (TDS).

The salinity guideline for the protection of aquatic ecosystems was used for the exceedance assessment. The values for this water quality indicator are also generally equivalent for the indicators values for drinking water and agricultural water use, although the latter can be crop specific. Guideline boundaries varied from State to State (see below) reflecting the variability of surface water conditions and management objectives.

The two pie charts present salinity results aggregated from individual monitoring stations to represent the salinity status of the entire basin. They show the relative proportion of the basin area that was classified as having good, fair or poor water quality in terms of salinity guideline exceedances and the relative proportion of the basin area that was assessed as having increasing, decreasing or static salinity trends.

The proportion of the basin for which no data was available is also presented and provides an indication of the monitoring coverage of the basin for salinity.

Exceedance

Chart of Salinity - exceed

Return to legends and listing

Surface Water pH

Trend

Chart of Surface Water pH - trend

The acidity or alkalinity of surface waters is measured in units of pH which are a logarithmic scale measure of the concentration of free hydrogen (H+) ions in solution. Values at the low end of the pH scale (1-7) represent extreme to neutral acidity, while values at the high end of the pH scale (7-14) are a measure of the neutral to extreme alkalinity of water.

The pH guideline for the protection of aquatic ecosystems was used for the exceedance assessment. Guideline boundaries varied from State to State (see below) reflecting the variability of surface water conditions and management objectives.

The two pie charts present pH results aggregated from individual monitoring station to represent the pH status of the entire basin. They show the relative proportion of the basin area that was classified as having good, fair or poor water quality in terms of pH guideline exceedances and the relative proportion of the basin area that was assessed as having increasing, decreasing or static pH trends.

The proportion of the basin for which no data was available is also presented and provides an indication of the monitoring coverage of the basin for pH.

Exceedance

Chart of Surface Water pH - exceed

Return to legends and listing

Nutrients

Trend - total nitrogen

Chart of Surface Water total nitrogen - trend

Trend - total phosphorus

Chart of Surface Water total phosphorous - trend

There are a number of nutrients that effect the quality of surface waters. These include nitrogen, phosphorous and organic carbon. These nutrients can occur in a range of chemical forms. Two measure of nutrient concentration in surface waters, total nitrogen and total phosphorus were assessed as part of the Audit. Total Nitrogen - is a measure that sums the concentration of the major forms of nitrogen including ammonia, organic nitrogen, nitrate and nitrite. Total phosphorus - is a measure that sums the concentration of all forms of phosphorus in the water column including dissolved forms, insoluble particulate forms and phosphorus already incorporated in phytoplankton. Both variables require laboratory analysis of samples collected in the field for accurate measurement. While national guidelines for both total phosphorus and total nitrogen are established in units of micro grams per litre (m gL-1), State and Territory guideline specification and operational practice utilise units of milligrams per litre (mgL-1).

The total nitrogen and total phosphorus guidelines for the protection of aquatic ecosystems were used for the exceedance assessments. Guideline boundaries varied from State to State (see below) reflecting the variability of surface water conditions and management objectives.

The four pie charts present both total nitrogen and total phosphorus results aggregated from individual monitoring stations to represent the total nitrogen and total phosphorus status of the entire basin. They show the relative proportion of the basin area that was classified as having good, fair or poor water quality in terms of total nitrogen or total phosphorus guideline exceedances and the relative proportion of the basin area that was assessed as having increasing, decreasing or static total nitrogen or total phosphorus trends.

The proportion of the basin for which no data was available is also presented and provides an indication of the monitoring coverage of the basin for both nutrients.

Exceedance - total nitrogen

Chart of Surface Water total nitrogen - exceedance

Exceedance - total phosphorus

Chart of Surface Water total phosphorous - exceedance

Return to legends and listing

Turbidity

Trend

Chart of Surface Water Turbidity - trend

Turbidity is a measure of the clarity, 'dirtiness' or light scattering/absorbing capacity of water, which is roughly proportional to the type and concentration of suspended matter. It is therefore commonly used as an indicator of the amount of suspended solids in the water column. Turbidity is usually measured in Nephelometric Turbidity Units (NTU), which provide a measure of the capacity of light to penetrate through water. Total suspended solids (TSS) measured in milligrams per litre (mgL-1) is also used as a less accurate measure of turbidity in some instances and by some States (i.e., WA) although it is recognised that non-solid or dissolved substances within water can also affect turbidity.

The turbidity guideline for the protection of aquatic ecosystems was used for the exceedance assessment. Guideline boundaries varied from State to State (see below) reflecting the variability of surface water conditions and management objectives.

The two pie charts present turbidity results aggregated from individual monitoring stations to represent the turbidity status of the entire basin. They show the relative proportion of the basin area that was classified as having good, fair or poor water quality in terms of turbidity guideline exceedances and the relative proportion of the basin area that was assessed as having increasing, decreasing or static turbidity trends.

The proportion of the basin for which no data was available is also presented and provides an indication of the monitoring coverage of the basin for turbidity.

Exceedance

Chart of Surface Water Turbidity - exceedance

Return to legends and listing

Faecal coliforms

No Faecal Coliforms information exists for this basin

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Blue-green algae

No Blue-Green Algae information exists for this basin

Return to legends and listing

Further Information

Key

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