Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7
Water quality and sources of pollution (continued)
Eutrophication and algal blooms (continued)
The two major indicators of the condition of inland waters in relation to eutrophication and algal blooms are:
- nutrient enrichment of inland waters as measured by the concentrations of phosphorus
- the occurrence of algal blooms and especially blue-green algal blooms.
Figure 16 presents an assessment of river systems that are at risk from eutrophication and algal blooms due to phosphorus concentrations in rivers, streams and storages exceeding state and territory water quality guidelines. The assessment is based on water quality data collected between 1995 and 1999 by states and territories. An assessment of the trend in phosphorus concentrations was also undertaken to determine whether they were increasing, decreasing or showing no trend. Trend analyses were based on data collected in the last 7 to 10 years. Detailed information on river system and individual site exceedances and trends in phosphorus can found on the NLWRA website (http://www.nlwra.gov.au/ ).
Figure 16: River systems where phosphorus levels exceed state or territory guidelines for the protection of ecosystems
Source: National Land and Water Resources Audit 2001a.
Phosphorus data of sufficient quality were only available for the more developed and populated regions of Australia. Although total phosphorus is not the best indicator of nutrient enrichment, as the dissolved forms of the phosphorus are more bioavailable to algae, the measurement of phosphorus is more common and has occurred over a longer time period.
Phosphorus levels in rivers, streams and dams regularly exceeded state and territory water quality guidelines in all catchments of the Murray-Darling Basin except the Condamine in Queensland. Other river systems where phosphorus levels are considered a major issue are:
- Sydney and surrounding catchments
- northern New South Wales coastal catchments
- the coastal catchments of Melbourne and those west of the Victoria-South Australia border
- south-eastern Queensland and northern coastal catchments
- two small coastal drainage regions in Western Australia.
Phosphorus levels were lower in the less developed coastal areas of southern NSW, eastern Victoria and northern Queensland although they are still considered to be a significant issue is some sections of the river systems.
In Tasmania, only limited water quality monitoring of the Mersey, Huon, Great Forester, King Island and Ringarooma river systems has been undertaken. With the exception of King Island (Bobbi et al. 1999b), nutrient levels were low, although one or more tributaries of most river systems showed some evidence of nutrient enrichment (Bobbi 1998, 1999; Bobbi et al. 1999a). High nutrient and turbidity levels in King Island streams were caused by intensive agriculture on the island, unrestricted access of stock to riparian and stream areas, and erosion of nutrient-rich soil.
Increased nutrient and pesticide loads from Queensland rivers have been implicated as contributing to a variety of impacts on the Great Barrier Reef including a new outbreak of the crown-of-thorns starfish; increased coverage of macroalgae (e.g. kelp) at the expense of the coral reefs; and general environmental stress that makes coral reefs more susceptible to other impacts (GBRMPA 2000).
Queensland, New South Wales, Victoria, Western Australia and the Australian Capital Territory monitor their river systems and/or water storages for blue-green algae. Commonly, the risk posed by blue-algal blooms to humans and livestock is reported using a four level alert system based on the concentration of blue-green algal cells (see Table 19). The following assessment of blue-green algal blooms in each state and territory focuses on assessing the frequency and location of high alert levels.
|Alert level||Concentration of toxic blue-green algal cells (cells/mL)||Risk and actions|
|Nil||<500||No risk to recreation, drinking water and livestock water|
|Low||500-2000||Minor risk to recreation, drinking water and livestock|
|Medium||2000-15000||Algal warnings issued
Review of drinking water extraction
|High||>15000||Drinking water extraction banned without appropriate treatment
Water-based recreation banned
New South Wales has an extensive algal monitoring program with regular monthly monitoring of major water storages and known problem areas in river systems. The percentage of time a high alert level was recorded for selected sites is shown in Figure 17.
Figure 17: Blue-green algal high alert levels in New South Wales (1996-99)
Source: Department of Land and Water Conservation Blue-Green Algal Database & Sydney Water Blue-Green Algal Database.
Some water storages had high alert levels more than 25% of the time between 1996 and 1999 including the Windamere, Toonumbar, Carcoar and Burrinjuck dams. Most other water storages had high alert levels between 5% and 15% of the time. Blue-green algal blooms have been recorded in many of the northern coastal river systems but monitoring is undertaken in response to visual indications of an algal bloom rather than via a regular monitoring program. Blue-green algal blooms in the southern coastal waterways have been very infrequent. Other New South Wales waterways where blue-green algal blooms have been recorded since 1996 are Clarie Hall Dam, Cudgen Creek, Emigrant Creek Dam, Lake Ainsworth, Lismore Lake, Malpus Dam, Puddledock Dam, Namoi River, Menindee Lakes, Severn River, Williams River, Telahar Wetlands, Hunter River, Ellalong Lagoon, Karuah River, Myall Lakes, Centennial Park and Bicentennial Park.
Table 20 presents a summary of high alert levels in Victorian inland waters between 1996 and 1999. In 1997, fifty high alert levels were recorded, substantially more than any other year. The Lodden river system recorded the highest number of 'high' alert levels each year. Other river systems where blue-green algal blooms were common were the Broken, Bunyip, Maribyrnong and Wimmera river systems. The majority of blue-green algal blooms occurred in lakes, wetlands and water storages, rather than in rivers or streams.
|Murray - Riverina||1||0||0||0|
Source: Department of Natural Resources and the Environment (Victoria) Blue-Green Algal Database.
Regular monthly monitoring of some Queensland water storages and weirs began in 1997. Blue-green algal blooms occurred throughout winter in many water storages (see Figure 18). This pattern is different from the southern areas of Australia where blue-green algal blooms occur predominantly in late summer and autumn. High alert levels were measured at least 50% of the time in many dams indicating significant and persistent blue-green algal problems.
Figure 18: Percentage of time high alert levels were measured for blue-green algae in Queensland water storages (1997-99)
Source: Department of Natural Resources Blue-green Algal Database.
In water storages and river systems of the Australian Capital Territory, blue-green algal blooms were more common between 1991 and 1994 compared with 1995 to 1999 (Table 21). Overall, blooms were infrequent.
|Period||Water storage or lake||High alert levels|
|July 1991-June 1994||Lake Tuggeranong||2|
|Lake Burley Griffin||2|
|July 1994-June 1995||No data collected|
|July 1995-June 1999||Lake Tuggeranong||1|
Source: Environment ACT (pers. com.)
River systems in Western Australia affected by large blue-green algal blooms since 1996 include the Blackwood, Vasse, Serpentine and the Swan-Canning rivers. Large blue-green algal blooms occurred in the Blackwood, Vasse and Serpentine rivers between late 1998 and early 1999, with the bloom in the Vasse River persisting for over 5 months (http://www.wrc.wa.gov.au/public/ ).
Up until 1997, blue-green algal blooms in the Swan-Canning River occurred episodically. Since 1997, blue-green algal blooms have been recorded annually in late summer/early autumn. In early 2000, a large Microcystis bloom developed in the Swan-Canning River as a result of unseasonal and substantial rainfall in the catchment. Catchment run-off containing nutrient-rich soil from the upper catchments increased nutrient levels in the river by 6 to 8 times their normal concentrations. The resulting blue-green algal bloom closed the Swan-Canning River to recreational use for two weeks (http://www.wrc.wa.gov.au/srt/Alert/moreinfo.html ).
Algal blooms affect irrigated agriculture and livestock production. Toxins produced by some blue-green algal blooms can affect the liver and nervous systems of livestock (ANZECC/AWRC 1992). The impacts on irrigated agriculture are mainly economic and include additional costs associated with unblocking pressurised irrigation systems, increased filter backwashing and adjustment of irrigation offtakes (Atech 2000). Generally, water is still suitable for irrigation despite having a high concentration of algal cells. Algal blooms cost Australian irrigators approximately $15 million per year (Atech 2000).
Most of the water used in livestock farming is from farm dams. The cost to farmers (excluding irrigators) from algal blooms in farm dams is $30 million per year and in other water resources, $15 million a year (Atech 2000). The costs of algal blooms in farm dams arise from monitoring, algicides, exclusion of stock, carting of water, loss of feed and stock losses.
The economic losses to recreation and aesthetics due to algal blooms is $96 million per year (Atech 2000). In the Sydney-coastal basin, persistent blue-green algal blooms occur in lakes in Centennial Park and Bicentennial Park. Also, sections of Hawkesbury-Nepean River are regularly closed to water-based recreation due to blue-green algal blooms (Mann et al. 1999). Many of the inland reservoirs that have reported blue-green algal blooms are also popular water-based recreational resources for inland communities (e.g. Lake Burrinjuck). Since 1996, the most significant loss of recreational amenity due to an algal bloom was in the Swan-Canning River in early 2000, when the river was closed to recreation for two weeks due to a Microcystis bloom.
Table 22 provides a summary of drinking water reservoirs affected by blue-green algal blooms since 1995.
|State||Algal blooms in major water storages|
|New South Wales||High blue-green algal alert levels recorded in the following water storages: Windamere; Toonumbar; Carcoar; Burrinjuck; Wyangala; Copeton; Pindari; Chaffey; Burrendong dams (see Figure 17)|
|Victoria||Number of algal blooms affecting town water supplies: 1993/94 - 7 blooms; 1994/95 - 9 blooms; 1995/96 - 4 blooms; 1996/97 - 18 blooms; 1997/98 - 16 blooms; 1998/99 - 21 bloomsA|
|Queensland||Blue-green algal blooms regularly measured in water storages; however, the number of drinking water storages affected is unknown (see Figure 18)|
|South Australia||Blue-green algal blooms (Anabaena circinalis) have been recorded periodically near water supply off-takes along the Murray RiverB|
|Tasmania||Algal blooms occurred in a number of Tasmanian water supply damsC|
|Other states & territories||No reported blue-green algal blooms in drinking water storages|
A Victorian Blue-Green Algal Database (DNRE 1999).
B SA EPA 1998.
C David Fuller, DPWIE (pers. com.).
- Nutrient levels in rivers, streams and dams regularly exceeded state and territory water quality guidelines in all catchments of the Murray-Darling Basin except the Condamine in Queensland; coastal catchments of Melbourne and those west to the Victoria-South Australia border; Sydney and surrounding catchments; northern New South Wales coastal catchments; south-eastern Queensland and northern coastal catchments; and two small coastal drainage regions in Western Australia.
- Blue-green algal blooms that persist for over six months have been recorded in many water storages in Queensland and New South Wales and are indicative of highly eutrophic systems. In Victoria and Western Australia, blue-green algal blooms are regularly recorded in some river systems in late summer and early autumn. The total cost to agriculture from algal blooms is estimated to be $60 million a year. Loss of amenity to the community from algal blooms is estimated to cost $96 million a year.