Inland Waters Theme Report
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 management of eutrophication and algal blooms is a catchment-based issue in most states and territories, though larger regional organisations such as the Murray-Darling Basin Committee have also developed eutrophication and algal management strategies (MDBC 1994) that encompass many river systems. As the processes that contribute to the development of algal blooms are highly complex and are dependent on the characteristics of the catchment and human activities (such as flow regulation), management responses to reduce eutrophication and algal blooms must be tailored to individual catchments. Research by state organisations, catchment management bodies, CSIRO and the National Eutrophication Management Project has contributed substantially to our knowledge base.
The most desirable long-term strategy for reducing eutrophication and algal blooms is to reduce the amounts of nitrogen and/or phosphorus entering inland waters. Since 1996 there has been some improvement in reducing the contribution of point sources through higher wastewater reuse, improved wastewater treatment and greater regulation of point-source discharges through licensing.
Algal blooms will continue to be a common occurrence in many inland waters despite efforts to reduce point and diffuse source pollution. Although diffuse sources are the major contributors to nutrient enrichment, it appears from the nutrient and algal bloom data above that there has been no reduction in their contribution since 1996. This is expected as many of the management strategies for reducing diffuse pollution are long-term and will require substantial investment and time (e.g. revegetation of bare catchment areas) before there is any noticeable improvement. Existing management strategies for diffuse source pollution control are primarily based on improving current land management practices such as fertiliser application, erosion control, riparian vegetation protection, increasing vegetation cover and reducing land clearing. These issues are covered in greater detail in the Land Theme Report and are summarised below. It should be noted that many of the measures to control soil erosion, such as riparian vegetation protection, increasing vegetation cover and reducing land clearing, will have collateral benefits for managing other problems such as salinity. This emphasises the importance of taking an integrated approach in developing land and water management strategies.
Australian aquatic ecosystems exist in one of two states, either clear and macrophyte-dominated or turbid and algae-dominated (Scheffer 1998). The switch from a macrophyte-dominated ecosystem to an algal-dominated system is a result of a complex interaction of land-use changes, vegetation clearance and flow, and is highly resistant to switching back to its former state (Harris 2001). Eroded soils already deposited into waterways will provide a source of nutrients for decades into the future. In response to the long-term threat of algal blooms, management strategies to control blooms through physical, chemical and biological manipulations have also been developed. These include destratification of reservoirs, using environmental flows to flush nutrients and algal blooms and introduction of native fish species. There have been some new developments and successes using these methods to control algal blooms since 1996. These are discussed in greater detail below.
The National Eutrophication Management Program (NEMP) began in 1995 with the objectives of:
- gaining an improved understanding of the processes leading to the initiation and development of algal blooms
- developing techniques to prevent and manage eutrophication
- effectively communicating the outcomes of the previous two objectives.
A review undertaken in 2000 (Chudleigh & Simpson 2000) found that projects funded by the NEMP had substantially increased the knowledge of the processes and causes of algal bloom development, especially factors such as sources of nutrients, nutrient and light availability and river flow effects. There has been no advance in knowledge on the impacts of episodic algal blooms on aquatic ecosystems, an aspect of algal blooms that yet has to be fully researched.
Based on the outcomes of the NEMP projects, tools and techniques to help natural resource managers to reduce and manage eutrophication and algal blooms are currently being developed. These include decision support tools, predictive modelling techniques and biological control methods. The effectiveness and adoption of these measures on a national basis cannot be assessed at the present time.
The National Water Quality Management Strategy (NWQMS) aims to meet the future needs for good water quality by providing national guidelines for water quality management. It is a joint strategy developed by two ministerial councils - the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) and the Australian and New Zealand Environment and Conservation Council (ANZECC). The National Health and Medical Research Council is involved in aspects of the strategy which affect public health.
The NWQMS policy objective is:
to achieve sustainable use of the nation's water resources by protecting and enhancing their quality while maintaining economic and social development.
The strategy aims to provide a consistent approach to water quality management through guidelines which promote a shared national objective while allowing flexibility to respond to regional and local differences. The NWQMS aims to provide guidelines to government and community organisations to assist in:
- the management of water resources, including fresh waters, coastal waters and groundwater
- decisions on the quality aspects of water, sewerage and drainage services
- facilitating and coordinating the application of the various strategies of government for the management of water resources and the quality of the services provided by water authorities.
Apart from the core document prepared jointly by ARMCANZ and ANZECC ('Policies and Principles - A Reference Document') which is the cornerstone of the national water quality management strategy, 20 other guidelines also form part of the strategy. Each of these other guidelines focuses on a part of the water cycle, or on a particular activity within the water cycle.
Algal bloom contingency plans are implemented when a blue-green (or toxic) algal bloom is detected and may include additional sampling and monitoring, issuing press releases, erecting warning signs, banning water-based recreation, notifying relevant authorities, the cessation of drinking water extraction and the provision of temporary alternative water treatment facilities.
In the early 1990s, the New South Wales Blue-Green Algae Task Force coordinated the preparation of contingency plans for most of the state's waterways. As well as contingency plans for individual waterways and storages, regional and statewide plans and reporting structures were also developed to ensure that responses and resources are coordinated at a higher level (Barwon Region Regional Algal Coordinating Committee 1999). Contingency plans have also been prepared for waterways where the major risk to human health is via recreation rather than drinking water supply (e.g. Hawkesbury-Nepean River). In Tasmania, rather than having specific contingency plans for each waterway, management guidelines have been established that cover all waterways (DPIWE 1999). These guidelines provide broad procedures to follow based on different algal alert levels. In most Victorian drinking-water catchments, algal bloom contingency plans have also been developed.
There are two major short-term strategies to reduce nutrient enrichment and the risk of algal blooms: artificial destratification and using environmental flows to increase flushing.
Many of Australia's river pools and impoundments become stratified, with the bottom layer of water and sediments becoming oxygen deficient. This produces a change in bottom water and sediment chemistry and increases the movement of bioavailable phosphorus and nitrogen from the sediments to the water, thus increasing the risk of algal blooms. Many reservoirs affected by algal blooms have installed destratification devices that increase water movement by physical agitation or increase the aeration of oxygen deficient water.
The use of environmental water allocations (or flows) to flush and dilute nutrients and algae and reduce periods of low or no flow is one of the most effective tools to reduce the risk of algal blooms. The allocation of water for the environment is discussed in greater detail in Environmental flow allocations. The release of environmental water allocations to 'flush' algal blooms has to be carefully managed to ensure that it mimics natural flow conditions wherever possible and does not cause additional pollution downstream (e.g. high nutrients and cold-water thermal pollution).
Flow management can be used to prevent algal blooms from forming, rather than use flushing flows to break up existing blooms. Manipulating flow is an important tool in weir management for example, where flow can be used to prevent stratification in weir pools, and increase turbulence and turbidity to provide light limitation.
There have been some preliminary indications that using environmental water allocations to increase flow and reduce the risk of algal blooms has been successful. In 1997, environmental water allocations from the Macquarie and Namoi rivers in New South Wales were used to flush the Darling River of a developing blue-green algal bloom (NSW EPA 2000). The cap on water diversions in the Murray-Darling Basin and the planned establishment of environmental flow allocations for most regulated river systems in Australia over the next 5 to 10 years will help in management of algal blooms in many affected areas.
Other strategies and tools that are currently being investigated include:
- 'Phoslock' - a clay that is sprayed on to sediments to reduce the movement of phosphorus from the sediments into the water column
- biomanipulation, including the introduction of native piscivorous fish (e.g. Australian bass), to displace planktivorous fish, alter zooplankton communities and reduce algal blooms (Chudleigh & Simpson 2000)
- temporarily increasing water turbidity to limit the amount of light available to algal blooms.
Reducing the rate of soil loss from catchments is essential to decrease the contribution of diffuse nutrient sources. This can be achieved by reducing the pressure on existing catchment and riparian vegetation, by revegetation of cleared areas and by better management of agricultural and urban lands. These responses are discussed in greater detail in the Land Theme Report and are summarised below.
Of all land uses, agriculture has the highest contribution to soil losses and the lowest adoption of effective erosion control measures, although there has been some improvement in agricultural land management practices since 1996. A greater proportion of farmers are now aware of land degradation issues, land management tools and sustainable practices through programs such as Landcare. The actual adoption of better land management practices has been geographically patchy and has been driven by economic considerations (i.e. loss of productive land). Over the past 10 years, land clearing rates in all states and territories except Queensland has decreased, mainly due to improved land-clearing controls. However, the rate of clearing woody vegetation still exceeds regrowth and replanting, and the clearing of small areas of remnant vegetation continues.
Riparian vegetation restoration is discussed in Aquatic ecosystems.
The most effective way of reducing pollutants from point-source discharges is to reuse wastewater beneficially. Potential wastewater reuse options include irrigation, mining and industrial processes or cooling water. Domestic reuse, although an option, is not widespread in Australia (ABS 2000). The reuse of wastewater has the added benefit of substituting for water extractions. Presented in Figure 19 are the annual volumes of wastewater reused by each state between 1993/94 and 1996/97. In New South Wales, Victoria, Queensland and Western Australia wastewater reuse has increased, while in the remaining states and territories the reuse volumes have not changed substantially.
Figure 19: Volume of wastewater reused by each state annually (1993/94 to 1996/97)
Source: Australian Bureau of Statistics 2000.
In terms of wastewater reuse per capita, the Northern Territory has the highest wastewater reuse followed by Western Australia and Queensland. New South Wales has the lowest wastewater reuse per capita.
Nationally, wastewater reuse has increased from 4.7% in 1993/94 to 6.5% in 1996/97 of total volume of wastewater generated. The industrial sector accounted for approximately 50% of wastewater reuse with the commercial and rural sectors accounting for approximately 25% of total reuse in 1996/97 (ABS 2000). Direct wastewater reuse has been predicted to continue to increase post 1997 (see the Human Settlements Theme Report).
Improved treatment of wastewater to remove nutrients before the disposal to inland waters is another method for reducing point-source pollution. There is only limited information on improvements in wastewater treatment from the major water and sewage authorities and this is discussed in detail in the Human Settlements Theme Report.
In New South Wales (which is the state with the highest point-source discharge of nutrients to inland waters), sewage treatment plants outside the metropolitan areas are gradually being upgraded and this includes reducing the quantity of phosphorus discharged. The introduction of load-based licensing in New South Wales in 1999 was aimed at accelerating the upgrade process.
Introduction of load-based licensing to control water pollution from point sources [IW Indicator 3.9]
Load-based licensing uses economic incentives and penalties to encourage point-source polluters to reduce their discharges of pollutants and nutrients into the environment. Ideally load-based licensing schemes should:
- provide economic incentives for reducing pollutant emissions
- be based on the quantity and toxicity of the pollutants emitted
- reflect the costs to the environment and society
- consider the sensitivity and assimilative capacity of the environment being affected
- have some flexibility to allow the trading of emission permits (Brunton 1999).
Most states and territories have pollution licensing schemes that do not meet the model presented above (Brunton 1999). For example in Victoria, the Environment Protection (Fees) Regulations 1991 imposes licence fees for discharges to water based on a flat fee and a load-based fee. The load-based fee is only a minor proportion of the total fee and largely does not reflect the toxicity of the pollutant and the sensitivity or assimilative capacity of the affected environment, and does not provide any incentive to reduce emissions (Brunton 1999). Other states' and territories' water pollution control legislation has similar deficiencies to Victoria's except for New South Wales, Western Australia, the Australian Capital Territory and discharges to the marine environment in South Australia.
New South Wales introduced new regulatory tools in 1999 through the Protection of the Environment Operations Act 1997 (POEO Act 1997) to regulate point-source discharges to freshwater, estuarine and marine environments. Under the POEO Act 1997, a new licence system known as the Load-Based Licensing Scheme, has been introduced. The new system progressively introduces emission load limits and links licence fees to the total pollutant loads emitted from each licensed premise. The purpose of the pollution load fees is to provide rewards and incentives to polluters to reduce their emissions - the smaller the load, the lower the fee (NSW EPA 2001). The fee varies to reflect the quantity and types of pollutants discharged and the sensitivity of the environment. Anecdotal evidence indicates that the new realistic licensing fees are forcing many local government organisations to bring forward upgrades of sewage treatment plants to reduce nutrient discharges.
Stormwater management plans are the strategies for the reduction of diffuse-source pollution from urban areas and other activities (e.g. road construction) in the catchment apart from agriculture. Stormwater management plans for all urban and rural catchments in New South Wales will be completed by 2001 (NSW EPA 2001). In Victoria, nutrient management plans have been prepared by catchment management authorities for all river systems under the framework of the state's Nutrient Management Strategy (see http://www.nre.vic.gov.au/ ). Additional funding is provided to catchment management authorities for programs to reduce nutrient pollution of water resources. Stormwater management principles and best management practices for urban areas have also been developed in other states.
- There are a number of Commonwealth programs and strategies to reduce and manage the impact of algal blooms and eutrophication including the National Eutrophication Management Program, National Water Quality Management Strategy and the Murray-Darling Basin Commission's Algal Management Strategy.
- States and territories have focused on reducing nutrient pollution of inland waters. This includes licensing of point-source discharges, protection and restoration of riparian and catchment vegetation to minimise soil erosion, increasing wastewater reuse and wastewater treatment, developing stormwater and land management plans for specific catchments and developing guidelines and best management practices for polluting land uses. Efforts in reducing point-source nutrient pollution appear to be working in many states and territories; however, diffuse point-source pollution continues to be a major problem because of the scale of impacts and because the solutions to controlling this type of pollution require widespread change to land management practices.
- Many of the measures proposed to reduce soil loss are the same as those to prevent and reduce salinity, namely tree planting and revegetation, improved land management, restoration of riparian vegetation and retirement of unsustainable land uses. Integrated strategies to address both issues (and others such as pesticides) are required at a local catchment level to ensure that resources are used effectively.
- Responses to manage and reduce the impact of algal blooms include the use of environmental water allocations for flushing and diluting algal blooms, destratification devices and algal bloom contingency plans. Algal blooms are likely to be a long-term problem in many inland waters so developing effective measures to minimise their impacts is important.