State of the Environment Report 2007
All wetlands and waterways are susceptible to eutrophication. The term 'eutrophic' comes from a Greek word meaning 'well fed'. Eutrophication refers to the ecological changes that result from excess levels of nutrients in waterways and wetlands, often resulting in prolific aquatic plant growth and algal blooms. Nitrogen and phosphorus are usually the most important nutrients that influence this process but other micronutrients can also play a role.
Although eutrophication is a slow natural process, it is dramatically accelerated by artificially high nutrient levels. Nutrients can either come from diffuse sources (such as fertiliser runoff from farms or urban areas), or via point sources from specific locations (such as sewerage treatment facilities or livestock feedlots). Other factors contributing to eutrophic conditions include stagnation of water, accumulation of fine sediment (with phosphorus attached) and continual accumulation and decay of organic matter. Loss of fringing vegetation can also increase water temperature and light availability, thereby enhancing the potential for algal blooms to occur.
Excess nutrients in water often result in algal blooms, proliferation of weeds and pests (e.g. midges and mosquitoes), and other ecological changes. If persistent, this may result in a simplification of an ecosystem and a loss of biodiversity. Excessive weed and algal growth may also render some wetlands and waterways unsuitable for use as water supplies or for recreation, and may also increase the risk of flooding. Some species of algae (e.g. blue-green algae) produce toxins which can be harmful or even fatal to humans, fish and animals. Fish deaths are also commonly associated with decomposing algal blooms, which causes de-oxygenation of the water. Many algal blooms also cause unsightly water discolouration and foul odours as they decay.
Estuaries in the South West are particularly vulnerable to nutrient enrichment, as they have evolved under naturally low nutrient conditions and many catchments now support intensive land uses. Nutrient levels vary significantly in South West estuaries (Figures IW7.1 & IW7.2) and are related to estuary size, rate of flushing and catchment land uses. Estuarine nutrient levels are generally stable over time, requiring several decades of monitoring to detect change. The Peel-Harvey estuarine system is an exception, with construction of the Dawesville Channel making this estuary more marine-like and dramatically lowering nutrient levels and algal activity. While most nutrient-enriched estuaries experience elevated algal blooms, some estuaries (such as the Oldfield and Moore) have naturally dark, tea-coloured water that is less favourable for algal growth. Estuaries in the rangelands are not well monitored for nutrients or algal activity.
![Figure IW7.1: Total nitrogen concentrations in South West estuaries. [Data source: Department of Environment [ver. 2005]. Note: Red line indicates ANZECC guideline level for estuaries in the South West (ANZECC and ARMCANZ, 2000). DC = Dawesville Channel.]](/site/files/images/Figure-IW7.1_Large.jpg)
![Figure IW7.2: Total phosphorus concentrations in South West estuaries. [Data source: Department of Environment [ver. 2005]. Note: Red line indicates ANZECC guideline level for estuaries in the South West (ANZECC and ARMCANZ, 2000). DC = Dawesville Channel.]](/site/files/images/Figure-IW7.2_Large.jpg)
About one-third of monitored rivers have low levels of the nutrients nitrogen and phosphorus. Low nutrient levels are typically found in rivers with forested catchments. High levels of nutrients are usually found in waterways draining cleared urban and agriculture catchments, such as along the Swan Coastal Plain. Many of these waterways have catchments with coastal sandy soils that are well known for leaching nutrients. Waterways in the Wheatbelt and rangelands are not well monitored for nutrients, partly due to their remoteness and the intermittent nature of flows. Short-term changes (1997-2003) in nitrogen and phosphorus levels have been noted for some rivers of the Swan-Canning estuarine system, Leschenault Inlet, Peel-Harvey estuarine system, Princess Royal and Oyster harbours, and the Blackwood River and some south coast rivers (Figures IW7.3 & IW7.4). Further analysis is required to determine if these are indicative of longer-term trends linked to catchment land uses, management practices, altered flow regimes or changes in rainfall.
![Figure IW7.3: Total nitrogen status and trend in Western Australian rivers, 1997–2003. [Data source: Department of Environment [ver. 2005]; Analysis: EPA; Presentation: EPA.]](/site/files/images/Figure-IW7.3_Large.jpg)
![Figure IW7.4: Total phosphorus status and trend in Western Australian rivers, 1997–2003. [Data source: Department of Environment [ver. 2005]; Analysis: EPA; Presentation: EPA.]](/site/files/images/Figure-IW7.4_Large.jpg)
Long term monitoring of nutrients in wetlands is mostly limited to specific research studies in the Perth urban area. For example, previous studies have found very high nutrient levels in Lake Monger, a small urban lake close to Perth city. With fertilising of nearby lawns, phosphorus concentrations of up to 0.8 mg/L were recorded and the lake experienced frequent blooms of Anabaena and Microcystis species (Lund, 1995). The lake has since received significant management attention, rehabilitation and nutrient reduction efforts. Other past studies of wetlands on the Gnangara Mound found elevated phosphorus levels; for example, Gingin (0.46 mg/L), Nowerup (0.36 mg/L), Carabooda (0.29 mg/L), Neerabup (0.24 mg/L) and Coogee (0.14 mg/L) all linked to semi-rural land uses (Wrigley et. al, 1991). However, many Perth wetlands have since experienced significant catchment land use change and some are now receiving more management attention. Some Perth urban wetlands, such as Lake Joondalup and Lake Goolelall, experience ongoing midge problems linked to eutrophication.
Algal blooms and associated events (such as fish kills, unpleasant odours, mussel contamination and closure to recreation) regularly affect many rivers and estuaries in WA (Figure IW7.5). About 110 wetlands and waterways have a recorded history of algal bloom problems (V Hosja, Department of Environment, pers. comm.). Most are situated in the State's South West and many are at risk of toxic, blue-green algal blooms including those due to Nodularia, Anabaena and Microcystis species. Blue-green algae are not the only harmful types of bloom organisms, with some dinoflagellate and diatom species capable of producing toxins that accumulate in shellfish, cause fish deaths, and irritate swimmers. Harmless algal blooms are also capable of causing discolouration of waterways and causing foul odours and deoxygenation events as they decompose. Several shallow river and estuarine systems (including Vasse-Wonnerup, Leschenault, Peel-Harvey and Princess Royal estuarine systems) support excessive macroalgal growth linked to high nutrient levels.
The Peel-Harvey Estuary near Mandurah was well known for almost annual blue-green algal blooms (i.e. Nodularia sp.) from 1978 to 1994. Construction of the Dawesville Channel in 1994 increased ocean flushing and there have been no more blue-green algal blooms in the estuary. Unfortunately, blooms still frequently occur in the Serpentine and Harvey rivers. Catchment modelling indicates that agricultural activities contribute most nutrients to the rivers and estuary (about 70%). Developed urban areas represent 6% of catchment area but contribute about 30% of nutrient input. Estimates indicate that full development of the planning schemes for the Mandurah area will increase nutrient export up to four-fold (Department of Environment & Department of Agriculture, unpublished data).
In January 2000 a major toxic blue-green algal bloom (Microcystis sp.) occurred in the Swan-Canning Estuary, near Perth (Swan River Trust, 2000). The bloom resulted in unprecedented closure (12 days) of the whole estuary and its rivers to fishing and recreation. Unseasonably high summer rainfall and subsequent flushing of nutrients from inland agricultural areas helped create ideal conditions for the bloom. It was estimated that over 800 tonnes of nitrogen and 35 tonnes of phosphorus entered the Swan and Avon rivers during this single event, representing 108% and 88% (respectively) of these nutrients normally delivered in one year. Perfect conditions for bloom growth were created by typical summer conditions, including high temperatures, low cloud and calm conditions. The bloom died when river flows subsided and estuary salinity levels returned to normal (summer) conditions. This incident demonstrated how catchment fertiliser use can contribute to algal bloom problems.
Since 2000, about 15-35 accidental fish kills have been reported in WA each year, with 70% occurring in major waterways of the State's South West. It has been estimated that nearly 30% of accidental fish kill events can be attributed to toxic algal blooms and low oxygen levels following a bloom collapse (T Rose, Department of Environment, pers. comm.). In 2003, more than 110 000 fish died in the lower Serpentine River near Mandurah and more than 100 000 died in the Swan Estuary following dinoflagellate blooms (Karlodinium sp.) toxic to fish. In 2004 more than 50 000 fish died in the lower parts of the Serpentine and Collie rivers.
Nutrients are transported to inland waters by either point or diffuse sources. Point sources (such as septic tanks, sewage treatment plants, landfill sites, industrial waste, and intensive livestock industries including piggeries, dairies and feedlots) can contribute high levels of nutrients from small areas. In contrast, diffuse sources including urban gardens, stormwater and farmland generally contribute nutrients from a widespread area. Nutrient transport through catchments can be very fast in areas with sandy, wet soils. In contrast, soils with a high clay, loam or iron content help to bind nutrients and minimise algal bloom risk to inland waters.
Clearing of vegetation or harvesting of crops can reduce uptake of soil nutrients, which may subsequently be lost to inland waters. Nutrient loss may also be enhanced where erosion or acidification processes occur. Uncontrolled livestock access to waterways and wetlands can damage fringing vegetation and contribute nutrients from faecal waste. Altered water regimes may also exacerbate algal blooms, particularly when water levels are significantly reduced and waters stagnate. Poor land use planning in the past has contributed to eutrophication problems, with a lack of consideration given to the proximity to sensitive environments of nutrient-intensive land uses.
One of the major and most widespread sources of nutrients to inland waters is from fertiliser applied to residential lawns and gardens, broadacre farms and horticulture. There is a tendency for some householders to over-fertilise lawns and gardens in the false belief that more fertiliser results in a greener garden. Lack of soil testing by farmers also results in excessive fertiliser application to crops or pastures. With only about 10% of Australia's population, WA is one of the largest consumers of fertilisers. For example, in 2002, 399 000 tonnes of nitrogen-based fertiliser (26% of Australia's total use), 428 000 tonnes of phosphate-based fertiliser (24% of Australia's use) and 495 000 tonnes of compound and blended fertiliser (28% of Australia's use) were applied to WA soils (Australian Bureau of Statistics, 2002). These levels of application are in part attributed to the State's nutrient deficient soils and large wheat crop production.
Across the State about 1000 wastewater overflows occurred in 2003-04. Of these, about 100 events were greater than 2000 L, requiring formal investigation under the Environmental Protection Act 1986. In Perth approximately 300 million litres of raw wastewater is collected from households, businesses and industry and transported via a network of 9000 km of pipes to treatment plants. Infrequent overflows occur due to blockages, burst pipes and power failures (Figure IW7.6). The total amount of nutrients entering the Swan and Canning rivers from wastewater overflows is very small (less than 0.1%) compared to other catchment sources (Water Corporation, 2003).
State Algal Bloom Management Strategy: A draft strategy has been developed with the intention of further developing an understanding of the causes of algal blooms, maintaining surveillance of susceptible waterways, reducing nutrient inputs, enhancing community understanding of algal blooms, and developing appropriate nutrient management options.
Legislation and policies: Various policies are in place to reduce the pressure of nutrient enrichment (and other water pollutants) on inland waters, including environmental protection policies for the Swan-Canning and Peel-Harvey estuaries and Gnangara Mound. The Environmental Protection (Swan and Canning rivers) Policy is to be implemented using the management framework RiverPlan. The Swan and Canning Rivers Management Act was enacted in October 2006 but remains inoperational as at April 2007. It proposes the establishment of a Riverpark, improved coordination of agency activities, and improved management action and enforcement. A draft State environmental policy and action plan is being considered to phase out highly soluble phosphate fertilisers within four years in environmentally sensitive areas.
Nutrient management programs: This initiative is the single largest program addressing eutrophication in WA. The Swan River Trust initiated the Swan-Canning Cleanup Program in 1994 in response to increasing incidences of algal blooms in the Swan and Canning rivers. In 1999 an action plan was released which brought government, industry, business and the community together to improve catchment management, planning processes, engineering solutions and monitoring. A recent evaluation of the plan found that 77% of initiatives had been implemented, including about one million seedlings planted, about 280 km of fencing constructed, nearly 25 km of foreshore enhancement and about 1000 property plans developed. Longer timeframes are needed to determine if the action plan has been successful in reducing diffuse nutrient sources (Swan River Trust, 2005). In 2006, the second phase of the program the Healthy Rivers Action Plan was launched, representing a 5 year $40 million program focusing on reducing nutrient input. Many other nutrient reduction programs and plans are currently underway throughout South West WA, including the Healthy Rivers Action Plan, Wilson Inlet Nutrient Reduction Action Plan, Dairy Catch, Lower Vasse River Cleanup Program and the development of a Peel-Harvey Water Quality Improvement Plan.
Natural Heritage Trust/National Action Plan for Salinity and Water Quality (NHT/NAP) programs: All regional Natural Resource Management groups have recognised eutrophication as a major threat to inland waters. They are implementing projects to manage nutrient export to affected waterways and protection of valued natural assets at risk. The Coastal Catchments Initiative is a NHT sub-program that focuses on reducing nutrients discharged to coastal hotspots, through development of water quality improvement plans and funding of related projects. Identified hotspots in WA include the Peel-Harvey, Vasse-Wonnerup and Swan-Canning estuaries and Geographe Bay.
Wastewater: The Water Corporation is overseeing the replacement of household septic tanks with connection to deep sewerage. Before the program began in 1994, 25% of Perth properties and 40% of country properties were using septic tanks. In other state capitals the average is 4%. When the program is completed in 2019, an extra 100 000 properties will be connected to deep sewerage, diverting many hundred tonnes of nutrients from entering inland waters (Water Corporation, 2004). The Water Corporation commenced a Riverwise program in 1997, upgrading 110 wastewater pump stations close to the Swan-Canning River system. This has resulted in a 60% reduction in overflows to the rivers, thereby reducing nutrient input.
National Eutrophication Management Program: was established by Land and Water Australia and the Murray Darling Basin Commission to focus strategic research and development on nutrient sources and transport, factors initiating algal blooms, the role of sediments in transporting nutrients, and evaluation of the effectiveness of management actions. One of the focus areas for this work has been Wilson Inlet in WA where an action plan has been prepared to address eutrophication.
Stormwater Management Manual: has been developed by the Department of Water to provide policy, planning principles, and on-ground best practice advice for the management and reuse of stormwater. It builds on the traditional objective of local flood protection by enhancing water quality, protecting ecosystems and providing liveable and attractive communities.
Agriculture Extension Program: develops and demonstrates to farmers effective agricultural practices that reduce or eliminate nutrients leaching from farms (e.g. soil testing to determine application rates, soil tillage, erosion control). Recent surveys indicate that 74% of Wheatbelt farmers undertake regular soil testing for nutrient levels, whereas 68% of farmers in higher rainfall parts of the South West undertake regular testing (Department of Agriculture, 2006). Between 45-50% of South West farmers protect river frontages from grazing animals, whereas only one-third of pastoralists use this management practice (Department of Agriculture, 2006).
Instream remediation: Several instream remediation activities have been trialled in recent years to combat existing algal blooms. Examples include the use of oxygenation (bubbling of oxygen through the water column) and sediment remediation (applying modified clays that bind phosphorus) in the Canning and Vasse rivers. Both methods have proven successful in limiting algal blooms and deoxygenation events in these rivers, although both are recognised as short-term management options. Construction of the Dawesville Channel in 1994 represents the single largest remediation project for a eutrophication problem, providing a permanent artificial breach between the Peel-Harvey estuarine system and the ocean. While controlling blue-green algal blooms, the channel has significantly modified local ecology.
Soil remediation: Alkaloam or 'red-mud' has been trialled by the Department of Agriculture in Peel-Harvey catchments to reduce phosphorus export from sandy agricultural soils. Paddock trials show that nutrient loss from agricultural soils can be reduced by an average of 50%. A modified clay developed by CSIRO has been trialled for use in the Canning and Vasse rivers, with results showing it can remove more than 95% of dissolved phosphorus from the water column (Swan River Trust, 2001).
Eutrophic conditions can drastically alter biodiversity in wetlands and waterways, rapidly turning them into algae and weed-dominated systems. Algal blooms, particularly if toxic, can cause fish kills, ruin water supplies, prevent recreational activities and affect amenity values. Nutrient-enriched waters provide ideal habitat for opportunistic aquatic weeds that can rapidly grow and clog irrigation and stormwater pipes. Excessive macroalgae washing up on beaches may cause offensive smells, become a health problem for nearby residents, affect property values and be a nuisance for beach users, fishers and tourists. Many eutrophic wetlands provide ample food sources for midge and mosquito populations and occasional outbreaks of vector-borne disease can be a major health problem for local communities (e.g. Ross River virus). Nutrient enrichment of groundwater can reduce the suitability of water supplies because of the possibility of nitrate toxicity. Unless a thorough systematic approach is used to keep nutrients on the land and planning controls are strengthened, the problem will not be solved.
4.21 Finalise and implement the draft State Algal Bloom Management Strategy.
4.22 Strengthen land use controls and planning mechanisms to identify and phase out high nutrient exporting land uses that are unable to meet nutrient reduction targets.
4.23 Revise regional and town planning schemes to ensure they minimise nutrient export from various land uses.
4.24 Develop and implement a State environmental policy to phase out the use of high water soluble phosphate fertilisers in relevant catchments and soil types.
