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Issues Water QualityConditionHarvesting and Marine FarmingGlobal Change |
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At a glance The issue Pollutants enter an estuary from a variety of sources, which can be divided into two categories-diffuse and point sources. Diffuse source pollution is probably the chief cause of water quality degradation in terms of organic matter, suspended solids, nutrients and chemical contaminants. Diffuse sources include run-off from urban, agricultural and forestry land, mine sites, landfill and other contaminated sites. Point sources are discharged at a single site from a single source. The scale and effect of point source discharges vary considerably, but large discharges can have marked local impacts and are often the most visible forms of pollution. Large industries and wastewater treatment plants (WWTPs) produce the majority of point discharges, while urban and rural run-off account for the bulk of diffuse discharges. The discharge of inadequately treated waste water from heavy industrial plants into inland or coastal waters has the potential to cause significant environmental harm and human health problems. The design of industrial waste water treatment systems can often be complex and is very industry specific. Typically they must treat large quantities of effluent, and the process often results in the recovery of solid material that must either be disposed of to landfill, or reintroduced to the industrial process. The setting of appropriate environmental quality standards for the receiving waters has also proven to be a difficult exercise for environmental authorities, far more so than the task of setting ambient air quality standards. Discharges into estuaries can cause a number of adverse affects on the estuarine environment, aquatic organisms and human health. Discharges can lead to poor water quality, stained shorelines, unpleasant odours and colourations, health risks to humans, mutations and mortality in aquatic organisms, loss of recreational value, and the accumulation of toxins in the food chain. Unless otherwise stated, the following information is based on an estuarine water quality review prepared by DPIWE (Dowson 2002) for the SoE Report. This updates a similar report prepared for the last SoE Report by DPIWE in 1996. The State of the Derwent Report for 2003 provides more detailed information on the condition of the Derwent estuary and pollutant sources (Green & Coughanowr 2003). This 'At a glance' section provides an overview of the issue of discharges to estuaries. More detailed information and references are available in the Discharges to Estuaries Issue Report. Although there are currently no indicators presented within this Issue Report, there is some discussion of data available in the section on Assessing and measuring the current situation within the Issue Report. A recommendation is presented, which is related to the issue of discharges to estuaries: Integrated Management of Catchments, Coasts and Estuaries. Favourable news - Tasmanian heavy industries are licenced by the State Government, and operate according to regularly reviewed environmental management plans, which address waste water emissions, and whose commitments are usually incorporated into the facility's operating permit conditions. In addition, most heavy industries have established environmental management systems based on the ISO 14001 standard.
- Records show a decrease in many contaminant indicators in the Derwent estuary. There has been a sharp decrease in faecal bacterial loads (>90%) and heavy metal loads (>50%), and a decrease in total suspended solids (TSS) (17%).
- Pasminco Hobart zinc smelter has decreased heavy metal discharges into the Derwent estuary through management actions and structural changes. The smelter's process changes in the mid-1990s enabled it to cease the production of jarosite, instead producing a product that is shipped to Pasminco's lead smelter at Port Pirie in South Australia. At this site the product is processed into a vitreous slag that is acceptable for land disposal. This change of process allowed Pasminco Hobart to cease ocean dumping of jarosite waste, in compliance with the London Sea Dumping Convention. Pasminco has constructed an effluent treatment plant to reduce wastes, wetlands to treat on-site stormwater and a deep horizontal extraction well to intercept polluted groundwater.
- Norske Skog paper mill has reduced the discharge of TSS (38%), resin acids (22%) and biological oxygen demand BOD) (5%), as well as reducing the toxicity of effluent being discharged into the Derwent estuary.
- A suite of studies was carried out in the 1990s as a major cooperative venture between the State and Australian governments, and recommended a remediation strategy. The Mount Lyell Remediation Final Report (1997) is available from the State Government.
- The majority of capital investment within Tasmanian heavy industries to initiate systems for reducing discharge to estuaries occurred before the last SoE Report (1997), and this investment is providing on-going environmental benefit. Some of the approaches taken by heavy industry to mitigate water pollution problems included engineering waste-water treatment systems and groundwater intercept systems, covering stockpiles to avoid leachate production, and improving site stormwater controls.
- Reporting on industry emissions through the National Pollutant Inventory is mandatory in Tasmania (under Section 43 of the Environmental Management and Pollution Control Act 1994), and from July 2001 reporting against 90 substances has been required (an increase from the original 36 substances) (DPIWE 2002).
- Brighton and Bridgewater sewage treatment plants (STPs) have ceased discharging into the Derwent under normal operations and commenced a full effluent reuse program for the irrigation of specialist crops. Brighton Council has also initiated a program to capture and reuse stormwater (DPIWE 2000).
- In 2000, the Derwent Estuary Management Agreement was signed by the State Government, six local councils and three industrial/commercial organisations for the purpose of monitoring and reporting on the environmental conditions of the Derwent. The Derwent Estuary Program (DEP) introduced formal partnership agreements to monitor and report on the state of the Derwent and has helped implement priority projects such as effluent rescue, stormwater management and habitat management and restoration. The involvement of Pasminco and Norske Skog in the DEP is significant in both resources and time through, in particular, monthly monitoring in conjunction with DPIWE.
- The State of the Derwent Report was released in November 2003 (Green & Coughanowr 2003).
- All STPs in the Tamar estuary have been upgraded to include secondary treatment with disinfection. As a result there has been a significant decrease in bacterial levels in the estuary.
- The Huon Estuary Study 2000 indicated that trace metal levels in the sediments and water are below national guidelines in most areas (CSIRO 2000).
- The construction of a 1,300m long ocean outfall at Burnie in 1997 has significantly increased the near shore water quality. The marine environment is now returning to the status typical of coastal waters.
- The first detailed assessment of Tasmania's estuaries was completed in 1999-2000 (Murphy et al. 2003). The assessment will provide baseline water quality data for comparative assessments, determining water indicator levels and proposing appropriate monitoring protocols.
Unfavourable news - Trends since 1996 indicate a slight increase in nutrient loads being discharged into the Derwent estuary. The increase has been caused by increased discharges from STPs and waste water treatment plants (WWTPs). An increase has occurred in discharged dissolved inorganic nitrogen (DIN) (8%), total phosphorus (TP) (17%) and biochemical oxygen demand (BOD) (15%).
- Pasminco Hobart zinc smelter still discharges significant amounts of sulphuric acid (3,100 tonnes in 2001-02) and fluoride (30 tonnes in 2001-02) (National Pollutant Inventory 2003). Zinc levels in mid-estuary sites are still above recommended standards.
- The combined sewage/stormwater system in Launceston is a major contributor of water contamination in the Tamar estuary, especially after heavy rainfall events. Illegal connections feed rainwater into the sewers causing the STPs to become overloaded, therefore discharging raw sewage directly into the estuary. The levels of total nitrogen (TN) and TP in the upper estuary are above the default trigger values set by the ANZECC 2000 guidelines.
- All three STPs in the Huon estuary have been found to discharge BOD, suspended solids and thermotolerant coliforms in excess of their permit limits. Port Cygnet has complied with the performance requirements since late 1998 on the majority of occasions, Geeveston has had several non-compliance occasions, while Ranelagh has very rarely complied with the required levels for thermotolerant coliforms.
- On the west coast, several mining facilities, such as Goldamere at Savage River, and the Renison Bell mine, are associated with discharge of contaminants to local waters. The principal concern is the Mount Lyell copper mine, which has a history of acid mine drainage and waste water discharge from mining operations that killed virtually all aquatic life in the King and Queen rivers. This situation continues today, and a large delta of contaminated sediment has formed in Macquarie Harbour. According to the National Pollutant Inventory database, in 2002 the mine discharged 440 tonnes of copper, 930 tonnes of manganese, 16,000 tonnes of sulphuric acid, and 8 tonnes of fluoride, statistics which dwarf all other database entries for heavy industrial waste water emissions.
- Concentrations of copper in Macquarie Harbour at the mouth of the King River have been recorded at levels as high as 2000ppb (ANZECC guidelines recommend a maximum copper concentration of 1.3ppb in marine waters) caused by discharges and drainage from the Mt Lyell mine. Virtually all water samples taken from the harbour exceed the ANZECC guidelines. Unless effective remedial action is taken, acid and heavy metal drainage will continue to be discharged from Mt Lyell for many hundreds of years.
- Both the Strahan and Queenstown STPs do not comply with microbiological discharge limits and on many occasions the Strahan STP discharges excessive BOD and suspended solids.
- The open cut magnetite mine at Savage River discharges large quantities of heavy metals into the Savage River, which eventually flow into the Pieman River on the west coast. Major pollutants include manganese (870 tonnes in 2001-02), cobalt (11 tonnes in 2001-02), copper, fluoride, arsenic, nickel, zinc, lead, mercury, chromium and cadmium (National Pollutant Inventory 2003).
Uncertain news - The difficulty of quantifying diffuse source inputs leads to uncertainty when managing discharges into estuaries. Diffuse source pollution is probably the major cause of water quality degradation in terms of organic matter, suspended solids, nutrients and chemical contaminants.
- The challenge of acquiring funding provides uncertainty for programs developed for broad-scale and long-term estuarine water quality monitoring (Murphy et al. 2003).
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