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Issues Water QualityConditionHarvesting and Marine FarmingGlobal Change |
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At a glance 
The issue Healthy waterways are necessary to maintain the variety of aquatic habitats, and the economic, social and environmental systems that rely on them. The quality of Tasmania's estuarine waters is integral to sustainability. However, as important sites for human settlement, tourism and recreation, estuaries have been under significant human pressure. Many estuaries have a number of water quality issues stemming principally from catchment land uses and discharges from point sources. Key issues include heavy metal contamination, elevated nutrient concentrations, depressed dissolved oxygen levels, organically enriched sediments, and intermittent faecal contamination of recreational areas. Some major estuaries-such as the Huon-have, in general, very good water quality. This 'At a glance' section provides an overview of the issue of water quality in Tasmanian estuaries. More detailed information and references are contained in the Water Quality in Tasmanian Estuaries Issue Report. Four indicators are provided within this report (see Indicators section). Other related issue reports include Water Quality and Water Quantity and Water Use in the Inland Waters and Wetlands Chapter. A recommendation is presented on Integrated Management of Catchments, Coasts and Estuaries. Favourable news - Significant strategic and coordinated management is being achieved to protect the Derwent Estuary through the Derwent Estuary Program (DEP) established in 1999. In December 2001, the DEP Environmental Management Plan was finalised and endorsed by the Premier, the Mayors of Greater Hobart councils, and the Australian Government. A five year agreement was signed to progressively implement this plan. Key aspects of implementation include environmental monitoring and reporting, coordination of regional activities, and the implementation of priority projects such as effluent reuse, stormwater management and habitat mapping and restoration.
- Since 1996 there have been significant reductions in pollutant loads to the Derwent, particularly faecal bacteria (greater than 90%) and heavy metal loads (greater than 50%), and a decrease in Total Suspended Solids loads (17%). During the past three years, most sites have met recreational water quality guidelines for primary contact, particularly the main recreational beaches to the south of the Tasman Bridge. Long-term data sets for heavy metals suggest significant decreases in water column concentrations of zinc, cadmium and other metals over the past 30 years (DPIWE 2000). There still remain, however, a number of significant environmental issues for the Derwent Estuary (see 'Unfavourable News'). The State of the Derwent Report 2003 was released in November 2003.
- The Huon estuary has, in general, good water quality. It has two principal inputs-the Huon River and seawater-which are both of a high environmental quality. The Huon Estuary Study (CSIRO 2000) recommended that the upper Huon catchment should be carefully maintained to protect this main source of freshwater into the estuary.
- A study was conducted by the Tasmanian Aquaculture and Fisheries Institute (TAFI) with funding under the Natural Heritage Trust to assess water quality in Tasmanian estuaries (Murphy et al. 2003). Major objectives of the study were to provide baseline water quality data and determine water quality indicator levels for 22 Tasmanian estuaries. The study has been important in informing this State of the Environment assessment of estuarine water quality. The tables presented in the following links show that the majority of estuaries monitored fall in the low to medium ranges for concentrations of chlorophyll a, turbidity, and nutrients, but that some estuaries showed elevated levels of these parameters.
- For this SoE Report, data for a number of estuaries were assessed for the core environmental indicator entitled 'percentage exceedences of ANZECC water quality guidelines for a suite of microbiological and chemical water quality parameters'. Percentage exceedences of faecal coliforms between 1996-01 were low (less than 6% exceedences for samples) for the Huon Estuary and Great Oyster Bay. Further information is contained in the Indicators section in the Issue Report.
Unfavourable news- The Derwent estuary has a number of environmental issues and remains a significantly degraded estuary. Key issues include heavy metal contamination, elevated nutrient concentrations, depressed dissolved oxygen, organically enriched sediments, introduced marine pests, loss of estuarine habitat and species, and intermittent faecal contamination of recreational areas. For example, the majority of sediments within the Derwent do not meet sediment quality guidelines for a number of heavy metals, particularly for mercury (99% of area in excess of guidelines), lead (87%), zinc (68%) and cadmium (64%) (Dowson 2002).
- The Tamar estuary is impacted by human activities (urban and agricultural run-off, sewage and industrial discharges, and indirect drainage from mine sites) producing contaminants such as pathogens, hydrocarbons, metals, organic matter, nutrients and sediment, and introduced marine pests. Heavy metals-particularly zinc, cadmium, lead and copper-appear to be elevated in several areas of the Tamar, notably the upper estuary around Launceston and the lower estuary in Deceitful Cove and Middle Arm. Sediment analysed indicates contamination for total arsenic, chromium, copper, lead and zinc at a number of sites. The levels of heavy metals in shellfish from the estuary, specifically zinc and copper, are in excess of the recommended Australian and international guidelines and it has been recommended that oysters collected in the estuary should not be eaten. Nutrient inputs from the sewage treatment plants and agricultural and urban stormwater run-off are potentially significant, but the Tamar is not presently known to experience algal blooms.
- In the northern part of Macquarie Harbour, heavy metals coming from the Mt Lyell copper mine over the last 100 years continue to be a primary source of contamination by copper, aluminium, zinc and other metals entering the harbour from the King River. The contaminants are dispersed by wind mixing and currents. Three populations measured in Macquarie Harbour-benthic invertebrates, fish, and phytoplankton-are impoverished because of mining inputs. It was estimated that over 100 million cubic metres of material, containing toxic heavy metals, have been deposited in the banks and bed of the King River, its delta and northern Macquarie Harbour since 1930 (Koehnken 1996). The vast deposits of highly contaminated sediment will remain an impediment to the recovery of the benthic invertebrate communities, even as the water quality of the harbour is improved.
- The TAFI study of estuarine water quality has indicated that estuaries in the north-east may be susceptible to eutrophication. Ansons Bay regularly recorded high to very high chlorophyll a levels, while the upstream sections of Little Musselroe Estuary and Boobyalla Inlet have, on occasions, recorded high levels. The Meredith, Browns and Don River estuaries have also shown high to very high chlorophyll a concentrations on some occasions (Murphy et al. 2003).
- Indicator levels for turbidity were generally medium to high in estuaries on the north coast (Boags bioregion) especially within Duck Bay, Port Sorell and the Mersey and Don River estuaries. A large rainfall event in July 1999 was associated with very high turbidity at Browns River (Bruny bioregion). Medium to high turbidity (associated with naturally high tannin levels) was recorded in the Franklin bioregion, and in Boobyalla Inlet in the north-east. Turbidity was usually low in estuaries in the Davey and Freycinet bioregions. The TAFI study indicated that estuaries in the Don River, Duck Bay and Boobyalla Inlet (Boags bioregion), all showed very high median nitrogen values. The median level in the Black River was also high.
- Moderate levels of primary contact guideline exceedences for faecal coliforms in the north-west of Tasmania may be the result of intensive dairy farming in the catchments surrounding the Duck and Big Bays. Runoff from this agricultural land may result in washing of untreated stock faeces into the estuaries during wet periods.
- In the Huon estuary, the CSIRO (2000) predicted through modelling that if the 1997 fin-fish marine farm loads were doubled this would increase the risk of greater frequency and density of summer phytoplankton blooms. With four times the load the system would be on the brink of significant risk of prolonged blooms.
Uncertain news- The availability of data for the analysis of Tasmanian estuarine water quality is still poor outside the Derwent Estuary. This is despite improvements in the last five years through studies undertaken by TAFI on water quality (Murphy et al. 2003), the CSIRO on the Huon Estuary (CSIRO 2000), and estuarine condition and naturalness (Edgar et al. 1999). This is due to the lack of on-going monitoring in most estuaries around the State. To date, data analysis has been restricted to only a very small number of water quality parameters or to 'once-off' studies. The lack of data limits the ability to conduct trend analyses of water quality in the various estuaries that would provide important information for land management practices, ecosystem health and human health. Follow-up monitoring on a consistent and regular basis is needed to establish whether baseline conditions are being met or exceeded.
- There is uncertainty about the relative contributions and impacts of different nutrient sources in estuaries from land use in catchments, sewage treatment plants, fish farms and the Southern Ocean.
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