EstuariesOverview of Tasmania's Estuaries
General Characteristics and Classification
The Importance of Estuaries
Threats to Tasmanian Estuaries
Water Quality in Tasmanian Estuaries
An estuary is “a semi-enclosed or periodically closed coastal body of water in which the aquatic environment is affected by both freshwater and marine systems”. Tasmania has many types of estuaries including coastal inlets, drowned river valleys, barrier estuaries, river estuaries and coastal lagoons.
water quality within the estuary.
1) Coastal Inlets (e.g. West Inlet, East Inlet)
Enclosed marine embayments with wide mouths that lack large riverine inputs but have detectable reduction in salinity from small creeks after heavy rainfall. Generally well mixed and can be hypersaline in summer.
2) Drowned River Valleys (e.g. Tamar Estuary, Derwent Estuary, Huon Estuary)
Estuaries with wide river mouths, rocky headlands and deep channels and can be stratified.
3) Barrier (or Bar) Estuaries
Estuaries with sandbars across their mouths. Can be permanently-open (e.g. Prosser River, Ansons Bay) or seasonally-closed (e.g. Wanderer Estuary, Browns River) and can be stratified.
4) River Estuaries (e.g. Don River, Pieman River)
Estuaries where fast flowing rivers discharge into the sea with little bar or lagoon development and poor water mixing.
5) Coastal Lagoons (e.g. Grants Lagoon, Cameron Inlet)
Saline lagoons with irregular input and infrequent openings to the sea. Incursion by seawater generally occurs only after extreme runoff events or tidal or artificial breaching of the sand barrier. Can be hypersaline in summer.
Catchments in the west, north-west and south are characterised by high rainfall and runoff, resulting a predominance of river estuaries, whereas catchments in the east and north-east are relatively dry and barrier estuaries and coastal lagoons dominate. Estuaries in the north possess much greater tidal ranges (approximately 3 m) than those on the east, south and west coasts (1 m).
Estuaries are essential for the survival of many birds, fish and mammals. Estuaries have been referred to as the "nurseries of the sea", as they provide many species of fish with sheltered waters for spawning and safe habitat for juveniles to develop. Many commercially valuable fish species, depend on estuaries during some point in their life cycles. Some migratory wader birds rely on estuaries as resting and feeding grounds during their long journeys.
Boating, fishing, swimming and bird watching are just a few of the many recreational pursuits people enjoy in and around estuaries. Estuaries are often cultural and historical centres for coastal communities, serving as focal points for celebrations, customs and heritage. In Tasmania, many of the remaining aboriginal sites are situated along estuarine shorelines. In addition, estuaries provide considerable aesthetic enjoyment for the people who live around them.
Five conservation classes were identified:
Refer to the Conservation Significance Classifications for a breakdown of Tasmanian estuaries.
The study of Edgar et al. (1999) identified nine potential threats to the biological resources and conservation value of Tasmanian estuaries. These were:
Many estuaries on the north coast were considered as unhealthy, relative to other estuaries in the State, with elevated turbidity, nitrogen and phosphorous concentrations, particularly the Duck Bay and Don River estuaries. Estuaries in the north-east, such as Boobyalla Inlet, Little Musselroe River and Ansons Bay had high nitrogen or chlorophyll concentrations and may be susceptible to eutrophication. In comparison, estuaries in the other regions studied were generally healthy, with indicator levels in the low to medium range; the exceptions being Browns and Meredith Rivers and, on occasion, the Douglas River.
For information on other water monitoring and conservation programs being undertaken in Tasmania, see Pesticide Monitoring in Water Catchments and the Conservation of Freshwater Ecosystem Values Program.
Murphy, R.J., Crawford, C.M., and Barmuta, L. (2003) Estuarine Health in Tasmania, status and indicators: water quality. Tasmanian Aquaculture and Fisheries Institute Technical Report Series 16. 114pp.
Saenger, P. (1995). The status of Australian estuaries and enclosed marine waters. In Zann, L. and Kailola, P. (eds). State of the Marine Environment Report for Australia. Technical annex 1: The Marine Environment. p 53-60.
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