Tasmania's Wetlands

Tasmania's varied topography and rainfall, which ranges from over 4000 mm in parts of the West Coast to less than 500 mm in parts of the East Coast, has meant that Tasmania has developed a wide range of wetland types.

Tasmania has many special wetlands, 10 are internationally significant and 89 are listed in A Directory of Important Wetlands in Australia. These wetlands range in size from one to 27,142 hectares and include permanent and semi-permanent water bodies.

Wetlands can be permanent, seasonal or ephemeral. Permanent wetlands hold water all year round (although the level may drop during dry times). Seasonal wetlands hold water regularly at certain times of year, and ephemeral wetlands may dry out for years at a time, but reappear when enough rain has fallen. Seasonal and ephemeral wetlands come within the Ramsar meaning of "temporary" wetlands, meaning intermittent/irregular rivers, streams, and creeks and seasonal/intermittent lakes, marshes and pools.

Tasmania's Bioregions

Tasmania's wetlands are listed in eight bioregions:

• King
• Northern Slopes
• Furneaux
• West
• Central Highlands
• Northern Midlands
• Ben Lomond
• Southern Ranges
• South Esk

Alpine Wetlands

Large areas of Tasmania's landscape were shaped by multiple glaciations that have left thousands of lakes and small tarns in alpine areas.

Rare wetland types are found in Tasmania's alpine and sub-alpine areas such as sphagnum bogs, string bogs and staircase ponds, formed from the remains of bolster heaths.

• Sphagnum bogs - acidic peatlands dominated by species of sphagnum moss. Sphagnum bogs typically occur in valleys where nutrients are washed into the area from the surrounding slopes.
• String bogs - areas of peatland characterized by ridges of peat and vegetation, interspersed with depressions that often contain shallow ponds.
• Staircase ponds - a landscape feature where pools occur in a "stepped" formation down a slope. The ponds are usually separated by bands of vegetation. They tend to dominate in permanently water-saturated situations exposed to extreme conditions of wind and prolonged snow.

Moorland Wetlands

Tasmania's west and south west contain large areas of buttongrass moorland, much of it having developed on or contributed to the formation of peat soils, which form a very distinctive vegetation type. Water often lies on the surface and periodically dries out.

The peat soils form some of the most extensive blanket bogs (peatlands that cover undulating terrain) in the southern hemisphere (SDAC 1996).

Macquarie Island, which is part of Tasmania, also has extensive wetlands. These include vast, waterlogged, heavily vegetated areas on a raised coastal platform, forming a mire based on deep peat beds (DEST/PWS 1996).

Estuarine Wetlands

Tasmania also has numerous coastal lagoons, either cut off from the sea by dune systems, or permanently or intermittently open to the sea. Tasmania also has many estuaries; areas influenced by fresh and marine water. The combination of sheltered conditions and inputs from both marine and terrestrial sources means that coastal wetlands are especially rich in plant and animal life. They can be brackish or saline.

Saltmarshes are found along most low energy coasts above the high tide mark and provide food and habitat for numerous animals.

Inland Saline Wetlands

Saline wetlands also occur inland, in the driest parts of the Midlands near Tunbridge and Ross, near Cape Portland in the north-east, and in the Furneaux Group. Most of these have developed as deflation hollows during drier windy times and often have a lunette on the downwind side. Mostly, these are seasonally inundated herblands, but saltpans also occur in the Midlands (Kirkpatrick & Tyler 1988).

Township Lagoon, a saline wetland in the Midlands.

Freshwater Wetlands

Freshwater wetlands in Tasmania include:

• Swamp forests in the north west and King Island
• Deep permanent freshwater marshes on the west coast and King Island
• Shallow freshwater marshes that may dry out either seasonally or in particularly dry years are concentrated in the wetter parts of the Midlands, in the north east and on Flinders and Cape Barren Island.

Subterranean Wetlands

About 10% of Tasmania is underlain by carbonate rocks, some of which is karstic, meaning dissolved by water, causing interesting landforms, including cave systems. Many of these contain unique physical and biological features.

The extensive swamplands in the north west have developed on karstic depressions. The typical surface expression of karst as a wetland are sinkholes or dolines (depressions draining underground into karst). Poljes are large karstic depressions up to several kilometres across. Poljes at Mole Creek and Dismal Swamp are the best-developed in Australia.

Subterranean wetlands support a diverse fauna that is often distinct from that of surface waters (Kiernan 1984).

Australia's most diverse temperate cave fauna associations are found in large cave systems found in Tasmanian Ordovician limestones and Precambrian dolomites. Habitats range from flowing underground streams to still lakes at the present water table. Below the water table, large, water-filled passages are the present focus of much cave formation and contain troglobitic fauna. Above the water table pools remain in long abandoned high-level cave passages, fed only be seepage and drip waters. These are extremely fragile ecosystems, from both the geomorphological and biological perspective.

References

DEST / PWS (Department of Environment, Sport and Territories (Commonwealth) and Tasmanian Parks and Wildlife Service), 1996, Nomination of Macquarie Island by the Government of Australia for Inscription on the World Heritage List. Prepared by DEST in association with PWS.

Environment Australia, 2001, A Directory of Important Wetlands in Australia (Third Edition 2001), Natural Heritage Trust and National Wetlands Program.

Kiernan, K., 1984, Land Use in Karst Areas : Forestry Operations and the Mole Creek Caves, Report to the Forestry Commission and National Parks and Wildlife Service, Tasmania

Kirkpatrick, J.B., and Tyler, P.A., 1988 "Tasmanian Wetlands and their Conservation" in The Conservation of Australian Wetlands, eds A.J. McComb and P.S. Lake, Surrey Beatty and Sons and the World Wildlife Fund (Australia).

SDAC 1996, State of the Environment: Vol 1: Conditions and Trends, Sustainable Development Advisory Council, Hobart