What are coastal wetlands?
Wetlands are “areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres and may incorporate riparian and coastal zones adjacent to the wetlands, and islands or bodies of marine water deeper than six metres at low tide lying within the wetlands”1. In the coastal context, wetland habitats may include seagrass meadows (and other aquatic macrophyte beds), mangrove areas or saltmarsh swamps, dune lakes, wave-dominated and tide-dominated deltas, wave-dominated and tide-dominated estuaries, strandplains and coastal lagoons, coral reefs, sand/mudflats, tidal creeks, coastal floodplains, distributary channels, drainage depressions, ox-bow lakes, back levee swamps, sedge lands, and swamp forests.
Figure 1. Australia’s Coastal Ramsar Wetland Sites: 1. Coburg Peninsula; 3. Moulting Lagoon; 4. Logan Lagoon; 5. Lavinia; 6. Pitt Water-Orielton Lagoon; 7. Apsley Marshes; 8. East Coast Cape Barren Island Lagoons; 9. Flood Plain Lower Ringarooma River; 10. Jocks Lagoon; 12. Little Waterhouse Lake; 13. Corner Inlet; 18. Port Phillip Bay (western shoreline); 19. Western Port; 21. Gippsland Lakes; 23. Towra Point Nature Reserve; 24. Kooragang Nature Reserve; 25. Coorong and Lakes Alexandrina and Albert; 31. Ord River Floodplain; 33. Roebuck Bay; 34. Eighty-Mile Beach; 35. Forrestdale and Thomsons Lakes; 36. Peel-Yalgorup System; 38. Vasse-Wonnerup System; 39. Lake Warden System; 41. Moreton Bay; 42. Bowling Green Bay; 44. Shoalwater and Corio Bays; 51. Great Sandy Strait; 52. Myall Lakes; 54. Becher Point Wetlands; 55. Lake Gore; and 57. Edithvale-Seaford Wetlands.
Significance of wetlands
Coastal wetlands have many environmental values: groundwater recharge; water storage and flood mitigation; water purification (including denitrification); shoreline stabilisation and storm protection; nutrient and sediment retention and export; and tourism and recreational amenity2. Many wetland areas have cultural significance to Aboriginal people, and relics of earlier occupation are often found on their shores. Wetlands are also amongst the most productive ecosystems in the world. As such, they are sinks for carbon dioxide and are cauldrons of biodiversity.
Wetlands provide foraging and nursery habitat for many fish, crustaceans and molluscs, including species of commercial and recreational value, and are therefore critical to Australia’s fishing industries. They are also important feeding, breeding and roosting areas for waterbirds, including migratory species, and a provide a refuge for inland species in times of drought. The goods and services supplied by wetland ecosystems are worth $19 trillion1. That comprises 57% of the total worth of global ecosystems1.
The removal of wetlands causes a loss of critical habitat and biodiversity. In addition, it increases runoff and sediment and nutrient loads (with possible eutrophication) to coastal waterways, and increases low-pH drainage from acid sulfate soils3.
What causes coastal wetland areas to change?
- Land use impacts within catchments, particularly those that contribute to increased fine sediment and nutrient loads. Nutrients and sediments emanating from diffuse sources (e.g. intensive agriculture and urban stormwater) in catchments can be particularly large and difficult to control.
- Drainage and/or filling for agricultural, urban or industrial development – the latter are closely tied to population density.
- Drainage for mosquito control.
- Degradation by pollutants such as acid drainage, nutrients, metal contaminants and salinity.
- River regulation, barrages, infrastructure and floodplain structures can modify flow volumes and hydrological regimes including natural flooding, drying and tidal-flushing patterns. The impoundment density indicator can be used to estimate the pressure imposed by such hydrological changes.
- Intensive uses such as aquaculture, dredging and shipping port infrastructure.
- See also specific impacts listed under seagrasses, mangroves, salt marshes and sand/mudflats.
Considerations for measurement and interpretation
Mapping changes in the habitat characteristics and distributions of coastal wetlands is relatively straightforward. Aerial photography and satellite imagery can be used, although ground truthing by local agencies is advised.
Existing information and data
Mangroves and coastal saltmarsh of Victoria: Distribution, condition, threats and management comprises the first State-wide assessment of the wetlands that fringe the coast of Victoria. The 514 page report examines the diversity of wetland types and plant communities along the Victorian coast and provides analysis of the ecological condition and major threats to coastal wetlands in Victoria. It also includes the first fine-scale mapping of all current mangrove and saltmarsh wetlands in Victoria.
The Wetlands Section at the Department of Environment, Water, Heritage and the Arts collaborates with all levels of government to promote the conservation, repair and wise use of wetlands. The Migratory waterbirds website at Department of the Environment, Water, Heritage and the Arts provides information about Australia’s obligations under the Convention on Migratory Species (Bonn Convention) and the Ramsar Convention on Wetlands, and international treaties such as the China-Australia and Japan-Australia Migratory Bird Agreements (CAMBA and JAMBA). The Ramsar Convention1 is an inter-governmental treaty dedicated to the wise use and conservation of wetlands. Australia has 57 Ramsar-listed wetlands of international importance, and these cover an estimated area of ~5.3 million ha3. Many of the Ramsar-listed wetlands are found in coastal areas (Figure 1). The latest information on Australia’s Ramsar-listed wetlands can be found in the The Ramsar Sites Database at Department of the Environment, Water, Heritage and the Arts.
The Wetlands Policy of the Commonwealth Government of Australia and guidelines for State of the Environment reporting (i.e. for changes in mangrove, seagrass, saltmarsh and sand/mudflats areas) are also available at Department of the Environment, Water, Heritage and the Arts. In addition, the Migratory waterbirds website has many links to wetland websites in Australia and overseas and to related legislation, conventions and policies. One such website is Wetland Care Australia, a non-profit company dedicated to the restoration of degraded wetlands.
The OzCoasts database contains mapped areas of mangrove, saltmarsh and sand/mudflats for a large number of Australian waterways. However no differentiation has been made between mangroves and Melaluca stands in this database.
More information on habitat removal/disturbance.
Jim Tait, Wetland Care Australia