Wetlands need water to exist and to support animal and plant life. Coastal and inland wetlands are at risk from the changes that global warming will bring to rainfall, evaporation rates and sea levels.
Projected decreases in rainfall and river flows will affect some wetlands in southern Australia. For example, on the Swan coastal plain of Western Australia, seasonal wetlands used by waders and waterfowl may disappear due to lower rainfall and less recharge of ground water (Arnold 1988). The Southern Fleurieu swamps in South Australia are vulnerable to lower water flows and increased evaporation due to temperature increases (Grady, 2001).
Climate change will cause reductions in the flow of many rivers, particularly in southern Australia because of less rainfall in winter and greater rates of evaporation For example, by 2050 there will be a 12-35 percent reduction in mean flow into the Murray-Darling Basin (Pittock and Wratt, 2001).
Kakadu National Park’s freshwater wetlands
Kakadu’s World Heritage listed freshwater wetlands make up about 90 percent of the coastal zone of the National Park and cover 195, 000 hectares. Three million waterbirds use the Kakadu wetlands to feed and breed and it is also home for turtles, frogs and fish.
The low-lying coastal plains in Kakadu are just 0.2 – 1.2 metres above mean high water level (Eliot et al., 1999). Many of northern Australia’s freshwater lagoons and floodplains are similar to Kakadu, low-lying and vulnerable to projected sea-level rises of 10 – 30 cms by 2030 (IPCCb 2001).
Sea level rise as a result of global warming may be beginning to show in Kakadu. There is evidence that freshwater environments are converting to saltwater wetlands, leading to extensive dieback of paperbark and freshwater grasses across these plains (Bell et al., 2001).
Aboriginal owners of Kakadu are finding that the rate of sea-level intrusion is faster than normal and is reaching new areas.
This is resulting in a loss of swamp grass and paperbark trees, and appears to be changing the distribution of long-necked turtles (McGregor, 2001).
Saltwater intrusion has occurred naturally before in Kakadu, and this led to an expansion of mangroves. Mangroves are important wetlands in their own right, but the loss of freshwater wetlands will damage the dependent wildlife, traditional uses of the wetlands, and tourist interest in the lagoons, floodplains and birds (Eliot et.al, 1999).
The wetlands are important for Aboriginal people who hunt and gather food from the wetlands throughout the year - Waterlilies are collected for the stems and the seeds; Magpie Geese and long-necked turtles are hunted (McGregor, 2001).
Yellow Waters wetland is a major drawcard for the 200,000 visitors to Kakadu each year. The Park also employs many people, with 130 tour operators taking people to the Park to visit the wetlands (Environment Australia, 2001). Tourism expenditure in the Top End region of the Northern Territory was $419 million in 2000 – 2001 (Northern Territory Tourist Commission, 2001).
The Macquarie Marshes are one of the largest semi-permanent wetlands in south-eastern Australia, located near Dubbo in NSW. It is an internationally recognised breeding area for 42 species of waterbirds, including Magpie Geese and Brolgas. In 1984 the wetlands supported at least 80,000 waterbirds (Kingsford 1995).
By 2030 rainfall in the Macquarie Valley may be 3 – 10 percent lower, evaporation 3 – 10 percent higher and mean annual flows into the Marshes reduced by 11 – 32 percent (Hassell and Associates, 1998).
Climate change is likely to cause a decline in the wetland’s vegetation by up to 40 percent, and fewer numbers and less frequent breeding of waterbirds and other wetland animals, such as turtles and frogs. It is not clear if these species will find other places to breed, as the Macquarie Marshes is one of the only wetlands in the Murray Darling Basin (Hassell and Associates, 1998).
The estimated economic losses of climate change to the region are between $38 - $152 million per year, or a 6 – 22 percent reduction of agriculture’s contribution to the local economy (Hassell and Associates, 1998).
Lake Bullenmerri is Victoria’s deepest natural lake – in 1990, it was about 63 metres deep. As it has no streams feeding or draining, its level is dominated by rainfall and evaporation and very sensitive to climate change. Records have been kept for the lake since 1841, and since that time lake levels have fallen by approximately 20 metres (Jones et al 2001). The records and other evidence from the lake suggest that the last 20 years is the driest period for western Victoria in 10, 000 years (Bowler, 2001). While the reductions in depth began before greenhouse-related warming, the declining trend is now beyond the range of natural variability and falling at a rate faster than average (Bowler, 2001).
Rivers and agriculture in NSW and Victoria
River ecosystems provide essential water resources for farming communities. South-eastern Australian rivers are already under stress with great demand for water supply to the key national food growing regions in NSW and Victoria.
Current efforts to repair the Murray Darling river system will be undone by 2050, with climate change causing a reduction in the system’s mean flow of up to 30 percent.
CSIRO research indicates a clear future trend towards decreased winter and spring rainfall across much of southern Australia and decreased snow levels. Both of these climate conditions are important for recharging Australian rivers such as the Murray Darling (CSIRO 2001). This decrease in rainfall will see flows into rivers reduced by up to 30 percent by 2030 for the Ovens, Goulburn and Macquarie Rivers, and by 2050 for the Murray-Darling (Hassall & Assoc, 1998 ; Pittock et al, 1997 ; Pittock & Wratt 2001).
Image courtesy of World Wide Fund For Nature