map
EnviroNorth > All Regions > Waterways and wetlands > Threats to wetlands

Threats to wetlands

The tropical savannas region is rich with wetland areas that, compared to other wetlands in southern Australia, are in good ecological condition. However, they are increasingly facing a number of serious threats, most of which fall under the following categories. For more information on some of these threats, click on the Continuing Pages above.

Changes to natural water flows |Pollution |Vegetation loss |Saltwater intrusion |Introduced plants and animals | Natural processes | References |

Changes to natural water flows

This can be caused by activities such as artificial drainage, the pumping of groundwater for irrigation, the construction of dams and weirs and the loss of vegetation. Plants and animals that inhabit wetlands may exist in a fine balance with a particular water regime. When this water regime is changed it can have disastrous consequences for the plants and animals that depend on it.

Pollution

Water pollution can be caused by many activities and can impact on wetlands in a variety of ways. Using chemicals, such as fertilisers and pesticides, in the catchment of wetlands can lead to a build of up too many nutrients in the water. The result can be an algal bloom. This alga can be toxic to some animals, and can deplete the water of oxygen; suffocating fish.

Pollutants and toxic materials may find their way into wetlands from mines or processing plants, industrial areas and through accidental chemical/oil spills. Potential pollution of wetlands from the mining of bauxite, gold and uranium mining in the region is a constant possibility. Pollutants from the hulls of boast entering estuaries, creeks and rivers can also create a problem.

More commonly, visitors to creeks, rivers and rock holes pollute wetlands by leaving fishing gear behind, throwing rubbish overboard or swimming in small rock holes with lashings of sunscreen or insect repellent on! These chemicals will wash off the skin and affect the finely balanced ecosystems that exist in these pools. These contaminating substances can be harmful to wildlife and can greatly reduce the water quality of the wetland.

Vegetation loss

Surrounding vegetation can play an important role in the functioning of wetlands. The vegetation assists in maintaining regular wetland water regimes, provides habitat and food for fauna and protects against salinity and erosion; which together create a healthy wetland. The loss of vegetation through clearing will result in the loss of these values.

Saltwater intrusion

Saltwater intrusion into freshwater wetlands is a problem in the tropical savannas region. It is set to become the number one threat to wetlands in the region with predicted climate change and associated sea level rise.

The issue is that low-lying coastal plains that support freshwater wetlands are often close to or even below the level reached by the highest tides. Saltwater intrusion can occur if tidal banks are eroded, for example when buffalo or cattle trample them. Saltwater from the tidal waters can then flow into surrounding low-lying swamps and other fresh water wetlands making them salty.

It is predicted that future climate change will cause some rise in sea level. Even a small rise in sea level combined with the large tidal range of northern Australia will create a rapid extension of tidal-creek systems. This is seen on the coastal plains of the Mary River in northern Australia. Tidal-creek systems have extended more than 30 km inland in 50 years, invading freshwater wetlands and destroying associated vegetation over an area of at least 17000 ha (Knighton et al 1991). In the case of the Mary River, the large tidal range, the very flat floodplains and uncontrolled feral buffalo have all contributed to the rapid rate of expansion. Saltwater intrusion changes the vegetation communities and aquatic fauna species present. Entire paperbark ( Melaleuca ) forests once living in shallow wetland areas have died because the level of salt in intruding water has become intolerable.

Introduced plants and animals

Invasion of wetlands by exotic plant species such as salvinia ( Salvinia molesta ), mimosa ( Mimosa pigra ) and para grass ( Brachiara mutica ) have created large-scale ecosystem change in regions of the tropical savannas. In places these introduced species can create monocultures, outcompeting native plants and reducing habitat availability and diversity. Weeds also choke wetlands, prevent fauna from accessing the water and reduce good nesting sites. Research into biological control agents to control one weed, Mimosa pigra, has had some success in thick stands of the plant, see link at right.

Wetlands of the tropical savannas also suffer from the effects of feral animals. These include cattle, buffalo, pigs, wild horses, cane toads and fish (e.g. carp and mosquito fish). Introduced fish can out-compete native species while cane toads poison most native species that eat them. Cattle, buffalo and horses trample banks, muddying and fouling wetlands and destroying habitat whilst pigs root around disturbing plants and wetland fauna whilst spreading the seeds of weeds that stick in their course muddy hair.

Natural processes

Fire, floods, cyclones and drought are all naturally occurring processes that have the potential to damage wetland environments. Fire can cause a massive change to the habitat available for wildlife around wetlands. Floods, cyclones and drought can impact the natural water regime of the water body and the vegetation surrounding the wetlands. The tropical savannas region experiences the impacts of several cyclones each season. Large areas of wetland habitat, including Melaleuca forests were toppled during the 2005-2006 cyclone season. It will take decades for some of these habitats to return to pre-cyclone conditions.

Other threats to wetlands come from fire, poor pastoral practices including overstocking and pumping of water from wetlands for irrigation and the creation of ponded pastures.

An example of one tropical savannas wetland region under threat is that found in the Gulf Country. The wetlands here are biologically rich and important for local and international fauna. However they face threats typical to many other wetland areas in the tropical savannas.

The Gulf has one of the largest intact wetland systems left in Australia: the Karumba–Burketown wetlands, which encompass an area of 2.2 million hectares. Extensive marine, estuarine and freshwater wetlands are the distinctive features of the land. These wetlands are an extremely important site for more than 22 species of migratory wading shorebirds and waterbirds, which visit the Gulf each year. The sheer number and variety of migratory birds makes the Gulf a place of international conservation significance.

Twenty-three percent of Australia's surface water flows through this landscape. The health of the Gulf's rivers supports the existence of many of the communities and industries including fishing and tourism that exist in the region. Threats to these wetlands potentially include the development of irrigated agriculture in northern Queensland including cotton. Broad scale irrigation will draw water from the wetlands and could alter the natural wet/dry seasonal cycle, increasing the potential for salinity. There are also concerns that proposals to expand existing mining operations in the region could also pose a threat to the Gulf's spectacular rivers and wetlands.

References

Knighton, A, D., Mills, K. & Woodroffe, C.D. 1991, 'Tidal-creek extension and saltwater intrusion in northern Australia', Geology: Vol. 19, No. 8, pp. 831–834.