Threats to wetlands
Wetlands are among the most threatened ecosystems in Australia and the world. Many wetlands in NSW have been significantly altered or destroyed by diversion or drainage of their water, disturbance to their catchments, and the introduction of pest animals and plants.
In inland NSW, for example, there has been a 50 per cent decline in the area of the Macquarie Marshes and a 75 per cent decline in the area of the Gwydir River wetlands. In coastal NSW, 60 per cent of wetlands have been lost or degraded over the past 200 years.
A number of wetland communities are now recognised as endangered under the NSW Threatened Species Conservation Act 1995. See a list of endangered wetland communities.
The major threats to wetlands are as follows.
1. River regulation and water diversion
Ideally, a healthy wetland should retain a natural flow of water. What constitutes a 'natural flow' varies substantially among rivers and wetlands. Humans have altered the natural flow regime of rivers and wetlands in various ways.
We have altered river flows to mitigate the impact of flooding and extract water for urbanisation and agricultural development. Many NSW wetlands are receiving flows of less water, less often and at unnatural times of the year, from rivers and overland runoff. Some wetlands have become completely isolated from the river systems that once nourished them. These areas may become permanently dry and disappear.
In other cases, we use wetlands to store water for town supply or irrigation. As a result, the wetlands no longer dry out as they would naturally during drought.
These changes threaten and often kill the plants and animals that rely on natural water flows. The NSW Scientific Committee has identified the 'alteration to the natural flow regimes of rivers and streams and their floodplains and wetlands' as a key threatening process in NSW. Read the full key threatening process listing.
2. Catchment-scale disturbance
Changes in a catchment's land use, due to urbanisation and agriculture and other types of development, can have profound effects on the functioning of aquatic systems.
Downstream of development, there can be increases in the loads of nutrients (such as nitrogen and phosphorus) and suspended solids entering waterways in runoff after rain. The extra nutrients are rapidly taken up by some types of aquatic plants, particularly macroalgae and phytoplankton. The numbers of these plants increase, and they become dominant over plants living on the sediment, such as seagrasses and benthic microalgae.
These changes in plant dominance have profound effects on the animals that depend on aquatic environments as a source of food and refuge - and as a nursery for their young.
3. Introduction of weeds and pest animals
Weeds and pest animals compete with native wetland species and habitats, and may replace them altogether. Find out more about weeds and pest animals.
4. Climate change
The global climate is changing, and there is now strong evidence and international consensus that a significant part of this change is due to increasing concentrations of greenhouse gases in the atmosphere. Higher levels of atmospheric greenhouse gases also mean that our climate will continue to change throughout this century and beyond.
In NSW, each decade since 1950 has seen a 0.15°C increase in the annual mean maximum temperature and a 14.3 mm decrease in annual rainfall (CSIRO 2006). The latest climate change scenarios for Australia, developed by the CSIRO, include:
- increased risk of drought
- increased soil erosion and dryland salinity
- more hot days
- greater bushfire risk.
The question is not 'will the climate change?' but rather 'how will it change, and what are the consequences for regions and for wetlands?'
Higher temperatures and reduced rainfall will impact on the extent of wetlands in western NSW. Sea level rises appear to be implicated in the successional decline of salt marsh habitat and increase in mangrove habitat in coastal estuaries (Wilton 2002).
The National Biodiversity and Climate Change Action Plan 2004-2007 aims to minimise the impacts of climate change. Objective 3 of the action plan is concerned with inland aquatic and semi-aquatic ecosystems. Objective 4 focuses on minimising the impacts of climate change on marine, estuarine and coastal ecosystems.
For further information about climate change, go to the Department of Climate Change and Energy Efficiency website.
More information
Page last updated: 12 April 2011
