lake benger
Lake Benger - Photo © J Lawn/ Parks and Wildlife

Many wetlands in Western Australia have been destroyed or degraded since European settlement.

More detailed information about threats to wetlands and how to manage them can be found in:

Alteration of natural water regimes

The normal patter of water flow in a wetlands can be affected by activities such as:

Plants and animals that inhabit wetlands are often dependent on a particular water regime, and may be affected by changes in water levels and flow.

Loss of vegetation

The vegetation that occurs in wetlands is an important component of the ecosystem.

Vegetation:

  • assists in maintaining natural wetland water regimes
  • provides habitat and food for animals
  • protects against salinity and erosion
  • provides soil stability
  • filters pollutants
  • provides natural beauty
  • helps maintain a healthy wetland.

Loss of vegetation can have serious effects an ecosystem.

Introduction of invasive species

Weeds invade and compete with native plant species for resources.

Feral animals are known for their destructive impact on wetland areas, and can disrupt the intricate food chains that exist within the ecosystem.

Invasive species introduced into wetlands include:

Effect of salinity on wetlands
(note intrusion of samphire as a result of
clearing) - Photo © M Rogers/ Parks and Wildlife

Salinity

Salinisation and related changes to hydrological processes (e.g. inundation or flooding) are widespread issues in agricultural areas.

  • This is can occur when the native vegetation (which is perennial and deep-rooted) is replaced with introduced annual crops and pasture (which are shallow-rooted).
    • Because annual crop and pasture species use less water than native vegetation, this can result in a rise in the water table.
    • As the water rises, it brings up dissolved salts that have accumulated in the surface layers of the soil.

Some mining activities, such as brine discharge, can also cause salination in wetlands. 

Changes to water quality

Variations to water quality including acidification and salinisation can harm wetland environments.

  • Changes to the pH of water can threaten the health of plants and animals that depend on the water.
    • Increasing water acidity (a low pH) can liberate metals and other pollutants into water increasing their potential to damage aquatic wildlife, or affect the accessibility of essential nutrients.
    • Similarly, increasing alkalinity can also harm wetland ecosystems. Changes in water pH may make ions, such as potassium, calcium or magnesium, unavailable to plants and animals, affecting their survival. For example, native aquatic molluscs cannot survive where chemical conditions prevent or restrict their shell building capacity.
  • Increased input of the nutrients phosphorus and nitrogen associated with farming and the removal of deep rooted perennial may lead to artificially high concentrations of these nutrients in the catchment's water, resulting in excessive growth of naturally occurring organisms, such as algae. Excessive growth of algae can deplete oxygen levels in the water making the water unsuitable for aquatic wildlife

Waterlogging

Waterlogging occurs when the soil is so wet that there is insufficient oxygen in the soil for plant roots to respire (breathe). Waterlogging can originate from:

  • increases in the volume of surface water
  • rising groundwater
  • active groundwater discharge.

If the period of waterlogging is too long, many plants will drown.

Surface water erosion and sedimentation

Changes in the way water behaves in the landscape can also impact on the soils in the catchment.

  • In the absence of vegetation, water can move quickly across the land, causing erosion of the topsoil, moving it downstream.
  • Deposition of the topsoil downstream can change the flow path of a drainage line and may clog pools or riffle zones, altering the habitat and ultimately the speed at which water moves in the channel.
  • In serious cases, water driven erosion can result in deeply cut drainage channels with fast flowing water, further increasing the chances of instream and bank erosion. This, in turn, may cause native riparian vegetation to be physically washed downstream, further accelerating erosion processes, while the deposition of sediment in zones where the water moves slower can result in substantial increases in turbidity, localised waterlogging and inundation as surface water flow is obstructed by the sediment.

Changes to wetland hydroperiod

Hydroperiod refers to the length of time that wetlands are influenced by water (surface and/or groundwater).

As a consequence of the clearing of native vegetation, there has been a substantial increase in the volume of surface water runoff and the volume of groundwater discharge in the catchments. In many catchments, this has substantially altered the timing and area of inundation of many wetlands. This can cause negative environmental impacts regardless of water quality.

Water pollution

Bulrush weed invasion of wetland
- Photo © M Rogers/ Parks and Wildlife

Wetland water bodies can be contaminated by various activities, including:

  • the use of chemicals (such as fertilisers and pesticides) in the wetland's catchment
  • the drainage of pollutants and toxic materials into wetlands
  • accidental chemical/oil spills.

Some pollutants can be harmful to wildlife and can greatly reduce the water quality of the wetland.

The use of fertilisers in the wetlands catchment can cause nutrient enrichment in the wetland.

  • This has the potential to cause algal blooms in the water body.
  • These blooms in turn may be toxic to some animals, particularly fish and waterbirds, and result in events such as fish kills.

Natural processes

Fire, floods, cyclones and drought are all naturally-occurring processes that have the potential to alter and damage wetland environments.

Fire can remove or change habitat available for wildlife around wetlands.

Maintaining and improving habitat for nature conservation, including through revegetation, can protect and improve wetlands and assist in conserving biodiversity.