By Rowland Benjamin

Like many other ecosystems, wetlands worldwide are constantly under threat by human activities. Many wetlands have been badly degraded by activities such as drainage, land clearing and conversion for agriculture, farming practices, mining, pollution, hunting, as well as urban and industrial development. Large areas of wetlands have already been converted or developed and therefore degraded or destroyed. In developing countries this drainage and conversion into agricultural land is still a significant problem but not as much for developed countries. It is important to manage wetlands wisely to ensure that their important values are maintained in the long-term.

In many developed countries the following issues are likely to be of the greatest threat to wetlands:

• Alteration of natural water regimes - Plants and animals that inhabit wetlands are often dependent on a particular water regime, and may be affected by changes in natural water regimes. This can be caused by activities such as artificial drainage, the extraction of groundwater for urbanisation and agricultural development, the construction of dams and weirs and altering floodwater to mitigate the impact of flooding. This can result in wetlands becoming completely isolated from river systems that would normally nourish them and may result in these wetlands becoming permanently dry causing them to disappear

• Loss of vegetation - The vegetation that occurs around wetlands is an important component of the ecosystem and is often specially adapted for the wet conditions. This vegetation assists in maintaining regular wetland water regimes, provides habitat and food for fauna, protects against salinity and erosion, provides natural beauty and helps maintain a healthy wetland. The loss of vegetation will result in the loss of these values for both the organisms that depend on them for survival as well as humans

• Salinity and flooding - These are widespread issues in agricultural areas and are generally caused by the replacement of perennial deep rooted native vegetation with shallow rooted annual crops and pasture; i.e. farming. Because annual crop and pasture species use less water than native vegetation, this can result in a rise in the water table bringing with it dissolved salts that have accumulated in the surface layers of the soil. The effects of salinity and flooding on wetlands include a reduction in water quality, the alteration of aquatic invertebrate communities, and the death of wetland plants that cannot tolerate high levels of salt in the soil or the extended period of flooding

• Water pollution - The contamination of a water body can be caused by various activities, including the use of chemicals such as fertilisers and pesticides, in the catchment of wetlands, the drainage of pollutants and toxic materials into wetlands, and accidental chemical or oil spills from factories. Some contaminating substances can be harmful to wildlife and can greatly reduce the water quality of the wetland. The use of fertilisers on farms and urban gardens, as well as the input of sewage into the wetland catchment can cause nutrient enrichment in the wetland. This has the potential to cause algal blooms in the water body. These blooms may be toxic to some fauna, such as fish and waterbirds

• Introduction of invasive species - This includes the introduction of weeds and feral animals (such as carp, mosquito fish, salvinia, grasses, donkeys, goats and camels) into the wetland environment. Weed invasion creates competition for resources with native plant species. Feral animals are known for their destructive impact on wetland areas and can disrupt the intricate food chains that exist within the ecosystem

• Global climate change - Climate change may affect wetlands through increased air temperatures, increased frequency and severity of storms, droughts and floods, increased atmospheric carbon dioxide concentration and sea level rise which may also increase the salinity levels in the wetland as a result. All of these could affect species composition and wetland functions

• Natural processes - Fire, flood, 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. Flooding, cyclones and drought can impact the natural water regime of the water body and the vegetation surrounding the wetlands.

  Return to Wetlands - Introduction