Rietvlei Rondevlei

What is a wetland?

  • Wetlands are areas where terrestrial and aquatic ecosystems come together.
  • In a wetland, the water table is at or near the surface of the ground. The land is either temporarily or permanently covered with shallow water.
  • The depth of the water table changes from year to year and season to season, depending on the amount of rainfall and how much groundwater is used (e.g. absorbed by plants or pumped out by people with bore holes and well points).
  • The water in wetlands can be fresh or brackish as in estuaries. Estuaries form at river mouths: fresh water from the river mixes with seawater that pushes into the estuary when the tide comes in.

 

 

 

 

 

 

Types of wetlands

Wetlands can be found from the tops of mountains right down to the sea. Rivers link the wetlands within a catchment. Wetlands include:
All these wetland types are found in South Africa. All except mangrove swamps occur in Cape Town.

 

 

 

 

 

 

Wetlands and rivers map of the
City of Cape Town - click!

Where are Cape Town's wetlands?

  • In the lowlands of Cape Town there used to be many marsh and floodplain wetlands known as “vleis”. In the past, most of these wetlands were seasonal – flooded in winter but dry in summer.
  • Sand is usually well drained, so how did these wetlands form in the sandy soil of Cape Town’s lowlands? In many parts of the city there are layers of rock (calcrete, ferricrete or silcrete) under the sand. The rock prevents the water from soaking away, causing it to form pools when it rains.
  • Urban development has changed Cape Town’s wetlands radically. Many small wetlands have been drained or filled in, while others have become permanent lakes because they receive large volumes of water from storm-water drains, e.g. Zeekoevlei and Princessvlei.
  • Today very few seasonal wetlands remain in Cape Town. The Isoetes Vlei at Edith Stephens Wetland Park  and seasonal salt marshes at Blouvlei near Century City are two examples.
  • Cape Town’s major estuaries include Zandvlei and Rietvlei. A number of the smaller rivers in the City also end in estuaries. Estuaries are vitally important to the fishing industry: they act as “nurseries” where baby fish can grow before returning to the sea.

 

 

 

 

 

 

Bulrushes and sedges Cape Pondweed

What plants grow in wetlands?

  • The soil in wetlands is waterlogged and anaerobic so plants that live in wetlands need to be specially adapted to survive.

  • Typical Wetland plants include:

    • Emergent plants like reeds, rushes and sedges
    • Rooted plants with floating leaves like water lilies and waterblommetjies
    • Floating plants that are not rooted in the mud – there are no indigenous plants in this category in South Africa.

  • Many wetlands in South Africa are invaded by alien plants. Most of these are floating plants that are not rooted in the mud, like the water hyacinth and water lettuce.

  • Normal land plants grow around wetlands where the soil is not waterlogged.

 

 

 

 

 

 

Hippopotamus Cape River Frog
Common Platanna Marsh Terrapin
What animals live in wetlands?
  • Wetlands are home to a wide variety of both invertebrates and vertebrates, which depend on the water for all or part of their life cycles.
  • Animal groups that are plentiful in wetland areas include insects (both larvae and adults), fish, amphibians, birds and mammals.
  • Wetlands are not only important for local animals, but also for “international travellers”! Many water birds migrate from Europe and Asia to South Africa every year to avoid the northern winter and to feed. We therefore have an international duty to conserve our wetlands so that these birds can survive.
  • Some animals that once lived in Cape Town’s wetlands have become locally extinct. European settlers exterminated the hippopotamus from Cape Town’s wetlands in the early eighteenth century. In the 1980s, hippos were reintroduced to Rondevlei, which is right next to Zeekoevlei, which was named after these animals.

 

 

 

 

 

 

 Conserving wetlands
  • Wetlands are one of the most threatened ecosystems in the world.
  • South Africa has already lost more than half its wetlands.
  • A study in 2004 showed that less than one percent of seasonal wetlands are protected in South Africa.
  • Because of the rapid loss and degradation of wetlands, South Africa signed the Ramsar Convention, an international agreement to protect wetlands.
  • It is important to conserve wetlands because they benefit people and nature:

 

 

 

 

 

 

 

 

 

Conserving wetlands

 
Pied Kingfisher African Spoonbill
Greater Flamingo White Pelican