Wetlands cannot simply be described as just land or just water. They can actually be both at the same time, or seasonally aquatic, or terrestrial. According to Wetlands International, wetlands are:

“Areas on which water covers the soil or if water is present either at or near the surface of that soil. Water can also be present within the root zone, all year or just during various periods of time of the year.”

Common characteristics

All wetlands have two characteristics in common: water or ice and earth. For Wetlands International the most important common feature is their importance for nature and mankind. No other type of ecosystem is as important to millions of migratory birds, fish, amphibians, insects, plants and trees.

Furthermore, no other type of area is so important to mankind. It is Wetlands International’s mission to preserve the 6% of the planet’s surface that are designated as wetlands.

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Distribution of wetlands, US Dept. of Agriculture, NRCS 

Categorisation

 There are several ways in which to categorise wetlands. A wetland may be described as:

• Marshes/swamps: areas where water is more or less permanently at the surface and/or causing saturation of the soil (e.g. papyrus swamp, fen, peatlands)
• Shallow lakes: areas of permanent or semi-permanent water with little flow (e.g. ponds, salt lakes, volcanic crater lakes).
• Coasts: areas between land and open sea that are not influenced by rivers (e.g. shorelines, beaches, mangroves and coral reefs)
• Estuaries: where rivers meet the sea and water changes from fresh to salt as it meets the sea (e.g. deltas, tidal mudflats and salt marches)
• Floodplains: areas next to the permanent course of a river that extends to the edge of the valley (e.g. ox-bow lakes and river-islands)

Value of Wetlands

In every country and climatic zone, from the polar regions to the tropics, wetlands provide the basis for human survival  and development. Wetlands include inland rivers, lakes and peatswamps, coastal lagoons, estuaries and reefs and human-made wetlands such as rice-fields. People and wetlands are interdependent: wetlands provide food and water, control floods, stabilise shorelines, mitigate climate change and are home to a wide range of biodiversity.

Despite their overwhelming values, wetlands are the most highly threatened ecosystems on the planet. Demand for their services is likely to intensify as human populations increase and development accelerates.