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Wetlands can be defined as "areas of marsh, fern, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, or salty, including areas of marine water the depth of which at low tides does not exceed six metres".

Wetlands may be found where the land is wet enough (i.e. saturated or flooded) for long enough to be favourable to certain types of plants, especially those adapted to anaerobic soil conditions (i.e. soil without oxygen).  Wetlands have a variety of different water regimes.  These range from permanently waterlogged areas, which remain flooded or saturated to the surface for the entire year, to temporarily waterlogged areas which are flooded or saturated too close to the soil surface for as little as a few weeks in the year.

There are different types of wetlands depending on location and local environmental conditions, these include:

• Estuaries: where rivers meet the sea and salinity is intermediate between salt and freshwater (e.g. deltas, mudflats and salt-marshes);
• Marine: are those not influenced by river flows (e.g. shore lines and coral reefs);
• Riverine: include land periodically inundated by river overtopping (e.g. flooded forests, oxbow lakes);
• Palustrine: where there is more or less permanent water (e.g. papyrus swamp, marshes and ferns);
• Lacusterine: those found in areas of permanent water with little flow (e.g. ponds, kettle lakes, volcanic crater lakes).

The most common characteristics of wetlands are:

• Moist soil conditions forming and providing a route for oxygen to move down into the soil. 
• The water regime has a strong effect on the colour patterns of the soil, well drained soils are usually red/brown in colour but soils in wetlands are generally grey in colour as a result of the anaerobic conditions.

Wetlands have existed for a long time and along some of the major rivers of the world including the Tigris, Euphrates, Niger and the Nile and have nurtured the great civilisations of history.  The importance of wetlands has however changed with time, in the distant past wetlands produced and preserved many of the fossil fuels (coal and oil) upon which we depend today.

Wetlands have also provided fish, drinking water, pasture land and transport and were part of the cultural history of early people.  Wetlands were a central element of mythology, art and religion.  Wetlands should be recognised as life support systems, rather than the more common misconception that wetlands are sources of diseases and something over which mankind should exert its influence.

Next week we shall continue this series on wetlands with a full examination of their roles and values, and the benefits of wetlands to humans.

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