What is a Wetland?What is a wetland? There is no easy anwer to this question. The key features of wetlands are:
- permanent or temporary flooding
- the presence of water-saturated soil
- the presence of aquatic vegetation
 | Many governments have formulated their own definitions of wetlands because of country-specific political and legal requirements. The broadest definition of wetlands is probably the definition used by the Ramsar convention, which states that:
wetlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish, or salt including areas of marine water, the depth of which at low tide does not exceed 6 metres".
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Practically speaking, this definition includes a variety of systems such as marshes, floodplains, peatlands, rivers, lakes, salt marshes, mangroves, estuaries, sea grass beds and even coral reefs. Artificial systems like rice fields, reservoirs, fishponds and constructed wetlands for wastewater treatment are also covered by the definition.
Categories of wetlandsWetlands can be categorised according to several distinctive characteristics, e.g.,
- soil type: wetlands with mineral soils versus wetlands with peat (organic) soils
- hydrology: seasonally or continually flooded wetlands
- water source: rainfall, groundwater, or surface flow
- vegetation type: wetlands dominated by woody vegetation versus those dominated by reeds, or grasses and sedges, or mosses
- salinity: freshwater (mostly inland) versus brackish/seawater (coastal) wetlands
- pH: wetlands with neutral pH versus more acid wetlands. Most acid wetlands occur in the northern hemisphere of the world.
- origin: natural versus artificial. Artificial (or constructed) wetlands are human-made structures often with a very specific goal. Many constructed wetlands are aimed at water treatment for urban centres or industries. Other artificial wetlands are ricefields, aquaculture ponds and irrigation ponds and canals.
Classification systemsSeveral wetland classification systems have been designed, e.g., by the Ramsar Convention, the Canadian Government and the United States Fish and Wildlife Service. The broadest level of the U.S. system distinguishes:
- Marine wetlands: wetlands bordering open ocean areas
- Estuarine wetlands: tidal coastal wetlands that are connected to the sea and where freshwater runoff dilutes the seawater occasionally or continuously
- Riverine wetlands: freshwater (<0.5 ppt salinity) wetlands contained in a river channel and without dominant vegetation
- Lacustrine wetlands: wetlands without dominant vegetation (less than 30% coverage) and larger than 8 ha or deeper than 2 m (deepest part).
- Palustrine wetlands: all non-tidal freshwater (<0.5 ppt salinity) wetlands dominated by vegetation. Wetlands not dominated by vegetation but smaller than 8 ha and less than 2 m deep (deepest part) also belong to this group.
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Wetlands Introduction 
