Value of Wetlands in General

Wetlands:

Provide habitat and encourage species diversity
Refuges and buffers to environmental fluctuations, e.g. drought
Storm protection and flood mitigation
Shoreline stabilisation and erosion control
Water storage
Groundwater recharge (into the underground aquifers)
Groundwater discharge
water purification via retention of sediments and pollutants
stabilisation of local climate conditions

Wetlands also provide economic benefits including:

water supply (quantity and quality)
fisheries (over 2/3 of the world's fish harvest)
timber production
energy resources, such as peat and plant matter
wildlife resources
transport
recreation and tourism opportunities
agriculture, through the maintenance of water tables and nutrient retention in floodplains .

According to the The Ramsar Convention Bureau:

Wetlands are among the world's most productive environments. They are cradles of biological diversity, providing the water and primary productivity upon which countless species of plants and animals depend for survival. They support high concentrations of birds, mammals, reptiles, amphibians, fish and invertebrate species. Of the 20,000 species of fish in the world, more than 40% live in fresh water. Wetlands are also important storehouses of plant genetic material. Rice, for example, which is a common wetland plant, is the staple diet of more than half of humanity...

Unfortunately, and in spite of important progress made in recent decades, wetlands continue to be among the world's most threatened ecosystems, owing mainly to ongoing drainage, conversion, pollution, and over-exploitation of their resources.

According to the World Conservation Union (IUCN):

Already 50% of the world's wetlands have been lost. The degradation of wetlands puts the livelihoods of communities and the biological diversity at risk. Over 800 freshwater species worldwide are now threatened with extinction.

The Ramsar Convention Bureau, What are Wetlands?, http://www.ramsar.org/about_infopack_1e.htm, The official Ramsar Convention website, 5 February 2000.

IUCN, Wetlands and Water Resources Program, http://iucn.org/themes/wetlands/wetlands.html, 2000.