Wetland ecosystems provide great natural assets accounting for 6% of global land area but have often been considered as obstacles to those wishing to colonise land and make it agriculturally productive. They are in fact very productive areas for not only plant life but also fish, wildfowl and wetland agriculture. Their importance is still not fully understood and attitudes towards wetlands have been changing noticeably over recent decades as more information is learnt about their values and functions.

'Wetlands' occupy the land between aquatic and truly terrestrial environments. The commonly accepted definition of a wetland is the area between permanently wet and generally dry land. The definition given in the RAMSAR Convention of 1971 outlined wetlands as "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 six metres". Even with the use of commonly accepted definitions, wetlands are often unstable systems and in a constant state of flux thus making a precise definition almost impossible.

There are a multitude of processes responsible for the formation of the numerous types of wetland and each process is important when considered in respect to the particular type of wetland. Similarly the hydrological regime is different for each of the diverse types according to their geographical location, history, dominant plants, chemistry, soil or sediment characteristics (Maitby 1986). The hydrology is usually very complex, furthermore, and wetlands are often dependent on influences far beyond their own boundaries, and many are still not fully understood or appreciated.

The value of wetlands has changed according to the perceived functions that they serve. Today they can support a multitude of activities including agriculture and fisheries and be economically productive despite being inherently uninhabitable and in a constant state of flux.

In the past wetlands presented an obstacle to those wishing to colonise land and make it productive and prior to technological change development was mostly impossible. Once the technological problems were overcome the threats to wetlands increased and their future became even more uncertain as it became possible to drain, clear and totally transform many types of wetland. With the widespread loss of vast wetland areas their conservation value began to increase as the habitat became rarer and rarer. Much of Europe’s wetlands were lost when the Dutch engineers exported their technical expertise in land reclamation in the late middle ages. In the 1500s, the ‘Golden Age’, the Dutch began draining polders using windmills and in the early 1600s engineers such as Vermuyden began using expertise abroad (Williams 1990b). In the United States vast destruction of wetlands also took place following the arrival of Europeans and the flood protection measures of the late nineteenth century.

Drained wetland was often considered superior to undrained wetland and no positive values were seen in ‘wasted’ land, left in its natural state. The changing attitudes towards wetlands have resulted in the recognition of many more of the functions that they perform and they are now more widely appreciated. Furthermore the traditional uses of wetlands, such as reed harvesting, hunting, fishing and rice cultivation that have low environmental impacts, have been recognised as sustainable economic activities. The survival of many types of wetlands now in fact depends on the preservation of traditional agricultural techniques.

The value of many wetlands is still assessed in terms of their financial value once converted to another use. In Britain the Land Drainage Acts of 1930 and 1976 were created to oversee drainage and liberal grants were made available. During the second world war drainage grants of up to 50% were given in England and Wales. Much of the marshy areas on the Camargue were destroyed in the 1970s and l980s to create holiday resorts for French tourists, financed and organised by the French government. Wetland destruction is still supported and financed by many governments, the Common Agricultural Policy grants made available to those farmers within the EC wishing to drain and "improve" their land being one example of this. Wetland conversion rates vary greatly between one country and another often according to the relative abundance of wetlands in each area. Most losses do in fact occur in coastal areas rather than inland wetlands, probably due to the far greater variety of pressures on these areas.

Functions of Wetlands

Michael Williams (1990a) gave four categories of function; physical/hydrological, chemical, biological, and socio-economic as follows.

Physical/Hydrological functions.

• Flood mitigation - temporary runoff stores protecting down stream areas.

• Coastal protection - wetlands reduce erosion and absorb wave energy.

• Recharging Aquifers - some, but not all wetlands suppress upwelling salt waters.

• Sediment trapping - clear suspended sediment and flocculate clay particles at the interface between fresh and salt waters.

• Atmospheric and Climatic fluctuations - wetlands may act as carbon sinks.

Chemical Functions.

• Pollution trapping - trap and filter out pollutants, especially nitrogen and phosphorous by plant uptake or bacterial metabolism.

• Removal of toxic residues - removed by ion exchange and absorption onto clay particles.

• Waste processing - by high primary productivity rates, sedimentation rates and bacterial action in the sediments.

Biological Functions.

• Productivity - highly productive ecosystems with many perennials and few woody species.

• Habitats - for a wide variety of plants and animals. Especially important for wildfowl and migrating bird species

Socio-Economic Benefits and Values.

• Consumptive values which are all benefits gained from the wetlands and may lead to their modification or transformation.

• Food - the fundamental reason for wetland transformation throughout time.

• Fish, fowl and fauna - possibly as much as 60-65% of the worlds fish and shellfish are caught in wetlands.

• Fuel - peat has been cut for centuries as a fuel source.

• Fibres - forests provide important sources of fibres.

• Non-consumptive benefits. These include scenic, recreational, aesthetic, archaeological, scientific, heritage and historical benefits which are difficult to define or quantify.

The assessment of the values of wetlands is very difficult due to the diverse nature of the many types, their functions and their numerous products. Similarly as attitudes move away from the dominionistic and utilitarian and become more realistic the general preservation-development conflict takes over (Mercer 1990). Recreational activities and potential are being considered more in many countries as leisure time and expendable income increase. However, uncontrolled recreation can lead to severe environmental degradation as demonstrated by the case of the Norfolk broads which have suffered from population pressure. For example, the large increase in the use of pleasure boats has lead to bank erosion and water quality problems. Hunting, which is a traditional activity in much of the Mediterranean can lead to severe degradation of bird populations and has lead to lobbying by many organisations.