Introduction

Wetlands have played a crucial role in human history. Major stages of the evolution of the life itself probably took place in nutrient-rich coastal waters. Some of the first prehistoric cultures, such as those of the early mesolithic settlements around the post-glacial lake margins and coasts of Europe and those of the coastal Indian communities in North America, depended on wetlands for food and materials for building, shelter and clothing (Maltby, 1991). Boulé (1994) in his excellent overview on an early history of wetland ecology pointed out that the early Sumerians knew the names of plants and animals that occupied the marshes of the Tigris and Euphrates Rivers, as evidenced by clay tablets on which those names were inscribed (Kramer, 1981). The Babylonians, who followed the Sumerians in Mezopotamia, not only had names for wetland plant species, but also established municipal reed beds and reeds harvested from these beds were used to make rugs, coarse mats to strengthen walls of clay brick, and very fine mats to serve as a foundation for dikes made from material dredged from the rivers (the original filter fabric).

The value of a wetland is a measure of its importance to society. Wetland functions are valued to various degrees by society, but there is no precise, general relationship between wetland functions and the value of wetlands to society, and values can be difficult to determine objectively. A wetland’s value can be weighed directly or relative to other uses that could be made of the site; thus, the location of a wetland affects its value to society (Lewis 1995).

Wetlands are transitional environments. In a spatial context, they lie between dry land and open water – at the coast, around inland lakes and rivers, or as mires draped across the landscape. In an ecological context, wetlands are intermediate between terrestrial and aquatic ecosystems. In a temporal context, most wetlands are destined either to evolve into dry land as a result of lowered water tables, sedimentation and plant succession, or to be submerged by rising water tables associated with relative sea-level rise or climatic change. Wetlands often form part of a large continuum of community type, and therefore it is difficult to set boundaries. Consequently, few definitions adequately describe wetlands with the problem of definition usually arising on the edges of wetland, toward either wetter or drier conditions (Vymazal, 1995a).