Wetlands, are a result of an interaction between a variety of factors (geological, climatic, anthropogenic, etc.) which give rise to zones where there is a runoff concentration, whose supply (surface, groundwater or a combination of both) allows the water level to remain constant.
Although wetlands constitute one of the outstanding and singular elements in the landscape of a semi-arid zone, the required attention has not been given to them until recent times. An overall approach must be made to these ecological systems in order to be able to develop management strategies which permit the long-term conservation and ecological and cultural integrity of these functional units. If management strategies are to be developed, it is essential that wetlands be considered as forming an integral part of the water cycle in a state of permanent interaction with the river basins (Montes, 1994).
The Spanish Directorate General of Hydraulic Works published in 1990 a document entitled "Estudio de las Zonas Húmedas de la España Peninsular. Inventario y Tipificación", (Wetlands on the Spanish Mainland, Inventory and Typification). This inventory contains the characteristics of 1,544 wetlands. Some of them are coastal phenomena (The Mar Menor, the Marshlands of the Guadalquivir, etc.), while others are lakes (Sanabria, Bañolas, Albufera, etc.) and the rest are all wetlands in the strictest sense of the word. Over 50% of the wetlands featured in this document are related to aquifers, 440 cover a surface area of more than ten hectares, but only 25 are in excess of 1,000 ha (MOPTMA-MINER, 1994).
In Spain, the current wetland surface area has dropped from 1,240 km2 to 800 km2 -excluding the Guadalquivir marshlands- (MOPTMA-MINER, 1994). This reduction is a consequence of different human activities, such as draining in order to reduce the risk to human health, and the lowering of the water table for water supply. The most remarkable example of the latter affect the river Guadiana (Tablas de Daimiel, Ojos del Guadiana, etc.) where excessive groundwater pumping has not only brought about socio-economic problems, but has also led to the disappearance of numerous wetland areas.
Because the surface area covered by wetlands is relatively limited, to state that they play a key role in controlling the ecological processes taking place on a regional or European level would be an exaggeration. Nevertheless, the locally important hydrological, chemical, biological and ecological properties of wetlands and their socio-economic value is beyond question (Montes y Bifani, 1991).