The different types of wetlands present in the Mediterranean
Mediterranean wetlands include a wide variety of natural habitats: river deltas, lakes, and marshes (freshwater, brackish or saline), permanent watercourses and wadis, riverside forests subject to flooding; and also salinas and dammed reservoirs.
It is at the mouths of the main rivers that coastal wetlands are most frequently found: the silt and sand carried down to the sea are deposited at the point where the river reaches still water that is not influenced by tides, and thereby give rise to dunes, marshes and new spits of land which advance towards the sea, the whole forming a delta.
A typical natural delta therefore comprises a whole range of wetlands whose salinity tends in general to rise with increasing proximity to the sea. The absence of tides in the Mediterranean is especially favourable for the formation of deltas, but major permanent watercourses are few in number and are mainly fed by water originating from outside the region (as are the * Rhone, the Po, the Guadalquivir, and the Nile).
Coastal lagoons and saltmarshes
The sediments brought down by a watercourse are usually deposited a few hundred metres offshore, when the sea currents have slowed down the rate of flow of the river. Subsequently, the sand deposits are moulded by the currents, often creating offshore bars parallel with the coastline, behind which lagoons are formed. These lagoons are usually linked to the sea via a channel, and they may also be fed by the watercourse. Growth of the offshore bars may result in the closing off of some lagoons of which the waters then become less saline (as is the case in the Languedoc region). Others have been artificially cut off from the sea in order to drain them for agriculture (as with the Drana lagoon in Greece).
The biggest areas of lagoons and saltmarshes in the Mediterranean extend along 200 km of the coastline of Provence and Languedoc-Roussillon in the south of France, from Venice to Trieste in northern Italy, and on the Tunisian coast, not forgetting the Po delta. For its part, Egypt has almost a quarter of the remaining Mediterranean coastal wetlands, the majority in the form of lagoons in the vast region of the Nile delta.
These are formed either in land-locked areas or through the decline in salinity of lagoons that become separated from the sea and are fed by watercourses (as in the Nile, Rhone, and Po deltas). In North Africa there are few permanent lakes, apart from marine and deltaic lagoons, as open water quickly disappears as a result of the high rate of evaporation.
Of the hundreds of freshwater marshes which used to exist along the Mediterranean coast, very few remain today, and their flooding regime is nearly always at least partly under human control. They include a range of habitat types, from reedbeds surrounding lakes to grazed wet grasslands in the deltas or along the major river channels.
Floodplains and floodplain forests
Most of the wetlands which used to exist in the floodplains have been systematically drained over the course of the last two millennia. At the same time, the major riparian forests (of willows and poplars), which used to grow along the lower reaches of the majority of watercourses in the Mediterranean region, have almost completely disappeared as a result of clearing or drainage. A small number of freshwater marshes remain in the floodplains of the Po and the Tagus, and in France in the Languedoc, and some floodplain forests around Lake Skadar in Montenegro, in the Pinios and Nestos deltas, and around Lake Kerkini in Greece, as well as in the Kizilirmak delta and around Lake Manyas in Turkey.
Owing to the absence of tides in the major part of the Mediterranean Sea, there are very few large areas of mudflats between the upper and lower tidal limits, the exception being part of the Gulf of Gabès situated between the southern Tunisian coast and the Kneïs islands.
Continental salt lakes
Salt lakes (“chotts”, “sebkhas”) rank among the largest wetlands of the Mediterranean Basin. The most important are in North Africa, where the combined effects of sudden torrential rain and rapid runoff in quasi-desert landscapes sometimes result in the formation of wide expanses of water within continental depressions. In chotts, the permanent vegetation is sparse, with islets of greenery whenever water is present. Invertebrates here are limited to a handful of species which are adapted to xeric conditions, and waterbirds are rare. Sebkhas are shallow depressions which hold water for longer periods and usually only dry up at the height of summer. The vegetated ones are usually much smaller than the others, as they gather and retain water better and are less salty.
In the Sahara and over a large part of the Levant, there is abundant underground water, derived from seepage over the course of wetter periods during the region’s geological history. One of the most important of these oases for fauna and flora is Azraq in Jordan. It supports some rare reptiles; it is also an important stopover point for migrating birds.
Salinas, when they are being worked, constitute wetlands which have a significant artificial element, but which are nevertheless of very high value. Salinas provide a habitat that is increasingly important for birds and, when they have been closed down, they must be managed for the benefit of wildlife. In saltpans with low salinity, certain species of salt-tolerant plants and fish can thrive; on the other hand, in more saline pans, only brine shrimps can survive. The regular seasonal cycles at the salinas enable the availability of food supplies to be guaranteed and, as a result, an abundant bird community to be supported.
These constitute a type of wetland that is becoming increasingly significant in the Mediterranean Basin. Reservoirs, constructed in the mountains, can replace, to a certain extent, the wetlands of the downstream plains. They may also play an important role in deltas. For example, the small floodwater storage reservoir of Valle Santa, near Ravenna in the Po delta, has enabled some of the last marshes of the Po floodplain to be safeguarded, containing reedbeds, water lilies, pike, and tench. This site is currently listed under the Ramsar Convention.
Unfortunately, most reservoirs are built in very steeply sloping areas, which greatly limits the possibilities for the development of shallow marshes around the edges, and in many of them the water level can fall sharply and in an irregular way, further reducing the chances for the growth of vegetation on the banks.