Topics: Soil, Surface runoff, River Pages: 5 (1347 words) Published: May 28, 2013
What is a Wetland ?

Wetlands are habitats that fall somewhere on the environmental spectrum between land and water. Since wetlands lie at the interface of terrestrial and aquatic habitats, they possess a unique mixture of species, conditions, and interactions. As a result, wetlands are among our planet's most diverse and varied habitats. Wetlands are defined by the soils, hydrology, and species that occur within them. Wetland soils, also known as hydric soils, are shaped by water. These soils are saturated or even submerged all or part of the year. Hydric soils vary depending on the composition of the soil and water in the area and therefore, wetlands vary greatly throughout the world. Wetlands occur in all ecological regions throughout the world except Antarctica. There are wetlands in the Arctic (which include fens, swamps, marshes, and bogs), wetlands along coastlines (such as mangrove forests, coastal swamps, and tidal marshes), and wetlands throughout inland regions (ponds, marshes, swamps, vernal pools, and riparian systems). Wetlands are highly productive communities and provide habitat and food resources for a wide range of species. Wetlands have a high level of nutrients and coupled with the availability of water they provide ideal habitat for fish, amphibians, shellfish, and insects. Additionally, many birds and mammals rely on wetlands for food, water, breeding grounds, and shelter.

Wetland Wildlife







Importance of wetlands

Wetlands play an essential part in the regulation of river flow, they filter pollutants and fertilizers, they are spawning zones for some species of fish (pike in particular). They also provide a habitat for plants, insects, batrachians and birds… | The present valleys and river beds were formed in the aftermath of the last glacial periods (erosion, deposits of sand and gravel), followed by a return to the present climate (deposits of fine organic or mineral alluvial silt and ongoing erosion). Different types of features can be distinguished : from the river bed carved out of the rock to alluvial valleys formed from a succession of deposits of gravel, fine sand and peat. | The expanse of groundwater in these deposits when they are well developed can constitute a large reserve which absorbs the variations of water flow. Alluvial deposits act rather like sponges which absorb surplus water before releasing it later. In these alluvial areas part of the water follows the course of the river: this drainage can represent a large volume. This water has been filtered, has a more constant temperature and constitutes a reserve of good quality water.

When the flow of water from the river basin has to cross these alluvial formations before joining rivers significant quantities of nitrates or pesticides contained in the water are eliminated by the action of bacteria trapped in the soil or by the vegetation. These two functions – regulation of flow and retention of diffused pollutants from the river basin –combined with the positive effects on the fauna such as providing a specific habitat for fish (a safe area for spawning for some species and pike in particular spawn in flooded grasslands) and bird life make these areas very important ecological zones. | In traditional landscapes these wetlands have specific features: wet grasslands, rushes, willows, etc. but in some regions the systematic drainage of this water-logged soil has resulted in the disappearance of these buffer zones. Even worse corn culture which leaves the earth laid bare for long periods, and which needs large quantities of fertilizers and pesticides appears to be disastrous for rivers downstream: sudden rises in water level, low water levels, poor water quality. Sand and gravel extraction in large alluvial valleys has also transformed the landscape. The consequences of these industries are often negative : floodwater no longer spreads out...
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