Aquatic ecology and Biodiversity

Unit 9- Freshwater environment

9.4. Wetland ecosystems
The wetlands encompass diverse and heterogeneous assemblage of habitats ranging from lakes, estuaries, river flood plains, mangroves, coral reef and other related ecosystems. Wetlands are shallow water bodies in which water keeps up for most part of the year and recedes below the surface level during the dry season. The biotic community undergoes changes from aquatic/marshy to mesophytic types in space and time. These are complex hydrological and biogeochemical systems and have been recognized as distinctly separate ecosystems between the terrestrial and aquatic ones.

The Ramsar Convention defines wetlands as are area of marsh, fen, peat land 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. This definition talks about the maximum water depth in case of marine areas, for these to qualify as wetlands. However, it does not indicate the same for other aquatic bodies. Therefore, it becomes difficult to classify other aquatic bodies into wetland group.
Every year February two is observed World Wetlands Day. It marks the date of the signing of the Convention on Wetlands on 2 February 1971, in the Iranian city of Ramsar on the shores of the Caspian Sea. Therefore, this Convention came to be known as the Ramsar Convention (1971). Making an encouraging beginning in the year 1997, each year on 2 February, government agencies, non-governmental organizations, groups of citizens at all levels of the community commemorate this day by undertaking actions aimed at raising public awareness of wetland values and benefits.
This definition emphasizes three key attributes of wetlands:

• Hydrology which is a degree of flooding of soil saturation,
• Wetland vegetation (hydrophytes)
• Hydric soils.

There are three main types of wetlands viz., bogs, marshes, and swamps. Bogs form in depressions left by ancient ice sheets. Sphagnum moss grows well in the acidic water of bogs.

Bogs

Marshes are shallow flooded areas along rivers. Cattails and other tall grasses live in marshes.

Marshes

Swamps are actually slowly flowing shallow rivers which look like flooded forests. Although not all wetland areas are covered by water year round, they still have enough moisture content and the correct soils to support their specific aquatic plants and animals.

Swamps

Another important wetland area is the estuary. Estuaries are formed where rivers meet the sea. They contain a mixture of fresh and salt water. Estuaries are important nursery areas for many types of fish and shellfish. Waterfowl also depend heavily on estuaries for nesting, feeding and resting place during migration.