Wetlands of Sri Lanka

By Aravinda DASSANAYAKE

A wetland is generally an area which has soil that is saturated (filled) with moisture, such as a swamp or marsh. You must have read our article on wetlands some time back.

Bundala lagoon

It is noteworthy to mention that Sri Lanka has a geography which supports the formation of wetlands to a great extent. Due to diverse geographical settings, wetlands of different areas display different characteristics.

Until quite recently, the importance of wetlands was not identified in Sri Lanka. Most of the time, they were drained and used as construction space and for garbage dumps.

However, the significance these wetlands have in the eco-system of the environment has now been identified. Therefore, in today’s article let’s look at the different types of wetlands in our country and their different uses.

The wetlands that are found in the country could be divided into three categories as follows;
 
1. Inland natural freshwater wetlands
2. Marine and salt water wetlands
3. Man-made wetlands

Inland natural freshwater wetlands

These are the wetlands that are formed by internal waterways such as rivers, lakes, natural reservoirs and marshes. Within this category, there are a few sub-categories. One type contains all the streams and rivers which in total account for about 4,500 kilometres of waterways.

There is also a category known as ‘Villu’ wetlands. These are quite large lakes which are floodplain lakes that could be seen on river bends. These are prominent in the Mahaweli floodplain in the East of the country.

Freshwater marshes also come under this category; they are shallow depressions (sunken areas) that get fed by river floodwater or groundwater seepage. The Muthurajawela Marsh is a classic example of such a freshwater marsh.

Another type called ‘freshwater swamp forests’, which is in fact a later stage of the freshwater marshes, are also found. In this stage, certain trees adapt to thrive in the shallow stagnant water of the marsh.

The Walauwa-Watta Wathurana Swamp Forest, located in the Kalu Ganga basin, is a good example of this type and it is said that freshwater swamp forests are the rarest type of wetlands in the country.

Marine and salt water wetlands

Simply put, these are wetlands that are found in the coastal areas of the country where a mixture of freshwater and salt water, resulting from tidal fluctuations, exists within the wetland.

Maduganga estuary

Such wetlands could be found in estuaries where rivers flow in to the sea.

There is a special variation of these wetlands called mangroves which contain diverse plant communities like in freshwater swamp forests. Typical examples of estuaries with mangrove wetlands in Sri Lanka are the Maduganga estuary, Bentota estuary and Kalaoya estuary.

Lagoons such as Bundala Lagoon, Mundel Lake and Kalametiya Lagoon also come under this category and these could also contain mangrove formations. Salt wetlands are found in coral reefs which generally reside below six metres in depth.

These are found in the Gulf of Mannar region, Trincomalee to Kalmunai in the east coast and in several areas of the south and south-western coast, including Rumassala and Hikkaduwa. A unique type of salt wetland is found in the Wilpattu National Park, which is an inland wetland containing salt water.

Man-made wetlands

These are wetlands that had been created by humans ever since the beginning of civilization in the country.

The primary man-made wetlands are reservoirs or ‘wewas’ and it is noteworthy to mention that Sri Lanka probably has the highest number of man-made water bodies in the world with an estimated total of more than 10,000 ‘wewas’ countrywide. In addition, the wetlands created for aquaculture and agriculture also fall under this category.

How are they useful?

The interaction between soil, water, plants and animals in the wetlands enable many functions which are useful to people as well as the entire eco-system. In addition, these perform a range of functions which are extremely important.

Where uses are concerned, wetlands become useful in applications related to water supply, medicinal herbs, salt, agriculture and tourism. Important herbs such as ‘Lunuwarana’ and ‘Neeramulliya’ are taken from marshes.

Muthurajawela marsh

In addition, a range of raw materials such as ‘Kaduru’ and Pandanus leaves, which are necessary for traditional crafts, are also extracted from marshes and mangroves. The Hambantota lagoon is the main provider of salt and in addition, areas like the Bundala wetland are popular for tourism and recreation.

Where functions are concerned, marshes play a vital role in the mitigation (reducing) of floods, purification of water and as a carbon sink where carbon dioxide is accumulated.

Tanks also help to mitigate floods. Mangroves, marshes and sea-grass beds become extremely important in the eco-system as breeding habitats for a wide variety of fish. Mangroves and coral reefs provide protection from storms and erosion.

The biodiversity of wetlands, which supports a range of animal and plant species, is very significant.

For example, among the total inland species with backbones in Sri Lanka, about 30 per cent are ecologically dependent on wetlands. Among the migratory birds that visit Sri Lanka annually, more than 50 per cent are directly dependent on wetlands for food and shelter.