in Sri Lanka - Ministry of Environment

Present Status of Fresh Water Aquatic Flora in Sri LankaDeepthi YakandawalaDepartment of Botany, University of PerdeniyaIntroductionSri Lanka is an island surrounded by the Indian Ocean. However, only four percent of thecountry’s land area is covered by water (FAO, 2011). Those land areas that are permanentlyor seasonally inundated together with its floral and faunal communities are considered asan aquatic ecosystem. The fresh aquatic ecosystems of the country include rivers, streams,marshes, swamp forests and villus. Apart from these natural habitats, man-made tanks,reservoirs, and rice fields also contribute to the diversity. Based on the definition of the RAMSARconvention (1987), all these ecosystems are broadly defined as wetlands.Sri Lanka has an extensive network of rivers and streams, most of which arise from the southcentralmassif that rises to 2500 m above sea level. In all, there are 103 distinct natural riversmany of which are perennial, while those in the dry zone are seasonal. The Mahaweli riverbasin which drains 16% of the island (Madduma Bandara, 2000), carries water from the wetzone to the dry zone, supporting many marshes, riverine vegetation, and flood plains. A freshwater marsh is a shallow depression receiving water from a river either directly or by surfacerun-off of river floods and ground water seepage. The Muthurajawela marsh is the longestpeat bog in Sri Lanka and, together with the Negombo estuary, forms an integrated coastalwetland ecosystem extending over 6,232 ha (CEA/Euroconsult, 1994a). Several fresh watermarshes are found within the Wilpattu National Park in the lowland dry zone. Horton Plainsrepresent montane grassland marshes at an altitude of 2000 m. The late succession stage ofa fresh water marsh is referred as a fresh water swamp forest. Fresh water swamps compriseof trees that are adapted to grow in shallow stagnant water and are inundated seasonally withriver water. Fresh water swamps are considered the rarest wetland type in Sri Lanka andthe Walauwatta-Wathurana swamp forest, located in the Kalu Ganga river basin, is a typicalexample that extends 12 ha in the southwestern part of the island (CEA/Euroconsult, 1994b).Even though there are no large natural lakes in the island, a number of flood plain lakes thatare commonly referred to as villu, occur in the dry zone. These extend over a total area of12,500 ha, the largest being the inter-connected Handapan and Pendiya villu system of theMahaweli villu system (CEA/Euroconsult, 1995).Owing to its unique hydraulic civilization, Sri Lanka is endowed with a rich array of manmadelakes and canals accounting over 10,000 countrywide, covering more than 127,070ha (Jayasinghe, 2000), especially in the dry zone. They range from small and medium sizedtanks such as Thithawella tank (Kurunegala) to larger tanks/reservoirs such as the ParakramaSamudraya. Associated with these are paddy fields characterized by the presence of seasonalstanding waters contributing to agronomically managed marshes that extend over 12%(708,000 ha) of total land area. Paddy is cultivated in all the agro-ecological zones except atvery high elevations. Victoria, Randenigala, Rantambe and Kotmale are recent reservoirs thatwere added into the list. Man-made wetlands are broadly categorized into three groups, whichare further divided in to nine different wetland types: Aqua-cultural (fish and shrimp ponds),Agricultural (farm/small tanks, irrigated land, and seasonal flooded fields) and Industrial/urban186