Maduganga Estuary

Location: 60 19’ 0 N and 800 1’ 0 E to 60 12’ 0 N and 800 6’ 0 E; 698313 N and 391234 E to 685398 N and 400430 E; 88 km south of Colombo and 35km north of Galle in the Galle District, of the Southern Province.

Area: 915 ha (The total surface area of the 15 islands is 145 ha and the total area of water surface is 770 ha)

Altitude: 0 – 377 m (The water body of Maduganga is less than 1 m above MSL. The highest location of the catchment is 377 m above MSL at a location called Hippan Kanda).

Overview: Maduganga is a relatively unspoilt estuary with a dense growth of mangrove vegetation harbouring high biodiversity. The area was declared a Ramsar site in 2003.

Physical features: Maduganga is located in the southwestern region of Sri Lanka where the southwestern group of crystalline rocks, which is one of the upper Paleozoic rock formations, predominates. Bog and half bog soils dominate this area. A total of 15 islands within the estuary are surrounded by water throughout the year, with Ma Duwa, Mirala Duwa and Dik Duwa forming the large islands. The Maduganga basin is situated in the wet zone of the country which experiences high rainfall during the northwest monsoon (average rainfall is 2,217 mm annually and subject to flooding). The mean monthly temperature is on average 27.20C. Maduganga is generally shallow, with a maximum depth of 2.5 m in most places (the deepest point is 3 m and the shallowest is 1.25 m). Tidal influence is small with a maximum of 10 cm. The temperature of the surface water is within the range of 30.1-33.70C. The pH range in Maduganga is between 6.95 and 8.98. The level of salinity depends on the tides, inflow of freshwater via different streams and whether the lagoon mouth is open or closed. Near the mouth of the estuary, the salinity levels vary between 6.7 – 20.8 ppt and gradually decrease with distance from the mouth. The estuary is connected to the sea by a narrow canal and the mouth of the estuary is often blocked by a naturally formed sand bar. It receives water from three major streams; Boralessa Ela, Heen Ela and Magala Ela.

Ecological features: The estuarine area comprises of 10 different wetland vegetation types including mangroves, mangrove scrub, mangrove mixed swamps, bank scrubs, tall shrub swamps, palm swamps, tall sedge brackish marshes, dwarf sedge brackish marshes, gramineous bogs and lentic macrophytes. These vegetation types have contributed to a rich biodiversity, with 303 plant species belonging to 95 families. Mangroves (Rhizophora-Bruguiera-Sonneratia community) and mangrove mixed swamps (Rhizophora-Dolichandrone- Hibiscus community) are the most abundant (125 ha) vegetation types. The abundance of mangrove species such as Brugueira sexangula, B. gymnorrhiza and Sonneratia caseolaris is higher towards the northern reaches of the estuary, where salinity is lower. Conversely, Xylocarpus granatum and Lumnitzera littorea are abundant in the southern reaches, closer to the mouth of the estuary, where the salinity is higher. This mixed vegetation makes Maduganga an ideal ecotone for a variety of bird species, including aquatic and terrestrial forms. 111 species of birds, of which 10% are winter migrants have been recorded from the area. Due to the lack of shorelines and mudflats, there is a low presence of waders. In total, 248 vertebrate species have been recorded, which include 70 species of fish, 12 amphibians, 31 reptiles, 111 bird species (13 winter migrants) and 24 mammal species. Of the invertebrates, 50 species of butterflies and 25 species of molluscs (14 terrestrial and 11 brackish water) have also been recorded.

Noteworthy fauna: Of the 248 species of vertebrates, 20 species are endemic (2 fish, 3 amphibians, 7 reptiles, 6 birds and 2 mammals) and 30 are nationally threatened (2 fish, 4 amphibians, 11 reptiles, 7 birds, and 6 mammals). About one third (23 species) of the fish species in Maduganga consist of typical brackish water forms such as Ambassis spp., Leiognathus spp., Monodactylus argenteus, Therapon jabua, Periopthalmus koelrenteri and Chanos chanos. The endemic fish include Puntius singhala and Clarias brachysoma. Among the amphibians, Bufo atukoralei, Rana gracilis and Polypedates cruciger are endemic. The Water monitor (Varanus salvator) is the most common aquatic reptile, while the other aquatic reptiles include Crocodylus porosus, C. palustris, Lissemys punctata, Melanochelys trijuga, Achrochordus granulatus and the endemic Xenochrophis asperrimus. The python (Python molurus) is also present on islands covered with dense mangroves. About 35% of the bird species recorded are those associated with wetland ecosystems, such as herons, egrets, cormorants, teals, waders and kingfishers. The area supports a large population of Little green heron (Butorides striatus). Rare mammals in the area include Lutra lutra, Prionailurus viverrinus and Axis porcinus. The most common molluscs in mangrove habitats include Telescopium telescopium, Cerithedia cingulata, and Nerita polita. The most common crustacean species recorded in the Maduganga estuary include the Mud Crab (Scylla serrata), Grapsid Crabs (Chiromantes spp.), the Mud Lobster (Thalassina anomala) and the White Prawn (Penaeus indicus).

Noteworthy flora: According to studies, Maduganga has perhaps one of the last remaining tracts of pristine mangrove forest in both the biogeographic regions to which it belongs (south-western wet coastal zone) as well as in Sri Lanka in general. It harbours a small population of a very rare, threatened mangrove species, Lumnitzera littorea. The most abundant mangrove species is Rhizophora apiculata. It also harbours 19 endemic species, and 8 that are nationally threatened. A rare orchid (Vanilla walkerae) can be found in one of the islands. The islands also harbour non-mangrove endemic woody species such as Mesua ferrea, Dillenia retusa, Chionanthus albidiflorus and Cleistanthus pallidus.

Land use: Fishing (estuarine and sea), agriculture, forestry, and tourism related activities. Small scale coconut retting can be found in a few places around the estuary. Kraal fishery is a traditional fishing practice associated with the estuary. The main agricultural crops around the estuary are paddy, coconut, cinnamon, pepper, fruit trees and vegetables. Cinnamon has also been cultivated in some of the islands. Only few families are engaged in animal husbandry. Coir is a major industry in the area.

Possible changes in land use: Some of the islands have been identified for tourism development activities, which would include the construction of tourism related infrastructure. This could result in the clearance of mangrove and other natural vegetation in such islands.

Hydrological and biophysical values: Maduganga has an important role in flood control. Its hydrology is influenced by the presence of a sandbar at the mouth and the amount of rainfall it receives. When the lagoon mouth is fully closed, heavy rainfall causes flooding and subsequent problems for inhabitants. Due to frequent flooding and high saline conditions, only the paddy fields in the upper reaches are cultivated and 304 ha of land have been abandoned. A number of natural waterways are connected to the estuarine system and their flow through rates have been controlled by the construction of regulators and bunds. The wetland also plays an important role in nutrient retention. Since large amounts of fertilizers are used in cinnamon plantations, run-off causes nutrients to enter the estuary, preventing groundwater pollution.

Social and cultural values: Several old Buddhist temples are found within the Maduganga environs. The most prominent historical monument in the Maduganga area is the temple at Kothduwa Island with its sacred Bo tree. According to the Bodhiwansha, a historical chronicle of ancient Sri Lanka, this Bo tree is one of the 32 buds that sprang from the Sri Maha Bodhi in Anuradhapura, and was planted during the reign of King Pandith Parakramabahu II. According to Lanka Deepa Warnana, another historical chronicle, the Sacred Tooth Relic had been kept here for protection from the Portuguese during the period of King Weediya Bandara. There is also a mosque at Welithara (Jumma Masjid), which is known to be over 400 years old at which an annual religious festival is held.

Scientific research and monitoring: A study is being conducted on the hydrology of the lagoon to prepare a model on water circulation patterns within the Maduganga. In 2000, IUCN undertook a systematic survey to document the status of biodiversity in this wetland.

Conservation education: Under the ADB funded CRMP, several awareness and educational campaigns were conducted. A visitor centre to educate tourists was constructed through the CRMP, which will be managed by the local community.

Recreation and tourism: Maduganga has a high potential for nature-based tourism development, due to its scenic and biodiversity value. In 2002 the CTB declared this area as a tourist development area. At present there are about 10 small-scale hotels operating with boat tours being the main recreation activity. Local as well as foreign tourists frequently visit this site in motorboats, to experience the scenic beauty and biodiversity of this site.

Conservation measures taken: The DWC declared this site and its surroundings (2,300 ha) a sanctuary in July 2006. The area has been recognized as a priority wetland for conservation, with two conservation management plans being developed during the last two decades by the CEA and the Forest Department. In 2003 the area was declared a Ramsar site. A SAM Plan is being prepared under the ADB funded CRMP.

Conservation measures proposed: Recommendations for management have been listed in the SAM Plan produced by the CCD through the CRMP. Additionally, this site is a proposed EPA under the NEA of the CEA.

Disturbance and threats: The clearing of mangroves to establish large areas of cinnamon plantations and the extensive use of fertilizers is threatening the quality of lagoon water. The groynes constructed in the 1970s cause frequent flooding and prevent water exchange with the sea. The irrigation channels and structures do not function properly nor are they maintained. Invasive alien species such as Najas marina and Annona glabra not only replace native species but also hinder navigation within the lagoon. Discharge of sewage and garbage (including sawdust) is on the increase at Maduganga. The high-powered (20-25 horse power diesel engines), motorized boats operating in the lagoon also contribute to the deterioration of habitats. River bank erosion occurs as a result of sand mining, which disrupts the water currents in the lower reaches of Maduganga.

Land tenure: The 15 islands in the Maduganga estuary are privately owned. Most of the surrounding land is also privately owned.

Management authority and jurisdication: There are several agencies, which have management authority of different aspects of the Maduganga. The most important ones are: DWC (wildlife): Forest Department (forests); Irrigation Department (maintenance of irrigation structures); CCD (preparation and the implementation of the SAM plan).

References: Bambaradeniya et al. (2002b); CCD (2006d); CEA/ARCADIS Euroconsult (1997b); IUCN Sri Lanka (2000); www.ramsar.org; Sri Lanka Tourist Board (2002);