Wetlands in Loktak Lake

LOKTAK LAKE Manipur

Location: 24’35’N, 93° 50’E; 20 km southwest of Imphal, Bishnupur district, Manipur
Area: 26,000 ha
Altitude: 770 m
Biogeographical province: 4.9.4
Wetland type: 14

Description of site: A large but shrinking freshwater lake in the upper drainage of Manipur river. It is the remnant of a much bigger lake (223,000 ha) which occupied the Manipur Valley in early geologic times. This has gradually contracted to the present-day Loktak Lake, covering 26,000 ha. The Lake is of neo-tectonic origin and, through the years, has been influenced by fluvio-lacustrial processes. The upper sediments are about 20,000 years old. Loktak remains one of the largest freshwater lakes in India, although in recent decades, much of it has been reclaimed for agriculture. The Lake has no definite shoreline: the expanse of water and its depth varies with the season. Morphometric features are: maximum length: 26 km; maximum breadth: 13 km; maximum depth: 4.58 m; average depth: 2.07 m; catchment area: 98,000 ha; and total volume of water: 598.36 million cubic metres. The lake has 12 islands of which four are inhabited. There are 54 villages along the periphery, including five townships. There are also 600 floating hutments on the lake
The main water body is surrounded on all sides by shallow water stagnating over swampy land. The drainage system of the Manipur river valley comprises two groups of rivers. The first group consisting of Iril, Imphal, Thoubal, Khuga, and Chakpi does not feed the lake directly but does so through the Khurdoak, Khordak, and Ungamlen channels. The second group consists of Nambol, Nambul, and Thongjarol which flow directly into the Lake. The discharging capacity of the Lake is restricted by an eight - metre high rocky barrier called Sugnu hump, which reduces the river velocity and reverses water currents during the monsoon. This backflow feeds water to the Loktak Lake through the Khurdoak, Khordak, and Ungamlen channels. During the lean season, water drains out of the Lake. Thus, Loktak acts as a temporary reservoir. A channel connects Loktak Lake to Keibul Lamjao National Park (site 79) to the southeast. Both lakes are drained by Manipur river along their eastern flanks

Climatic conditions: Tropical monsoon climate, with an average annual rainfall of 1183 mm; temperature ranges from 0° to 35°C. The driest months are February and March

Principal vegetation: Some 212 plant species belonging to 62 families have been identified. The principal vegetation types including submergent, emergent, and floating macrophytes are characterised by the dominance of Eichhornia crassipes, Nymphaea sp., Nelumbo sp.,Trapa natans, Phragmites karka, Zizania latifolia, Polygonum sp., Scirpus sp., Saccharum spontaneum, Setaria pallidefusca, Hydrilla verticillata, Ceratophyllum demersum, Utricularia stellaris, and Marsilea quadrifolia, Eichhornia crassipes and species of Polygonum, Vallisneria, and Trapa dominate. The dominant phytoplankton are Dinobryon, Tachelomonas, Euglena, Ceratium and. Cyclotella

Land tenure: The area under Keibul Lamjao National Park (4050 ha) is under the control of the State Forest Department. Another 500 ha of the main lake is under the State Fishery Department. The remaining areas are either private farmlands or open fishery areas Conservation measures taken: The Lake has been accorded international importance by its designation as a Ramsay Site in 1990. It has also been selected for special conservation and management by the Ministry of Environment and Forests, Government of India. A Loktak Development Authority was constituted in 1987 to plan and monitor the management and development of the Lake. Weed removal is being undertaken, for which substantial funds have been sanctioned

Conservation measures proposed: Manipur Univeristy, the nodal university identified by the government to provide research inputs on the Lake, has suggested the establishment of a permanent research and monitoring station for carrying out scientific investigations, management planning, monitoring, and evaluation of the Lake, ecosystem

Land use: Used extensively by the people of Manipur Valley as a source of water for irrigation and domestic use, fishing, hunting, livestock grazing, and gathering of aquatic vegetation. The surrounding areas are under intensive cultivation Possible changes in land use and proposed development projects: The fragile ecosystem of the Lake is seriously threatened by the damming of the Lake for the construction of the Loktak hydroelectric project. The construction of the Ithai barrage on Khordak, cut in 1979, has impeded the passage of migratory fishes, obstructed the flushing out of sediments and weeds, besides causing hydrological changes. Expansion of tourism facilities and transport network are likely to increase pressure on the Lake

Disturbances and threats: Some 4000 ha of the Lake margins have already been reclaimed for rice cultivation, and the conversion process continues. The Lake is also being increasingly threatened by the inflow of domestic sewage, fertilisers and pesticides from the catchment, which is causing eutrophication. Increased growth of ‘phumdi’ (floating soil-vegetation mats, characteristic of the Lake) and water hyacinth are accompanying problems. Fishermen build thatched huts as temporary dwellings. The expansion of phumdi has encouraged the proliferation of huts, currently totalling about 1000. Over-fishing is another problem, and hunting pressure onwaterfowl is heavy, with migratory ducks being shot in large numbers for sale in the markets of Imphal city. The catchment of Loktak Lake suffers from severe deforestation and concomitant soil erosion, resulting in increased siltation. Shifting cultivation on the surrounding hill slopes, involving the cutting and burning of forest for only three or four seasons at a stretch, further aggravates this problem.
A road is being constructed on the eastern and western peripheries of the Lake. It is predicted that in the coming years, human settlements, shops, and other establishments will develop along the road, adding to the pollution of the Lake. Many bunds are being built, projecting into the Lake. These are under pisciculture, but are likely to be converted into paddy fields in future causing the Lake to shrink further. A road has been constructed through the Lake linking Imphal with the island of Sendra (located in the centre of the Lake) where a tourist resort has been developed

Economic and social values: Loktak Lake is a significant tourist attraction, although it is a restricted area for foreigners. Considered the lifeline of Manipur valley, the Lake provides livelihood to more than 100,000 people. Its waters provide irrigation to 40,000 ha of agricultural land. Sixty per cent of the capture fishery production of Manipur State comes from Loktak. Aquatic plants are harvested for their food and commercial values. The hydroelectric power project supplies 105 mega watts of power Fauna: A great diversity of invertebrate and vertebrate fauna are associated with Loktak. About 364 species have been identified, including 83 species of fish; 5 species of amphibians; 31 species of reptiles; 106 species of birds, and 32 species of mammals. In the past, the Lake was known to have been an extremely important wintering area for migratory waterfowl, particularly ducks, but no recent information is available. Some of the species commonly seen here are: pintail, common teal, mallard, gadwall, wigeon, garganey, shoveler, barheaded goose, pochard, ferruginous duck, red crested pochard, brahminy duck, and white pelican. Among the mammals, the highly endangered sangai or brow-antlered deer (Cervus eldi eldi) is the most important. Other mammals include hog deer (Axis porcinus), common otter (Lutra lutra), large Indian civet (Viverra zibetha), small Indian civet (Viverricula indica), and Indian wild boar (Sus scrofa). Among the reptiles, Python molurus is noteworthy. The ichthyofauna is dominated by air-breathing fishes such as Channa striatus, C. punctatus, Anabas testudineus, and Clarias batrachus. The Lake is also a breeding ground for several migratory fishes such as Osteobrama belangeri, Labeo deco, L. bats, Wallago attu, Puntius sarana, Puntius ticto, and Cyprinus carpio. The zooplankton include Diaptomus, Dfflugia, Keratella, Brachionus, and Nauplii larvae Special floral values: This regions supports rare endemic plants such as Zizania latifolia, locally called “fishing kambong”, and Iris bakeri locally called “kombirei”. A distinctive feature of the Lake is the floating mats of vegetation known as phumdi, formed by the accumulation of run-off soil particles and vegetable matter which get bound by the roots of various aquatic plant and grass species. Bhatia (1979) listed 65 macrophytic species composing phumdi