Pariksha SaathiLesson 5 of 10 · Environment and Ecology
Wetlands, Mangroves and Coral Reefs of India
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What wetlands are
Wetlands are areas where water covers the soil or lies near the surface for at least part of the year: marshes, swamps, lakes, floodplains, peatlands, lagoons, estuaries, mangroves and even paddy fields. The Ramsar Convention's definition also includes marine water up to a depth of 6 metres at low tide. Wetlands are called the kidneys of the landscape because they filter sediments and pollutants. They also recharge groundwater, soak up floods, store carbon, support fisheries and give wintering grounds to migratory birds that reach India along the Central Asian Flyway.
The Ramsar Convention
The Convention on Wetlands of International Importance was signed on 2 February 1971 at Ramsar, a town on Iran's Caspian Sea coast, and came into force in 1975; 2 February is World Wetlands Day. It is the only global treaty devoted to a single ecosystem. India became a party in 1982, and its first two Ramsar sites, Chilika Lake in Odisha and Keoladeo National Park in Rajasthan, were designated in 1981. The Montreux Record, set up in 1990, lists Ramsar sites where harmful ecological change has occurred or is likely. Chilika was put on it in 1993 and removed in 2002, after a new mouth to the sea restored its salinity and fish catch; Keoladeo and Loktak have also been placed on the record.
Important lakes and wetlands
Chilika in Odisha is Asia's largest brackish-water lagoon, home to Irrawaddy dolphins and to the Nalabana bird sanctuary. Pulicat, on the Andhra Pradesh-Tamil Nadu border, is India's second-largest brackish lagoon and is separated from the sea by Sriharikota island. Loktak in Manipur, the largest freshwater lake of north-east India, has floating mats of vegetation called phumdis. Wular in Jammu and Kashmir, fed by the Jhelum, is one of Asia's largest freshwater lakes; Sambhar in Rajasthan is India's largest inland salt lake; Vembanad in Kerala is India's longest lake; Kolleru in Andhra Pradesh lies between the Godavari and Krishna deltas; and Harike in Punjab forms where the Beas meets the Sutlej. The East Kolkata Wetlands treat the city's sewage naturally through fish ponds, and Lonar in Maharashtra fills a crater made by a meteorite impact.
Mangroves
Mangroves are salt-tolerant trees and shrubs of the intertidal zone of tropical coasts, estuaries and deltas. They cope with salty, waterlogged, oxygen-poor mud through special adaptations: breathing roots (pneumatophores) that grow upward out of the mud, stilt or prop roots for support, and vivipary, in which seeds germinate while still on the parent tree. Mangroves act as a natural wall against cyclones, storm surges and tsunamis, as was seen in the 2004 Indian Ocean tsunami; they hold the soil against erosion, serve as nurseries for fish, prawns and crabs, and store large amounts of blue carbon. India's east coast has more mangroves than the west coast because its large river deltas have gentle slopes and broad mudflats.
Mangrove regions of India
The Sundarbans, in the delta of the Ganga, Brahmaputra and Meghna shared by India and Bangladesh, is the largest mangrove forest in the world. It is named after the sundari tree, is home to the Royal Bengal tiger, and its Indian national park became a World Heritage Site in 1987. Bhitarkanika in Odisha, in the Brahmani-Baitarani delta, is India's second-largest mangrove ecosystem and is famous for saltwater crocodiles; the nearby Gahirmatha coast sees mass nesting (arribada) of olive ridley turtles. Other mangrove areas are Coringa in the Godavari delta of Andhra Pradesh, Pichavaram near Chidambaram in Tamil Nadu, the Gulf of Kutch in Gujarat and the creeks of the Andaman and Nicobar Islands.
Coral reefs
Corals are tiny marine animals called polyps, relatives of the jellyfish, that build skeletons of calcium carbonate. Reef-building corals live in partnership with algae called zooxanthellae, which live inside their tissues, give them colour and supply food by photosynthesis. They need warm, clear, shallow and salty water, and reefs are called the rainforests of the sea because of their rich life. Fringing reefs grow close to the shore, barrier reefs are separated from it by a lagoon, and atolls are rings of reef around a central lagoon, explained by Charles Darwin's subsidence theory. When the sea becomes too warm, corals expel their algae and turn white; this coral bleaching can kill whole reefs. Australia's Great Barrier Reef is the world's largest reef system.
Coral reefs of India
India has four main reef areas. The Gulf of Mannar, between Tamil Nadu and Sri Lanka, has fringing reefs around a chain of small islands and is both a marine national park and a biosphere reserve. The Gulf of Kutch in Gujarat has India's northernmost reefs, which survive wide changes in temperature and salinity. Lakshadweep is made up of coral atolls, and the Andaman and Nicobar Islands have rich fringing reefs with the greatest variety of corals. Smaller patches occur on the west coast, such as at Malvan in Maharashtra. Corals are protected under the Wildlife (Protection) Act, and coasts, mangroves and reefs are guarded by the Coastal Regulation Zone notification, first issued in 1991 under the Environment (Protection) Act 1986.
Key facts
- Ramsar Convention: signed 2 February 1971 at Ramsar, Iran (Caspian Sea coast); in force 1975; 2 February is World Wetlands Day; India joined in 1982.
- India's first Ramsar sites (1981): Chilika Lake (Odisha) and Keoladeo National Park (Rajasthan).
- Montreux Record (1990): list of Ramsar sites under threat; Chilika was added in 1993 and removed in 2002 after restoration.
- Chilika: Asia's largest brackish-water lagoon, with Irrawaddy dolphins; Pulicat: India's second-largest brackish lagoon, separated from the sea by Sriharikota.
- Lake facts: Loktak (Manipur) has phumdis; Sambhar (Rajasthan) is the largest inland salt lake; Vembanad (Kerala) is the longest lake; Harike is at the Beas-Sutlej meeting point.
- Mangrove adaptations: pneumatophores (breathing roots), stilt roots and vivipary (seeds germinate on the parent tree).
- Sundarbans: world's largest mangrove forest, named after the sundari tree, Royal Bengal tiger, World Heritage Site 1987; Bhitarkanika (Odisha) is India's second-largest mangrove area.
- Coral bleaching: warm water makes corals expel their zooxanthellae algae and turn white.
- India's four reef areas: Gulf of Mannar and Gulf of Kutch (fringing reefs), Lakshadweep (atolls), Andaman and Nicobar Islands (richest fringing reefs).
Quick revision
Ramsar Convention 2 February 1971, Iran, in force 1975; India party 1982; first Indian sites Chilika and Keoladeo 1981; Montreux Record 1990, Chilika removed 2002; Chilika largest brackish lagoon in Asia; Sambhar largest inland salt lake; Loktak phumdis; mangroves: pneumatophores, vivipary; Sundarbans largest mangrove forest, WHS 1987; Bhitarkanika second; corals with zooxanthellae; reefs: Gulf of Mannar, Gulf of Kutch, Lakshadweep atolls, Andaman and Nicobar; CRZ 1991.