Types of Wetlands in India

ISRO had prepared a national wetlands atlas on the basis of satellite image. It mapped 2,31,195 wetlands in India during 2017-18. They comprise around 4.86% of the total geographic area of India. India has also designated 75 wetlands as Wetlands of International Importance under Ramsar Convention. As of 2023, the number of Ramsar sites globally is around 2,466. Also, number of inland wetlands in India is more than number of coastal wetlands. The number of manmade wetlands in India is more than the natural wetlands.

There are several ways to classify the wetlands as follows:

Tidal and Non-tidal wetlands

Tidal wetlands have a saltwater influence from sea tides while non-tidal ones depend mainly on inland freshwater sources.

Tidal Wetlands

Tidal wetlands are areas that experience periodic inundation by tides. The inlet and outlet channels are influenced by the ocean’s tides and allow saltwater to enter and mix with freshwater. They include:

• Mangroves: Found mainly in the Sundarbans delta region shared by India and Bangladesh and the Andaman Islands. The dominant mangroves here are Sundari, Gewa, and Goran trees.
• Mudflats: Seen along India’s western and eastern coastal regions. Some major mudflats are found in the Gulf of Kutch in Gujarat and the deltas of the Ganga, Mahanadi and Godavri rivers along the eastern coast. They are made of fine silt and clay.
• Salt Marshes: Coastal wetland areas with salt tolerant grasses, herbs and low shrubs. Some salt marshes exist around Mumbai and in the Sundarbans delta.

Non-Tidal Wetlands

Non-tidal wetlands have inland water sources and no major connection with sea tides. They are mostly fed by rivers, streams, surface runoff or groundwater. Examples include:

• Lakes: Dal Lake in Kashmir, Loktak Lake in Manipur
• Oxbow lakes: Formed in the Ganga and Brahmaputra river plains through changing river courses. Eg: Deepor Beel in Assam
• River floodplains: Wet grasslands and lands along rivers like Yamuna and Ganga that get seasonally flooded.
• Swamps/Marshes: Freshwater wetlands with mineral-rich water and decaying plant matter. Eg: East Kolkata Wetlands

Wetlands by Water Type

Wetlands contain areas flooded or soaked with water for all or part of the year. They are commonly categorized by the type of water present:

Freshwater Wetlands

These contain primarily freshwater with low salt concentrations, usually less than 0.5 parts per thousand (ppt). Sources are precipitation, groundwater, rivers, and lakes. Vegetation includes cattails, bulrushes, grasses, trees like willows, and more.

Examples:

• Loktak Lake (Manipur) – Largest freshwater lake in Northeast India
• Wular Lake (Jammu & Kashmir) – One of the largest freshwater lakes in India
• Bhoj Wetlands (Madhya Pradesh) – Man-made freshwater wetland dating back to the 11th century

Brackish Water Wetlands

Brackish wetlands have slightly salty water, ranging between 0.5 to 30 ppt. They include coastal areas where seawater mixes with freshwater brought by rivers. Mangrove swamps are a common brackish wetland. Vegetation varies from freshwater species to salt-tolerant species.

Examples:

• Chilika Lake (Odisha) – Largest brackish water coastal lagoon
• Pulicat Lake (Tamil Nadu) – Second largest brackish water body after Chilika lake
• Mangrove forests of Sundarbans (West Bengal) – Mix of freshwater and seawater create brackish conditions suitable for mangroves

Saline Wetlands

Saline or saltwater wetlands have high salinity levels, over 30 ppt. Seawater has an average of 35 ppt. Salt marshes and salt flats fall into this group. Salt-tolerant grasses, sedges and rushes grow in salt marshes.

Examples:

• Rann of Kutch (Gujarat) – Large salt marsh in the Thar desert
• Nawa Tal and Nal Tal lakes (Uttarakhand) – Saline and alkaline lake system
• Salt pans of coastal Gujarat – Saline waters diverted into shallow ponds for salt production

Alkaline Wetlands

Alkaline or “soda” wetlands contain water high in carbonates and are above neutral pH. The water has sodium (Na), carbonate (CO3) and bicarbonate (HCO3) ions. Vegetation includes salt-tolerant grasses and chenopod shrubs.

Examples:

• Sambhar Salt Lake (Rajasthan) – India’s largest inland salt lake, also highly alkaline
• Bakhar Lake (Jammu & Kashmir) – Alkaline wetland with salt efflorescence deposits
• Lonar Lake (Maharashtra) – Saline and alkaline lake created by a meteorite strike

Inland and Coastal wetlands

Inland Wetlands

Inland wetlands are found inland, away from the coastline. They include:

• Lakes: Formed in natural depressions in the landscape or by river meanders getting cut off. Freshwater lakes like Dal Lake in Kashmir and Wular Lake in Jammu & Kashmir.
• Rivers/River Floodplains: Lands alongside rivers flooded by monsoon waters. For example, the Ganga River floodplains.
• Marshes & Swamps: Contain mineral-rich waters and decaying vegetation. Example – East Kolkata Wetlands.
• Reservoirs: Human-made wetlands formed by damming rivers, like the Hirakud Reservoir in Odisha.
• Oxbow Lakes: Formed when a river meander gets cut off from the main river. Eg. Deepor Beel in Assam.

The vegetation depends on water composition but commonly includes reeds, grasses, herbs, shrubs and aquatic plants.

Coastal Wetlands

Coastal wetlands form at the interface of land and sea. Types found in India:

• Mangroves: Salt-tolerant trees with aerial roots that cope with coastal flooding. Eg. Sundarbans Delta.
• Lagoons: Shallow bodies separated from the sea by sandbanks, coral or shingle. Eg. Chilika lake, Pulicat lake.
• Estuaries: Partially-enclosed zones where freshwater meets the sea. Eg Godavari and Krishna estuaries.
• Mudflats/Salt Flats: Found in sheltered bays and estuaries containing soft mud and salty water. Eg. Gulf of Kutch.
• Coral Reefs: Diverse underwater ecosystems formed by coral skeletons. Eg. Coral reefs of the Lakshadweep islands.

The vegetation includes mangroves, sea grasses, salt marshes, and more which can tolerate saline waters.