Wetland Ecosystem

Wetlands are ecotones or transition zones between terrestrial and aquatic ecosystems. These areas have distinct environmental features, including hydric soils (with low oxygen levels), periodic flooding from nearby deepwater habitats, and hydrophytes—plants adapted to waterlogged soils.

Wetland Definition (Ramsar Convention and Indian Rules)

Under the Ramsar Convention and Wetlands (Conservation and Management) Rules, 2017, a wetland is defined as:

• An area of marsh, fen, peatland, or water—natural or artificial, permanent or temporary.
• Water may be static or flowing, fresh, brackish, or salty.
• Includes marine areas with water depths not exceeding six meters at low tide.

Difference Between Oligotrophic and Eutrophic 

Estuarine

Definition and Formation

• An estuary is a partially enclosed coastal area with brackish water (salinity of 0-35 ppt) formed where freshwater from rivers or streams meets the ocean. Examples of estuaries include river mouths, coastal bays, tidal marshes, lagoons, and deltas.
• Estuaries are shaped by rising sea levels, movement of sand and sandbars, glacial processes, and tectonic activity, and they experience tidal influences that bring periodic seawater flooding. In narrow estuaries, tidal bores can significantly impact the ecosystem, sometimes causing ecological damage.

Importance of Estuaries

1. Ecological Importance
   • Ecotone Zone: Estuaries serve as transition zones between river and marine environments, creating highly productive ecosystems where freshwater meets saline water.
   • Biodiversity Refuge: Minimal wave action provides a calm environment, supporting diverse aquatic species. Mangrove forests on estuary coasts help reduce wind damage during storms.
   • Sediment Accumulation: Saline water encourages the precipitation of fine alluvium, aiding in delta formation. Mangroves trap suspended mud and sand, filtering the water.
   • Natural Filtration: Estuaries store and recycle nutrients, trap sediments, and detoxify pollutants, acting as natural water filters for surrounding ecosystems.
2. Economic Importance
   • Human Settlement: Approximately 60% of the world’s population resides along estuaries and coasts due to rich resources and accessibility.
   • Ports and Harbors: Estuaries, with their protected waters, are ideal for constructing ports and harbors, making them economically significant areas.
   • Rich Resources: Estuarine ecosystems support various natural resources, such as fisheries and seagrass beds, which contribute to local economies.

Estuarine Vegetation and Biodiversity

• Adaptive Species: The brackish water and fluctuating salinity in estuaries support plants and animals that can osmoregulate. Salinity and tidal range influence the distribution and diversity of organisms.
• Dynamic Ecosystem: Due to variable river flow, tides, and sediment distribution, estuaries are dynamic and support diverse habitats such as mangroves, salt marshes, seagrass, and mudflats.
• Species Diversity:
  • Terrestrial: Includes wood storks, pelicans, coniferous and deciduous trees, and butterflies.
  • Aquatic: Estuaries house unique species like sea turtles, sea lions, salt grasses, and bulrushes.
  • Phytoplankton and Vegetation: dominant phytoplankton include diatoms, dinoflagellates, green algae, and blue-green algae, with seagrasses near the coast and mangrove forests at river mouths and deltas.

Indian Estuarine Ecosystem

• India has 14 major, 44 medium, and 162 minor rivers that drain into the sea through estuaries, with the most large estuaries on the east coast.
• Estuaries on the west coast tend to be smaller. Major estuaries often house important seaports, such as Mormugao Port on the Zuari Estuary.

Threats to the Indian Estuarine Ecosystem

• Water Flow Modifications: Alterations in river catchments impact estuarine water flow (e.g., Hooghly, Godavari, Pulicat).
• Pollution: Discharge from industries and urban sewage contributes significantly to estuarine pollution.
• Navigation and Dredging: Heavy dredging for navigation and shipping, especially in areas like Hooghly, disrupts estuarine habitats.
• Urbanization and Industrialization: Expansion of settlements, agriculture, and solid waste dumping in catchment areas cause habitat degradation.
• Intensive Aquaculture: Fish and prawn farming obstruct migratory paths of species in areas like Chilka and Pulicat.
• Environmental Pollution in Pens: Feeding practices in aquaculture contribute to pollution (e.g., Chilka).
• Destruction of Biodiversity: Practices like prawn seed collection using fine mesh nets harm biodiversity in regions such as Hooghly, Chilka, and Pulicat.
• Rising Water Levels: Submergence of catchment areas due to increasing water levels poses a long-term threat.

Difference between Lagoons and Esturies 

Mangroves

• Mangroves are salt-tolerant evergreen shrubs or small trees, typically ranging from 8 to 20 meters in height. They form a distinctive littoral forest ecosystem, thriving in coastal regions below the high-water level of spring tides.
•  The most favorable locations for mangrove growth are areas where abundant silt is deposited by rivers or on the backshore of accreting sandy beaches. 
• They are commonly found in brackish waters along sheltered low-lying coasts, estuaries, mudflats, tidal creeks, backwaters, marshes, and lagoons in tropical and subtropical regions.

Adaptive Mechanisms of Mangroves

Mangroves have evolved a range of morphological and physiological adaptations to survive in challenging environments characterized by high salinity, tidal inundation, and low oxygen availability.

Mangroves In India 

As per the India State of Forest Report, 2021, the mangrove cover in the country has been estimated at 4992 sq km with net increment of 17 sq.km in the year 2021 as compared to 2019.

Mangroves in India are vital coastal ecosystems that provide crucial habitat for diverse flora and fauna, including unique species like the Royal Bengal tiger and saltwater crocodiles. They are predominantly found in regions such as the Sundarbans and Bhitarkanika, where they play essential roles in protecting shorelines from erosion, supporting fisheries, and maintaining water quality.

Sundarbans Mangrove Forests

About

• The Sundarbans is the largest mangrove forest in the world, spanning the delta region of the Padma, Meghna, and Brahmaputra river basins in the Bay of Bengal. 
• Located primarily in West Bengal, India, and Bangladesh, this UNESCO World Heritage Site covers approximately 10,000 square kilometers, with around 4,262 square kilometers situated in India.

Biodiversity

• The Sundarbans is renowned for its rich biodiversity, hosting a unique assemblage of flora and fauna. Key species include the Royal Bengal tiger, saltwater crocodiles, and various species of crabs and migratory birds
• . The mangrove ecosystem is characterized by dominant species such as Sundari (Heritiera fomes), Goran (Ceriops tagal), and Khalsi (Aegiceras corniculatum), contributing to its ecological complexity and resilience.

Ecosystem Importance

• The Sundarbans plays a crucial role in coastal protection, serving as a natural buffer against storm surges and cyclones. It supports local communities through fishing, honey collection, and ecotourism, providing essential livelihoods. 
• Additionally, the forest contributes to carbon sequestration and helps maintain water quality, making it vital for environmental health and sustainability.

Bhitarkanika Mangrove Forests

About

• Bhitarkanika Mangroves are located in the Kendrapara district of Odisha, India, at the confluence of the Brahmani and Baitarani rivers near the Bay of Bengal.
•  Covering an area of approximately 672 square kilometers, it is the second-largest mangrove forest in India and is recognized as a National Park and a Ramsar Wetland.

Biodiversity

• Bhitarkanika is known for its rich biodiversity, home to several rare and endangered species. It supports populations of saltwater crocodiles, various fish species, and migratory birds. 
• Dominant mangrove species in this forest include Rhizophora, Avicennia, and 
• Bruguiera, which are integral to its ecological structure.

Ecosystem Importance

• The Bhitarkanika Mangroves serve as critical breeding grounds for many fish species, supporting local fisheries and agriculture. They play a vital role in carbon sequestration and coastal protection, helping mitigate the impacts of climate change. 
• Additionally, the forest provides livelihoods for local communities through fishing and sustainable harvesting, underscoring its significance for both ecological and human well-being.

Global Status of Mangrove Cover

Why Mangroves Are Not Found Beyond the Subtropics

Mangroves primarily thrive in the tropics and subtropics, specifically within the latitudinal range of 24° N to 38° S.

Reasons are - 

• Salt Filtration System:
  They possess a complex salt filtration system that allows them to manage high salinity levels in their environment, essential for survival in brackish water conditions.
• Energy Requirements:
  The adaptive mechanisms of mangroves, such as salt filtration and water retention, are energy-intensive. They require substantial amounts of solar radiation, which is less available in regions beyond the subtropics.
• Climate Limitations:
  The cooler temperatures and reduced sunlight in higher latitudes limit the growth and reproduction of mangrove species, which prefer warm, tropical climates.

Importance of Mangroves

Threats to Mangroves

1. Aquaculture, Agriculture, and Salt Ponds

Threats:

• Mangroves are nutrient-rich, making them attractive for agriculture.
• Significant portions of mangrove forests have been cleared for shrimp farming, mariculture, and crop cultivation, as well as for the creation of salt ponds.

Consequences:

• Chemical Contamination: Shrimp and other species in artificial ponds are often fed diets containing chemicals that can enter the food chain.
• Eutrophication: The excess nutrients from concentrated feed lead to eutrophication, harming surrounding marine habitats by lowering oxygen levels.

2. Coastal Development and Lumbering

Threats:

• Direct harvesting of mangrove wood and leaf products contributes to deforestation.
• Wetland habitats are converted for coastal development projects, such as hotels, resorts, infrastructure, desalination plants, and port facilities.
• Mangrove wood is valued for construction, fencing, fuel, and high-quality charcoal production, leading to habitat loss.

Consequences:

• Habitat Loss and Climate Vulnerability: Interruptions in tidal regimes result in lost balance between freshwater and saltwater, leading to altered hydrology, erosion, and increased pollution.
• Impact on Rivers: Changes in flooding, drainage, filtration, sedimentation, temperature, and salinity affect aquatic species, including subsistence fish species vital for coastal communities.
• Loss of Species and Genetic Diversity: The loss of mangrove trees and associated species (e.g., birds, snakes, crabs) diminishes genetic diversity and the specific adaptations evolved to cope with local environmental conditions.

Measures to protect the Mangroves 

Importance of Wetland

Reasons for Wetland depletions 

Measures to protect the Wetland 

Ramsar Convention on Wetlands

The Ramsar Convention on Wetlands is an international treaty dedicated to the conservation and sustainable use of wetlands. It was signed on February 2, 1971, in Ramsar, Iran, and is recognized annually as World Wetlands Day. As of now, there are 172 parties to the convention, with India becoming a party in 1982.

Core Philosophy
The central tenet of the Ramsar Convention is the principle of “wise use”, which emphasizes the maintenance of the ecological character of wetlands to support sustainable development. This approach encourages the balance between human needs and the ecological integrity of wetland ecosystems.

India's Commitment
India has made significant strides in wetland conservation through various national policies and programs, including the National Wetland Conservation Programme. The country has designated several wetlands as Ramsar sites to enhance their protection and management.