Wetlands in Urban Ecosystems: Concepts and Ecological Importance

Cities are usually defined by what is built – roads, buildings, drains, flyovers. But every healthy city also depends on something far less visible: the soggy, in-between landscapes called wetlands. These are the lakes, marshes, mangroves, paddy fields and floodplains that quietly clean water, absorb floods and keep urban temperatures in check. As cities expand and concrete swallows open land, understanding what wetlands actually are – and what we lose when they disappear – has become a basic question in urban development.

What exactly is a wetland? 🔗

The most widely accepted definition comes from the Ramsar Convention on Wetlands, an intergovernmental treaty signed in the Iranian town of Ramsar in 1971. The treaty deliberately keeps its definition broad. Wetlands are described as areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or saline, including areas of marine water whose depth at low tide does not exceed six metres.

This wide framing is intentional. It allows the treaty to cover an enormous range of habitats – from a Himalayan glacial lake to a coastal mangrove forest, from a village pond to a sewage-fed fishery on the edge of Kolkata. The six-metre marine limit was reportedly chosen because it represents the maximum depth to which sea ducks usually dive to feed, an interesting reminder that wetlands were first protected with migratory birds in mind.

Types of wetlands 🔗

To make this broad category usable, the Ramsar Convention adopted a classification system with 42 wetland types grouped into three categories: marine and coastal wetlands, inland wetlands, and human-made wetlands. Ecologists, however, often use a simpler five-part grouping that is easier to remember.

Marine wetlands are shallow coastal areas, including coral reefs, rocky shores and seagrass beds. Estuarine wetlands form where rivers meet the sea and include deltas, tidal marshes, mangrove swamps and lagoons – the Sundarbans is a classic estuarine wetland. Lacustrine wetlands are associated with lakes, while riverine wetlands run along rivers and streams. Palustrine wetlands, from the Latin word for marshy, include freshwater marshes, swamps and bogs that are not directly connected to a river or a lake.

Beyond these natural categories, the Convention also recognises human-made wetlands such as reservoirs, irrigation tanks, fish and shrimp ponds, salt pans, sewage treatment lagoons and farm ponds. In a country like ours, with thousands of village tanks and temple ponds, this is far from a minor category – many of our most ecologically active wetlands are partly or entirely engineered.

Lagoons, estuaries and ephemeral wetlands 🔗

Three subtypes deserve a closer look because they appear repeatedly in urban planning debates. Lagoons are shallow water bodies separated from the sea by a narrow strip of land – Chilika in Odisha and Pulicat between Andhra Pradesh and Tamil Nadu are among the largest brackish lagoons in Asia. Estuaries are transition zones where freshwater rivers mix with seawater, producing nutrient-rich habitats that support fisheries and bird life. Ephemeral wetlands, sometimes called seasonal or intermittent wetlands, hold water only during certain months – typically the monsoon – and dry up for the rest of the year. They look like empty grassland in summer but are crucial breeding grounds for amphibians, insects and migratory birds, and they often go unnoticed and unprotected because they do not look like “real” water bodies most of the year.

Wetland ecosystem services 🔗

The reason wetlands matter to a city is not simply that they look pleasant. They perform measurable ecological work that would be ruinously expensive to replicate with concrete infrastructure. The Millennium Ecosystem Assessment groups these benefits into four categories, and wetlands deliver in all four.

Provisioning services 🔗

These are the tangible goods that wetlands supply. Fish, freshwater, fodder, fuelwood, medicinal plants, rice grown in flooded paddies, salt from coastal pans – all of these come directly out of wetland ecosystems. A review of wetlands in India notes that tanks, ponds, lakes and reservoirs have long supplied multi-use water for irrigation, domestic needs, fisheries and recreation. In coastal regions, mangrove-lined estuaries are the nurseries for commercially important fish species, which means even the seafood eaten far from the coast often originates in a wetland.

Regulating services 🔗

This is where wetlands earn their reputation as the “kidneys” of a landscape. Wetlands slow down water, allowing sediment and pollutants to settle and microorganisms to break down organic matter. They recharge groundwater, moderate floods by holding excess monsoon runoff, stabilise shorelines against erosion and storms, and sequester carbon in waterlogged soils that prevent decomposition. A policy review describes wetlands as natural “sponges” that absorb excess rainfall, mitigate flash floods and slowly release water to aquifers in dry periods. The implication for cities is direct: a city with intact wetlands has cheaper flood control than a city that has paved them over.

Cultural services 🔗

Wetlands also produce intangible value. Pilgrimage sites along rivers, sacred groves around temple tanks, fishing communities whose identity is built around lakes, bird-watching tourism in places like Bharatpur – these are all cultural services. The aesthetic and recreational value of a clean urban lake is one of the few non-monetary services that real estate markets recognise, often crudely, in the form of “lake-facing” property prices.

Supporting services 🔗

Underpinning everything else are supporting services – nutrient cycling, soil formation, primary production and habitat provision for biodiversity. Although wetlands cover only a small share of the earth’s surface, they support a disproportionately large number of species. Conservation experts point out that provisioning services are usually prioritised because they have an obvious price tag, while regulating, cultural and supporting services are routinely undervalued even though they are economically and environmentally enormous.

Why wetlands matter inside cities 🔗

Urban wetlands are the wetlands that fall within or just outside city limits. They face a peculiar problem: their land is among the most valuable in the country, and their services are largely free, which makes them easy targets for “development”. The numbers are stark. Estimates by Wetlands International South Asia suggest that nearly 30 percent of natural wetlands have been lost in the last three decades, with Chennai losing 90 percent, Mumbai 71 percent, Hyderabad 55 percent, Bengaluru 56 percent, Ahmedabad 57 percent and Delhi-NCR 38 percent of their wetland area. Each of these cities has since faced predictable consequences – urban flooding, water shortages, and collapsing groundwater tables.

Freshwater supply and groundwater recharge 🔗

Urban wetlands are reservoirs in the most literal sense. They store rainwater, recharge aquifers and provide a buffer between scarcity and abundance. Bengaluru’s network of interconnected tanks, built centuries ago by successive dynasties, once supplied the city’s drinking water. As tanks were filled in for layouts and bus stands, the city became dependent on water pumped over long distances from the Cauvery, with rising costs and political conflict. The lesson is that an urban wetland is not just a pretty water body – it is a piece of the city’s water infrastructure.

Climate regulation and flood control 🔗

Wetlands act as urban thermostats. Open water and wet soil absorb heat slowly and release it slowly, moderating the urban heat island effect that makes Indian cities increasingly uncomfortable. During heavy rainfall, wetlands store excess water and release it gradually, which is exactly the function that storm drains struggle to perform once they are clogged or undersized. Policy analyses of urban flooding consistently link extreme flood events in Chennai, Mumbai and Bengaluru to the systematic loss of wetlands and the encroachment of natural drainage channels.

Biodiversity and natural waste treatment 🔗

Urban wetlands shelter biodiversity that has nowhere else to go in a built-up landscape – migratory waterfowl, fish, amphibians, dragonflies and aquatic plants. The most famous Indian example of an urban wetland doing multiple jobs at once is the East Kolkata Wetlands, a 12,500-hectare mosaic of fish ponds, paddy fields and vegetable plots on the eastern edge of Kolkata. Designated a Ramsar site in 2002, the wetland receives close to a thousand million litres of city sewage every day. The sewage is exposed to sunlight in shallow ponds, where algae and microorganisms break down organic waste, and the nutrient-rich water then supports a large sewage-fed fishery and vegetable cultivation. The Climate Group describes it as the world’s largest natural resource recovery ecosystem, providing waste treatment, food and livelihoods at virtually no cost to the municipality.

Yet even East Kolkata Wetlands is under constant pressure from real estate expansion, illegal landfilling and pollution from heavy metals – a reminder that recognition alone does not guarantee protection.

Where policy meets the bulldozer 🔗

India has a legal framework for wetland protection, including the Wetlands (Conservation and Management) Rules, 2017, the National Wetlands Conservation Programme, and Ramsar designation for 98 sites covering more than 1.3 million hectares as of 2026. The gap, as several reviews note, lies in implementation – in mapping smaller urban wetlands, in resisting encroachment, in valuing services that do not show up in a municipal budget, and in involving local communities who have the strongest stake in keeping these systems alive. Urban wetlands will survive only when planners treat them as infrastructure rather than as vacant land waiting to be filled.

What do you think? If a city has to choose between a new housing layout and protecting a sewage-fed wetland that quietly treats its waste for free, how should that choice be made – and who should make it?

References

1. https://www.ramsar.org/sites/default/files/documents/library/info2007-01-e.pdf
2. https://www.dcceew.gov.au/water/wetlands/ramsar/wetland-type-classification
3. https://www.sciencedirect.com/science/article/pii/S221458181400010X
4. https://www.drishtiias.com/daily-updates/daily-news-editorials/saving-indias-wetlands
5. https://www.indiawaterportal.org/environment/sustainability/rethinking-wetland-conservation-and-climate-resilience-in-india
6. https://www.downtoearth.org.in/environment/the-state-of-india-s-urban-wetlands-and-why-they-need-to-be-protected-urgently-78456
7. https://www.orfonline.org/english/research/governing-urban-wetlands-in-india-a-pathway-to-sustainable-urbanisation
8. https://ekwma.in/ek/
9. https://www.theclimategroup.org/our-work/publications/east-kolkata-wetlands-ekw-community-led-nature-based-solution-combat-climate
10. https://moef.gov.in/uploads/2017/09/Wetlands-Rules-2017.pdf