Wetlands are water-rich natural resources that are found in rivers and deltas. The wetlands include rivers with their flood plains, lakes, swamps, salt marshes, mangroves, coral reefs, etc. Wetlands are the places where most of the urbanism takes place. Wetlands provide space for agriculture, fish farming, and the purification of air. When wetlands integrate with the ecosystem of urbanism around it and become a significant part of the ecosystem it is called an urban wetland. The threat towards wetlands rises when wetlands are taken for granted.
The wetlands can be broadly classified as swamp, marshes, bogs, and fens. To understand the functions and values provided by wetlands the HGM approach is most effective. The types of wetlands based on hydrologic regimes and landscape position or HGM (hydrogeomorphic) approach are as follows:
a) Depressional –
These wetlands are formed due to the presence of topographic depression with the countered landscape. Functions and values- Flood storage, Habitat, Pollution treatment, and Erosion control
b) Slope –
These wetlands are formed due to the surface discharge of groundwater on sloping land. Functions and values- Habitat, Pollution prevention, and Erosion control
c) Flat –
These wetlands are formed on low topographical gradients like old glacial lake beds with moderate to abundant rainfall. Functions and values- Habitat, Pollution prevention, Flood storage, and Limited recreational
d) Riverine –
These wetlands are found with the rivers and their flood plains. Functions and values- Flood transportation and storage, Shoreline protection with erosion control, Pollution treatment, Fish and bird habitat, and Recreation.
e) Fringe –
These wetlands are found adjacent to lakes and estuaries. Functions and values- Habitat, Pollution treatment, Water supply protection, Shoreline protection with erosion control, and Recreation.
Wetlands play a key role in the urban ecosystem for their functions and values. Wetlands provide lots of services when it is integrated with an urban ecosystem. Here is the list of services that wetland provides –
a) Pollutant removal –
The removal of pollutants from the water helps in the maintenance of drinking water quality, processing sewage water, retention of sediments, filtration of runoffs, and transportation of organic matter. Artificial means of pollutant removal consume a lot of energy and indirectly harm the ecosystem.
b) Flood attenuation –
Wetlands provide storage of downstream flood water and help the particulates to settle out. It also protects the downstream properties and ensures public safety.
c) Groundwater recharge –
Wetlands help to maintain the groundwater flow and restrict saltwater to leak with groundwater.
d) Shoreline protection –
Fringe wetlands provide shoreline protection by protecting the vegetative lands and absorbs the surge of stormwater.
e) Wildlife habitat –
Wetland is home to aquatic, avian, and terrestrial flora and fauna species. Wetlands act as a connective wildlife corridor and foraging grounds for migrating birds.
f) Other services –
Wetlands are often restored as a recreational areas like walkways, angling, bird watching, hiking, etc. Wetlands are also used for education, aesthetics, and commercial aspects too.
Wetlands are natural resources that filtrate water, protect us from disaster, and have a rich biodiversity. Despite helping us for urban settlement, wetlands face a large number of threats throughout the globe. The major threats faced by wetlands are –
a) The rapid change in land use due to urban and rural development - The wetlands are being converted to agricultural fields and then transformed to land for human settlement. It results in a decrease of capacity to groundwater recharge of wetlands.
b) Encroachment of wetland lands - This occurs due to corruption in management. This results in the reduction of wetlands area without any plan to recover it.
c) Settlement on embankments - This occurs due to overpopulation and the increase of slum areas.
East Kolkata Wetlands- Settlement on Embankments of Finger ponds (Photo courtesy- Souktik Bhattacherjee)
d) Dumping on waste - This degrades wetlands which reduces their water storage capacity.
e) Degrade mangroves and coral reefs – This gives coastal cities exposure to storms.
f) Burn or drain peatlands - This produces lots of carbons that are built up over centuries.
g) Flow constrictions - Harming the flow of wetlands water results in floods and degrade the wetlands.
h) Increase in stormwater runoffs - This occurs due to unplanned urban development around the wetlands. It results in an overflow of wetlands.
i) Increase in salinity of wetlands - This occurs due to urban development and construction of roads over the wetlands. It results in the extinction of numerous species in the region.
It’s estimated that wetlands consist of 7% of the earth’s surface and have an output of 45% of total natural productivity and ecosystem services. In the last hundred years, 50% of the wetlands have disappeared. Measurements and policies must be made to conserve wetlands and integrate them with urban development. Here’s the list of regulations that are taken to reduce the wetlands loss:
a) The activities like setting up industries in vicinity, dumping of waste materials, manufacture or storage of hazardous substances, any permanent construction, etc are restricted in wetlands.
b) The regulated activities include unsustainable grazing, harvesting of resources, releasing treated effluents, aquaculture, agriculture, etc.
c) A wetlands management corporation is formed which identifies and documents new wetlands and looks after the wetlands.
d) An assessment of social, cultural, environmental, and economic aspects of the wetlands must be conducted to use wetlands effectively. Socio-economic assessment on these aspects must be conducted to provide a better life to people dependent on wetlands.
A wetland may die off and stop functioning properly. It may occur due to human’s direct or indirect impact or any natural changes. Urban development around the wetlands may receive heavy damage due to the non-functioning of wetlands. A wetland can be restored after a proper assessment of the amount of wetland suffered damage. The factors on which the assessment for wetland restoration is done are as follows:
a) Budget - The total funding available for the wetland restoration must be determined.
b) Time scale limitations - A specific amount of time can be allocated for the wetland restoration. With the increase of time, the cost of the project increases, and another environmental issue may occur.
c) Project goals - After proper assessment of the wetlands the restoration work may occur by achieving smaller goals. Timeframe and costs of each goal must be made.
d) Level of disturbance - The level of disturbance towards society and nature must be thought off. These disturbances must be minimized and solved to restore the wetlands.
e) Landscape and ecological constraints - The ecosystem of the wetlands must not be harmed. Local landscape elements must be used to create a minimum disturbance.
f) Political and administrative agendas - The political and administrative agendas must be taken care of while restoring the wetlands.
g) Socioeconomic priorities -
Prescribed natural regeneration - This method of wetland restoration is the cheapest. The wetlands are left untouched and nature grows itself.
Assisted natural regeneration - Few interventions like the burning of bushes, introduction of new species, etc are made to restore the wetlands.
Partial reconstruction - The approach to restoring wetlands requires an understanding of wetlands at the local level. Natural regeneration and assisted regeneration both are done to restore the wetlands
Complete reconstruction - This is the most expensive method and requires engineering skills. After total restoration, it’s important to let nature regenerate itself and wetlands function properly.
East Kolkata Wetlands- People cleaning pond (Photo courtesy- Souktik Bhattacherjee)
Case studies of wetlands around the world reflect how wetlands are being used, degraded over time, and regenerated. Here are some of the case studies made:
a) East Kolkata Wetlands, India
East Kolkata Wetlands is a perfect example of a wetland that is integrated with the city. It is the world’s largest sewage-fed aquaculture. The sewage water is naturally treated in the wetlands and prevents the city from flooding stormwaters. The wetlands subsidize the food for the city, by reducing the transportation cost to almost zero. For several decades, the natural sewage treatment went unnoticed. Dr. Dhrubajyoti Ghosh, while working as an engineer at the Government of West Bengal's Water & Sanitation Department went to find of what happens to the city’s sewage. The East Kolkata wetlands cover an area of 125 square kilometers which consists of salt marshes, agricultural fields, sewage farms, and settling ponds. Due to this late discovery, the wetland has degraded from 92% waterbodies to less than 10% in the last two decades. The city is growing rapidly, the population is increasing and the wetland is dying. The wetlands rules and regulations must be made stricter and must be protected from encroachments. Social awareness about wetlands and the habitats must be increased in society so that people can understand their value and prevent further degradation.
East Kolkata Wetlands (Photo courtesy- Souktik Bhattacherjee)
b) Urban Wetland London
A few years back, the Themes river flooded due to heavy rainfall which resulted in the cancellation of 150 Wimbledon Matches. After that, the London Wetland center and 42 hectares of land are turned into wetlands. The urban wetland is constructed with Barn Elms Waterworks to maintain the water urban system and improve the city’s biodiversity. After the wetlands have been built, the wetland has become a breeding ground for several reptiles and birds. The wetland center is open to the public and visitors. It has a visitor’s center, exhibition spaces, and organized excursions for the visitors.
Urban Wetlands London. (Photo courtesy- urbangreenbluegrids.com)
After the Industrial Revolution, human beings started to depend on machines. So, the futurist's visions were a world fully automated and far from nature. Today if we look at the Pragmatic utopian visions, we could understand what nature can give us. The well-being of humans lies in co-existing with nature. Wetlands if properly utilized, artificially created, or conserved will subsidize the urban development depends on it. The total worth of wetlands is estimated to be 47 trillion USD a year (Marine and Freshwater Research Journal). As responsible citizens of this world, we must work towards a better understanding of our mother earth and sustainable utilization of resources.