Conservation of shallow water bodies: Ecological consequences due to multiple anthropogenic stressors

In this Anthropocene era, human interference can be seen in every component of Earth’s ecosystem. Due to such human-mediated changes, the loss of freshwater habitats such as lakes, ponds and wetlands, as well as their aquatic biodiversity and water quality are becoming a major concern. 

Freshwater ecosystems are of enormous ecological importance and human need (such as drinking water and inland fisheries). Freshwater habitat, mainly urban and peri-urban wetland ecosystems, requires special attention for wise use and a sustainable future. 

Wetlands are of enormous ecological significance and one of the most important ecosystems on Earth. Often called “nature’s kidneys” and “nature’s supermarket”, wetlands support millions of people by providing food, and water, and controlling floods and storm surges.  

In India, according to National Lake Conservation Programme (NLCP), lakes can be defined as “waterbodies which have a minimum water depth of 3 metres, with a surface area more than 10 hectares and minimum or little aquatic vegetation”. 

When referring to shallow lakes (less than threemetres deep) with abundant growth of aquatic macrophytes. Because of its shallow nature, sunlight penetrates the bottom of the water body. 

The temperature is isothermal, with a continuous mixing process (circulating top-to-bottom on a regular basis, especially in a tropical country like India). Over time, these water bodies get filled by sediments coming from the catchment. ‘

Hence, the depth of the water column gradually declines. This is quite obvious that a small change in the temperature and rainfall pattern would have a cascade of ecological effects on this type of water body.  

From 1901-2018, India’s average temperature has risen by 0.7 degrees Celsius. The rise is attributed to greenhouse gas-induced warming as well as land-use and land-cover change, according to a 2020 report by the Union Ministry of Earth Sciences. 

Such changes in temperature and heat distribution across the regional scale will have an impact on the rainfall pattern. Therefore, under the context of the current climate change scenario, there is an increasing threat to India’s natural ecosystems, freshwater resources and agriculture, which ultimately impact biodiversity, food, water security, public health and society as a whole.

To illustrate this point, an example of Surajpur Bird Sanctuary may be cited. It is a part of the Dadri wetlands, which is designated as a reserve forest. It is located in tehsil Dadri, district Gautam Buddha Nagar. 

This is an excellent example of a freshwater natural wetland within an urban setting (Yamuna river basin). This is a rain-fed wetland (around 60 hectares surface area) and gets freshwater from the Hawalia drain, which is attached to Hindon river and the Tilapta irrigation canal. It comprises of many species of flora and fauna. Such natural urban wetlands are of enormous ecological importance. 

In October 2019, the water level in Surajpur wetlands was low with high algal production as well as smell and odour issues. There could be several reasons for such limnological changes. 

In 2019 from September-October, the Ganga canal-cleaning operation was going on. It is possible the canal was closed during that time and the Surajpur wetland did not receive freshwater from the Tilapta canal. 

Probably, because of insufficient intake of water, deficient rain and high air temperature, the water level was low. If the wetland does not receive adequate rainwater or canal water even for a short duration, a change in the hydrological settings may significantly affect the aquaticecosystem's physical, chemical and biological properties. 

Partial drying up of Surajpur wetlands due to low water level in 2019

The phytoplankton (algal) communities are extremely sensitive to changes in their environment, especially the physical conditions of a lake or the aquatic system. 

Generally, shallow water bodies are more nutrient-enriched, which promotes the primary production of phytoplankton. 

Not only are the nutrients coming from the catchment, but the internal loading of phosphorus may also increase the phosphorus in the system thus favouring the algal growth. 

An ecosystem is highly complex; it has many components, its interactions are nonlinear, and its dynamics can be unprecedented. Anthropogenic activities shape an ecosystem and modify its structure and function, and self-reinforcing processes can shift and lead to temporary or permanent regime shifts. 

Over time, the Surajpur wetland experienced urbanisation, land-use change and low water levels for certain periods, which destroyed the habitats of many floral or faunal species, despite several conservation initiatives. 

Water level fluctuation in Surajpur Bird Sanctuary (Google Earth images)

Natural water bodies of cities and peri-urban areas are impacted by rapid urbanisation and change its natural state at an alarming rate. Delhi has more than 1,000 lakes, wetlands and ponds, according to the estimates of the Delhi Wetland Authority.

But most of these are threatened by rampant encroachment (both planned and unplanned), pollution through dumping of solid waste and construction debris as well as disposal of untreated sewage and septage. 

Rejuvenating Delhi’s wetlands through eco-restoration will not only improve the environmental quality of the city life by providing aesthetically developed water bodies but will also enhance local water resources and develop the city’s water resilience for the future. 

There are a few restoration projects which are already being implemented under the supervision of Delhi Development Authority (DDA). 

For example, in the Dheerpur wetland area, currently a restoration project is underway in collaboration with the Centre of Urban Ecology and Sustainability, Ambedkar University (Delhi) and DDA. 

DDA has also proposed to create a “Constructed Wetland System” in the Yamuna flood plain near the DND flyway. 

The United Nations declared 2021-2030 the Decade on Ecosystem Restoration with the aim to conserve and restore the terrestrial, aquatic and marine ecosystems. It is imperative to act fast to conserve the urban and peri-urban wetlands for supporting livelihood, aesthetic value and the environment as a whole for a sustainable future.

Moumita Karmakar is Assistant Professor, School of Humanities and Social Sciences, Shiv Nadar Institution of Eminence

Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth

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