Lastest project Pallikaranai catchment

Assessment of water quality of the lakes of the Pallikaranai catchment, Chennai, India

 

Water quality has been one of the most widespread research topics for decades, along with water scarcity as one of the problems humans are facing. The United Nations has expressed their concerns about this issue in several occasions, remarkably in 2016 with the Sustainable Development Goals, that included the Sustainable Development Goal number 6: "Ensure availability and sustainable management of water and sanitation for all”.

 

In India, the main sources of fresh-water supply are surface and ground water and their easy access to anthropogenic activities have affected them much. Due to the over exploitation of water resources and increased pollution, the whole country is facing the scarcity of fresh-water resources.

In the present study, in cooperation with Professor Indumathi Nambi’s group at IIT Madras, we chose the Pallikaranai catchment in Chennai as our study area, which includes a set of lakes in a cascading system facing a few problems. The main current problems are 1) there are numbers of encroachments from which sewage is directly let into the lake, 2) waste water from the Pallavaram Municipality is discharged into the lake, 3) the lakes are suffering from heavy eutrophication, 4) there is currently no regulation for waste water disposal and no assessment indices and 5) the reduction of biodiversity in the study area. In these regards, we aim 1) to display the long-term water quality before and after monsoon season, 2) to show how cascading system affects the lake water quality, 3) thus to implement and complete the lake restoration protocol in the future water quality assessment and monitoring work.

Fig. 1 shows a map of the Pallikaranai catchment. The upper stream lakes, Chitlapakkam, Selaiyur and Rajakilpakkam, flow into Sembakkam Lake. Afterwards, the excess of it flows into Nanmangalam Lake. Other downstream lakes are Keelkatalai, Narayanapuram and the catchment outlet Okkiyam Maduvu.

Fig. 1: Lakes and sampling points’ distribution in Pallikaranai catchment

 

Our results showed that the lakes are suffering from heavy pollution. COD levels were especially high during August and September and reached values over two-thirds of the average of wastewater in developing countries (Fig. 2). In the case of the levels of chlorophyll A, they were extremely high in Chitlapakkam Lake and suggested a severe eutrophication that might affect the biodiversity (Fig. 2).

 

 

Fig. 2: Results of COD in the seven lakes and the marshland of the Pallikaranai catchment (Chennai, India).

 

 

 

Fig. 3: Results of chlorophyll A in the seven lakes and the marshland of the Pallikaranai catchment (Chennai, India).

 

The effect of the monsoon on the water quality of the lakes was also evident. It performed better after the monsoon season than in the dry season. It was an extremely dry year in Chennai in 2019, the lakes stayed disconnected and stagnated for most of the year. As a consequence of that, the Keelkattalai Lake (Fig. 4) was dry between July and September. The first rainfalls increased the flow, connected the lake cascading system and probably diluted all the contamination and concentrations got lower. This could be the reason why all the lakes reached the best condition in December. Sembakkam Lake is the only one currently being restored with the help of international NGO The Nature Conservancy. More similar work should be implemented in other water bodies.

 

                 

 

Fig. 4: Keelkattalai Lake in drought in July (left) and with overflow in December (right)

 

There is the urgency to improve the water quality, since the water bodies are close to human’s living area. Measures could be taken, like building more waste water treatment plants (WWTPs) that prevents sewage to be discharge to the lakes without any previous treatment. Within the studied catchment, there is currently only one WWTP, which is not enough. Additionally, thresholds should be set to restrict the concentration of discharged nutrients into water. Also, to move the dump sites present in the area that contribute to the spread of disease vectors and pollution. We also suggest a science-based, careful selection of reintroduction species of local submerged macrophytes for self-purification of the lakes.

 

 

Contributors

Dr. Daniel Rosado, Prof. Indumathi Nambi, Xiuming Sun, Lukas Paul Loose, Dr. Yueming Qu, Prof. Nicola Fohrer

Funded by:

The Care Earth Trust

The Nature Conservancy

Indo German Centre for Sustainability

Deutsche Hydrologische Gesellschaft