THE THREE most significant water bodies, including the man-made Sukhna Lake in Chandigarh, have high levels of organic matter that monopolise the oxygen, and prevent aquatic life from flourishing. The State of the Environment Report-2016 released by the Chandigarh Administration on Wednesday details that in 2016, the level of biochemcial oxygen demand (BOD) was very high at several points of time in 2016 in Sukhna, Dhanas and the lake in Sector 42.
BOD, also biological oxygen demand, is the amount of dissolved oxygen that aerobic — that is, oxygen-using — biological microorganisms need to break down organic material present in a given water sample at certain temperature over a specific time period. The presence of large quantities of algae means that aerobic bacteria that decompose the algae will use up enormous amounts of oxygen. This tells on the levels of dissolved oxygen (DO) in the water.
The report states that all three water bodies reported low levels of DO, which according to experts, is not sufficient to support aquatic life. Santosh Kumar, director, department of environment-cum-chief conservator of forest and wildlife, told Chandigarh Newsline that BOD levels should be below 10. About the Sukhna lake, the report said that the BOD level was recorded highest 29 in July 2016. High levels of BOD means high organic matter in the water, which may be a result of pollutants such as sewerage, waste such as paper, or chemicals from fertilisers.
The report highlights that DO levels dropped twice in Sukhna Lake in the months of July and September last year with the Chandigarh Pollution Control Board levels showing the levels were 2.3 and 1.4 respectively. DO levels of below 5 ppm cannot support most varieties of fish and take a heavy toll on biodiveristy in the water.
While the report does not discuss the impact of low DO levels in Chandigarh’s water bodies, there have been reported incidents of mass deaths of fish in Dhanas in 2015-16 and to a lesser extent in 2017, both attributed to the low DO level in the lake, due to the release of sewerage into the water. At Dhanas lake, the UT report stated that the DO levels dropped twice to less than 1 in May and June 2016, and was 2 in December. Santosh said his department had initiated corrective measures and an oxidation pond was formed. “Since then there has been no such incident,” he said.
“It is not a good sign to have higher levels of BOD. The presence of BOD indicates that presence of organic load was higher than inside the lake,” said Yogesh Kumar Rawal, Assistant Professor at Department of Zoology, Panjab University, who has done a study on the water quality of the Sukhna Lake in 2015. At Sector 42 lake, DO level was 3.2 in July 2016.
“We should take all necessary measures so that organic matter from the surrounding areas shouldn’t enter into the lake. There is a need to identify the factors leading to depletion of DO during a particular month as per the report,” said Professor Suman Mor from the department of environment studies, Panjab University.