Absence of foul stench, change in water colour at Thane creek during lockdown: Study

Researchers have recorded an improvement in the water quality of Thane creek, including areas within the flamingo sanctuary, during the lockdown period.

Flamingos spotted at Thane creek(HT Photo)

An absence of foul order and a change in the water colour were the main observations as industrial waste discharge was negligible but domestic sewage continued.

This is the first water quality assessment for the Mumbai region during the lockdown, done by the Maharashtra forest department and Bombay Natural History Society (BNHS) released on Saturday. “Areas along the creek that previously had water colour with dark black patches, due to industrial waste, had turned brown. Some portions of the creek even had clear water, and the foul stench, observed during sampling every month, was missing,” said Mrugank Prabhu, scientist, BNHS who led the study.

Nathuram Kokare, range forest officer (Thane creek) said, “Bird numbers, including flamingos, have increased at deeper ends of the creek where they did not go before. This is also because fishing activities have completely stopped.”

Samples were collected during high tide from 14 locations at the creek along a km-long stretch covering Vitava in Thane till Koparkhairne, Navi Mumbai on the east bank, and Kanjurmarg in Mumbai (part of the flamingo sanctuary) to Vitava on the west bank. Samples were compared with levels during January, February and March. The results (all average values) showed lowest turbidity levels (a measure of haziness in water caused by sediments and algae) in four months during April at 30.7 Formazin Nephelometric Unit (FNU), which ranged between 44.2 and 76.72 FNU in previous months.

Deepak Apte, director, BNHS said, “Highly populated areas surrounding the creek drain effluents and sewage when there are no restrictions (like the lockdown). In this case, an industrial effluent reduction is visible but not domestic sewage. This is, however, a preliminary study and we need many more sampling exercises, the status of polluting sources, and impact on local biodiversity to conclude.”

The most striking factor was a drastic rise in oxidation-reduction potential (ORP) - a measure the ability of a river or creek to cleanse itself or break down waste - during April. The parameter fell from 45.2 millivolts (mV) in February to 6.86 mV in March and shot up to 148.22 mV in April. “When the ORP value is high, there is a lot of oxygen present in the water. High ORP level means better water quality,” said Prabhu. As compared to the dissolved oxygen level (present in water) was marginally higher than in previous months.

Independent researcher and member of the Mangrove Society of India Pramod Salaskar who was not part of the study said, “High ORP is indicative of healthy water quality with low toxicity of metals and contaminants. ORP should read as high as 300-500 mV for the best water quality. However, in this study, the level of dissolved oxygen does not compliment high ORP. We must investigate whether high ORP was caused by effluents as byproducts while producing sanitisers by industries,” he said.

According to the mangrove cell, there are over 200 bird species (flamingos and waders being dominant) at Thane creek, which is also home to 68 insects, 29 butterflies and moths, nine mangrove species among other biodiversity. Owing to high water pollution, a Salim Ali Centre for Ornithology and Natural History (SACON) study had recorded a drop in fish species from 69 to just seven. In August 2016, the state had declared the northern part of the creek as a flamingo sanctuary spread across 1,690 hectares and proposed a 3.4 sq. km buffer zone around it last year. “The lockdown has allowed us to capture the background water quality levels if the industrial discharge is at its minimum. Based on this analysis and future studies, we will strategise on how to reduce overall water pollution once the lockdown is called off,” said Virendra Tiwari, additional principal chief conservator of forest (Mangrove cell).