Thane creek wetlands need to be saved
The wetland and the adjacent Thane Creek Flamingo Sanctuary are globally significant, serving as a stop for migratory birds
Last week, this newspaper reported a study that warned about the shrinking wetlands along Thane creek.
The study by Bombay Natural History Society (BNHS), which looked at wetlands around the Bhandup sewage pumping station (BPS), said that sedimentation and encroachments have shrunk its area from 3.5 square km in 1973 to just over one square km in 2018.
Thane creek, located between Mumbai harbour — with two shipping hubs, the Mumbai Port and the Jawaharlal Nehru Port on its south the Ulhas River on its north — is 26 kms long and its narrower upper areas have mudflats, salt pans and diversity-rich mangrove forests. Studies by groups like Salim Ali Centre for Ornithology and Natural History and BN Bandodkar College of Science Thane and Bombay Natural History Society have found that the creek is home to more than 160 bird species and nine species of mangrove trees, besides fish, crustaceans and insects.
These species and phytoplankton, single-celled plants that form the basic life-building block in aquatic systems, providing food for shrimp, snails and fish, are important for sustaining the local fishing industry.
The wetland and the adjacent Thane Creek Flamingo Sanctuary are globally significant, serving as a stop for migratory birds using the Central Asian Flyway which stretches across Asia, Europe and the Arctic and Indian Oceans. There are four near-threatened bird species and 14 migratory ones in the area, which fall under schedule I of the Wildlife Protection Act, 1972, giving these birds a high grade of protective status.
Significantly, it is the second-largest natural area in Mumbai, next to the Sanjay Gandhi National Park (SGNP), spread over 59 square km, according to the Forest Survey of India.
In May 2018, the Maharashtra government had announced the creation of the Thane Creek Flamingo Sanctuary on 1,690.5 hectare (1.6 sq km). Additionally, the state government recently has proposed to create a 34 sq km buffer zone around the sanctuary.
Despite its status as a protected sanctuary, the creek is threatened by pollution and encroachments. Research by Ryerson University, Toronto had reported that a third of the mangrove forests in the Mumbai Metropolitan Area has been lost to urbanisation since the 1970s.
A study by the civil engineering department of the Indian Institute of Technology – Bombay (IIT-B), meant to understand the siltation problem in the two ports, said that around one metre of silt is deposited annually in the harbour basin, forcing the port companies to spend money on dredging the navigational channel to keep it deep enough for ships.
Another study, by BN Bandodkar College of Science, Thane, said the creek’s biodiversity has declined over the decades because of industrialisation and expansion of urban areas on its banks. The study found low dissolved oxygen, high nutrients from run off and siltation. The high nutrients can lead to excessive growth of phytoplankton that can choke other life.
The BNHS study said construction around the creek has changed its natural state dramatically. Constructed area in the wetlands has increased from 132 hectare to 787 hectare since the 1970s. This has resulted in a 70% drop in the wetland area (mudflats) — from 344 hectare in 1973 to 100.3 hectare in 2018.
Sedimentation has narrowed the creek and reduced its water area, but mangrove cover has increased by 53%, from 652 hectare in 1973 to 999 hectare in 2018. While this is good as the expansion of mangroves has increased the creek’s cover, most of the new mangrove growth is from one species that can thrive in poor water quality. This means a decline in diversity.
But the creek can be restored to health. Studies have said that lower stretches of the creek, where it is wider and flushed by tides, still support relatively higher diversity because pollution gets diluted. This section has mangroves and birds, including the creek’s most well-known visitors, flamingos. Desilting, treatment of sewage before it is released into the creek, mangrove plantations and conservation projects that partner with the local fishing community can revive the ecosystem.