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Habitat alteration, unchecked sewage discharge led to decline in thriving zooplankton in Pashan lake, finds study

🔴 Government-led restoration works including desilting, re-contouring, construction of retaining wall and an artificial island were carried out in 2008 - 2013.

Written by Anjali Marar | Pune |
Updated: December 23, 2021 8:07:29 am
pashan lake, pune lake, pune newsPashan lake in Pune. (File Photo)

A study by two Pune-based scientists has noted a significant reduction in the Cladocera (a zooplankton commonly known as water flea) species growing in Pashan lake during the last one decade.

Though there are multiple contributory factors for this reduction, the release of untreated sewage water and habitat alteration were cited as the most predominant.

Located to the southwest of Pune city, this lake was formed due to damming of river Ramnadi sometime in the early 1900s and was known to possess rich biodiversity spanning macrophytes, aquatic invertebrates and birds. But rampant urbanization around the lake in later years led to a steady decline in this biodiversity, affecting both the variety and habitat spread.

Researchers Sameer Padhye of Biologia Life Science LLP and Mihir Kulkarni from CSIR – Centre for Cellular and Molecular Biology studied Cladocera at this site in two phases — in 2009 – 2010 and in 2016 —  and noted a drastic fall. From 28 Cladocera species and families recorded during the 2009 – 2010 survey, the count dropped to nine species in 2016.  Government-led restoration works including desilting, re-contouring, construction of retaining wall and an artificial island were carried out in 2008 – 2013. But this effort did more harm than good, as spreads of aquatic plants including Pisita and Eichornia (water hyacinth) were observed growing here thereafter.

“The altered shape of the lake, along with the increased nutrient concentrations like phosphates and nitrates, helps in the rapid and uncontrolled growth of Eichornia and Pistia,” said Padhye.

Some of the other factors listed in the recent study include introduction of non-native fish, alteration of habitat structure, removal of aquatic macrophytes and removal of egg banks from the site.

“The habitat modifications could have a prominent impact. Among the habitat modifications, the construction of the embankment and removal of the natural littoral vegetation have completely destroyed the shallower micro-habitats for many species,” said Kulkarni.

A permanent solution and better management of the floating plants at Pashan lake can be achieved by addressing the invasive fish and sewage discharge.

Otherwise, many of the aquatic species communities will continue to suffer in future, the researchers warned.

The duo also proposed scientific restoration of the lake from time to time.

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