COVID-19 lockdown affects zooplankton community structure in dolphin appearing site of the River Ganga at Patna

Abstract

The advent of the 2019 Corona virus impacted day-to day human activities and the nationwide lockdown in India completely paralyzed life (midnight of 24th March, to 31st June, 2020). However, this complete halt of human activity allowed the Ganga ecosystem to realise its maximum self-purification potential, resulting in the improvement of flow regime, water quality and over all restoration of the river. The most common manifestation of restoration of an aquatic ecosystem is zooplankton community structure; i.e. relative proportion of various functional feeding groups. The present study compares selected water quality parameters (DO, BOD, pH, Total coliform, Fecal coliform), and zooplankton community structure estimated during the lockdown period with the values recorded for the same period in previous three years at dolphin appearing site near Kalighat, (25° 37′ 19.398″ N; 85° 9′ 55.8972″ E), middle of the Patna city and Mittal Ghat (downstream site of the Patna City) at Gurhatta (25° 36′24.5772″ N; 85° 13′ 1.6788″ E). During each sampling, the dolphin emergence site and frequency were monitored for three hours duration. Monthly zooplankton samples were collected at both the sites using a 53 µm mesh size plankton net beginning January 2018 by filtering 45-50 l of river water. Zooplankton were identified and segregated based on functional feeding groups. The values of dissolved oxygen were significantly higher, whereas that of BOD level, total coliform and total fecal coliform were lower during the lockdown period than those in previous years. Detailed analyses revealed that relative proportions of Cladocera were significantly higher, whereas that of bacterivorous Rotifera were significantly lower than the previous values of the same months. The highly indicator species at both the sampling sites was Moina micrura during March-May 2020; in previous years it was Brachionus rotifers 8.8 (ind l-1) at Kalighat and Moina micrura (15 ind l-1) at Gurhatta. Our results suggest that during the lockdown the dolphin appearing sites at both stations shifted towards the riverbank whereas, zooplankton community structure changed towards algaevorous Cladocera without affecting overall species richness.