Spatio-temporal changes of hydro-chemical parameters in the estuarine part of the River Ganges under altered hydrological regime and its impact on biotic communities.

Abstract

Hooghly estuary, the lowermost part of River Ganges in India, following the construction of Farakka barrage in 1975, witnessed improved freshwater inflow in the estuarine stretch of the river with significant impact on the salinity regime, water transparency, suspended sediments and nutrient load leading to alternations in the distribution and abundance of fish and other biotic organisms like plankton and benthos. A detailed seasonal study was conducted in Hooghly estuary during 2010–2012 to evaluate the spatio-temporal changes in selected physico-chemical parameters like temperature, transparency, pH, free CO2, dissolved oxygen, specific conductivity, total alkalinity, total hardness, salinity, available nutrients like nitrate, phosphate and silicate under the present hydrological regime in determining the distribution of fish and other aquatic organisms. The salinity based zonation during pre-Farakka period apparently stands modified with a downward shift of freshwater zone. Accordingly, distribution and abundance of biotic communities like plankton and fish now present a completely different scenario from the past.