An assessment of the temporal alterations in the trophic status and habitat heterogeneity of the anthropogenically influenced Bhagirathi-Hooghly estuary in reference to phytoplankton community and environmental variables.

Abstract

The Bhagirathi-Hooghly estuary represents one of the most populated estuaries in the Indian subcontinent with dense settlements along its course. The concomitant high anthropogenic influences and enhancement of nutrient load due to uncontrolled discharges from non-point source in monsoon play important role in habitat variability and consequential changes in the water quality of the estuary. Even though such nutrient loadings are expected to cause significant changes in the ecosystem functioning, a documentation of the habitat heterogeneity has largely remained unavailable from this important yet unmonitored estuary. Thus, the present work aims at assessment of water quality and trophic status of the habitat by application of a combination of abiotic and phytoplankton-specific indices as recommended by different international and national authorities. Results suggest that water quality deteriorated during periods of seasonal precipitation due to enhanced nutrient loadings that culminated in altering the trophic status of habitat. Comparisons with regard to international standards further corroborated the influence of seasonal precipitation on water quality and trophic status of the habitat. Phytoplankton functional groups largely reflected the changing nature of the habitat well, with dominance of those taxa that are more persistent under warm, nutrient replete shallow euphotic depths of the habitat. These findings further suggest that it is essential to regularly monitor the health of this estuarine ecosystem to as to sustain the different life forms that will be essential for the livelihood of people in this area.