Impact of monsoon-induced discharge on phytoplankton community structure in the tropical Indian estuaries

Abstract

To understand the influence of monsoon-induced river discharge and associated environmental changes on phytoplankton community structure in the Indian estuaries, physical and biogeochemical parameters were collected from 28 major and medium estuaries along the Indian coast during the peak discharge period. Relatively higher river discharge was recorded in the estuaries located in northern India associated with higher suspended particulate matter (SPM), which arrested light penetration, resulting in a decreased in phytoplankton abundance and biomass. In contrast, higher phytoplankton abundance and biomass were observed in the estuaries located in southern India due to lower discharge and SPM than northern India. Diatoms were the dominant phytoplankton group in the Indian estuaries, except in estuaries located in the southeast coast, where blue–green algae predominate due to the existence of brackish water and stagnant water conditions due to less discharge. Higher phytoplankton diversity was observed in the south Indian estuaries than north Indian estuaries due to the long water residence time in the former. A present study is revealing that the magnitude of river discharge and SPM load seems to be the primary factors controlling phytoplankton abundances and community composition in the Indian estuaries.