Influence of river discharge on plankton metabolic rates in the tropical monsoon driven

To examine the influence of river discharge on plankton metabolic balance in a monsoon driven tropical estuary, daily variations in physico-chemical and nutrients characteristics were studied over a period of 15 months (September 2007 to November 2008) at a fixed location (Yanam) in the Godavari estuary, India. River discharge was at its peak during July to September with a sharp decrease in the middle of December and complete cessation thereafter. Significant amount of dissolved inorganic nitrogen (DIN, of 22-26 μmol l-1) and dissolved inorganic phosphate (DIP, of 3-4 μmol l-1) along with suspended materials (0.2-0.5 g l-1) were found at the study region during the peak discharge period. A net heterotrophy with low gross primary production (GPP) occurred during the peak discharge period. The Chlorophyll a (Chl a) varied between 4 and 18 mg m-3 that reached maximum levels when river discharge and suspended loads decreased by>75 % compared to that during peak period. High productivity was sustained for about one and half months during October-November when net community production (NCP) turned from net heterotrophy to autotrophy in the photic zone. Rapid decrease in nutrients (DIN and DIP by ~15 and 1.4 μmol l-1, respectively) was observed during the peak Chl a period of two weeks. Chl a in the post monsoon (October