Author(s): K. K. Balachandran; T. Joseph; J. S. Paimpillil

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Abstract: The Cochin backwater system (Vembanad Lake) is dominated by anthropogenic influences with 19 million m3 of fresh water discharged to Arabian Sea along with substantial amounts of nutrients during and immediately after southwest monsoon season. The long-term trends in nutrients showed build-ups with a two-fold increase in dissolved phosphate and silicate in 42 years. The nutrient fluxes into coastal region were influenced by fluxes from backwater, upwelling, coastal circulation, Bay of Bengal water mass and mud bank formation. The transfer coefficient from primary to secondary level production was only 7% in Cochin backwater and the excess production in backwater contributed to the production in coastal waters. Contrary to the earlier reports that southwest coastal waters of India remain oligotrophic, the present study isolates a possible link between Vembanad Lake that supplies primary nutrients to the adjacent coastal waters and precondition it for rich primary production during non-monsoon months. The causative factors discussed are indicative of existence of a subterranean flow connecting Vembanad Lake to the adjacent coastal waters through the submerged porous lime shell beds. Continuous nutrient entry through such process is bound to upset coastal water productivity pattern. The coastal waters in Arabian Sea off Cochin do not reflect many of its anthropogenic impacts and still governed by natural oceanographic processes.

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Year: 2003