Tidal cycle and the environmental features of Cochin backwater (a tropical estuary)

Abstract

In the Cochin Backwater, Kerala, India the tides are of a mixed, semidiurnal type with a maximum range of about 1 m. Two high and two low water-marks occur each day, with an appreciable difference in range and time. The various environmental features such as temperature, salinity, dissolved oxygen, pH, seston, nutrients, alkalinity and chlorophyll are greatly influenced by the tidal rhythm. The differences in almost all these parameters are more marked at the surface than at the bottom. The magnitudes of variation are not consistent and largely depend upon the time of the year. Diurnal changes in dissolved oxygen followed the course of daily sunlight intensity. Gross primary production gave a similar day and night cycle. Because of high turbidity in the estuary, the primary production was much higher at the surface than at 1 m