Changes in the environmental features of the Zuari and Mandovi estuaries in relation to tides

Abstract

Changes in the temperature, salinity, pH and dissolved oxygen in relation to tidal rhythm were found to be well marked in the Zuari and Mandovi estuaries. Seasonal differences in the hydrographical factors of the two estuaries are considerably influenced by the south-west monsoon. In the Zuari estuary, during the post-monsoon months, almost marine conditions seem to prevail with a little freshwater drainage whereas in the Mandovi estuary the freshwater discharge continues throughout the year which influences the environmental features. The two estuaries are rich in inorganic phosphate-P, the source of which in the Zuari estuary appears to be largely from the neritic waters whereas the input of inorganic phosphate-P in the Mandovi estuary seems to be influenced by the river-water. The rate of production was high in the samples from the two estuaries during the monsoon month. Changes in the rate of production induced by the tides corresponded with those in the inorganic phosphate-P, chlorophylla and the phytoplankton abundance. Probably the flora associated with the lower salinity dominates the crop of phytoplankton throughout the year in the Mandovi estuary whereas in the Zuari estuary the preponderance of the freshwater flora appears only during the monsoon month.