Variations of dissolved oxygen in Mandovi and Zuari estuaries

67-71During non-monsoon months the estuaries were well mixed showing uniform oxygen concentrations from surface to bottom. However, during monsoon months both the estuaries showed stratified conditions with surface water showing high oxygen concentration and bottom water very low concentration. The stations at the freshwater end showed relatively higher oxygen concentration than the stations at the sea-end. Plots of oxygen against salinity showed peaks at the extreme ends (freshwater and seawater). Another peak at intermediate salinity 18 to 24 x 10-3 was also observed. The upper reaches of Mandovi showed supersaturation with respect to dissolved oxygen while the lower reaches showed undersaturation. The Zuari showed under-saturation through the entire length