Diel variations in hydrographic conditions during different seasons in the Cochin Harbour (Cochin Backwaters)

190-195Stratification in salinity and temperature values is prevalent during SW monsoon in the Cochin Harbour area, particularly so when there is paucity of rains. Existence of a long standing stable homogeneous water mass is not observed in any season even though there is a tendency for overlapping of the values at different depths towards the end of the postmonsoon period as well as in the premonsoon period. Lowest salinity and temperature values are recorded during monsoon and the highest during premonsoon period. Concentration of phosphate phosphorus and nitrite nitrogen is also lowest during monsoon and highest during premonsoon period suggesting that the nutrient concentration is not immediately enriched by monsoon rains. Dissolved oxygen values are always undersaturated at all depths and in all seasons. This has been attributed to the utilisation of dissolved oxygen for the decomposition of organic matter. The observations suggest that the deepening of the mouth of the estuary and the connected channels for navigational purposes has resulted in the transportation of more sea water into the estuary during high tide throughout the year which would have been impossible otherwise. It is indicated that further deepening of the mouth and the channels to facilitate Super Tanker traffic might bring in more volume of sea water than at present into the Cochin Harbour area and also into the upper reaches of the estuary. The Salt Water Barrier constructed recently at Thanneermukkom (near the head of the estuary) may reduce the amount of fresh water discharged into the sea. These changes will be favourable for the expansion of balanids and other members of the fouling community more than at present. However, it may adversely affect the clambeds that support the local lime industry