Hydrobiological studies in the gradient zone of the Vellar Estuary: 1. Physico-chemical parameters

Abstract

The physico-chemical aspects in the gradient zone of the Vellar Estuary, Tamil Nadu, India were studied for a period of two years from January 1977 to December 1978. Water samples were collected at high and low tides of both day and night. Rainfall was very high during the period of investigation and this brought lot of changes in the physico-chemical and biological parameters of this estuary. Tidal range was low ( 2 m). Variation in water temperature was mostly influenced by the atmospheric temperature rather than tidal influence. Variation in salinity was more conspicuous ( 1 ppt to 36 ppt) during early postmonsoon late premonsoon and some collections in monsoon season, but during summer, homogenous conditions prevailed. Dissolved oxygen showed invariably high values during low tides of day time. However, the variation between high and low tide was not significant. Light attenuation coefficient was low during summer when the estuary was dominated by clear neritic water and high during monsoon season owing to the heavy freshwater flow. Although no definite tidal variation in light attenuation coefficient was noticed, the values were generally higher during low tides. pH showed no definite seasonal or tidal variation. The surface-bottom difference in all the parameters was insignificant owing to the shallowness of the estuary