Seasonal variability of physico-chemical characteristics of the Haldia channel of Hooghly estuary, India

Physical and chemical characteristics of the Hooghly estuary during winter (December 1997-January 1998), summer (May 1998) and post-monsoon (November 1998) seasons have been studied. Salinity varied spatially and temporally and seasonally during ebb and flood tide conditions. Water temperature showed a difference of 10 degrees C in winter to summer. Temperature did not vary much vertically as it is a well-mixed estuary. Strong currents exceeding 100 cm s(-1) were observed during peak ebb and flood tide conditions irrespective of the season. Longitudinal eddy diffusion coefficient (K-x) was estimated as 757 m s(-1) and 811 m(2) s(-1) during summer and post-monsoon seasons, respectively. The vertical eddy diffusion coefficient (epsilon(v)) was estimated as 0.0337 m(2) s(-1) during post-monsoon season. The salinity and current observations are compared with those obtained from models reported earlier. Values of pH, Dissolved Oxygen and Biological Oxygen Demand are within the threshold limits of the estuarine environment. Nutrients show seasonal variation in the estuarine environment. High values (160-2686 mg l(-1)) of total suspended matter were noticed both at surface and bottom in the study region showing the impact of fresh water and sediment transportation.