Physico-chemical and geochemical studies in Pulicat. lake, east coast of India

Physico-chemical parameters like pH, salinity, alkalinity, nutrients (nitrite, phosphate and silicate) and major ions (Ca, Mg, Na and K) were determined in 12 water samples and calcium carbonate, organic carbon, sand, silt, clay percentages and trace-element (Fe, Mn, As and Cd) concentrations were analysed in 12 sediment samples. The results show that the concentration of As in the sediments during premonsoon and postmonsoon ranges from 10.1 - 51.0 mu g/g and 18.3 - 57.3 mu g/g, respectively; for Cd, 3.6 - 8.6 mu g/g add 4.7 - 11.5 mu g/g. Salinity of the water samples during premonsoon ranges between 35.2 and 41.6 parts per thousand, and from 1.4 to 6.6 parts per thousand during postmonsoon. Alkalinity during premonsoon varies from 65.9 - 100.0 meq/l, and 229.4 - 275.5 meq/l during postmonsoon. The variations in the results are mainly due to the inflow of seawater during premonsoon and the riverine input during postmonsoon. This study shows that heavy rainfall, high run-off and the fresh water input increase the trace metal concentrations in the sediments during postmonsoon, whereas the increase during premonsoon is in response to decrease in clay content, Fe-Mn oxides and organic carbon. Application of arsenical herbicides in the river basin area and burning of coal in the nearby Ennore Thermal Power plant contribute arsenic and cadmium to this lake sediments.