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

Physico-chemical parameters like pH, salinity, alkalinity, nutrients (nitri te, phosphate and silicate) and major ions (Ca, Mg, Na and K) were determin ed in 12 water samples and calcium carbonate, organic carbon, sand, silt, c lay percentages and trace-element (Fe, Mn, As and Cd) concentrations were a nalysed 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 ad d 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 th ousand 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 concentra tions in the sediments during postmonsoon, whereas the increase during prem onsoon is in response to decrease in clay content, Fe-Mn oxides and organic carbon. Application of arsenical herbicides in the river basin area and bu rning of coal in the nearby Ennore Thermal Power plant contribute arsenic a nd cadmium to this lake sediments.