ROLE OF DIATOMS AS INDICATORS OF POLLUTION GRADIENTS

The impact of liquid wastes from a paper mill on the benthic diatoms i n flowing waters has been studied for a period of two years. Water and algal samples were analysed at monthly intervals at three sites along the course of the river, along with raw effluents. The water before t he confluence of effluents was well oxygenated with an alkaline pH. Or ganic matter, NH3 and nutrients were recorded at low concentrations. A t the entry of effluents, the water showed considerable decline in dis solved oxygen content, increase in organic matter, hardness, Cl, HCO3 and total dissolved solids. Diatoms constituted 61% by numerical abund ance and were reduced to 25% of total algae at the entry of effluents. Multiple regression analysis was employed to discover the relative im portance of various physicochemical variables on the abundance and dis tribution of diatoms at various sampling stations. Mathematical equati ons were derived involving the physicochemical variables for better pr ediction of algal number.