AUTHIGENIC MINERALIZATION AND DETRITAL CLAY BINDING BY FRESH-WATER BIOFILMS - THE BRAHMANI RIVER, INDIA

Epilithic biofilms, growing on submerged boulders, were collected upst ream and downstream of sites of industrial discharge into the Brahmani Rivet; Orissa Slate, India. Transmission electron microscopy (TEM) sh owed that the outer cell walls of attached bacteria in all samples wer e often encrusted with fine-grained (<1 mu m) inorganic precipitates. The density of mineralization ranged from a few epicellular grains to complete encrustation by clayey materials. Energy-dispersive x-ray spe ctroscopy (EDS) and selected-area electron diffraction (SAED) indicate d that the most abundant inorganic phase was a complex, poorly ordered , (Fe, All-silicate of variable composition, containing minor amounts of potassium. No trace metals were detected in the authigenic precipit ates. Bacterial cells were also found to entrap or adsorb detrital min erals such as kaolin, mica, quartz, iron oxide, and gibbsite onto thei r outer surfaces. Because epilithic microbial biofilms have a very lar ge and highly reactive surface area, binding of major solutes and/or s uspended detrital sediment will influence the chemical composition of the substrate-water interface and. ultimately contribute to the makeup of the river bottom sediment.