IDENTIFYING RESUSPENDED PARTICLES USING ISOTOPE RATIOS

Three simple methods were developed to estimate the proportion of part icles in lake water derived from resuspended material. These technique s use the different distributions of long and short-lived radioisotope s sorbed onto particles and were tested in the three basins of Lake Er ie using Be-7, Cs-137 and Po-210/Pb-210. While the concentration of Po -210 on particles did not vary significantly in the lake, resuspended particles were characterized by high concentrations of Cs-137 and low concentrations of Be-7. The distribution of these radioisotopes is con sistent with a simple mixing model in which the fraction of particles in the lake water derived from resuspension ranged from less-than-or-e qual-to 8% to about 100%. Higher concentrations of resuspended particl es were found in deeper samples from the nepheloid layer and in the sh allow western basin where thermal stratification was very weak.