Whole-Lake Metal Radiotracer Movement in Fertilized Lake Basins

Abstract

Seven radiotracers: 75Se, 203Hg, 85Sr, 134Cs, 59Fe, 65Zn, and 60Co were added to the separated basins of Lake 226, Experimental Lakes Area, northwestern Ontario. The basins, L226N and L226S were part of an ongoing eutrophication experiment in which C, N, and P were being added to L226N and C and N to L226S. The radiotracers moved to the sediments by sorption to settling particles and by being directly absorbed. The loss rates ranged from 3–8%∙d−1. Areal distribution in the sediments was largely governed by the percent sorbed to particles. Both basins exhibited seasonal anoxic hypolimnia in which redissolution of 59Fe, 60Co, and 203Hg was great, of 75Se, 85Sr, and 65Zn only minimal, and of 134Cs negligible. The overall behavior of each of the isotopes was nearly identical in the two basins, partly due to interbasin mixing. A least squares fit of the affinity for particles and loss rates to a whole-lake model yielded a settling velocity of 0.18 m∙d−1 and a benthic boundary layer of 370 μm thickness.