A multitracer study of radionuclides in Lake Zurich, Switzerland: 1. Comparison of atmospheric and sedimentary fluxes of 7Be, 10Be, 210Pb, 210Po, and 137Cs

Abstract

Atmospheric and sedimentary fluxes of natural ( i.e., 210Pb, 210Po, 7Be, and 10Be) and artificial (i.e., Chernobyl 137Cs ) radionuclides and particles through Lake Zurich (at 50 m and 130 m depth) between 1983 and 1987 were compared in order to establish trace metal pathways and their kinetics. Atmospheric fluxes averaged 0.83 dpm cm−2 yr−1 for 210Pb and 16.0 dpm cm−2 yr−1 for 7Be during 1984 to 1987. Vertical fluxes of 210Pb and 7Be, associated with settling particles, were measured in sediment traps deployed at 50 m and 130 m depth at a station near the deepest part of Lake Zurich. Average fluxes of 210Pb and 7Be at 50 m depth were 0.94 and 4.90 dpm cm−2 yr−1, respectively, and 16.5×107 atoms m−2 d−1 for 10Be. Sediment traps at 50 m quantitatively collected atmospherically deposited 210Pb falling through the water column. At 130 m depth, immediately above seasonally anoxic bottom waters, 210Pb, 10Be, and 137Cs fluxes were higher than at 50 m by up to 60% at times during the summer stagnation period. Sediment inventories of 210Pb and 10Be are in agreement with atmospheric nuclide fluxes, suggesting only moderate recycling of these nuclides in the bottom waters, whereas 137Cs inventory in the sediments is lower than expected from sediment trap fluxes, indicating immobilization of this nuclide.