A MODEL OF THE EXCHANGE OF INORGANIC CHEMICALS BETWEEN WATER AND SEDIMENTS

A simple mathematical model is developed to describe the movement of radioisotopes added to lake enclosures, first during initial loss from water to sediments, and second during release from sediments into isotope-free water. The model is based on the concept of “aquivalent” concentration, an equilibrium criterion analogous to fugacity, but suitable for involatile chemicals. It treats two homogeneous compartments, water and an active layer of sediments, and exchange by bidirectional diffusion, sediment deposition, and resuspension. Model simulations of isotope loss agree well with experimental results obtained for seven isotopes added to two lake enclosures. Simulations of isotope release from sediments were satisfactory but less accurate. The results illustrate that the behavior of isotopes can be estimated from their differing particle-sorption characteristics, as quantified by the isotope-specific Kp and by enclosure-specific suspended particle concentrations and sediment deposition/resuspension rates. © 1990, American Chemical Society. All rights reserved.