Diagnostic modeling of trace metal partitioning in south San Francisco Bay

The two-dimensional numerical model ELAmet was used to investigate the effect of adsorption kinetics on the apparent distribution coefficients of Cu, Cd, and Zn in south San Francisco Bay, California. The numerical experiments were designed to determine whether adsorption kinetics can control the basin-scale variability of the observed partitioning and to define the conditions under which adsorption kinetics could account for strong interannual variability in partitioning.

The numerical results indicate that aqueous speciation will control basin-scale spatial variations in the apparent distribution coefficient, K_d^a, if the system is close to equilibrium. However, basin-scale spatial variations in K_d^a are determined by the location of the sources of metal and the suspended solids concentration of the receiving water if the system is far from equilibrium. The overall spatial variability in K_d^a also increases as the system moves away from equilibrium.