Dept. of Environmental Science and Engineering
Oregon Graduate Institute of Science & Technology
A spatially and temporally explicit numerical model for the fate and transport of nonconservative metals in an estuarine environment was developed, tested, and applied. This model, known as ELAmet, solves the depth-averaged advection/dispersion/transformation equation on a 2-dimensional grid using a finite element formulation in an Eulerian-Lagrangian framework. The model incorporates aqueous speciation and adsorption/desorption, and accommodates chemical equilibria and kinetics simultaneously. Application of the model was done in two phases. A preliminary application was used to illustrate the concept of diagnostic modeling for a synthetic estuarine system. The possible effects of source location, chemical kinetics, and sediment deposition on the observed mixing plot (concentration as a function of salinity) was examined. The results indicate that the "true" mixing plot can occupy a 2-dimensional region in concentrationsalinity space, and that sparse field sampling may result in an incomplete representation of the mixing plot. In a more extensive application, ELAmet was used to investigate the effect of adsorption kinetics on the apparent distribution coefficients of copper, cadmium and zinc in South San Francisco Bay, California. The numerical experiments were designed with three goals in mind: 1) to use a spatially and temporally explicit modeling approach to extrapolate laboratory partitioning data to an environmental setting, 2) to establish that adsorption kinetics can control the basin-scale variability of the observed partitioning and therefore the apparent dependencies of partitioning on salinity and suspended solids, and 3) 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 the profile of the apparent distribution coefficient K[subscript]d[superscript]a if the system is close to equilibrium. However, if the system is far from equilibrium the profile of K[subscript]d[superscript]a and its apparent dependencies on salinity and suspended solids will be determined by the location of the sources of metal, and the suspended solids concentration of the receiving water. The results also indicate that the further the basin as a whole is from equilibrium, the greater the basin-scale variability in K[subscript]d[superscript]a that would likely be observed during a single sampling cruise. This work has interesting implications for the interpretation of field data from San Francisco Bay. Apparent distribution coefficients from two different years exhibit strong dissimilarities; K[subscript]d[superscript]a values for copper, cadmium, and zinc during 1989 are generally higher and more variable than those observed during 1985.
Wood, Tamara Michelle, "Numerical modeling of estuarine geochemistry" (1993). Scholar Archive. 134.