WA4 Metals in the Environment: Chemistry and Fate Issues
Room 16A/B, Level 4
8:00 AM - 12:00 PM, Wednesday, 12 November 2003
Chair: Bell, Russell ,
Co-chair: Campbell, Peter ,
(359) Sensitivity of metal fate and transport results to speciation estimates from different chemistry models.
Bhavsar, S1, Cheng, T2, Diamond, M1, Allen, H2, Gandhi, N1, Alfaro-De la Torre, M3, 1 University of Toronto, Toronto, ON, Canada2 University of Delaware, Newark, DE, USA3 Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
ABSTRACT- The distribution of metal species, which is controlled by site-specific ambient chemistry, influences metal fate in aquatic systems. We investigated the sensitivity of fate results to metal speciation estimates using TRANSPEC, a coupled metal fate-TRANsport and SPECiation/complexation model. We used two speciation models, MINEQL+ and WHAM. MINEQL+ supports an extensive database for many elements whereas the WHAM is more fully developed for trace metal-DOM interactions. MINEQL+ uses a more flexible structure while WHAM has a robust assembly that does not entertain solubility limitations and redox reactions. MINEQL+ and WHAM provide similar estimates of aqueous speciation (not including DOM) and surface complexation to iron oxyhydroxides, but WHAM considers sorption to clays and to organic components of particles. TRANSPEC sequentially couples a speciation/complexation model with our fugacity/aquivalence-based multispecies fate model. This model explicitly considers ambient chemistry by estimating metal speciation and partition coefficients, Kd, and tracks multiple, interconverting species in the water column and two vertical sediment layers of a lake. The steady-state version TRANSPEC was used to assess the fate of Zn and Cd in a meso- and a eutrophic lake that differ in metal and DOM concentrations (Ross and Tantare Lakes, respectively). MINEQL+ estimates less metal sorption to DOM which influences estimated rates of sediment-water diffusive exchange. Depending on redox conditions in the upper sediment layer, particularly in the eutrophic lake, diffusive exchange is secondary to particle transport as the dominant transport process. Thus, speciation estimates obtained from MINEQL+ and WHAM changes metal fate under some but not all conditions.
Key words: coupled model, speciation and fate, metals in lakes, multispecies metal model