Development of a coupled metal speciation‐fate model for surface aquatic systems

Abstract

A coupled metal transport and speciation model (TRANSPEC) has been developed for surface aquatic systems that explicitly considers the influence of metal speciation on fate. The TRANSPEC, which is general to most metal and surface aquatic systems, is constructed by sequentially coupling the speciation/complexation module (in this application MINEQL+) with the fugacity/aquivalence approach for the fate calculations. This model formulation increases the mechanistic detail, predictive power, and fidelity to reality of current fugacity-aquivalence fate models for metals by estimating aqueous speciation and complexation, rather than relying on empirically derived partition coefficients. A pseudo-steady state version of TRANSPEC was used to simulate Zn dynamics in Ross Lake (Flin Flon, MB, Canada) that received elevated metal and organic matter inputs for over 50 years. Field studies revealed that ZnS forms soluble ZnL, Zn2+, and ZnSO4(0) increasing pore water concentrations when surficial sediments turn oxic during fall. The model results for three seasonal scenarios suggest that Zn remobilization is driven by resuspension of insoluble ZnS and the contribution of diffusion is negligible, even during fall when ZnS dissolves to increase the concentration of soluble species under oxic conditions in the sediments. The low diffusive flux is due to the binding of Zn to colloidal dissolved organic matter (DOM) for which sediment-water diffusion is relatively slow, a result that was obtained as a result of considering metal speciation in the fate calculations.

Impacts and prognosis of natural resource development on water and wetlands in Canada’s boreal zone

“…However, arsenic concentrations increased through that period to the end of the study, apparently the result of remobilization of arsenic stored in sediments (Martin and Pedersen 2002). Similarly, a lake near Flin Flon, Manitoba, that received metal loadings for more than 50 years from metal mining and processing in the region showed increasing levels of zinc in recent years despite improved water treatment and reduced discharges of zinc (Bhavsar et al 2004). They attributed the increased zinc concentrations to mobilization of historically deposited zinc in the lake drainage basin.…”

Contaminant fate and transport in the Venice Lagoon: Results from a multi-segment multimedia model

“…In order to account for metal chemistry and phase, Bhavsar et al (2004) introduced the TRANsport-SPECiation model or TRANSPEC, where a speciation-complexation model is loosely coupled with the multi-species aquivalence fate and transport model (Diamond et al, 1992). The speciation-complexation model calculates two system-and speciesspecific values of K d s (distribution coefficients): K dCD (colloidal-to-dissolved phases) and K dPD (particulate-to-dissolved phases) for total metal and metal species based on ambient aqueous phase chemistry.…”

“…Diffusion between the water column and upper sediment was enhanced by a factor of two to account for bio-irrigation (Wang and Matisoff, 1997;Wijsman et al, 2002). Diffusion of colloidally bound metals was calculated according to the DOC concentration gradient (Bhavsar et al, 2004) with the MTC obtained from Valsaraj et al (1993Valsaraj et al ( , 1996. Pore water DOC measurements were obtained from four sediment cores representing segments 2, 6 and 7.…”

“…We segmented the Lagoon according to modelled hydrodynamic circulation patterns (Solidoro et al, 2004a) and explicitly considered sediment erosion. In addition, for metals we incorporated the loosely coupled TRANsport and SPECiation model (TRANSPEC) (Bhavsar et al, 2004) to account for metal chemistry. Below, we describe the model and its parameterization for the Venice Lagoon.…”

Modelling, Transport and Assessment of Aquatic Toxic Metals in Coastal Ecosystems

“…Thus, it is important to differentiate between the typical characteristic climate periods in the study area, such as summertime and wintertime, because the dynamics can significantly change [54]; for instance, they have influence on parameters that define the transport of solutes such as salinity [55] or sediments [26,56,57]. For the purpose of yielding to results which can be compared with stationary measurements in situ, we selected wet and dry seasons for this study, as they are detailed in Table 1.…”