Sl. Smith et Pr. Jaffe, MODELING THE TRANSPORT AND REACTION OF TRACE-METALS IN WATER-SATURATED SOILS AND SEDIMENTS, Water resources research, 34(11), 1998, pp. 3135-3147
A model has been formulated of the equilibrium speciation, kinetic rea
ction, and transport of trace metals in the presence of biodegradation
of organic substrates in saturated porous media. Kinetics of various
processes (biodegradation, chemical reactions, and precipitation and d
issolution of minerals) together with transport processes (advection,
bioturbation, and diffusive/dispersive mixing) are quantified in a set
of coupled mass balance equations (for the organic substrate, electro
n accepters, reduced species, and trace metals). These steady state, o
ne-dimensional equations are discretized using a second-order-accurate
finite difference approximation. A pE is estimated at each node in th
e domain on the basis the concentrations calculated and the half react
ion for the dominant terminal electron acceptor at that location. The
dynamic model is coupled iteratively to a modified version of the U.S.
Environmental Protection Agency's MINTEQA2, which calculates equilibr
ium chemical speciation (including aqueous speciation, adsorption, and
precipitation of minerals) at each node of the domain. The primary de
pendent variables are the total dissolved concentrations of the aqueou
s species together with the solid concentrations of the minerals. To d
emonstrate that this formulation can simulate biodegradation using rea
ction rates consistent with published values, simulations are compared
to data from the sediment pore waters of a small lake. Simulations ar
e presented of the transport and reaction of arsenic in lake sediments
to illustrate how this model can be used to evaluate trends in trace
metal mobility as affected by various water quality parameters through
their influence on the biogeochemistry of natural systems.