LINKAGES BETWEEN BIOAVAILABILITY AND EQUILIBRIUM KINETICS IN A FRESHWATER SYSTEM

Metal speciation in freshwater systems is a function of the dissolved concentration of inorganic and organic ligands. The ligand concentration is then, in turn, a function of the chemical and physical hydrology of the system. With the assumption that a system is under steady state conditions or at least in a quantifiable non-steady state conditions it is possible to quantify the availability of metal species in the dissolved load of rivers. By quantifying the spatial and temporal variations of these species it is then possible to develop a model of bioavailability and so assess the toxicology of these metals in the system under investigation.

Through a series of equilibrium kinetic models, end-member mixing models, and species abundance data we assessed the impact of above background metal concentrations in the Spring River of Arkansas. The impact of metal concentrations is assessed by identification of the potential sources of metals and the chemical processes controlling metal transformations from bioavailable to non-bioavailable forms. Samples were collected at least once a month from 12 sites within the Spring River using trace metal clean techniques. Speciation modeling using equilibrium models such as PHREEQC and MINETAQ. End-members were identified by modified Q-mode factor analysis (e.g., EMMA). Based on our data and models we were able to quantify spatial and temporal variation in metal species bioavailability. These data were then compared to fish population data to explore the impact on the populations (age and growth structure) of toxic and bioavailable metal concentrations.