A dynamic model of bioavailability of metals in constructed wetland sediments

Abstract Constructed wetlands used for stormwater treatment accumulate metals primarily in their sediment. This sediment has the potential to produce toxic effects in benthic or aquatic organisms. Bioavailability of metals in sediments is directly linked to pore water metal activity. The mechanisms that influence pore water metal activity include physical, chemical, and biological processes. A system dynamics model was developed to represent these processes and the major influences affecting pore water metal activity in a treatment wetland receiving stormwater influent. The model structure and behavior were tested and validated using several system dynamics validation techniques. The model was run using metal specific parameter values typical of metals commonly found in stormwater runoff. Simulation results demonstrate that chemical processes of acid volatile sulfide (AVS) and organic carbon in binding metal in reduced sediments are the greatest influences in controlling metal bioavailability. The effect of bioturbation, as represented in the model, was negligible. The amount of organic carbon in the sediment plays the biggest role in controlling metal bioavailability in the long run.