A finite element model of mercury species fate in the Detroit River water column and sediment

As mercury is considered one of the most toxic metals found in the environment, its speciation is an important consideration in any representation of its fate, transport and availability for biogeochemical reactions. A speciation model was developed to estimate the concentrations for three mercury components—elemental mercury, divalent mercury and methyl mercury in the Detroit River water column and sediment. The model is based on the solution of six continuity equations for water column and sediment in the Detroit River, using FEMLAB software as a solver applies the finite element method under the MATLAB environment.; As the water residence time in Detroit River is considered long compared to rapid kinetic processes, the model is considered to be at steady state. The steady state average concentrations for three mercury species in the water column indicate that the higher concentrations of three mercury species were found in shore segments while mid-river segments for both water column and sediment were recorded less concentration. The relative magnitude of three mercury species in the water column is in the order of Hg+2 > MHg > Hg0. In sediment, the higher concentration for the three species were recorded in the same segments of higher water concentrations with the relative magnitude of Hg0 >> Hg+2 > MHg.; The Detroit River water column mercury species mass balances showed that this model is a mass conservative, where total input is equal to the total output. A good matching was found between the model output and the simplified cases for which analytical solutions was available for idealized geometries and linear reaction kinetics. Also, the program was tested for robustness by estimating zero input concentrations. This gives zero output concentrations for all species, which indicate that the model doesn't create results.; For future work, we would recommend that Detroit River should be studied in a three dimensional system with attention to study each species' kinetics at air/water and water/sediment surface microlayer. Also the bio-concentration factor for each species in each level of food chain should be taken into consideration.