Using iron amendments to reduce mercury methylation in engineered wetland sediments

One potential drawback of wetland construction and restoration is the formation of monomethylmercury (MHg).; The research described in this dissertation was designed to test the hypothesis that addition of iron to wetland sediments decreases the extent of net mercury methylation by decreasing the activity of sulfide, and therefore the concentration of neutral, bioavailable mercury-sulfide complexes. This hypothesis was tested with a series of laboratory microcosm experiments.; Batch microcosm experiments employing pure cultures of the sulfate-reducing bacterium Desulfobulbus propionicus (1pr3) (Chapter 2) indicated that net mercury methylation decreased with increasing [Fe(II)]. The decrease in net mercury methylation was not attributable to the effect of iron on sulfate reduction rates. Instead, filterable mercury measurements and chemical equilibrium speciation model results suggest that the lower net MHg production in the high-iron treatments was due to a decrease in sulfide activity and a concomitant decrease in the concentration of dissolved, bioavailable inorganic mercury.; Sediment slurry experiments conducted using sediment and surface water from five estuarine wetlands (Chapter 3) were qualitatively consistent with the results of the pure culture experiments. Addition of 25 to 30 mM (or 0.07 mmol g-1 w.w.) Fe(II) to wetland sediments significantly decreased net mercury methylation relative to unamended controls.; Flow-through microcosm experiments designed to simulate conditions found in freshwater treatment wetlands and tidal salt marshes (Chapter 4) showed that significantly less methylmercury was present in the effluent of the iron-amended treatments, compared with the unamended controls. Significantly lower sulfide concentrations were measured in the effluent of the iron-amended treatments relative to the unamended controls for both the freshwater (after 8 days) and seawater (during the entire experiment) microcosms. (Abstract shortened by UMI.)...