Remediation using biochar as a soil amendment, is a useful technique that can be applied at both low cost and low impact to terrestrial and aquatic ecosystems to immobilize and decrease toxicity. In this study, floodplain sediment was collected locally from Phinizy Swamp, which experiences annual periodic flooding. Flooding events provide anaerobic conditions which can stimulate methylation of Hg and trophic transfer. Flooding conditions were simulated in this microcosm study with spiked inorganic HgCl2, and biochar treatment; rice husk and peanut hull biochar, both applied unmodified and sulfur modified at 10 and 40 g Kg-1. Results indicate that biochars reduced the overall concentration of THg in all treatments compared to controls. However, the % MeHg slightly increased in sulfur-modified treatments compared to unmodified biochars and controls over time. This may indicate that increases in bioavailable Hg and methylation potential are related to sulfur-modified biochar interactions in the mixed sediment layer.