The following six figures show the experimental setup and data.  The first figure shows the chambers with light-occluding foil covers.  Tests were performed in triplicate on chambers with either oxic or anoxic water columns, and with or without iron addition.  After six months the overlying water, sediment solids and sediment porewater were analyzed.  The second figure shows an anoxic chamber treated with FeO and the presence of oligochaete galleries.  The third and forth figures show that MeHg is higher in untreated chambers, especially under anoxic conditions.  The fifth figures shows the effects of iron addition on overlying water under both oxic and anoxic conditions.  MeHg was below the detection limit in both cases.  The last figure shows the shift in MeHg concentrations caused by iron addition compared to controls.  MeHg production decreases at the surface and increases at depth, and with a net decrease in total production.
Anoxic chamber with FeO addition