partmentalization) but no additional water quality features (i.e., scenario 2 in Box 4-1), it is anticipated that fish mercury concentrations would decrease. With the restoration of sheet flow the interaction of water with wetlands will likely facilitate the removal of sulfate, thereby reducing methyl mercury formation and fish mercury concentrations. Additionally, increased phosphorus concentrations associated with scenario 2 lead to greater biodilution of mercury.
This projected outcome of hydrologic change is based on considerable speculation about the driver of system response (i.e., biodilution). Other outcomes may occur. Alternating drying and wetting cycles can facilitate mineralization of organic sulfur in peat deposition, releasing sulfate followed by the methylation associated with the subsequent sulfate reduction. Restoration of a more normal hydroperiod to the Everglades would likely diminish this phenomenon and could decrease fish mercury concentrations. Also the committee has assumed that elimination of channelized flow with decompartmentalization would decrease sulfate transport southward and decrease fish mercury concentrations. However, a more distributed transport of sulfate, which would be a by-product of decompartmentalization, would likely spread out mercury contamination in fish. The committee believes this action would result in an overall decrease in fish mercury concentrations, but this management action could increase fish mercury concentrations in areas of the Everglades that previously have not experienced high concentrations.
If improved controls on phosphorus supply decrease phosphorus loading to the Everglades, fish mercury concentrations could increase. This response would be due to decreases in biomass production associated with decreases in nutrient loading and a resulting decrease in the biodilution of fish mercury. Finally, management measures that involve simultaneous increases in discharge and decreases in phosphorus would likely decrease fish mercury because of the effectiveness of decompartmentalization in the immobilization of sulfate (but see above discussion). These effects are summarized in Table 4-1.
Most of the historical Everglades was underlain by organic-rich peat soils (Figure 4-16), approximately 2 to 10 feet thick. The peat soil’s thickness decreased toward the southern Everglades, where it formed a thin, sometimes patchy layer over marl soils (McVoy et al., 2011).8 In addition to providing the substrate for the sawgrass plains and ridge-and-slough landscapes, peat soils in the Everglades provided the critical elevation differences that hydrologically dif-
8Marl soils are comprised of calcitic mud deposited from calcareous periphyton and have lower organic content.