Comment on and Reinterpretation of Gabriel et al. (2014) ‘Fish Mercury and Surface Water Sulfate Relationships in the Everglades Protection Area’

Mercury (Hg) methylation and bioaccumulation is a major environmental issue in the Everglades Protection Area (EvPA). Therefore, it is critical to improve our predictive understanding of Hg dynamics. This commentary critically reviews a recently published manuscript concerning the possible relationship between Hg in fish tissue and surface water sulfate within EvPA marshes. The commentary addresses fundamental issues with the authors’ data analysis, results and interpretation as well as highlights inconsistencies with published literature and the lack of support for their suggested ecosystem management actions. A number of chemical, biological, and physical factors influence Hg methylation and bioaccumulation, and water sulfate is sometimes viewed as a keystone factor, Gabriel et al. (2014) conclude that Hg bioaccumulation is favored at elevated sulfate concentrations, and suggest mitigation strategies to reduce sulfate inputs to the EvPA. A careful review of their data and conclusions reveals major flaws and in fact, a more straightforward and defensible interpretation of their data would be that no predictable relationship exists between fish tissue Hg and surface water sulfate concentrations in south Florida. Given the complexity of Hg cycling and the influence of trophic and habitat characteristics on aquatic consumer Hg accumulation, expecting one parameter to predict Hg accumulation dynamics within fish species within a dynamic marsh environment is unrealistic. Furthermore, proposing any management guidance from this relationship with little to no quantitative statistical analysis is inappropriate and misleading.