Fish Mercury and Surface Water Sulfate Relationships in the Everglades Protection Area

Abstract

Few published studies present data on relationships between fish mercury and surface or pore water sulfate concentrations, particularly on an ecosystem-wide basis. Resource managers can use these relationships to identify the sulfate conditions that contain fish with health-concerning total mercury (THg) levels and to evaluate the role of sulfate in methyl-mercury (MeHg) production. In this study, we derived relationships between THg in three fish trophic levels (mosquitofish, sunfish, and age-1 largemouth bass) and surface water sulfate from 1998 to 2009 for multiple stations across the Everglades Protection Area (EPA). Results show the relationship between sulfate and fish THg in each fish type is nonlinear and largely skewed, similar to the relationship between MeHg production and sulfate concentration in peatland sediment pore water identified by other researchers. Peak fish THg levels occurred in ~1 to 12 mg/L sulfate conditions. There was significant variability in the fish THg data, and there were several instances of high-fish THg levels in high-sulfate conditions (>30 mg/L). Health-concerning fish THg levels were present in all surface water sulfate conditions; however, most of these levels occurred in 1–20 mg/L sulfate. The data in this study, including recent studies, show consistent and identifiable areas of high- and low-fish THg across the spectrum of surface water sulfate concentration, therefore, applying an ecosystem-wide sulfur strategy may be an effective management approach as it would significantly reduce MeHg risk in the EPA.

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

“…In fact, we suggest that their data demonstrate that no predictable relationship exists between sulfate and THg in fish of the Everglades. As a result, the management guidance in Gabriel et al (2014) for Hg and S in the Everglades is not justified by the data and information provided.…”

“…Even though Gabriel et al (2014) brought significant detail to the Materials and Methods, several key topics were overlooked that could materially influence the conclusions drawn by the authors. Topics lacking adequate coverage include: inclusion of monitoring locations outside of the actual EvPA, pairing fish tissue and surface water sulfate monitoring locations, the comparability of data normalizations, and most important, the lack of quantitative statistics.…”

“…3 (Gabriel et al 2014) problematic. While not discussed in the manuscript, different tissue types are associated with varying levels of Hg accumulation.…”

“…2. Gabriel et al (2014) used data from a small number of sampling sites (12 fish and 12 sulfate stations) with very different characteristics (Fig. 2).…”

Impact and Mitigation of Nutrient Pollution and Overland Water Flow Change on the Florida Everglades, USA

“…Sulfate stimulates the metabolic pathways of sulfate reducing bacteria in sediments, co-metabolizing inorganic mercury into methylmercury, a persistent, bioaccumulative and neuro-toxic compound that impacts the aquatic food chain. A relationship between surface water sulfate and total mercury in fish has identified water sulfate management as a target for mercury risk management in the Everglades Protection Area [53]. Over 4000 km 2 are contaminated with mercury and the Everglades has some of the highest observed mercury levels in fish for the U.S. [1,54].…”