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

Mark C Gabriel,Nicole Howard,Todd Z Osborne

doi:10.1007/s00267-013-0224-4

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.

Highlights

Over the recent 20 years, the South Florida ecosystem has experienced excessive mercury bioaccumulation, resulting in widespread fish consumption advisories (FDOH 2008)
Peak fish THg levels were present in surface waters with sulfate concentration between 1 and 10 mg/L
The fish THg and sulfate relationships in our study are highly similar to relationships between MeHg production and sulfate in sediment pore water observed in other studies (Gilmour et al 1992, 2007; Benoit et al 1999a, b)

Summary

Introduction

Over the recent 20 years, the South Florida ecosystem has experienced excessive mercury bioaccumulation, resulting in widespread fish consumption advisories (FDOH 2008). The primary concern with mercury in ecosystems is the production and bioaccumulation of MeHg, a neurotoxin that poses a threat to humans (USEPA 2013) and wildlife (Eisler 1987; Spalding et al 2000) who consume fish and other biota. Field and laboratory experiments demonstrate that production of MeHg is enhanced by microbial sulfate reduction (MSR) under anoxic conditions (Gilmour et al 1992, 1998; Benoit et al 2003; Harmon et al 2004, 2007; Jeremiason et al 2006; Mitchell and Branfireun 2008; Shao et al 2012). Persistent MeHg production in the greater Everglades is primarily a result of a large quantity of (1) bioavailable mercury delivered by atmospheric deposition, (2) electron donors [labile dissolved organic carbon (DOC), e.g., lactate, acetate] Other Everglades factors such as circumneutral pH and highwater temperature aid efficient development of MeHg

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