Whole-lake nitrate addition for control of methylmercury in mercury-contaminated Onondaga Lake, NY David A. Matthews a,n , David B. Babcock b , John G. Nolan b , Anthony R. Prestigiacomo a , Steven W. Effler a , Charles T. Driscoll c , Svetoslava G. Todorova c , Kenneth M. Kuhr b a Upstate Freshwater Institute, P.O. Box 506, Syracuse, NY 13214, United States b Parsons, 301 Plainfield Road, Suite 350, Syracuse, NY 13212, United States c Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY 13244, United States article info Available online 17 May 2013 Keywords: Mercury Nitrate Sediment release Lakes Remediation abstract Methylmercury (MeHg) strongly bioaccumulates in aquatic food webs resulting in exposure to humans and wildlife through consumption of fish. Production of MeHg is promoted by anaerobic conditions and the supply of inorganic Hg (Hg 2+ ), sulfate (SO 4 2- ), and labile organic carbon. The anaerobic sediments of stratified lakes are particularly active zones for methylation of Hg 2+ and can be an important source of MeHg to the water column during summer anoxia and fall turnover. Nitrate (NO 3 – ) addition has recently been proposed as a novel approach for the control of MeHg accumulation in the hypolimnia of Hg- contaminated lakes. In 2011, a whole-lake NO 3 – addition pilot test was conducted in Hg-contaminated Onondaga Lake, NY with the objective of limiting release of MeHg from the pelagic sediments to the hypolimnion through maintenance of NO 3 – –N concentrations 41 mg N/L. A liquid calcium-nitrate solution was added to the hypolimnion as a neutrally buoyant plume approximately three times per week during the summer stratification interval. Maximum hypolimnetic concentrations of MeHg and soluble reactive phosphorus (SRP) decreased 94% and 95% from 2009 levels, suggesting increased sorption to Fe and Mn oxyhydroxides in surficial sediments as the regulating mechanism. Increased MeHg concentrations in the upper waters during fall turnover, which had been a generally recurring pattern, did not occur in 2011, resulting in decreased exposure of aquatic organisms to MeHg. Over the 1992–2011 interval, the hypolimnetic NO 3 – supply explained 85% and 95% of the interannual variations in hypolimnetic accumulations of SRP and MeHg, respectively. & 2013 Elsevier Inc. All rights reserved. 1. Introduction Bioaccumulation of mercury (Hg) in aquatic food webs is a global environmental problem (Mergler et al., 2007) that has been exacerbated by dramatic increases in anthropogenic inputs over the past 150 years (Fitzgerald et al., 1998). Atmospheric emissions from electric utilities, mining, and natural sources have caused widespread exposure of aquatic ecosystems to Hg, while direct discharges of inorganic Hg (Hg 2+ ) from mining and industrial operations, such as chlor-alkali facilities, generally result in more localized contamination of water, sediments, and biota. Human health risks associated with Hg contamination are primarily the result of consumption of contaminated fish. In the U.S., 81% of all fish consumption advisories in effect in 2010 were based at least partly on Hg, including 16,400,000 lake acres (USEPA, 2010). The organic form of mercury, methylmercury (MeHg), is of particular concern because it bioaccumulates strongly in aquatic food webs, resulting in toxic effects at upper trophic levels when concentrations are high (Sandheinrich and Wiener, 2011). Sulfate reducing bacteria (SRB) are the principal methylators of Hg 2+ (Benoit et al., 2003), though production of MeHg has also been attributed to iron-reducers (Fleming et al., 2006; Kerin et al., 2006) and syntrophic relationships between SRB and methanogens (Pak and Bartha, 1998). Production of MeHg is promoted by anaerobic conditions and the supply of Hg 2+ , sulfate (SO 4 2- ), and labile organic carbon. Sediments have been found to be an important source of MeHg to the water column in both coastal (Hammerschmidt and Fitzgerald, 2008; Hollweg et al., 2010) and freshwater (Regnell et al., 1997; Sellers et al., 2001) ecosystems. Anaerobic sediments and bottom waters of stratified lakes are particularly active zones for methylation of Hg 2+ and can be an important source of MeHg to the water column during summer anoxia and fall turnover (Herrin et al., 1998; Wollenberg and Peters, 2009). Phytoplankton actively uptake MeHg from the water column and represent the primary entry point for Hg in aquatic food webs (Pickhardt and Fisher, 2007). Accordingly, the MeHg concentra- tion in the water is the key factor determining the concentration of Hg in the biota (Morel et al., 1998; Rolfhus et al., 2011). Recent experimental evidence that fish and other aquatic biota respond directly and rapidly to changing Hg inputs (Harris et al., 2007; Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/envres Environmental Research 0013-9351/$ - see front matter & 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.envres.2013.03.011 n Corresponding author. Fax: +1 315 431 4969. E-mail address: damatthews@upstatefreshwater.org (D.A. Matthews). Environmental Research 125 (2013) 52–60