This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Environmental Research 119 (2012) 118–131 Contents lists available at SciVerse ScienceDirect Environmental Research journal homepage: www.elsevier.com/locate/envres Nutrient supply and mercury dynamics in marine ecosystems: A conceptual model$ Charles T. Driscoll a,n, Celia Y. Chen b, Chad R. Hammerschmidt c, Robert P. Mason d, Cynthia C. Gilmour e, Elsie M. Sunderland f, Ben K. Greenfield g, Kate L. Buckman b, Carl H. Lamborg h a Department of Civil and Environmental Engineering, Syracuse University, 151 Link Hall, Syracuse, NY 13244, USA b Department of Biological Sciences, Dartmouth College, HB 6044, Hanover, NH 03755, USA c Department of Earth & Environmental Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA d Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, USA e Smithsonian Environmental Research Center, PO Box 28, Edgewater, MD 21037, USA f Harvard School of Public Health, Harvard University, 401 Park Drive, Boston, MA 02215, USA g San Francisco Estuary Institute, 4911 Central Avenue, Richmond, CA 94804, USA h Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, USA article info abstract Available online 30 June 2012 There is increasing interest and concern over the impacts of mercury (Hg) inputs to marine ecosystems. One Keywords: of the challenges in assessing these effects is that the cycling and trophic transfer of Hg are strongly linked to Eutrophication other contaminants and disturbances. In addition to Hg, a major problem facing coastal waters is the impacts Coastal ecosystems of elevated nutrient, particularly nitrogen (N), inputs. Increases in nutrient loading alter coastal ecosystems in Marine ecosystems ways that should change the transport, transformations and fate of Hg, including increases in fixation of Mercury organic carbon and deposition to sediments, decreasesintheredoxstatusofsedimentsandchangesinfish Nitrogen habitat. In this paper we present a conceptual model which suggests that increases in loading of reactive N to Nutrients marine ecosystems might alter Hg dynamics, decreasing bioavailabilty and trophic transfer. This conceptual model is most applicable to coastal waters, but may also be relevant to the pelagic ocean. We present information from case studies that both support and challenge this conceptual model, including marine observations across a nutrient gradient; results of a nutrient-trophic transfer Hg model for pelagic and coastal ecosystems; observations of Hg species, and nutrients from coastal sediments in the northeastern U.S.; and an analysis of fish Hg concentrations in estuaries under different nutrient loadings. These case studies suggest that changes in nutrient loading can impact Hg dynamics in coastal and open ocean ecosystems. Unfortunately none of the case studies is comprehensive; each only addresses a portion of the conceptual model and has limitations. Nevertheless, our conceptual model has important management implications. Many estuaries near developed areas are impaired due to elevated nutrient inputs. Widespread efforts are underway to control N loading and restore coastal ecosystem function. An unintended consequence of nutrient control measures could be to exacerbate problems associated with Hg contamination. Additional focused research and monitoring are needed to critically examine the link between nutrient supply and Hg contamination of marine waters. & 2012 Elsevier Inc. All rights reserved. $This publication was made possible by NIH Grant Number P42 ES007373 from 1. Introduction the National Institute of Environmental Health Sciences (to CC and RM). Support also was provided by New York State Energy Research and Development Authority 1.1. Background on nutrients (nitrogen), organic carbon and (to CTD), the U.S. National Science Foundation in two separate grants (to CRH and to RM and CG), and the Hudson River Foundation (to RM). This is a contribution of mercury in estuaries the C-MERC initiative. This research has not involved human subjects or experimental animals. Increases in mercury (Hg) contamination of marine ecosys- n Corresponding author. Fax: þ1 315 443 1243. tems, primarily from anthropogenic inputs, have been largely E-mail addresses: [email protected] (C.T. Driscoll), [email protected] (C.Y. Chen), manifested through elevated concentrations of the more bioaccu- [email protected] (C.R. Hammerschmidt), mulative form methylmercury (MeHg) in food webs. Thousands [email protected] (R.P. Mason), [email protected] (C.C. Gilmour), of estuaries and freshwaters in all states and two territories of the [email protected] (E.M. Sunderland), United States are listed by the Environmental Protection Agency bengreenfi[email protected] (B.K. Greenfield), as impaired due to high concentrations of Hg in fish (Table 1). [email protected] (K.L. Buckman), [email protected] (C.H. Lamborg). However, most studies do not show a linear relationship between 0013-9351/$ - see front matter & 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.envres.2012.05.002 Author's personal copy C.T. Driscoll et al. / Environmental Research 119 (2012) 118–131 119 Table 1 eutrophication often leads to greater pelagic versus benthic Summary of waterbody impairments and Total Maximum Daily Loads (TMDLs) for production in estuaries (Paerl et al., 2001; Cloern, 2001). Further- mercury and nutrients in U.S. waters (total and coastal) based on state 303(d) lists more, when the algae die and decompose, oxygen in bottom submitted to and approved by EPA as required by the Clean Water Act. Source: U.S. EPA (Environmental Protection Agency), 2011a, 2011b. water is consumed. Low-oxygen conditions, or hypoxia, impair habitat of macrofauna, influence the cycling of elements at the Resource Contaminant 303(d) Waterbody Approved sediment-water interface, and can alter the dynamics of microbial c d impairments TMDLs processes, such as Hg methylation and MeHg demethylation. The degree of eutrophication an estuary can tolerate without adverse Total US Mercury 5,004 6946 waters effects depends on the amount of reactive N it receives as well as Total US Nutrientsb 16,075 8102 its physical characteristics, including size, depth, volume of fresh- waters water runoff, and rate of tidal flushing (water residence time) US coastal Mercury 196 51 (Cloern, 2001). watersa US coastal Nutrientsb 2,818 199 The widespread occurrence of coastal eutrophication in the watersa U.S. has led to regulation of nutrient loads under the U.S. Clean US coastal Mercury and 86 10 Water Act (CWA). As a first step in managing source loads, total a b waters nutrients maximum daily loads (TMDLs) for N (or nutrients) have been developed for a number of systems (Table 1). A TMDL is the a Note information reflects ‘‘assessed waters.’’ Only a small percentage of coastal waters have been assessed. ‘‘U.S. coastal waters’’ includes water classified estimated total amount (or load) of a pollutant that a water body by as coastal waters, bays or estuaries. can receive and maintain designated uses such as fishable/ b For this analysis, nutrient-related impairments and TMDLs include the swimmable water quality. When concentrations of contaminants following impairment categories: algal growth, ammonia, noxious aquatic plants, and/or nutrients in water bodies exceed thresholds for acceptable nutrients, and organic enrichment/oxygen depletion. c This column reflects the number of waterbody impairments and not the levels specified in the CWA, they are listed as impaired, which number of unique waters affected. triggers a requirement for a TMDL to be developed. TMDL also d The number of TMDLs for coastal waters reflect only those for which the refers to a regulatory process that States, Territories, and author- state provided information on waterbody type in the 303(d) listing. ized Tribes in the U.S. use to determine allowable pollutant concentrations in water bodies and mandate source controls to Hg inputs and MeHg concentrations in higher trophic level bring pollutant concentrations below this level (Lambert et al., organisms due to many ecosystem factors that can modify in press; Shipp and Cordy, 2002; Younos, 2005). causality. We hypothesize that one such factor, the nutrient Compared to N, less is known about the dynamics and effects status, alters Hg dynamics in marine ecosystems, and this is the of Hg in coastal and pelagic marine ecosystems. Even less is focus of this paper. known about the relationship between changes in N loading and Elevated inputs of nutrients have resulted in water quality MeHg bioaccumulation in ocean fisheries. In the freshwater problems for estuaries that are adjacent to or receive discharge literature, however, there are numerous field and experimental