Document Type





Eutrophication, Coastal Ecosystems, Marine Ecosystems, Mercury, Nitrogen, Nutrients


Civil and Environmental Engineering


There is increasing interest and concern over the impacts of mercury (Hg) inputs to marine 32 ecosystems. One of the challenges in assessing these effects is that the cycling and trophic 33 transfer of Hg are strongly linked to other contaminants and disturbances. In addition to Hg, a 34 major problem facing coastal waters is the impacts of elevated nutrient, particularly nitrogen 35 (N), inputs. Increases in nutrient loading alter coastal ecosystems in ways that should change 36 the transport, transformations and fate of Hg, including increases in fixation of organic carbon 37 and deposition to sediments, decreases in the redox status of sediments and changes in fish 38 habitat. In this paper we present a conceptual model which suggests that increases in loading 39 of reactive N to marine ecosystems might alter Hg dynamics, decreasing bioavailabilty and 40 trophic transfer. This conceptual model is most applicable to coastal waters, but may also be 41 relevant to the pelagic ocean. We present information from case studies that both support and 42 challenge this conceptual model, including marine observations across a nutrient gradient; 43 results of a nutrient‐trophic transfer Hg model for pelagic and coastal ecosystems; observations 44 of Hg species, and nutrients from coastal sediments in the northeastern U.S.; and an analysis of 45 fish Hg concentrations in estuaries under different nutrient loadings. These case studies suggest 46 that changes in nutrient loading can impact Hg dynamics in coastal and open ocean ecosystems. 47 Unfortunately none of the case studies is comprehensive; each only addresses a portion of the 48 conceptual model and has limitations. Nevertheless, our conceptual model has important 49 management implications. Many estuaries near developed areas are impaired due to elevated 50 nutrient inputs. Widespread efforts are underway to control N loading and restore coastal 51 ecosystem function. An unintended consequence of nutrient control measures could be to 3 exacerbate 52 problems associated with Hg contamination. Additional focused research and 53 monitoring are needed to critically examine the link between nutrient supply and Hg 54 contamination of marine waters.

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