Mining legacy across a wetland landscape: high mercury in Upper Peninsula (Michigan) rivers, lakes, and fish W. Charles Kerfoot, * a Noel R. Urban, b Cory P. McDonald, b Huanxin Zhang, c Ronald Rossmann, d Judith A. Perlinger, b Tanvir Khan, b Ashley Hendricks, b Mugdha Priyadarshini b and Morgan Bolstad b A geographic enigma is that present-day atmospheric deposition of mercury in the Upper Peninsula of Michigan is low (48%) and that regional industrial emissions have declined substantially (ca. 81% reduction) relative to downstate. Mercury levels should be declining. However, state (MDEQ) surveys of rivers and lakes revealed elevated total mercury (THg) in Upper Peninsula waters and sediment relative to downstate. Moreover, Western Upper Peninsula (WUP) fish possess higher methyl mercury (MeHg) levels than Northern Lower Peninsula (NLP) fish. A contributing explanation for elevated THg loading is that a century ago the Upper Peninsula was a major industrial region, centered on mining. Many regional ores (silver, copper, zinc, massive sulfides) contain mercury in part per million concentrations. Copper smelters and iron furnace-taconite operations broadcast mercury almost continuously for 140 years, whereas mills discharged tailings and old mine shafts leaked contaminated water. We show that mercury emissions from copper and iron operations were substantial (60–650 kg per year) and dispersed over relatively large areas. Moreover, lake sediments in the vicinity of mining operations have higher THg concentrations. Sediment profiles from the Keweenaw Waterway show that THg accumulation increased 50- to 400-fold above modern-day atmospheric deposition levels during active mining and smelting operations, with lingering MeHg effects. High MeHg concentrations are geographically correlated with low pH and dissolved organic carbon (DOC), a consequence of biogeochemical cycling in wetlands, characteristic of the Upper Peninsula. DOC can mobilize metals and elevate MeHg concentrations. We argue that mercury loading from mining is historically superimposed upon strong regional wetland effects, producing a combined elevation of both THg and MeHg in the Western Upper Peninsula. Environmental signicance The manuscript addresses the enigma of low atmospheric mercury deposition and falling emissions in modern-day Upper Peninsula environments, yet elevated THg and MeHg in rivers, lakes, and sh. For the rst time, we reconstruct 140 years of historical mercury emissions from copper and iron mining, showing how mercury was broadcast broadly around regional environments up to the present. We compare historical deposition rates with a combination of modeling and sediment core studies. Mining discharges (smelter emissions, tailing releases, mine sha seepage) appear superimposed upon high wetland methylation. With forest recovery, wetlands are becoming even more abundant. Rather than mercury concentrations in piscivorous sh declining due to reduced atmospheric inputs, we observe 1–3% increases. We show historically how the substantial mining inputs are superimposed upon wetland rebound with time delays in MeHg production, helping explain some of the curious reversals. Introduction Mercury contamination of the environment from human activity continues to be a global problem. 1–3 In 2015, 36 state- wide mercury advisories were issued in the United States for freshwater sh from lakes or rivers. 4 The extent of the problem is pervasive, as the 2010 National Listing of Fish Advisories included 4598 advisories that covered around 7.16 million hectares of lake area and 2.09 million km of river stretches, equivalent to 42 percent of the nation's total lake area and 36 a Department of Biological Sciences, Michigan Technological University, Houghton, MI 49931, USA. E-mail: wkerfoot@mtu.edu b Department of Civil & Environmental Engineering, Michigan Technological University, Houghton, MI 49931, USA c Department of Geological & Mining Engineering & Sciences, Michigan Technological University, Houghton, MI 49931, USA d Visiting Scientist, U.S. EPA, Mid-Continent Ecology Division, Large Lakes Research Station, Grosse Ile, MI 48138, USA Cite this: Environ. Sci.: Processes Impacts, 2018, 20, 708 Received 31st October 2017 Accepted 30th January 2018 DOI: 10.1039/c7em00521k rsc.li/espi 708 | Environ. Sci.: Processes Impacts, 2018, 20, 708–733 This journal is © The Royal Society of Chemistry 2018 Environmental Science Processes & Impacts PAPER Open Access Article. Published on 29 March 2018. Downloaded on 4/28/2019 12:21:08 PM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. View Article Online View Journal | View Issue