S5 Mercury in the Laurentian Great Lakes region

Tuesday, 26 July, 2011

TS5-O1 — 15:30-15:45
Authors: WIENER, James1, EVERS, David2, WILLIAMS, Kate2
(1) University of Wisconsin-La Crosse, wiener.jame@uwlax.edu; (2) BioDiversity Research Institute;

This session will examine mercury contamination and its ecological effects in the Laurentian Great Lakes region of North America, an area with substantial aquatic resources and mercury-contaminated landscapes, fish, and wildlife. Much of the session will focus on results of a synthesis of multimedia data on mercury from monitoring programs and research investigations across the Great Lakes region—an effort involving two bi-national workshops sponsored by the Great Lakes Air Deposition program. Geographic coverage of this synthesis included the Laurentian Great Lakes and inland waters in Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Ontario, Pennsylvania, Quebec, and Wisconsin. Analyses of dated lacustrine sediments show a consistent region-wide decrease in sedimentary mercury accumulation since the late 1980s, suggesting that controls on local and regional mercury emissions have reduced the supply of mercury to inland lakes across the region. Trend analyses, however, indicate that methylmercury exposure has increased in some piscivorous fish and wildlife since the 1990s or early 2000s in parts of the region. The factors causing recent increases in bioaccumulation of methylmercury in some areas of the Great Lakes region are poorly understood, but the observed temporal patterns imply that changing environmental conditions in some areas have increased the bioavailability of mercury for methylation or entry (as methylmercury) into aquatic food webs. Featured presentations in this session will examine spatiotemporal patterns in wet and dry atmospheric deposition of mercury, bioaccumulation of mercury in fish and piscivorous birds, assessments of risks to fish and wildlife, and policies concerning mercury in the Great Lakes region.

TS5-O2 — 15:45-16:00
Authors: DREVNICK, Paul E1, ENGSTROM, Daniel R2, DRISCOLL, Charles T3, BALOGH, Steven J4, KAMMAN, Neil C5, LONG, David T6, MUIR, Derek GC7, PARSONS, Matthew J6, ROLFHUS, Kristofer R8, ROSSMANN, Ronald9, SWAIN, Edward B10
(1) Université du Québec, paul.drevnick@ete.inrs.ca; (2) Science Museum of Minnesota; (3) Syracuse University; (4) Metropolitan Council Environmental Services; (5) Vermont Department of Environmental Conservation; (6) Michigan State University; (7) Environment Canada; (8) University of Wisconsin-La Crosse; (9) U.S. Environmental Protection Agency; (10) Minnesota Pollution Control Agency.

Data from 103 sediment cores from the Great Lakes and inland lakes of the Great Lakes airshed were compiled to examine patterns of historical and recent changes in mercury (Hg) loading from wastewater and atmospheric deposition. Sediment stratigraphy from the lower Laurentian Great Lakes shows that Hg loading peaked about 1950, followed by marked declines associated with decreased industrial use of Hg and enhanced effluent control. In contrast, Lake Superior exhibits a subdued pattern of increasing sediment Hg deposition over a longer period followed by a recent decrease that is suggestive of a largely atmospheric source—a pattern that is consistent with sediment cores from many inland lakes across the Great Lakes airshed. We observed some spatial differences in pre-industrial, peak and modern sediment-Hg flux in the inland lakes, with greater fluxes in eastern lakes compared with those in the central or western portion of the region. In contrast, Hg flux ratios (peak to pre-industrial, modern to pre-industrial and modern to peak) and year of peak Hg flux are remarkably similar across the region, suggesting that elevated sediment Hg deposition in eastern lakes may be due to greater precipitation or greater watershed-area to lake-area ratios in that sub-region. Our analysis suggests that proximity to local/regional urban emission sources, watershed area to lake surface area, and pre-industrial (<1850) Hg flux, explain much of the variation in sediment Hg accumulation in inland lakes across the Great Lakes airshed. A consistent region-wide decrease (~20%) of sediment Hg flux since the late 1980s suggests that controls on local and regional Hg emissions have been effective in decreasing the supply of Hg to Lake Superior and inland lakes across the region.

TS5-O3 — 16:00-16:15
Authors: BLANCHARD, Pierrette1, ZHANG, Leiming1, BACKUS, Sean M.1, DAVID, Gay A.2, RISCH, Marty R.3, HOLSEN, Thomas M.4, MARSIK, Frank J.5, ST. LOUIS, Vincent L.6
(1) Environment Canada, pierrette.blanchard@ec.gc.ca; (2) University of Illinois; (3) United States Geological Survey; (4) Clarkson University; (5) University of Michigan; (6) University of Alberta.

Atmospheric deposition (dry and wet) is an important pathway for mercury to enter ecosystems. In the Great Lakes region, atmospheric measurements of mercury have been made for several years to estimate wet and dry deposition. Mercury in precipitation data obtained from several deposition networks, were analyzed to determine spatial and temporal trends specific to the Great Lakes region. Dry deposition of atmospheric mercury is calculated using an inference method from speciation measurements. Most recently, continuous mercury speciation data have been available at multiple sites in the Great Lakes region to allow comparison with regional deposition models. The inference of dry deposition using mercury speciation data needs verification through actual dry deposition measurements. Challenges associated with such measurements are many but advances are forthcoming. Finally, deposition to ecosystem must take into account land type and in particular the role of canopy in mercury fate. This presentation will provide an overview of synthesis papers that explore the contribution of gaseous elemental mercury, speciation mercury and mercury in precipitation to the overall atmospheric deposition in the Great Lakes basin.

TS5-O4 — 16:15-16:30
Authors: DENKENBERGER, Joseph S. 1, DRISCOLL, Charles T.1, BRANFIREUN, Brian2, ECKLEY, Chris S.3, SELVENDIRAN, Pranesh4
(1) Syracuse University, jsdenken@syr.edu; (2) University of Western Ontario; (3) Environment Canada; (4) LimnoTech.

Rates and controls on surface-air elemental mercury (Hgo) fluxes were reviewed in the literature and synthesized for the Great Lakes Basin (GLB). Fluxes were measured using a variety of methodological approaches, however most involved either dynamic flux chamber (DFC) or micrometeorological gradient (MM) techniques. For the majority of surfaces studied, surface fluxes were net positive (evasion). Studies show considerable heterogeneity in Hgo evasion rates across temporal and spatial scales. Evasion rates were selected that we considered representative for different land cover types in the GLB. A geographic information system (GIS) approach was utilized to estimate an overall annual Hg evasion rate for the GLB of 9.9 Mg/yr. Although somewhat uncertain, this value is less than our estimate of total Hg deposition (sum of wet, dry and litterfall Hg deposition) to the area 20.6 Mg/yr, suggesting that the Great Lakes watershed is a net sink for atmospheric Hg inputs. Predominant contributions to the annual evasion come from agricultural (~53%) and forest (~29%) lands, and the Great Lakes (~12%). Both forests in the watershed and the Great Lakes water bodies contributed substantially to the overall Hg mass evasion due to their considerable area relative to other cover designations. Areal evasion rates were similar across most land cover types, ranging from 2.6 to 7.8 µg/m2-yr, while higher rates were evident for urban (13.4 µg/m2-yr) and agricultural (25.4 µg/m2-yr) lands. Existing analytical and modeling methods for estimation of Hg evasion are discussed. There is considerable uncertainty in these estimates that could be at least partially remedied through a unified methodological approach to Hgo flux estimates in future studies.

TS5-O5 — 16:30-16:45
Authors: DENKENBERGER, Joseph S.1, DRISCOLL, Charles T.1, BRANFIREUN, Brian2
(1) Syracuse University, jsdenken@syr.edu; (2) University of Western Ontario.

>A mass balance of mercury (Hg) for Lake Ontario was performed cooperatively between researchers at Syracuse University and the University of Toronto, representing a binational effort to develop a comprehensive understanding of fluvial sources of Hg for Lake Ontario. Samples were collected from four major rivers and five wastewater treatment plants from the United States, from five major rivers from Canada, as well as the Niagara River and the St Lawrence River. Mass transport of Hg species was determined by coupling fluvial concentration measurements with discharge data. Although Hg concentrations in wastewater effluents are significantly higher than ambient river concentrations, Hg loads from rivers greatly exceed those from wastewater treatment plants due to the greater inflow of water. Contrasting relationships between Hg and particulate matter were evident in rivers draining Lake Ontario watersheds due to differences in land cover and the position of impoundments within basins. Due to a strong relationship between Hg and particulate matter, Hg loads to the Lake are largely event-driven. Dissolved Hg concentrations are less affected by flow than particulate Hg concentrations, suggesting that the particulate Hg results from suspended solids runoff or sediment scour. As expected, the Niagara River is the dominant fluvial inflow of Hg to the lake and fluvial inputs greatly exceed losses. We compared fluvial Hg fluxes with the direct atmospheric exchange of Hg to Lake Ontario’s surface as estimated in the Lake Ontario Atmospheric Deposition Study (LOADS; Lai et al. 2007). This analysis suggests that atmospheric deposition is the major source of Hg inputs, while atmospheric emission is the major loss. Fluvial inputs are approximately half the magnitude of estimates of atmospheric deposition, and represent about 35% of total inputs. Fluvial losses are approximately one-fifth the magnitude of estimates of atmospheric evasion, and represent approximately 15% of total loss. Surprisingly, estimates of Hg inputs to Lake Ontario balance outputs.<

TS5-O6 — 16:45-17:00
Authors: MONSON, Bruce A.1, BHAVSAR, Satyendra P.2, SANDHEINRICH, Mark B. 3, WIENER, James G. 3
(1) Minnesota Pollution Control Agency, bruce.monson@state.mn.us; (2) Ontario Ministry of the Environment; (3) University of Wisconsin-La Crosse, River Studies Center;

This presentation synthesizes results from multiple regional assessments of mercury in fish from the Great Lakes Region. Compiled databases for mercury in the five Great Lakes and the surrounding inland waters were analyzed for spatiotemporal trends, ecological risk to top predator fish, and risk to loons and humans consuming yellow perch. Four decades of fish tissue monitoring, relying on reliable and consistent analytical methods, produced more than 100,000 records of mercury in fish. The BioDiversity Research Institute compiled MercNet as the main database based on data submissions from federal, state, and provincial monitoring programs. The records included fish from rivers and impoundments, but were dominated by top predator fish species in inland lakes. A statistical model based on 64,000 records of walleye and largemouth bass showed a significant overall downward trend in mercury concentrations between 1970 and 2009, with annual percent changes ranging from -0.69% to -0.87%. Across the region, average mercury concentrations in these two representative top predator species increased from west to east and from south to north. Seasonally, mercury concentrations were highest in the spring. A separate analysis of U.S. EPA’s Great Lakes fish monitoring data agreed with earlier presentations of Canadian monitoring results, showing that lake trout from Lake Superior had the highest mercury concentrations and walleye from Lake Erie the lowest. Mercury concentrations in Great Lakes lake trout have trended downward over the last decade (except for southern Lake Superior near the Apostle Islands), but Lake Erie walleye have recently trended upward. Because of the shifting levels of mercury concentrations, the dataset for risk analyses was limited to 1990 or later. Mercury concentrations in yellow perch from many of the region’s waters exceeded the dietary threshold concentrations for loons and humans. An analysis of risk to four piscivorous fish species found 44% of the walleye populations exceeded the threshold effect tissue concentration (0.2 mg/kg wet weight in whole body of standard-sized fish). The risk was less for the other three species (northern pike, largemouth bass, and smallmouth bass) than for walleye, but the conclusion is the same: fish populations, as well as the consumers of fish, would benefit from reductions in methylmercury concentrations in fish. While mercury concentrations in fish from the region are generally declining at nearly one percent per year, there is evidence for increasing mercury levels in some of the region’s fish populations.

TS5-O7 — 17:00-17:15
Authors: BASU, Niladri1, BOWERMAN, William2, EVERS, David3, MARTIN, Pamela4, MEYER, Michael5, SCHEUHAMMER, Tony4, STROM, Sean5
(1) University of Michigan, niladri@umich.edu; (2) Clemson University; (3) Biodiversity Research Institute; (4) Environment Canada; (5);

This talk will focus on the “wildlife” studies that are part of the collaborative Project for Integrating Multimedia Measurements of Mercury in the Great Lakes, sponsored by the Great Lakes Atmospheric Deposition (GLAD) Program. The overall Project goal is to compile, integrate, and interpret a wide variety of dispersed Hg data holdings. Here, we present data from fish-eating wildlife to address key questions concerning spatiotemporal patterns of environmental Hg contamination and resulting health effects in the Great Lakes region. The results presented follow 2+ year active participation among academic, governmental, and NGO partners. First we provide an overview of mercury and why it is of concern to piscivorous wildlife particularly in the Great Lakes region. Next we provide species-specific data concerning spatial and temporal patterns of exposure. Data will be presented from common loons, bald eagles, herring gulls, double crested cormorants, mink, and river otters. The risks (classified as low, medium, high) associated with these exposures will be characterized by comparing tissue residue values with data from controlled laboratory studies on common loons and mink. We will make judgments based on impairments to reproduction and behavior as these are ecologically relevant endpoints that can be scaled to population-level impacts. Results from all species across multiple geographical regions will be integrated to help document trends and patterns of mercury risk to piscivorous wildlife. The information presented here is expected to advance both policy development and scientific assessments regarding mercury risks to piscivorous wildlife in the Great Lakes region.

TS5-O8 — 17:15-17:30
Authors: TAYLOR MORGAN, Joy K.1, CAIN, Alexis2, BROOKS, Ned3
(1)MDEQ, taylorj1@michigan.gov; (2) U.S. EPA; (3) MPCA.

While mercury releases within the Great Lakes states have declined significantly, concentrations of mercury in fish still cause concern for human and ecosystem health in the Great Lakes Basin. This paper assesses the priority that mercury reduction ought to have in relation to some other environmental concerns, and explores the relative cost and benefits of mercury reduction policies, focusing on the United States side of the Basin. It also makes the case that because of long-range atmospheric transport, mercury pollution presents a “free-rider” problem for states. Despite nominal expectations for direct immediate environmental improvement, policy-makers in the Great Lakes states have chosen to lead on mercury (Hg) reduction, through: providing an example for others to follow; using cross-jurisdiction cooperation to leverage the benefits of leadership on Hg reduction and control; and, promoting voluntary actions. Recommendations for future opportunities include: focusing reduction efforts on the total mass of emissions rather than solely focusing on reduction of local deposition; utilizing all tools available in the Clean Air and Water Acts and coordinating mercury reduction policies in conjunction with climate change policies.

Tuesday, 26 July, 2011