ARTICLE pubs.acs.org/est
Increased Mercury Loadings to Western Canadian Alpine Lakes over the Past 150 Years Vanessa J. A. Phillips,§,*,† Vincent L. St. Louis,† Colin A. Cooke,^,‡ Rolf D. Vinebrooke,† and William O. Hobbs ||,‡ † ‡
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G2E9; Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G2E3
bS Supporting Information ABSTRACT: We reconstructed historical trends in mercury (Hg) accumulation over the past ∼150 years in nine western Canadian alpine lakes. Recent Hg accumulation rates (fluxes) ranged between ∼7 and 75 μg m-2 yr-1, which were an average of 1.8 times higher than preindustrial (i.e., pre-1850) fluxes. Increased Hg fluxes in these lakes were less than at lower elevation sites, showing that despite the potential for increased deposition, alpine lakes are no more susceptible to Hg accumulation. Unlike other studies, we found that geographic setting, changes in chlorophyll-inferred algal production, and climate were not significant predictors of [Hg] or Hg flux in lakes. Instead, our findings highlight how a combination of atmospheric deposition and site-specific processes, including organic matter supply and catchment weathering, better explain sequestration of Hg in alpine lakes.
’ INTRODUCTION Approximately 95% of atmospheric mercury (Hg) is gaseous elemental Hg0.1 Hg0 is released to the environment through both natural and anthropogenic sources.2 Since the onset of the industrial revolution (∼1850), the majority (70-80%) of global Hg emissions has come from anthropogenic sources, such as coal-fired energy production and waste incineration.3 The high vapor pressure and low oxidation potential of Hg0 enables a long atmospheric residence time of 0.5-2.0 years,1 allowing transportation of Hg0 across long distances before being oxidized to Hg(II) and scavenged through wet or dry deposition. Atmospheric Hg deposition has increased by 2- to 4-fold since the preindustrial era.4 Deposition rates vary among urban, forested, and agricultural areas,5 raising concerns that certain regions are more prone to Hg deposition than others. For example, potential altitudinal amplification (similar to persistent organic pollutants)6,7 and enhanced production of reactive gaseous Hg (RGM) in the troposphere8,9 may result in increased Hg deposition to alpine lakes. Diurnal wind patterns and high levels of precipitation may also cause high loads of Hg to be transported upward toward high-elevation environments,10 or draw down RGM-rich air from the troposphere.9 However, there is little information on the current and historical Hg accumulation in remote alpine lakes,8,9,11 despite the fact that a global 3-D chemical transport model (GEOS-Chem) predicts high RGM concentrations over high-elevation regions.12 The Canadian Rocky Mountains are one of the few areas in North America where aquatic ecosystems have remained relatively untouched by local anthropogenic impacts. Nonetheless, r 2011 American Chemical Society
high tissue methyl Hg concentrations have been recorded in fish from Canadian Mountain lakes,13 and government consumption advisories are in effect for all sport fish caught in Canadian Mountain Parks. This has resulted in concern over the susceptibility of this area to increased Hg deposition. The goals of our study were 3-fold: (1) quantify changes in Hg accumulation in alpine lakes during the modern industrial era; (2) compare changes in sedimentary Hg in alpine versus lower altitude sites to determine if accumulation rates are greater at higher elevations, and; (3) identify predictors (e.g., autochthonous primary production, climatic variables, industrial activity) of Hg accumulation in the study lakes.
’ MATERIALS AND METHODS Study Sites. We collected sediment cores from nine lakes located in Banff (David, Eiffel, Goat, Pipit and Sue lakes), Jasper (Curator and Caribou lakes), and Yoho (Oesa and Opabin lakes) National Parks in the Canadian Rocky Mountains (Figure 1). All sites were small ( 0.80) to weak (r2 < 0.20). Opabin and Pipit lake sediments show no relationships between %OM and [Hg], and there is no significant relationship when all the lakes are considered together (r2 = 0.02, p = 0.25). Moreover, at any given OM concentration, [Hg] spans an order of magnitude. Therefore, OM control of Hg supply to these systems appears to be site-specific. For example, at Oesa and Eiffel lakes, the catchment-driven increases in Hg flux noted above are likely related to an increase in the export of catchment-derived OM, as revealed by a tight coupling between %OM and [Hg] in these lakes (Figure 5). In contrast, %OM and [Hg] are only weakly related in David, Sue, and Pipit lakes, suggesting allochthonous input of Hg-laden inorganic material is of greater importance in these systems. Changes in Anthropogenic Emissions. While the export of Hg from watersheds has undoubtedly increased in recent decades, it is also clear from our sediment records that recent Hg flux rates remain elevated above preindustrial values. Hg flux records from Goat, Curator and Caribou lakes track [Hg] more closely than SR (Figure 2). Increases in sedimentation rate tend to dilute sediment [Hg] in these three lakes (r2 = -0.39, p < 0.01), suggesting Hg delivery to these lakes is controlled primarily by atmospheric deposition. We suggest these three lakes better record atmospheric Hg deposition patterns than changes in catchment-derived Hg. Decreases in industrial Hg consumption, new technologies that reduce Hg emissions from metal smelters and coal-burning utilities (e.g., SO2 and particulate scrubber devices), shifts from coal to natural gas based heating, and restrictions on waste incineration practices in North America have led to declines in anthropogenic Hg emissions during the 1990s and the early 2000s.30 In contrast to a large number of studies on less remote sites, which have shown decreases in Hg fluxes in lakes from the mid-1990s to present (e.g., ref 30), the most recent trends within our lakes are varied (Figure 2). Hg fluxes within Eiffel, Caribou, and Curator lakes reached their highest values recorded in the past decade, while David and Oesa lakes showed modest
increases and Goat Lake displayed modest declines. While conclusions based on a few lake-sediment stratigraphies for a region must remain tentative, we suggest that atmospheric Hg deposition rates to these remote lakes have increased since ∼1990, despite an overall decline in Canadian Hg emissions.34 An increase in atmospheric Hg deposition over the past decade is consistent with the increases in industrial emissions recorded in developing regions of the world, particularly from coal-fired power generation in Asia. Pacyna and Pacyna35 estimated that over 56% (1074 Mg) of the global annual emissions of Hg in 1995 originate in Asia, with roughly 552 Mg of that coming from China. Other studies have since calculated that Hg emissions from China alone had increased another ∼26% to 696 Mg by 2003.36 In comparison, North American anthropogenic sources comprised ∼11% (214 Mg) of global Hg emissions in 199535 but dropped by ∼60% to ∼126 Mg by 2003.36 To our knowledge, this is the first study to evaluate historical trends and processes affecting Hg accumulation in Canadian alpine lakes. Through strong regional feedback mechanisms (e.g., decreased lake-ice cover and melting glaciers), alpine regions display an elevated sensitivity to changes in climate and longrange transport of pollutants.28,37 Our results reveal site-specific responses to increased Hg deposition in ultraoligotrophic lakes of the Canadian Rockies. Overall, lakes within this region have experienced less of an increase in Hg flux than most of North America; however, processes that enhance both Hg export from catchment soils and in-lake production will likely result in increased sequestration of Hg in ultraoligotrophic alpine lakes with time.
’ ASSOCIATED CONTENT
bS
Supporting Information. A table of site characteristics, a photo of core composition, detailed analytical methods, 210Pb, OM, and SR profiles, graphs of climate parameters through time, a table of statistical results between Hg and climate parameters, and a list of references used in Figure 4c. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Phone: (306) 337-2545; fax: (306) 337-2410; e-mail: phillips.
[email protected]. Present Addresses §
University of Regina, SK, Canada. Yale University, CT, United States. Science Museum of Minnesota, MN, United States.
^
)
Figure 5. Regressions between %OM and [Hg] in our nine study lakes. ** Indicates significance at R = 0.05.
ARTICLE
’ ACKNOWLEDGMENT This project was funded by the Alberta Ingenuity Center for Water Research, a Lake Science Scholarship from the Alberta Lake Management Society, a Queen Elizabeth II Scholarship from the University of Alberta, and a Graduate Research Assistantship - Dissertation Award from the Department of Biological Sciences, University of Alberta. Thank you to Iain Phillips, Ian Seiferling, Mark Graham, Conrad Murphy, Jim Zettel, Patrick Thompson, Brian Parker, Erin Kelly, Jane Kirk, Jennifer Graydon and Brian Asher for help with the field, logistic and/or laboratory components of this project. We also thank three anonymous reviewers for their helpful comments. 2046
dx.doi.org/10.1021/es1031135 |Environ. Sci. Technol. 2011, 45, 2042–2047
Environmental Science & Technology
’ REFERENCES (1) Schroeder, W. H.; Munthe, J. Atmospheric mercury—An overview. Atmos. Environ. 1998, 32, 809–822. (2) Gustin, M. S.; Lindberg, S. E.; Weisberg, P. J. An update on the natural sources and sinks of atmospheric mercury. Appl. Geochem. 2008, 23, 482–493. (3) Mason, R. P.; Fitzgerald, W. F.; Morel, F. M. The biogeochemical cycling of elemental mercury—Anthropogenic influences. Geochim. Cosmochim. Acta 1994, 58, 3191–3198. (4) Lindberg, S. E.; Bullock, R.; Ebinghaus, R.; Engstrom, D. R.; Feng, X. B.; Fitzgerald, W. F.; Pirrone, N.; Prestbo, E. M.; Seigneur, C. A synthesis of progress and uncertainties in attributing the sources of mercury in deposition. Ambio. 2007, 36, 19–32. (5) Engstrom, D. R.; Balogh, S. J.; Swain, E. B. History of mercury inputs to Minnesota lakes: Influences of watershed disturbance and localized atmospheric deposition. Limnol Oceanog. 2007, 52, 2467–2483. (6) Blais, J. M.; Charpentie, S.; Pick, F.; Kimpe, L. E.; Amand, A. S.; Regnault-Roger, C. Mercury, polybrominated diphenyl ether, organochlorine pesticide, and polychlorinated biphenyl concentrations in fish from lakes along an elevation transect in the French Pyrenees. Ecotoxicol. Environ. Saf. 2006, 63, 91–99. (7) Mackay, D.; Wania, F.; Schroeder, W. H. Prospects for modeling the behavior and fate of mercury, globally and in aquatic systems. Water, Air, Soil Pollut. 1995, 80, 941–950. (8) Yang, H.; Engstrom, D. R.; Rose, N. L. Recent changes in atmospheric mercury deposition recorded in the sediments of remote equatorial lakes in the Rwenzori Mountains, Uganda. Environ. Sci. Technol. 2010, 44, 6570-6575, DOI: 10.1021/es101508p. (9) Drevnick, P. E.; Shinneman, A. L.; Lamborg, C. H.; Engstrom, D. R.; Bothner, M. H.; Oris, J. T. Mercury flux to sediments of Lake Tahoe, California-Nevada. Water, Air, Soil Pollut. 2009, 210, 399–407. (10) Daly, G. L.; Wania, F. Organic contaminants in mountains. Environ. Sci. Technol. 2005, 39, 385–398. (11) Mast, M. A.; Campbell, D. H.; Krabbenhoft, D. P.; Taylor, H. E. Mercury transport in a high-elevation watershed in Rocky Mountain National Park, Colorado. Water, Air, Soil Pollut. 2005, 164, 21–42. (12) Selin, N. E.; Jacob, D. J.; Park, R. J.; Yantosca, R. M.; Strode, S.; Jaegle, L.; Jaffe, D. Chemical cycling and deposition of atmospheric mercury: Global constraints from observations. J. Geophys. Res., [Atmos.] 2007, 112, D0230. (13) Kelly, E. N., Mercury in biota from Canadian Rocky Mountain Lakes. 2007. PhD Thesis, University of Alberta, Edmonton. (14) NRCan, The Atlas of Canada: Bedrock Geology. http://atlas. nrcan.gc.ca/site/english/maps/archives/3rdedition/environment/land/ 016 (accessed December 7, 2008). (15) Appleby, P. G. Three decades of dating recent sediments by fallout radionuclides: A review. The Holocene 2008, 18, 83–93. (16) Binford, M. W. Calculation and uncertainty analysis of 210Pb dates for PIRLA project lake sediment cores. J. Paleolimnol. 1990, 3, 253–267. (17) Heiri, O.; Lotter, A. F.; Lemcke, G. Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results. J. Paleolimnol. 2001, 25, 101–110. (18) Environment Canada, National Climate Archive. http://www. climate.weatheroffice.ec.gc.ca (accessed December 7, 2008). (19) Meyers, P. A.; Teranes, J. L. Sediment organic matter. In Tracking Environmental Change Using Lake Sediments. Vol. 2: Physical and Geochemical Methods; Smol, J. P.., Last, W. M.., Eds.; Kluwer Academic Publishers: Norwell, MA, 2001, pp 239-269. (20) G€alman, V.; Rydberg, J.; de-Luna, S.; Bindler, R.; Renberg, I. Carbon and nitrogen loss rates during aging of lake sediment: Changes over 27 years studied in varved lake sediment. Limnol. Oceanogr. 2008, 53, 1076–1082. (21) Lockhart, W. L.; Macdonald, R. W.; Outridge, P. M.; Wilkinson, P.; DeLaronde, J. B.; Rudd, J. W. M. Tests of the fidelity of lake sediment core records of mercury deposition to known histories of mercury contamination. Sci. Total Environ. 2000, 260, 3, 171-180.
ARTICLE
(22) Cooke, C.A..; Hobbs, W. O.; Michelutti, N.; Wolfe, A. P. Reliance on 210Pb chronology can compromise the inference of preindustrial Hg flux to lake sediments. Environ. Sci. Technol. 2010, 44, 1998–2003. (23) Friske, P. W. B.; Coker, W. B. Natural distribution of mercury in lake and stream sediments across Canada. Water, Air, Soil Pollut. 1995, 80, 1047–1051. (24) Landers, D. H.; Gubala, C.; Verta, M.; Lucotte, M.; Johansson, K.; Vlasova, T.; Lockhart, W. L. Using lake sediment mercury flux ratios to evaluate the regional and continental dimensions of mercury deposition in arctic and boreal ecosystems. Atmos. Environ. 1998, 32, 919–928. (25) Martinez-Cortizas, A.; Pontevedra-Pombal, X.; Garcia-Rodeja, E.; Novoa-Munoz, J. C.; Shotyk, W. Mercury in a Spanish peatbog : Archive of climate change and atmospheric metal deposition. Science. 1999, 284, 939–942. (26) Outridge, P. M.; Sanei, L. H.; Stern, G. A.; Hamilton, P. B.; Goodarzi, F. Evidence for control of mercury accumulation rates in Canadian High Arctic lake sediments by variations of aquatic primary productivity. Environ. Sci. Technol. 2007, 41, 5259–5265. (27) Stern, G. A.; Sanei, L. H.; Roach, P.; Dalaronde, J.; Outridge, P. M. Historical interrelated variations of mercury and aquatic organic matter in lake sediment cores from a subarctic lake in Yukon, Canada: further evidence toward the algal-mercury scavenging hypothesis. Environ. Sci. Technol. 2009, 43, 7684–7690. (28) Vinebrooke, R. D.; Thompson, P. L.; Hobbs, W. O.; Luckman, B. H.; Graham, M. D.; Wolfe, A. P. Glacially mediated impacts of climate warming on alpine lakes of the Canadian Rocky Mountains. Verh. - Int. Ver. Theor. Angew. Limnol. 2010, 30, 1449–1452. (29) Ask, J.; Karlsson, J.; Persson, L.; Ask, P.; Bystrom, P.; Jansson, M. Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes. Ecology 2009, 90 1923–1932. (30) Engstrom, D. R.; Swain, E. B. Recent declines in atmospheric mercury deposition in the upper Midwest. Environ. Sci. Technol. 1997, 31, 960–967. (31) Selvendiran, P.; Driscoll, C. T.; Montesdeoca, M. R.; Choi, H.; Holsen, T. M. Mercury dynamics and transport in two Adirondack lakes. Limnol. Oceanogr. 2009, 54, 413–427. (32) Regnell, O.; Watras, C. J.; Troedsson, B.; Helgee, A.; Hammar, T. Mercury in a boreal forest stream - role of historical mercury pollution, TOC, temperature and water discharge. Environ. Sci. Technol. 2009, 43, 3514–3521. (33) Kains, K.; Lucotte, M. Mercury concentrations in lake sediments - revisiting the predictive power of catchment morphometry and organic matter composition. Water, Air, Soil Pollut 2006, 170, 173–189. (34) Trip, A.; Allan, R. J. Sources, trends, implications and remediation of mercury contamination of lakes in remote areas of Canada. Water Sci. Technol. 2000, 42, 171–176. (35) Pacyna, E. G.; Pacyna, J. M. Global emission of mercury from anthropogenic sources in 1995. Water, Air, Soil Pollut. 2002, 137, 149– 165. (36) Wu, Y.; Wang, S.; Streets, D. G.; Hao, J.; Chan, M.; Jiang, J. Trends in anthropogenic mercury emissions in China from 1995 to 2003. Environ. Sci. Technol. 2006, 40, 5312–5318. (37) Saros, J. E.; Rose, K. C.; Clow, D. W.; Stephens, V. C.; Nurse, A. A.; Arnett, H.; Stone, J. R.; Williamson, C. E.; Wolfe A. P. Melting alpine glaciers enrich high-elevation lakes with reactive nitrogen. Environ. Sci. Technol. 2010, 44, 4891–4896.
2047
dx.doi.org/10.1021/es1031135 |Environ. Sci. Technol. 2011, 45, 2042–2047
