Factors affecting biotic mercury concentrations and biomagnification through lake food webs in the Canadian high Arctic

https://doi.org/10.1016/j.scitotenv.2014.04.133Get rights and content

Highlights

  • Mercury (Hg) in Arctic char and invertebrates from 6 Arctic lakes were compared

  • Food web biomagnification of Hg was variable across lakes

  • Aqueous ions were negative predictors of benthic invertebrate [MeHg]

  • Catchment size and nitrate were negative predictors of [THg] in young char

  • [Hg] in these biota were affected by physical-chemical characteristics of lakes

Abstract

In temperate regions of Canada, mercury (Hg) concentrations in biota and the magnitude of Hg biomagnification through food webs vary between neighboring lakes and are related to water chemistry variables and physical lake features. However, few studies have examined factors affecting the variable Hg concentrations in landlocked Arctic char (Salvelinus alpinus) or the biomagnification of Hg through their food webs. We estimated the food web structure of six high Arctic lakes near Resolute Bay, Nunavut, Canada, using stable carbon (δ13C) and nitrogen (δ15N) isotopes and measured Hg (total Hg (THg) in char, the only fish species, and methylmercury (MeHg) in chironomids and zooplankton) concentrations in biota collected in 2010 and 2011. Across lakes, δ13C showed that benthic carbon (chironomids) was the dominant food source for char. Regression models of log Hg versus δ15N (of char and benthic invertebrates) showed positive and significant slopes, indicting Hg biomagnification in all lakes, and higher slopes in some lakes than others. However, no principal components (PC) generated using all water chemistry data and physical characteristics of the lakes predicted the different slopes. The PC dominated by aqueous ions was a negative predictor of MeHg concentrations in chironomids, suggesting that water chemistry affects Hg bioavailability and MeHg concentrations in these lower-trophic-level organisms. Furthermore, regression intercepts were predicted by the PCs dominated by catchment area, aqueous ions, and MeHg. Weaker relationships were also found between THg in small char or MeHg in pelagic invertebrates and the PCs dominated by catchment area, and aqueous nitrate and MeHg. Results from these high Arctic lakes suggest that Hg biomagnification differs between systems and that their physical and chemical characteristics affect Hg concentrations in lower-trophic-level biota.

Introduction

Mercury (Hg) is a global pollutant because it undergoes long range transport to remote areas like the Canadian high Arctic. During the polar spring, gaseous elemental Hg (GEM) in the atmosphere photochemically reacts with halogen radicals to form particulate Hg(II), a process known as atmospheric Hg depletion events (AMDEs; Steffen et al., 2008). Hg(II) is subsequently deposited in wet and dry deposition around the high Arctic (Steffen et al., 2008, Loseto et al., 2004). In the summer, snow and ice melt water carry Hg(II) into lakes, where it can be methylated by sulfate reducing bacteria into its more toxic form, methylmercury (MeHg; Schaefer and Morel, 2009, Lehnherr et al., 2012a). In addition to within-lake methylation, snow melt also provides an important external source of MeHg to these lakes (Loseto et al., 2004, Semkin et al., 2005). Due to its rapid accumulation in protein-rich tissues and slow excretion, MeHg is the form of Hg that is bioaccumulated in organisms and biomagnified through food webs (Kidd et al., 2012, Kidd and Batchelar, 2012). Across Canada, Alaska and Greenland, char are often reported with Hg concentrations exceeding governmental consumption guidelines (0.5 ppm, wet wt.; Douglas et al., 2012, Health Canada, 2007).

Arctic char, the top predator in high Arctic lakes, has mean total Hg (THg; 95% of which is MeHg; Swanson and Kidd, 2010) concentrations that vary by up to 4.2-fold between neighboring (< 25 km) systems (means differ by up to 0.35 μg/g, wet wt; p < 0.05; Gantner et al., 2010b). Part of this variability can be explained by differences in the physical and biological characteristics of the fish themselves; generally, older, longer, heavier, and higher-trophic-level fishes have higher Hg concentrations (Muir et al., 2005, Gantner et al., 2009, Swanson and Kidd, 2010). Physical and chemical characteristics of lakes can also affect Hg concentrations and biomagnification through food webs (Kidd et al., 2012, Clayden et al., 2013). More specifically, fish and other biota from larger and deeper lakes and ones with higher catchment area: lake area (AC:AL) ratios have higher Hg concentrations (Evans et al., 2005, Clayden et al., 2013). Although water chemistry variables, such as dissolved organic carbon (DOC), have complex relationships with Hg, lakes with higher nutrients (indicative of productivity) tend to have biota with lower Hg concentrations (Ulrich et al., 2001) likely due to a dilution of Hg over a larger total biomass, an effect known as biodilution (Chen et al., 2004). Compared to southern environments, Arctic lakes can be very unproductive, with highly variable climatic and physiographic characteristics that are known to affect Hg transport and cycling (Douglas et al., 2012). However, little is known about how the size, nutrient concentrations, catchment area, and depth of high Arctic lakes affect biotic concentrations of Hg or its biomagnification through the food webs. Additionally, many water chemistry variables are inherently related, making statistical analyses of their effects on Hg concentrations in biota challenging.

To quantify the biomagnification of Hg through aquatic food webs, its concentrations in biota are regressed against their δ15N values (representative of trophic position; Jardine et al., 2006). This approach has been used extensively in systems from the tropics (Chasar et al., 2009, Chumchal et al., 2011, Kwon et al., 2012) to the Arctic (Atwell et al., 1998, Campbell et al., 2004, Gantner et al., 2012) and Hg concentrations in biota are consistently, positively related to their δ15N values in aquatic food webs. The slopes resulting from these regressions represent the magnitude of and average Hg transfer through food webs (Wyn et al., 2009, Lavoie et al., 2013), which vary between lakes for reasons that are mechanistically not understood (Kidd et al., 2012).

Our study compared the Hg concentrations of invertebrates and char, as well as the Hg biomagnification slopes, across six high Arctic lakes near Resolute Bay, Nunavut (NU), Canada. Given the well established relationships between biological characteristics (e.g. size, age, trophic level) and Hg concentrations in fish, we focussed this study on abiotic factors and examined whether the physical and chemical features of the lakes, which could affect the bioavailability of MeHg, would explain among-lake variability in Hg biomagnification through food webs and Hg concentrations in fish and invertebrates.

Section snippets

Study site

Six ultra-oligotrophic lakes located in the central Canadian Arctic Archipelago were chosen for our study. These lakes (Meretta, Resolute, Char, Small, North, and 9-Mile) are within a 20 km radius of one another and are located in the southwest corner of Cornwallis Island, NU, Canada (75°08′N 95°00′W; Fig. 1). Cornwallis Island is a polar desert, with a mean annual temperature and precipitation of - 16.4 °C and 150 mm, respectively (Antoniades et al., 2011). To the best of our knowledge, the six

Chemical and physical lake features

As is common in high Arctic systems, the lakes in our study generally had low primary productivity and nutrients (chl a, DOC, and PON; see SI for detailed tables). Water chemistry variables did, however, vary across lakes. For example, North Lake had 10 to 12 times higher concentrations (~ 0.12 mg/L) of nitrate and nitrite (NO3/NO2) when compared to all other lakes (0.01 mg/L in all cases; not statistically tested). Resolute Lake had the highest mean conductivity (360.3 μs/cm) and ion

Aqueous concentrations of Hg

MeHg concentrations in these systems were higher in deep water samples compared to surface waters. Previous studies have suggested that Hg(II) methylation in hypolimnetic waters (Eckley and Hintelmann, 2006) and/or lake sediments (Lehnherr et al., 2012a) are important contributors to aqueous MeHg concentrations in these lakes. In addition, %MeHg in water samples, a proxy for methylation rate (Lehnherr et al., 2012b), was 1 to 2% higher in deep water than surface water samples. Overall, %MeHg in

Acknowledgments

Funding and logistical support for this study was provided by the Natural Sciences and Engineering Research Council of Canada through their Canada Research Chair (950-211803) and Discovery (312237) Programs, the Northern Contaminants Program of Aboriginal Affairs and Northern Development Canada (project # M26), Environment Canada (Water Science and Technology Directorate), and the Polar Continental Shelf Program (Natural Resources Canada) in Resolute. The authors sincerely thank Brandy and

References (75)

  • R.A. Bodaly et al.

    Effect of urban sewage treatment on total and methyl mercury concentrations in effluents

    Biogeochem

    (1998)
  • K. Borgå et al.

    Trophic magnification factors: considerations of ecology, ecosystems, and study design

    Integr Environ Assess Manag

    (2012)
  • K.P. Burnham et al.

    Multimodel inference — understanding AIC and BIC in model selection

    Sociol Methods Res

    (2004)
  • L.M. Campbell et al.

    Mercury and other traces elements in a pelagic Arctic marine food web (Northwater Polynya, Baffin Bay)

    Sci Total Environ

    (2004)
  • P.A. Chambers et al.

    The impact of municipal wastewater effluents on Canadian waters; a review

    Water Qual Res J Can

    (1997)
  • L.C. Chasar et al.

    Mercury cycling in stream ecosystems 3. Trophic dynamics and methylmercury bioaccumulation

    Environ Sci Technol

    (2009)
  • A. Chase et al.

    The effects of dissolved organic matter on mercury biogeochemistry

    (2012)
  • C.Y. Chen et al.

    Patterns of Hg bioaccumulation and transfer in aquatic food webs across multi-lake studies in the northeast US

    Ecotoxicology

    (2004)
  • J. Chételat et al.

    Elevated methylmercury in High Arctic Daphnia and the role of productivity in controlling their distribution

    Glob Chang Biol

    (2009)
  • J. Chételat et al.

    Metamorphosis in chironomids, more than mercury supply, controls methylmercury transfer to fish in High Arctic lakes

    Environ Sci Technol

    (2008)
  • J. Chételat et al.

    Carbon sources for lake food webs in the Canadian High Arctic and other regions of Arctic North America

    Polar Biol

    (2010)
  • J. Chételat et al.

    Shifts in elemental composition, methylmercury content and δ15N ratio during growth of a High Arctic copepod

    Freshw Biol

    (2012)
  • M.H. Choi et al.

    Bioavailability of methylmercury to Sacramento Blackfish (Orthodon micrlepidotus): dissolved organic carbon effects

    Environ Toxicol Chem

    (1998)
  • M.M. Chumchal et al.

    Mercury speciation and biomagnification in the food webs of Caddo Lake, Texas and Louisiana, US, a subtropical freshwater ecosystem

    Environ Toxicol Chem

    (2011)
  • M.G. Clayden et al.

    Mercury biomagnification through food webs is affected by physical and chemical characteristics of lakes

    Environ Sci Technol

    (2013)
  • V. Daguené et al.

    Divalent base ions hamper Hg(II) uptake

    Environ Sci Technol

    (2012)
  • T.A. Douglas et al.

    The fate of mercury in Arctic terrestrial and aquatic ecosystems, a review

    Environ Chem

    (2012)
  • S.T. Edmonds et al.

    Geographic and seasonal variation in mercury exposure of the declining rusty blackbird

    Condor

    (2010)
  • M.S. Evans et al.

    Persistent organic pollutants and metals in the freshwater biota of the Canadian Subarctic and Arctic: an overview

    Sci Total Environ

    (2005)
  • N. Gantner et al.

    Temporal trends of mercury, cesium, potassium, selenium, and thallium in Arctic char (Salvelinus alpinus) from Lake Hazen, Nunavut, Canada: effects of trophic position, size, and age

    Environ Toxicol Chem

    (2009)
  • N. Gantner et al.

    Mercury concentrations in landlocked Arctic char (Salvelinus alpinus) from the Canadian Arctic. Part I: insights from trophic relationships in 18 lakes

    Environ Toxicol Chem

    (2010)
  • N. Gantner et al.

    Mercury concentrations in landlocked Arctic char (Salvelinus alpinus) from the Canadian Arctic. Part II: influence of lake biotic and abiotic characteristics on geographic trends in 27 populations

    Environ Toxicol Chem

    (2010)
  • N. Gantner et al.

    Physical and biological factors affecting mercury and perfluorinated contaminants in Arctic char

    Arctic

    (2012)
  • M.H. Graham

    Confronting multicollinearity in ecological multiple regression

    Ecology

    (2003)
  • B.D. Hall et al.

    Food as the dominant pathway of methylmercury uptake by fish

    Water Air Soil Pollut

    (1997)
  • C.R. Hammerschmidt et al.

    Photodecomposition of methylmercury in an Arctic Alaskan lake

    Environ Sci Technol

    (2006)
  • C.R. Hammerschmidt et al.

    Iron-mediated photochemical decomposition of methylmercury in an Arctic Alaskan lake

    Environ Sci Technol

    (2010)
  • Cited by (0)

    View full text