S4 (I) Mercury in the Arctic

Thursday, 28 July, 2011

RS4-O1 — 8:30-8:45
Authors: LOSETO, Lisa1, MACDONALD, Robie W.1
(1) Fisheries and Oceans Canada, lisa.loseto@dfo-mpo.gc.ca

Mercury (Hg) concentrations in Arctic marine top predators have been a concern largely stemming from their use as Inuit subsistence food. Trends in Hg over time and across Arctic regions demonstrate great variability and highlight the need to better understand the underlying mechanisms and processes of Hg cycling and bioavailability to food webs. The urgency to identify key processes is underscored by a changing climate reducing sea ice extent over the Arctic Ocean. Macdonald and Loseto (2010) defined four components of the Arctic Oceans’ Hg cycle that are poorly understood and yet may have large potential to alter Hg exposure to top predators. These components coincide as likely sources for key Arctic marine food webs (i.e. nearshore, benthic etc). How Hg enters food webs and reach concerning levels in top predators are governed by a) the relative bioavailability for uptake/absorption of Hg and/or methylmercury (MeHg) at the bottom of the food web, b) species specific characteristics that drive bioaccumulation, c) food web structure defining biomagnification, and d) predator feeding ecology that influences Hg exposure. Thus, by accounting for variability in predator foraging behaviour and food web structure and function, the impacts of trophism and initial Hg sources can be quantified. Here we use Arctic food webs and top predators together with Hg budgets for Arctic Ocean components to identify key factors driving top predator Hg concentrations. The use of fatty acids enabled appropriate food webs to be constructed and measure food web magnification factors among representative Arctic Ocean ecosystem components. Preliminary results show that with the consideration of predator specific foraging, the food web biomagnification slopes were consistent among food webs, thus eliminating trophism as a key factor defining predator variability. Higher Hg levels measured in offshore food webs likely reflect more bioavailable forms of Hg in the interior and deep ocean. While these initial findings support recent observations of high Hg in Arctic and tropical deep ocean marine fishes; it brings to question the importance of terrigenous and atmospheric Hg sources to offshore Arctic marine food webs.

RS4-O2 — 8:45-9:00
Authors: ST.LOUIS, Vincent L.1, DEROCHER, Andrew E. 1, STIRLING, Ian2, GRAYDON, Jennifer A.1, LEE, Caroline1, JOCKSCH, Erin3, RICHARDSON, Evan2, GHORPADE, Sarah1, KWAN, Alvin K.1, KIRK, Jane L.4
(1) University of Alberta, vince.stlouis@ualberta.ca; (2) Canadian Wildlife Services, Environment Canada; (3) jocksch@ualberta.ca; (4) Environment Canada.

Polar bears (Ursus maritimus) are being impacted by climate change and increased exposure to pollutants throughout their circumpolar range. In this study, we quantified concentrations of total mercury (THg) in the hair of polar bears from Canadian high- (southern Beaufort Sea; SBS) and sub- (western Hudson Bay; WHB) Arctic populations. Concentrations of THg in polar bears from the SBS population (14.8±6.6 µg g-1) were significantly higher than in polar bears from WHB (4.1±1.0 µg g-1). Based on 15N and 13C signatures in hair, polar bears from the SBS population appear to feed on a longer, more pelagic food web than those from WHB. Food web length and structure accounted for ~67% of the variation we found in THg concentrations amongst the two populations. Regional difference in THg concentrations in polar bears was likely also the result of regional differences in availability of methyl Hg (the toxic form of Hg that biomagnifies through food webs) at the base of the food webs. For example, concentrations of methylated Hg at mid-depths in the marine water column of the northern Canadian Arctic Archipelago were 79.8±37.3 pg L-1, whereas in HB, they only averaged 38.3±16.6 pg L-1. We conclude that a longer food web and higher pelagic concentrations of methylated Hg in the BS resulted in higher concentrations of THg in polar bears from the SBS region relative to those living along the western coast of HB.

RS4-O3 — 9:00-9:15
Authors: BRAUNE, Birgit1, GASTON, Anthony J.1, FERGUSON, Steven H.2
(1) Environment Canada, birgit.braune@ec.gc.ca; (2) Fisheries and Oceans Canada.

 Mercury exposure in seabirds occurs primarily via the diet. Significant increases in mercury concentrations have occurred in eggs of thick-billed murres (Uria lomvia) from Canada’s High Arctic since 1975. In contrast, mercury in murre eggs from northern Hudson Bay, which have been monitored since 1993, have shown no significant change. The reasons for these trends are complex, involving emissions from human activities as well as natural emissions, coupled with environmental and biological (e.g. food-web) processes which may also be affected by climate change. Warming ocean conditions and longer ice-free periods have been documented for Hudson Bay over the last 25 years. Arctic cod (Boreogadus saida) is the main prey of thick-billed murres at Prince Leopold Island in the high Arctic and, until the mid-1990s, was the most common prey item found in the diet of nestling murres throughout the Canadian Arctic. Since the early 1980s, however, a shift in the diet of thick-billed murres breeding on Coats Island in northern Hudson Bay has occurred, from arctic cod and benthic fish species to capelin (Mallotus villosus) and sandlance (Ammodytes hexaptera). Using d15N values as an index of trophic position, we have noted a decrease in trophic position as reflected in thick-billed murre eggs from Coats Island since 1998 compared with 1993 values. Fish samples collected from adult murres bringing food to their chicks on Coats Island were analyzed for mercury and other chemical contaminants to determine if exposure of thick-billed murres to contaminants through their diet on the breeding grounds has changed with the change in diet. The arctic cod fed to thick-billed murre chicks occupy a higher trophic position and have higher concentrations of total mercury in them than either the capelin or sandlance. The change in diet suggests that there may have been a shift to a lower exposure to contaminants through diet. Such dietary changes must be taken into account when evaluating contaminant temporal trends.

RS4-O4 — 9:15-9:30
Author: GAMBERG, Mary1
(1) Gamberg Consulting, mary.gamberg@northwestel.net

The Arctic terrestrial ecosystem in general has low levels of mercury and Arctic terrestrial wildlife is not currently at risk of mercury intoxication. Of the Arctic terrestrial species studied, caribou and mink have the highest concentrations of mercury reflecting their relatively mercury-rich diets of lichens and fish respectively. The Porcupine Caribou herd has been studied most extensively. Caribou collected in spring tend to have higher mercury concentrations than those collected in fall and both female mink and caribou tend to have higher levels than males. Although there is annual variation in mercury levels in the Porcupine caribou, concentrations have not changed significantly over the last two decades. The annual variation seems to be at least somewhat cyclic and is likely driven by environmental factors. Mercury concentrations in male and female caribou vary in similar fashions, but with the males lagging behind the females by about one year. This suggests that female caribou respond more quickly to environmental factors and are therefore more sensitive (and therefore vulnerable) to those particular environmental drivers. Annual variations in mercury concentrations may be related to the Pacific Decadal Oscillation, with caribou renal concentrations decreasing when the index is in a negative mode and increasing when the index is in a positive mode. Although limited work has been done on mercury in Arctic wolves, the simple lichen-caribou-wolf food chain can provide a valuable opportunity to explore the movement of and potential biomagnification of mercury through the Arctic ecosystem. A data gap exists with regard to mercury levels and dynamics in Arctic insects and insectivores and should be explored.

RS4-O5 — 9:30-9:45
Authors: BRYAN, Colleen1, DAVIS, W. Clay1, MOORS, Amanda J.1, PUGH, Rebecca1, RUST, Lauren1
(1) NIST, colleen.bryan@nist.gov

The Arctic Marine Mammal Tissue Archival Program (AMMTAP) has been collecting samples in collaboration with the National Institute of Standards and Technology (NIST) for long term temporal studies of marine mammal populations in the arctic region. These samples are collected according to standardized protocols and have been cryogenically preserved in the National Marine Mammal Tissue Bank (NMMTB). The Cook Inlet, Alaska population of beluga whales (Delphinapterus leucas) has been declining, prompting concern to further examine this population and compare mercury exposure concentrations in the Cook Inlet beluga population with all other beluga populations that have had samples banked in the NMMTB. Sixty-eight beluga whale liver samples were collected from 1989-2006 from Cook Inlet and the Eastern Chukchi Sea through Alaskan subsistence hunts and stranded animals. The animals in the beluga sample set were both male and female ranging in age from calf to adult. Declining populations have also been observed for Saint Paul Island, Alaska northern fur seals (Callorhinus ursinus) and mercury exposure concentrations were measured. From 1987-2007, sub-adult male northern fur seal liver samples were collected from rookeries around Saint Paul Island through Alaskan subsistence hunts and 35 samples were analyzed in this study. Total mercury was measured in liver samples by atomic absorption spectrometry (AAS). Total mercury concentrations in beluga liver were significantly (p = 0.0021) greater in the Eastern Chukchi Sea population than the Cook Inlet population. Male belugas in Cook Inlet had significantly greater (p = 0.0028) liver mercury concentrations than female belugas in the same population, while in the Eastern Chukchi Sea there was no statistical difference (p = 0.0964) between male and female mercury concentrations. As total beluga body length increased, total mercury concentrations increased significantly (p < 0.0001) in whale liver. Mercury concentrations in beluga whale liver increased at a greater rate in relation to body length in animals from the Eastern Chukchi Sea than Cook Inlet. Neither Cook Inlet nor the Eastern Chukchi Sea beluga whale populations exhibited a temporal trend related to mercury concentrations in liver. Mercury temporal trends will be examined in northern fur seal livers which do not have the possible confounding factors of both genders and multiple age classes in the study population. The evaluation of mercury exposure in beluga and northern fur seal populations demonstrates the value of long term environmental specimen banking for retrospective studies.

RS4-O6 — 9:45-10:00
Authors: POINT, David1, MASBOU, Jeremy2, SONKE, Jeroen E3, BECKER, Paul R4
(1)IRD, david.point@ird.fr; (2) UPS; (3) CNRS; (4) NIST.

Mercury impacts are enhanced at high latitudes with record concentration levels in Arctic marine wildlife, posing a health risk for northern people who consume these subsistence resources. Whereas a cascade of processes might ultimately link atmospheric Hg emissions to Hg concentrations in Arctic biota, the different temporal trend series in the Western and Eastern Arctic sectors suggest that other factors may be underpinning these trends. Recent work on mercury stable isotopes fractionation in seabird eggs from the Alaskan arctic revealed that mercury cycling may be linked to ice cover. Complementary measurements were performed on cryogenically archived marine mammal liver samples to document the extent of Hg stable isotopes fractionation in the Alaskan marine foodweb. Mercury stable isotope measurements were conducted in beluga whale (Delphinapterus leucas), ringed seal (Phoca hispida) and polar bear (Ursus maritimus) liver samples collected since 1988.

Significant variations in Hg MDF and MIF existed between the different species investigated and between individuals at the colony, group or stock level. Results on beluga whale showed clearly that Gulf of Alaska, Bering Sea and Chukchi Sea stocks were characterized by unique Hg MIF signatures, with values changing with latitude and matching earlier results obtained on seabird eggs. These results indicated that Hg-MIF may be used as a robust geographical tracer for describing habitat utilization and food webs connectivity between the grand Alaskan regions.

RS4-O7 — 10:00-10:15
Authors: BRANFIREUN, Brian1, PRICE, Jonathan2
(1) University of Western Ontario, bbranfir@uwo.ca; (2) University of Waterloo, Department of Geography.

It is well established that peatlands are important modifiers of downstream water quality in any catchment where they are found. Although small headwater peatlands are very important in controlling downstream water quality, there have been no attempts to scale up the process-based knowledge that we have about mercury cycling in small peatlands to the larger extensive peatland systems of the world. The Hudson Bay Lowlands (HBL) is the second largest peatland complex in the world with a total area of approximately 320000 sq km. In light the importance of the carbon stock and predictions of significant climate change impacts, research effort has gone into studying the carbon dynamics of the HBL peatlands however there has been no research on the role of the HBL peatlands in governing the water quality or quantity of the important tributaries of Hudson Bay. The published importance of mercury loading to the Hudson Bay/James Bay in terms of ecosystem and human impact stands in stark contrast with the limited data available for major tributaries. Perhaps of greatest importance are emerging concerns over land-use and/or climate changes in the HBL that affect peat hydrology and mercury dynamics; these concerns are based solely on conjecture because of the absence of empirical data.

As part of a study of the impacts of land-use change associated with mining activities in this region, we have been investigating the mercury and methylmercury dynamics of two small ‘headwater’ catchments that deliver runoff ultimately to the Attiwapiskat River. One catchment is influenced by a change in hydrology as a result of mine dewatering, and the other is a reference catchment subject only to natural variability in hydrology due to differences in seasonal and annual weather patterns. Our results over three years of study indicate that there is dramatic between-year variation in surface water total mercury and methylmercury concentrations (up to ~2x) for a given stream. Between streams, there is a similar range of variability driven largely by differing natural hydrological processes, calling into question are definition of a reference stream or watershed. Total and methylmercury concentrations are very low relative to more southerly peatland-dominated watersheds (e.g. 2008 mean THg and MeHg ~1 ng/L and ~ 50 pg/L respectively). Despite this, the aquatic organisms of these cold-water ecosystems are sensitive to even these low Hg concentrations because of their exceptionally slow growth rates.

RS4-O8 — 10:15-10:30
Authors: LEHNHERR, Igor1, ST. LOUIS, Vincent L.1, KIRK, Jane L.2
(1) University of Alberta, lehnherr@ualberta.ca; (2) Environment Canada.

Some freshwater fish in the Canadian Arctic contain levels of methylmercury (MeHg) that pose health risks to Inuit peoples harvesting these species as traditional food. In temperate regions, wetlands are known sources of MeHg; however, the importance of wetlands to Hg methylation in the Arctic is unclear and the sources of MeHg to arctic freshwater ecosystems are still unidentified. The objective of this study was to quantify MeHg production in wetland ponds near Lake Hazen (81°N, Ellesmere Island, Canada) and determine the biogeochemical controls on MeHg production. To quantify net in-pond production of MeHg during the summer seasons of 2005, 2007 and 2008, mass-balance budgets were constructed for two wetland ponds (Ponds 1 and 2) by measuring external MeHg inputs from atmospheric deposition, MeHg losses from photodemethylation, and changes in MeHg storage in the water column. Compared to nearby lakes, ponds (n=16) had elevated water MeHg concentrations (0.05-1.5 ng/L) and a high proportion of total Hg in the MeHg form (4-60%), suggesting that methylation is enhanced in those systems. MeHg inputs from precipitation were small (0.026-0.051 ng/m2/d). Photodemethylation was a sink for 77-122% of MeHg produced in-pond, and was controlled by the attenuation of UV-A radiation in the water column. In-pond MeHg production ranged from 14-40 ng/m2/d in Pond 1 and 1.7-1.9 ng/m2/d in Pond 2, comparable to values reported for temperate/boreal lakes and wetlands. Flooding of the Pond 1 wetland in 2008 due to rising water levels in nearby Lake Hazen resulted in increased MeHg production. Additionally, potential rates of Hg(II) methylation were quantified in intact sediment cores (n=29) from a number of ponds using Hg stable-isotope tracers to identify the factors controlling MeHg production. Potential methylation rates were high and exhibited nearly as much intra-site as inter-site variability. Sediment MeHg concentrations were significantly correlated to methylation potential and sediment total-Hg concentrations. Furthermore, pond water MeHg concentrations were positively correlated with sediment MeHg concentrations, indicators of anaerobic microbial decomposition of organic matter (pCH4, NH4+/NO3- ratio), and negatively correlated with UVA exposure and particulate carbon. However, no correlation with organic matter or sulfate was observed. Overall, our results demonstrate that Arctic wetland sediments are sources of MeHg comparable to freshwater sediments in temperate latitudes and that MeHg concentrations in water are controlled by production in sediments – itself a function of anaerobic microbial activity, methylation potential and Hg(II) availability – as well as photodemethylation in the water column.

Thursday, 28 July, 2011