Variations in Stable Isotope Fractionation of Hg in Food Webs of Arctic Lakes (original) (raw)
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Applied Geochemistry, 2008
Isotopic and chemical analyses were performed on crustaceans, forage fish, top predator fish, and sediment cores from Lake Ontario and two boreal forest lakes to investigate fractionation of the stable isotopes of Hg in aquatic ecosystems. Multicollector inductively coupled mass spectrometry was used to determine Hg isotope abundances. The Hg isotope data for all three lakes showed mass-independent variation in the organisms but only mass-dependent variation in the sediments. The massindependent isotope effect was characterised by (1) selective enrichment in isotopes of odd mass number ( 199 Hg and 201 Hg), (2) enrichment in 201 Hg relative to 199 Hg, (3) an inverse relationship between isotopes of odd and even mass number in fish, and (4) a positive correlation with methylHg (CH 3 Hg + ) concentration, and hence with trophic level (although lake whitefish were consistently anomalous, possibly owing to biochemical demethylation). Isotope signatures of species at the same trophic level varied with habitat and diet, differentiating between planktonic and benthic crustaceans and their predators, and between fish that frequent deep, cold water and fish of similar diet that prefer warmer, shallower water, because of corresponding differences in CH 3 Hg + and inorganic Hg content. Isotopic analysis of CH 3 Hg + and inorganic Hg extracted from lake trout proved that the mass-independent isotope effect was due to anomalously high abundances of 199 Hg and 201 Hg in CH 3 Hg + , as implied by the data for whole organisms, suggesting mass-independent fractionation during microbial methylation of Hg. The purely mass-dependent variation in the sediments is attributable to the fact that Hg in sediments is mostly inorganic. The mass-independent fractionation of Hg isotopes can be explained by effects of nuclear spin or nuclear field shift, or both, and penetration of the inner electron shells of Hg by valence electrons of Hg-binding ligands. The results of the research demonstrate that isotopic analysis of Hg could yield valuable information about the biogeochemical cycling of Hg. Crown
Journal of Applied Ecology, 2002
Stable isotope analysis has improved understanding of trophic relationships among biota. Coupled with contaminant analysis, stable isotope analysis has also been used for tracing the pattern and extent of biomagnification of contaminants in aquatic food webs. 2. Combined analysis of nitrogen ( δ 15 N) and carbon ( δ 13 C) isotopes from fish species in a sub-Arctic lake were related to tissue mercury (Hg) concentrations to assess whether carbon sources influenced Hg accumulation in fish, in addition to trophic position. 3. Statistical models were used to estimate Hg biomagnification and uptake, to elucidate Hg accumulation dynamics and to appraise the relative importance of Hg exposure routes for the fish species. 4. Species Hg contamination increased as a function of trophic position ( δ 15 N) and was inversely related to the δ 13 C signature. Species connected to the benthic food chain had lower Hg concentrations than species connected to the pelagic food chain. Species undergoing ontogenetic dietary shifts with increasing size, e.g. lake trout Salvelinus namaycush , also showed increased Hg concentrations with increasing reliance on pelagic fish as prey.
Mercury in the sediments of freshwater lakes in Ny-Ålesund, Arctic
Environmental Monitoring and Assessment, 2020
Mercury and its speciation in aquatic ecosystems have been assessed globally. Even though previous studies were limited to Arctic freshwater lakes, they are highly significant in the context of the changing climate. The present study is based on sediment samples collected from three Arctic freshwater lakes over a period of 4 years (2015-2018). The samples were analysed for total mercury (THg), methyl mercury (MHg), and various mercury fractions. The observed mean THg and MHg concentrations were 22.23 ng/g and 0.41 ng/g respectively; these values were comparable with those for other Arctic freshwater lakes. The mercury content significantly varied among the years as well as among the lakes. Changes in snowdrift and meltwater inputs, which are the major sources of water for the lakes, may have influenced the sediment mercury content along with geographical location and increased productivity. The results of MHg indicated the susceptibility of lake sediments to methylation. The major fractions observed were the organo-chelated form of mercury, followed by the elemental and water-soluble forms. These results indicate the availability of mercury for methylation. Hence, it is necessary to conduct more studies on the influence of climate change, mercury release through permafrost melting, and atmospheric deposition.
Features of the distribution of mercury in bottom sediments of Russian Arctic lakes
Goldschmidt2021 abstracts, 2021
The paper presents data on the features of Hg distribution and its input in dated bottom sediments in two Arctic lakes: Longtibeito on the Yamal Peninsula and Gol'tsovoe on the Gydan Peninsula. The Hg concentrations are much higher in the upper layers of the sediments, and the enrichment factors are 14 and 10 at background concentrations of 4.3 and 5.2 ng g-1 , respectively. The sedimentation rates in both lakes are fairly high: the rate for Longtibeito Lake varied relatively little and is 660 ± 75 g m-2 year-1 on average, and that for Gol'tsovoe Lake decreased toward upper layers from 791 to 513 g m-2 year-1. The fluxes of total Hg in these lakes are principally different, but their lithogenic fluxes are approximately equal: 5-7 μg m-2 year-1. Mercury flux into Longtibeito Lake is much higher than into Gol'tsovoe Lake and amounts to 41.5 μg m-2 year-1. Layer-by-layer grain-size analysis with determination of Hg in each fraction, highlights differences between the lakes. The total Hg concentration in a layer in Gol'tsovoe Lake is controlled by the fine fraction (<0.045 mm), whereas this fraction in Longtibeito Lake dominates because of the high mass percentage. It has been shown that bottom sediments contain large (>0.2 mm) particles with high Hg concentrations. One of the likely reasons for the increase in Hg concentration in the upper layers may have been the development of oil and gas fields in this territory.
Low-Level Mercury Speciation in Freshwaters by Isotope Dilution GC-ICP-MS
Environmental Science & Technology, 2009
Atmospheric deposition of anthropogenic Hg has led to increased Hg concentrations in many ecosystems. Modeling is an effective method for predicting the complex dynamics of Hg fate and transport in watersheds; such models require accurate concentrations for water column methylmercury, CH 3 Hg + , as input parameters, yet these concentrations are very difficult to measure precisely as they are so low. We developed a method for aqueous CH 3 Hg + quantification in Lake Champlain VT, where ambient CH 3 Hg + concentrations are < 0.04 ng l-1. The analysis utilized species specific isotope dilution, purge and trap, gas chromatography ICP-MS and provided instrument detection limits of ca 0.2 fM (0.04 pg l-1) and method detection limits of 15 fM (0.003 ng l-1) for CH 3 Hg + which are amongst the lowest reported. Artifactual methylation of inorganic Hg 2+ was shown to be minor and the precision of the isotope dilution method was generally < 5% relative standard deviation; much lower than would have been the case for an external calibration approach. The method is accurate even at low concentrations of ca. 0.025 ng l-1. This combination of precision, accuracy and low detection allow for quantification of significant differences in CH 3 Hg + concentration between bays and over time within bays of Lake Champlain where mean CH 3 Hg + concentrations differ by only 0.006 ng l-1 at concentrations as low as 0.014 ng l-1 .
Canadian Journal of Fisheries and Aquatic Sciences, 1998
Several recent studies have shown that the use of δ 15 N analysis to characterize trophic relationships can be useful for tracing biocontaminants in food webs. In this study, concentration of total mercury was measured in tissues from 112 individuals representing 27 species from the arctic marine food web of Lancaster Sound, Northwest Territories. Samples ranged from particulate organic matter through polar bears (Ursus maritimus). Using δ 15 N values to identify trophic position, we found that total mercury in muscle tissue biomagnified in this food web. Polar bears were a notable exception, having a lower mean mercury concentration than their main prey, ringed seals (Phoca hispida). Most vertebrates showed greater variance in mercury concentration than invertebrates, and there was a trend in seabirds toward increased variability in mercury concentration with trophic position. Within species, we found no evidence of bioaccumulation of mercury with age in the muscle tissue of clams (Mya truncata) or ringed seals. Because stable nitrogen isotopes illustrated the relationship in this biome between trophic position and mercury level on a continuous, quantitative scale, we were able to determine that log 10 [Hg] (µg/g dry weight) = 0.2(δ 15 N) -3.3. The measurement of δ 15 N values and mercury concentration allowed us to quantitatively assess mercury biomagnification within this extensive arctic marine food web.