Introduction

The Arctic is one of the least disturbed habitats on earth. Increased human activities including industrial and mining processes however, have affected the process of biogeochemical cycling of heavy metals in the region (Naeth and Wilkinson 2008). The impact of such activities on environment can be determined through elemental analysis of the sediments and vegetation collected from the area.

Biomonitoring of the environment for assessing environmental pollution by phytotoxic substances and heavy metal deposition has been carried out previously in the Arctic (Riget et al. 2000; Shevchenko et al. 2010; Søndergaard et al. 2011) as well as Antarctic regions (Olech et al. 2000; Osyczka et al. 2007; Lim et al. 2009; Cabrerizo et al. 2012) using lichens. Lichens are capable of absorbing elements directly from the atmosphere and accumulating them in their tissues. The concentrations present in the thalli reflect the environmental levels of these elements (Loppi et al. 2002; Paoli et al. 2012). Direct environmental monitoring of major, minor as well as trace metals has been done using water samples in the Antarctic (Abollino et al. 2004).

The present study was undertaken to examine and comparatively analyse the heavy metal levels existing on the land habitats and glaciers around Ny-Ålesund, Arctic. Ny-Ålesund, one of the busy areas of Svalbard, although appears less polluted than down the latitudes may have been certainly exposed to local and transboundary pollution. It was therefore of interest to measure the concentration of elements accumulated in the ice-free and ice-covered areas of the region. For this, the lichens were collected from the low-lying ice-free areas while the cryoconite samples from the glacier valleys where no lichens or mosses could be located. ‘Cryoconite’ is the rounded or granular, brownish-black debris occurring in holes on the glacier surface containing a wide array of microorganisms including bacteria, fungi, cyanobacteria, green algae, diatoms, rotifers, tardigrades and ciliates (Xu et al. 2010). The level of metals in these samples is of particular importance in environmental and geochemical studies as these data reflect the levels of local metals in soil, rocks and glaciers.

Materials and methods

Study area

Ny-Ålesund (78°55′ N, 11°56′ E) is on the west coast of Spitsbergen, the largest island of Svalbard archipelago. Topographical features of Ny-Ålesund include East and West glaciers, terminal moraines, glacial streams and rivers flowing northwards to Kongsfjord. The mean temperature in the coldest month (February) is −14°C while the warmest month (July) has a mean temperature of +5°C. The lichen sampling sites are situated at various lowland habitats such as wetland and plains (Fig. 1).

Fig. 1
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Sampling sites of lichen (L1–L8) and cryoconite (G1–G4)

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Cryoconite samples were collected from Midre Lovénbreen, a well-known polythermal valley glacier (Fig. 2a), located in Ny-Ålesund. Cryoconite holes (Fig. 2b) represent about 6 % of the glacier surface. Typically, the holes are about 8–30 cm deep and 5–50 cm in diameter. The mean temperature of the water in the cryoconite hole was +0.2 to −1.9°C and pH 7.1 to 8.6 (measured using Thermo Orion 4Star, USA).

Fig. 2
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a Midre Lovénbreen glacier b Cryoconite holes

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Specimen collection

All collections were done during Indian Arctic Expedition 2007 and 2009, in the Arctic summer months of July–August. Natural thalli of lichen species chosen for the study (Table 1) were collected from different low-lying localities (L1 to L7) in Ny-Ålesund, Arctic. These were identified on the basis of their morphology following Thomson (1984) and Olech and Alstrup (1989). At each sampling site, a minimum of six lichen samples (∼2.0 g) for each species were collected. The specimens were stored in sterile perforated plastic bags, transported to laboratory with dry ice and maintained at −5°C till used. A part of the material of each species has been preserved as dried herbarium specimen in Polar Herbarium at NCAOR, Goa, India. Cryoconite sediments were collected from four sampling sites at different altitudes over the glacier. The sampling locations were designated as G1, G2, G3 and G4. The collection ranged from an altitude of 273 m (G1) to 164 m (G4) (Table 1). Samples were collected from the cryoconite holes using a sterile syringe and stored in sterile ampules at low temperature (−20°C) until studied.

Table 1 List of lichen species used for the study
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Analytical procedure

The oven-dried lichen and cryoconite samples were powdered and 0.5 g each was digested in HNO3 and HCl and in HNO3 and H2O2, respectively. The digestion was carried out in a Teflon vessel at 180°C (Milestone, ‘Ethos’ advanced digestion system). Lithophiles (Al, Cr, Cs and V), siderophiles (Co, Fe Mn and Ni) and chalcophiles (As, Cd, Cu, Pb and Zn) were determined through inductively coupled plasma mass spectrometry (ICPMS; Thermo Scientific ICPMS-X series II) using Merck CertiPUR ICP multi-element standard solution XXI for MS. Elemental concentrations were recorded in ppm and in ppb. Variance in the data sets was tested for statistical significance through one-way ANOVA based on triplicate readings. A multivariate ordination analysis based on elemental concentration for each set was performed using principal coordinates (PAST software ver. 2.01, Hammer et al. 2001). Linear regression model of the Microsoft Excel Data Analysis package was used to determine the relation between the various elements.

Results and discussion

The elemental analysis illustrates that amongst the elements analysed, heavy metals Al and Fe were present in high concentration in all the four cryoconite samples while in lichens, Al was high in seven of the eight samples studied (L-1, L-2, L-3 L-5, L-6, L-7 and L-8) and Fe in L-4. The general scheme of elements in the decreasing order of their concentration for most of the cryoconite samples was Al > Fe > Mn > Zn > V > Pb > Cr > Ni > Cu > Co > As > Cs > Cd while that for the lichen samples was Al > Fe > Zn > Mn > Pb > Cu > Cs > Cr > Ni > V > Co > As > Cd. Similarity in trends in the two sample types confirms that the environment indeed contain these elements in that order of concentration which overtime got accumulated in these samples.

Concentrations of the various elements analysed (Table 2) illustrate that in case of lichens as well as cryoconite, minor variations do exist within the individual samples, collected in triplicates. Variations between samples collected from different locations, however, remained statistically significant at P < 0.01 for most elements, as computed through one-way ANOVA. Variability in the chemical parameters within and between the cryoconite holes has been reported previously by Fountain et al. (2008).

Table 2 Elemental concentration in Arctic lichen and cryoconite samples compared with the baseline values laid down for lichens from remote areas of North Canada (Chiarenzelli et al. 2001, as reported by Bergamaschi et al. 2004) and crustal values of Western Europe and Canada (Shaw et al. 1967, 1976, Wedepohl 1995)
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Principal coordinates ordination analysis (Fig. 3) using Bray–Curtis similarity index based on the elemental concentration in the samples groups the four high altitude sites G-1, G-2, G-3 and G-4 in a single cluster confirming their alike elemental concentration. Amongst the low altitude lichen samples, L-5 and L-8 were grouped together, segregated from the rest. The elements that are responsible for such a grouping are As, Co, Cr, Cs, Cu, Li, Mn, Ni, V and Zn in case of cryoconite samples and Al, As, Cd, Co, Cu, Fe, Pb and Zn in the case of lichens.

Fig. 3
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Principal coordinate analysis based on elemental concentration of the samples

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Although it is well-known that lichens growing in the area frequently accumulate variety of air-borne particles by virtue of their large surface area, wide intercellular spaces, thin or no upper cortex, long life span, high cell permeability and high ion exchange capacity (Scerbo et al. 2002; Aslan et al. 2004; Naeth and Wilkinson 2008), the overall comparison showed that most elements were present in high concentrations in the cryoconite samples (collected from high altitude glacier regions) as compared to the lichen samples (collected from low altitudinal areas) (Table 2). The difference in the two groups was found to be statistically significant at P < 0.01, except in the case of Cd and Cs.

Amongst the eight lichens studied, highest amount of elemental accumulation occurred in L-2 (Cladonia mediterranea) followed by L-1 (Cladonia amaurocraea), L-4 (Flavocetraria nivalis), L-6 (Pseudophebe pubescence), L-7 (Umbilicaria hyperborea), L-8 (Xanthoria elegans), L-5 (Physcia caesia) and L-3 (Cetraria fastigata). The element concentration data of lichen samples was compared for 10 elements (As, Cd, Co, Cr, Cs, Cu, Fe, Pb, V and Zn) with the baseline data from remote areas of North Canada as proposed by Bergamaschi et al. (2004) from Chiarenzelli et al. (2001). The baseline data indicated as B values in the lichen elemental accumulation plots (Fig. 4a–d) suggest that location from where L-2 sample was collected was the most polluted accumulating all the 10 elements at concentrations higher than the baseline values. Next, most polluted regions were those from where L-1 and L-6 samples were collected. L-8 was the least polluted region amongst those tested, accumulating only four elements (Cu, Pb, Zn and Cd) at concentrations higher than baseline value.

Fig. 4
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a–d Elemental accumulation in lichen samples. B values represent the baseline values for lichens as proposed by Bergamaschi et al. (2004) from Chiarenzelli et al. (2001)

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The lichens were grouped into two groups based on their thalli type—foliose and fruticose. The possibility of the effect of lichen thalli on the accumulation levels of elements was eliminated by significance tests of the two groups. The variation in the two groups was found to be statistically insignificant.

Based on their tolerance to physiological toxicity, threshold values of various heavy metals have been laid down of lichens in general. According to Nieboer et al. (1978), lichen species can tolerate Cd and Cu between 1–30 and 1–50 ppm, respectively. Threshold values for Pb in lichens are from 5 to 100 ppm, although above 15 ppm, the values are considered enhanced (Nieboer and Richardson 1981). For Zn, enhanced levels in lichens are above 500 ppm (Nieboer et al. 1978). Taking these values into account, the results of the present study indicate that a further increase in Pb concentration, in areas from which L-2 and L-4 lichen samples were collected, may threat the existence of lichen species.

When linear regression model was used to determine the relation between different elements, it was observed that except for Cd, Cs, Pb and Zn and to some extent Ni, most other elements showed correlation with one another (R 2 ≥ 0.9, Table 3) in terms of concentration. Presence of Cd, Pb, Cs, Ni and Zn in high concentration and their non-correlation with others indicates that these disturbing elements in all probability are sourced from anthropogenic activities.

Table 3 R 2 values indicating correlation between the various elements measured
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Probable sources of heavy metals

Crustal contribution

Atmospheric occurrence of various heavy metals is a contribution of rock and soil dust, sea salt spray and continental and biogenic emissions (Nriagu 1979). Factors such as precipitation, wind and air stability of an area determines the deposition patterns of air-borne dust particles (DiGiovanni and Fellin 2006). In order to evaluate the possible crustal contributions to the deposition of heavy metals in the cryoconite samples, the data was compared with crustal composition of refraction seismic profile of Western Europe and Canada (Shaw et al. 1967, 1976; Wedepohl 1995) [Table 2, Fig. 5a–d (indicated as C values)]. Comparison shows that the value of elements such as Co, V, Cr, Al, Ni, Mn, Cd and Fe were well below the levels found in the continental crust implying these elements to likely be the crustal contributions from rocks and soils of the region. In each one of the cryoconite samples, however, Ni and Cd were present in concentration higher than the continental crust levels. Elements such as As, Cs, Cu, Pb and Zn were present at elevated levels in all the four cryoconite samples examined. Further, comparison with lichen data suggests that the elements accumulated in lichens are generally well below the crustal values. Some exceptions to this were Zn in L-7, Pb and As in L-2 and Pb in L-4. Cd was present in high concentration in all the lichen samples while Cs accumulated in high concentration in six of eight samples tested.

Fig. 5
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a–d Elemental accumulation in cryoconite holes. C values represent the standard crustal contributions according to Shaw et al. (1967, 1976), Wedepohl (1995)

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Other natural and anthropogenic contribution

High concentration of heavy metals, especially Pb, Cu and Zn present in the cryoconite samples, which cannot be accounted for by crustal source, is likely a contribution from other natural and/or anthropogenic sources. The source of pollution could either be local deposition or long-distance transmission of heavy metal dust particles as reported in previous studies (DiGiovanni and Fellin 2006). In sheltered valleys, such as the glacier valley in the study area, the lower air layers become stable and prone to pollution (Benson 1987). High-velocity winds blowing from sea to land that collapses in the valley after striking against the mountainous terrain could bring about high-level deposition of heavy metal dust. Subsequent deposition of heavy metals and their accumulation in the cryoconite holes due to freeze–thaw cycles in the summer months year after year is likely the reason of extreme high levels of heavy metal presence in the cryoconite samples. Another factor that is likely to influence the elemental concentration in cryoconite is the presence of an abandoned mine in the region. Presence of an industrial city, Norilsk at about 2,270 km away in Russia could be a source of long-distance transmission of heavy metal pollution at higher altitudes of the region. The Siberian city of Norilsk is one of the ten most polluted industrial cities of the world and houses the world's largest heavy metals smelting complex. It disperses in air over 4 million tons of Cd, Cu, Pb, Ni, As and Zn, annually (Blacksmith Institute Project 2006).

The airport area and adjacent vehicular traffic may act as the local source of pollution in the low-lying areas thereby leading to contamination of the area (L-2 and L-4 sampling area) with Pb, as it is known that vehicular exhaust is one of the common sources of Pb pollution. The increase in cadmium concentration in most of the lichen samples could be likely due to the influence of sea salt spray (Hong et al. 2002), traffic in the area, coal burning activities (Scerbo et al. 2002) or even long-distance atmospheric transport by virtue of its highly volatile nature (Bergamaschi et al. 2004).

A multi-element study of biological samples along with baseline data comparison is an effective tool for environmental monitoring of pollution. Baseline data helps identify the elements that are sourced through anthropogenic activities. The present study holds significance as it compares the elemental data from high altitude cryoconite samples with the low-lying lichens and observes that the cryoconite samples accumulate higher concentrations of elements than the lichens. The study also points out to the fact that although the pollution levels at lower altitudes is not very high, further increase in the levels of Pb can affect the survival of lichen species in the region.

The higher altitudes glacier valleys even though less disturbed than the lowlands, are muddled up with high concentrations of elemental dust. Although too early to speculate, there occurs a possibility that if the dust continues to settle over these glaciers at this or higher rate, the albedos of snow would reduce, resulting in thinning of the glacier, thereby contributing to the anthropogenically induced global warming.

Further, since the elemental data was generated from samples following standard collection and analysis procedures as mentioned in the “Materials and methods” section and compared with baseline data from the remote regions of northern Canada, the average of the low concentrations for each element can probably form a baseline for monitoring quantum of atmospheric heavy metal deposition in future in Svalbard, Arctic.