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SPATIAL VARIATION AND CORRELATIONS OF MERCURY LEVELS IN THE TERRESTRIAL AND AQUATIC COMPONENTS OF A WETLAND DOMINATED ECOSYSTEM: KEJIMKUJIK PARK, NOVA SCOTIA, CANADA A. N. RENCZ1∗ , N. J. O’DRISCOLL2 , G. E. M. HALL1 , T. PERON1 , K. TELMER3 and N. M. BURGESS4 1 Geologic Survey of Canada, 601 Booth St., Ottawa, Canada, K1A 0E8; 2 University of Ottawa, Department of Biology, Station A, Ottawa, ON, Canada K1N 6N5; 3 University of Victoria, Department of Earth and Ocean Sciences, Victoria, B.C., Canada V8W 3P6; 4 Environment

Canada, Canadian Wildlife Service, St. Johns, Newfoundland, Canada A1N 4T3 (∗ author for correspondance, e-mail: [email protected]. )

(Received 15 August 2001; accepted 26 June 2002)

Abstract. This study investigates the ranges and spatial variation of mercury in various media in the wetland ecosystems of Kejimkujik Park, Nova Scotia. Mercury concentrations in five-year-old yellow perch (age based on regression analyses of existing data) ranged from 0.12–0.72 µg g−1 (wet weight basis) in 24 lakes. Mercury concentrations in red maple ranged from 5 to 41 ng g−1 and levels in white pine ranged from 5 to 58 ng g−1 , dry weight. Concentrations of total mercury were found to be significantly higher in epiphytic lichens (maximum of 660 ng g−1 ) and in feather mosses (maximum of 395 ng g−1 ) compared to vascular species. The soil Ah horizon exhibits the highest concentrations for both mercury and gold, with maximum values of 466 and 42.8 ng g−1 respectively; whereas the C-horizon appears to host the most Zn (maximum 209.9 µg g−1 ). Lake water pH and dissolved organic carbon (DOC) were the variables most highly correlated with mercury in lake waters and yellow perch. No correlations were observed between mercury in terrestrial components and mercury in yellow perch; however, mercury in yellow perch was correlated with P in leaf tissues of both red maple and white pine. The importance of understanding linkages between terrestrial and aquatic ecosystems is emphasized through this study. Keywords: correlations, DOC, mercury, methyl mercury, pH

1. Introduction Studies conducted within Kejimkujik National Park, Nova Scotia show that mercury concentrations in the blood of common loons (Gavia immer) are the highest recorded in North America (Burgess et al., 1998a). A recent paper by Scheuhammer et al. (2001) reviewed the values of mercury in piscivorous avian species as reported in the literature. Loons from Kejimkujik were found to have the highest reported levels of mercury. Some of the other high mercury values observed by Scheuhammer et al. (2001) were in related species such as the red-throated loon. These levels of mercury found in waterfowl blood (6 to 8 µg g−1 ) have been linked to deficiencies in behavioral and reproductive capacities (Heinz and HoffWater, Air, and Soil Pollution 143: 271–288, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.

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man, 1998; Hoffman and Moore, 1979; Beauchamp et al., 1997). Similarly, levels in yellow perch (Perca flavescens), a prey for the loon, have been found to be elevated in certain lakes in the park (Carter et al., 2001). However, little is known about the sources and concentrations of mercury in the vegetation and soil of the Kejimkujik freshwater ecosystem. The contribution of anthropogenic sources to the ecosystems of remote areas has been suggested by Fitzgerald (1998). The influx of mercury in Kejimkujik through precipitation has been recorded by Beauchamp et al. (1997) in moderate concentrations (7.0 ng L−1 median value for July-Dec 1996). There are a variety of known anthropogenic sources of atmospheric mercury. At the global and regional scales these include: the byproducts of fossil fuel combustion for electricity generation, combustion from vehicles, paint and fungicides used for agricultural and recreational industries (Stober et al., 1995). While atmospheric inputs of mercury to Kejimkujik are well established, studies in the Park have shown that there is no correlation between atmospheric input of mercury and the water and biota mercury concentrations (Clair et al., 1998). They suggest a link between the amount of wetland in a drainage basin and mercury concentrations in the fish, underscoring the significance of DOC in the mercury biogeochemical cycle. The role of natural sources and processes in contributing to the elevated levels of mercury in Kejimkujik Park have been presented by Vaidya et al. (2000); however the specific source remains unknown. Some potential geological sources of mercury include degassing along faults (Rasmussen et al., 1998) and along oceanic hydrothermal vents (Stoffers et al., 1999). Plouffe (1998) reported on high mercury concentrations associated with weathering of mercuric sulphide minerals and the associated mining activities. Regardless of source, the balance between methylation of inorganic mercury to methyl-mercury (MeHg) and demethylation to inorganic mercury poses the greatest health threat to biota. Methyl-mercury is the form of mercury that bio-accumulates within the food chain (Drever, 1997) and MeHg is the most toxic form of mercury. Various mechanisms have been implicated in the methylation and demethylation process (Watras and Huckabee, 1994). The important role of bogs in MeHg production has been emphasized by Perdue et al. (1988) and Lucotte et al. (1995; 1999). In lacustrine sediments Amyot et al. (1997) presented the idea that photochemistry may be the controlling factor on MeHg production. While past research has hinted at the importance of understanding mercury transport between the terrestrial and aquatic ecosystems very few papers have attempted to comprehensively explore their relationships on a large scale. The objectives of this paper were to examine the spatial variations of mercury in the various media (soil, vegetation, lake water, and fish) within Kejimkujik Park. Through an examination of correlations between these media some insight into mercury relationships may be assessed. In particular links between geology, vegetation, water and biota content may become clear through a spatial analysis of data. While past research in Kejimkujik has indicated elevated levels of mercury in biota (Burgess,

SPATIAL VARIATION AND CORRELATIONS OF MERCURY LEVELS

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Figure 1. Location of the study area: Kejimkujik National Park, Nova Scotia, Canada.

1998) no research has investigated ecosystem links that result in bioaccumulation. This paper is the first attempt at understanding mercury cycling in an integrated manner.

2. Setting Kejimkujik National Park is located on the Southern Upland of Nova Scotia (Figure 1). It is a low relief area lacking the major escarpments, mountains and valleys found in other parts of the province. Most of the visible landforms in the Park are a result of the last glaciation, which ended approximately 18,000 years ago. These landforms include drumlins, plains, eskers, glacial erratics (bedrock boulders) and shallow lakes connected by meandering streams. 2.1. B EDROCK GEOLOGY The bedrock of Kejimkujik Park is typical of rocks of the Meguma Terrane found throughout about 50% of the landmass of South Western Nova Scotia (Keppie, 2000). The area is underlain by two main rock sequences, each of which could be a source of mercury: 1) the Meguma Group of Cambro-Ordovician age and 2) the South Mountain Batholith and related intrusive rocks of Devono-Carboniferous age. Both rock sequences have mercury values ranging from less than 1 to several hundred ng g−1 (O’Driscoll et al., 2001).

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The Meguma Group consists of a lower grewacke unit (Goldenville Formation) and an overlying black, organic carbon-rich sulphidic slate (Halifax Formation). It underlies the south and eastern portions of Kejimkujik Park as well as most of the Atlantic shore of Nova Scotia. Rasmussen et al. (1997) indicated that the bedrock lithology, age and abundance of sulphide mineralization are very important to understanding mercury distribution. In particular pyritic black shales and mercury bearing Sphalerite (ZnS) are implicated as important sources of mercury. The South Mountain Batholith, which occupies most of the southwestern part of the Park, is comprised of two intrusive rock types referred to as the Davis Lake Leucomonzogranites and Kejimkujik Monzogranites (Horne and Corey, 1994). These rocks contain biotite inclusions that may have associated mercury. 2.2. S URFICIAL GEOLOGY The Park is mainly covered by stony till plain deposits, which tend to cover upland areas of the province and regions underlain by hard Pre-Cambrian and Paleozoic rocks. These tills were formed under the local ice caps that were prevalent in Nova Scotia during the ice age. These tills are characterized by a loose texture, sandy matrix, and abundant, locally derived, angular stones and boulders. In places the boulders are large, measuring up to 20 m across. Over the northern half of the park area, glacial debris is relatively thin (< 1 m). The area has low relief with a vague southeastward grooving as a record of the last main movement of the ice sheet that crossed Nova Scotia. The southern third of the park area features very elongate streamlined hills of glacial debris called drumlinoid ridges. Up to 20 km long, they record the main southeastward course of the ice sheet across Nova Scotia and give the terrain a strong southeast fabric. Most of the lakes occupy the narrow swales between the drumlins. Strong glacial action carved and molded the drumlinoid ridges from a thick blanket of granitic debris. Much of the lowland terrain of the park area is composed of thick glacial drift that has been molded into long drumlin ridges. The ridges were overlaid with mounds and hummocks of till during decay of the ice. In lakes, this terrain produces long knobby peninsulas and rows of islands. Drumlin hills predominate in the eastern portions of the park and beyond. Between the drumlins, the surface is slate bedrock, which has been glacially eroded into narrow parallel ridges trending perpendicular to the drumlins. 2.3. V EGETATION The forest cover of the Park is representative of the Atlantic Uplands forest region, and is composed of mixed coniferous and deciduous vegetation. There is a mixture of tree species but the dominant trees include: white pine (Pinus strobus), eastern hemlock (Tsuga canadensis), white birch (Betula papyrifera) and red maple (Acer rubrum). While past logging has disturbed much of the forest in the region, there is no logging within the Park. The average age of Kejimkujik National Park’s forests

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TABLE I Range of Hg and other elements in various media for Kejimkujik Park, N.S. Numbers in brackets are median values Media

Pinus strobus Acer rebrum Pleurozium schreberi Usnea sp.

N

Hg (total) Au ng g−1 ng g−1

56

5–58 (25) 125 5–76 (32) 8 45–395 (172) 45 66–660 (178) Soils- O 37 71–415 (219) Soils-Ah ng g−1 < 0.2 mm 47 43–460 (189) < 0.063 mm 47 43–466 (212) Soils-C 50 6–188 < 0.2 mm (58) < 0.063 mm 49 15–304 (88) Perca 24 µg g−1 flavescens1 lakes 0.12–0.72 Hg Total ng L−1 Water 50 0.3–3.7 lakes (1.5)

As µg g−1

0.13–59 (1.9) 0.14–13.2 (1)

0.14–1.5 (0.4) 0.13–5.8 (1.4) ng g−1 0.13–6.9 (1.3) 0.5–42.8 (2.4) 0.13–9.2 (0.95) 0.13–31.8 (1.1)

P %

Cd ng g−1

Zn µg g−1

0.08–0.25 (0.142) 0.09–0.41 (0.15)

0.01–0.24 (0.02) 0.01–0.84 (0.05)

13.2–60.1 (31.4) 10–53.9 (22.6)

0.10–0.89 (0.23) 0.05–0.89 (0.27) µg g−1 0.01–0.87 (0.27) 0.04–1.09 (0.27) 0.01–0.34 (0.02) 0.01–0.29 (0.07)

12.8–75.6 (28.9) 7.9–105.5 14.5–95.4 (36.9) (49.1) 4.3–109.8 (31.6) 3.7–97.2 (28.0) 1.9–161.8 (20.5) 2.7–209.9 (22.0)

5.12–30.57 (10.51) 6.24–15.04 (8.69 1.2–14.93 (4.02) 1.99–17.95 (5.5)

Cd µg L−1 0.01–0.05 (0.02)

Zn ng L−1 0.65–3.5 (2.14)

DOC µg L−1 2.3–13.2 (5.2)

0.02–0.13 (0.04) 0.4–15.1 0.04–0.14 (1.8) (0.079) µg g−1 0.7–34 0.02–0.35 (2.4) (0.06) 0.8–28.8 0.02–0.24 (2.8) (0.06) 0.3–74.9 0.00–0.13 (6) (0.03) 0.067–206.5 0.005–0.13 (7.9) (0.04)

MeHg pH ng L−1 0.06–1.4 4.17–6.18 (0.19, n = 15)

P µg L−1 < 0.05

LOI %

1. Carter et al., 2001.

is less than 100 yr as a result of fire and logging, however, a few groves of eastern hemlock have survived for over 300 yr.

3. Methods 3.1. S AMPLE COLLECTION AND ANALYSIS There are a variety of data that will be used in this study. A list of data used in this report is provided in Table I. A brief description of each environmental compartment follows.

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3.1.1. Lake water Fifty lakes, mostly within the boundaries of Kejimkujik National Park, were sampled by helicopter over a three-day period in October of 1997. Samples were filtered through 0.45 µm membranes to separate the dissolved from particulate load and then treated and stored at 4 ◦ C for subsequent chemical analyses. Water sample preservation methods varied depending on the analysis to be completed. Total mercury samples were preserved immediately to avoid loss of elemental mercury by volatilization. Water was filtered by syringe through a millipore sterivex syringetip cartridge filter and collected in polyproplene centrifuge tubes that contained 1% of 0.2 M BrCl by sample volume. The BrCl served to stabilize and oxidize all mercury species present to Hg2+ . Samples, for anion analysis, were similarly filtered and collected in 60 mL high-density polyethylene (HDPE) bottles with polypropylene closures but no chemical preservatives were added. Cation and trace element samples were filtered through a 0.45 µm (pore size) ashed mixed cellulose ester (nitrate and acetate) millipore syringe top membrane filters and collected in 125 mL HDPE bottles. They were then precisely acidified with trace metal grade HNO3 to pH < 2 within 8 h of collection. Further details on sampling methodology can be found in Telmer and Veizer (1999). Total mercury in water was analyzed by hydride generation/ICP-MS or by Cold Vapor Atomic Fluorescence Spectrophotometry (CV-AFS) for very low concentration samples. Methyl mercury was measured in water samples using sulfhydril cotton pre-concentration, followed by extraction with Copper sulfate and acidic potassium bromide in combination with di-chloro methane as outlined by Cai et al. (1996). Final Analysis was performed by gas chromatography-atomic fluorescence spectrometry using a Hewlett Packard GC modified with a pyrolysis unit connected to an AFS detector as developed by Poly Science Analytical. Quality control measured included calibration, standard additions for recovery, duplicates, and blanks. Recoveries ranged between 95–100% between batches with < 5% RSD on duplicates. Dissolved organic carbon (DOC) was measured by thermal decomposition followed by IR detection of CO2 . 3.1.2. Vegetation Samples of leaf and twig tissue from the dominant tree species were collected in and around Kejimkujik Park (as shown in Figure 3d). Dominant trees included: red maple (Acer rubrum), white pine (Pinus strobus), eastern hemlock (Tsuga canadensis) and white birch (Betula papyrifera). Limited sampling was done for feather mosses (Pleurozium schreberi) and an epiphytic tree lichen (Usnea sp.) Samples were placed in paper bags and air-dried. They were then sorted into leaf and twig tissue, ground to ensure homogeneity and analyzed with an internal standard reference material prepared at the Geological Survey of Canada for vegetation (recovery ranged = 95–100% which is within the precision of the analysis method for the reference). Trace elements including mercury were analyzed by aqua regia acid digestion followed by ICP-MS analysis. Mercury samples were also analyzed


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by pyrolysis followed by gold amalgamation AAS using a Milestone Advanced Mercury Analyzer (AMA-254) (Hall and Pelchat, 1997). 3.1.3. Soils Samples from three different soil horizons; O, Ah and the C-horizon, were collected. The O-horizon is the organic horizon, which contains more than 17% organic carbon. The A horizon is the mineral horizon (less than 17% organic carbon) near the surface in the zone of leaching, the Ah-horizon is the darkened area due to organic matter accumulation. The C-horizon is the mineral horizon generally unaffected by pedogenic processes except gleying and salt accumulation (Canada Department of Agriculture, 1978). Samples were placed in plastic bags and returned to the lab for air-drying and analyses. Organic layer (O) samples were sieved to a size fraction of < 0.2 mm whereas the Ah and C-horizon samples were separated into two size fractions: < 0.2 mm and < 0.063 mm. Analysis of trace elements was done by acid digestion followed by ICP-MS. Certified Reference Standards were submitted and 1 in 20 samples was a field duplicate. Canadian certified reference materials were used for quality control from the Canadian certified reference materials project CCRMP. Lake sediments were used (LKSD 1–4) as well as Soils (SO1-4). Certified reference materials from The Institute of Geophysical and Geochemical prospecting (IGGE: GSD2-10 and GSR2) as well as the National Institute for Science and Technology (NIST: SRM 2709, SRM 2711) were also periodically analyzed. The percentage recovery for the SRM ranged between 95–100% and was well within the standard deviations of the certified reference materials, while the % RSD of duplicates was generally < 5%. Mercury concentrations were determined by Milestone analysis (AMA) with a 45 sec drying time (20 sec for C-horizon) and a decomposition time of 170 sec as described by Hall and Pelchat (1997). Hall and Pelchat (1997) indicated that a ‘worst case’ precision of 10 ± 5% could be expected over the range of 4–6000 µg kg−1 . The QA/QC results obtained during this study were well within these values. 3.1.4. Fish chemistry The fish chemistry data used in this study were originally collected by Burgess et al. (1998). They sampled 678 yellow perch (Perca flavescens) from 24 different lakes in Kejimkujik Park and prepared their samples according to Environment Canada guidelines (Environment Canada, 1982). Total mercury content was analyzed by acidic digestion and stannous chloride reduction using cold vapor atomic absorbance spectroscopy (CVAAS) as the detector with values being expressed on a wet weight basis. Standard reference materials of dogfish muscle DORM-II were analyzed for quality control and recovery was well within guidelines. The original data set contains multiple samples (typically 5 to 10) from each of 24 lakes. It is well known that the concentration of total mercury in yellow perch is dependent upon fish age so the age factor must be considered. For this study a five-year-old

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fish was selected to express the mercury concentration as this was approximately the mean age of fish sampled (5.7 yr) and the mercury values were usually in a linear portion of the fish mercury versus fish age curve. A linear regression (y = mx + b) model was used to calculate the concentration of mercury in fish for each of the 24 lakes; where y = mercury concentration x = age of the fish, m = the slope of the regression line, and b = the y intercept. 3.2. DATA P REPARATION All data were compiled into a geo-referenced database using a Universal Transverse Mercator projection (UTM zone 20) with NAD 27. In order to relate the chemical properties of the terrestrial environment to that of the aquatic environment a point in polygon approach was taken. In this case the boundary of the polygon was identified as the outline of the catchment basin. This was manually calculated by identifying slope changes on 1/50,000 topographic map sheets. Each sample site was assigned a number, specific to one of the 24 basins in which it was included, and then median values within each catchment basin were calculated. The median values were subsequently used in data presentation including calculation of correlation coefficients. Correlation coefficients were calculated between metal concentrations (Au, Hg, As, Cd, Zn) and chemical properties such as mass loss on ignition (LOI) in the various media of the study (soil, vegetation, water). Outlying data points (Big Red and Luxton Lake) were removed from the data set in order to achieve a normally distributed data set for correlation analysis (tested with the Kolmogorov-Smirnov or Shapiro-Wilk Normality statistic where appropriate using the SPSS software package). Correlations were bivariate, assuming a two-tailed normal distribution. 4. Results and Discussion 4.1. DATA RANGES There were relatively broad ranges for mercury, gold, zinc, and arsenic concentrations for the various media and for the DOC content of the 24 lakes (Table I). Mercury concentrations in the fish (age calculated) varied from 0.199 to 0.454 µg g−1 . For the same 24 lakes there was a ten-fold range in the total mercury values in lake waters from 0.3 to 3.7 ng L−1 . These ranges in concentration are attributed to site differences, as lakes were sampled within a two-day period to minimize the effect of temporal changes. Methyl mercury values in lake water ranged from 0.06 to 1.4 ng L−1 with a mean of 0.19 ng L−1 (n = 15). The total mercury and methyl mercury levels in lake waters were comparable to values in the literature both within and outside the Park (Beauchamp et al., 1997; Clair et al., 1998; Vaidya et al., 2002). Vaidya et al., (2002) reported mercury values in lake water ranging from 1.36 to 4.51 ng L−1 within Kejimkujik Park.


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Mercury concentrations in the leaf tissue of red maple (Acer rubrum) ranged from 5 to 76 ng g−1 and levels in white pine (Pinus strobus) ranged from 5 to 58 ng g−1 (Table I). Rasmussen (1994) found that mercury in the foliage of trees (Abies balsamea and Acer saccharum) on the Canadian Shield were in the range of 16.5 to 65.5 ng g−1 . This compares well with the levels of mercury observed in foliage in Kejimkujik Park. Gold was also observed to have a wide range of values in white pine (0.13 to 59.9 ng g−1 ) and red maple (0.14 to 13.2 ng g−1 ). A limited sampling of the epiphytic lichen, Usnea sp. (n = 45) and a feather moss, Pleurozium schreberi (n = 8) was undertaken at a few of the sample points. Concentrations of mercury were higher in Usnea sp. (max value of 660 ng g−1 ) and in Pleurozium schreberi (max value of 395 ng g−1 ) than in the vascular species. Rasmussen (1994) found levels of mercury in lichen on the Canadian Shield ranging from 17.2 to 66.9 ng g−1 . These values are substantially lower than what was observed in Kejimkujik lichen. Several different soil horizons and soil fractions were sampled. The highest mercury concentrations were found in the silt and clay-sized fraction (< 0.063 mm) of the Ah-horizon (466 ng g−1 ) followed by the clay and silt sized fraction (< 0.2 mm) in the O horizon (415 ng g−1 ) and then by the C-horizon (304 ng g−1 in the < 0.063 mm fraction). These values are substantially higher than the mean values in each of the horizons (Table I). Ranges for zinc and arsenic were significantly higher in the C-horizon (< 0.063 mm fraction) than the O and Ah-horizon. Ranges for Zn and As in the C-horizon are from 2.7 to 209.9 µg g−1 and 0.07 to 206.5 respectively, with mean values of 22 µg g−1 and 7.9 µg g−1 . Gold and mercury were highest in the Ah horizon (< 0.063 mm fraction) when compared with the values found in the other horizons and fractions, with median values of 2.4 and 212 ng g−1 respectively. 4.2. C ORRELATIONS There was a significant correlation between mercury (total and methyl) in waters and DOC levels in lake water (Table II). Correlation coefficients of 0.87 and 0.72 between total and methyl-mercury, respectively, in lake waters and DOC were significant at the 99% confidence level. Correlation coefficients were also significant between DOC and levels of mercury in yellow perch (r2 = 0.42); however they were only significant at the 0.05 confidence level. Many researchers have observed mercury relations to DOC. Krabbenhoft et al. (1995) observed a two fold increase in the mercury content of a Northern Wisconsin creek with increases in DOC in the fall of the year. O’Driscoll and Evans (2000) observed that humic and fulvic acids are capable of binding substantial amounts of methyl mercury, and therefore DOC is able to transport methyl mercury from wetlands to lakes. There was a strong correlation between total and methyl mercury in lake water and concentrations of mercury in yellow perch (r = 0.56 and 0.56 respectively, Table II). There were variations in the patterns but the relationship appears to be

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TABLE II Correlation between Hg, trace elements, P and DOC in various media for 50 drainage basins in Kejimkujik Park, Nova Scotia Perch Hg n = 24 Water Chemistry

Vegetation Red Maple White pine Tree Lichen Humus < 0.2 mm

Ah Horizon < 0.2 mm

< 0.063 mm

C Horizon < 0.2 mm

< 0.063 mm

Water MeHg n = 15

DOC n = 50

0.72b 0.57a 0.36

0.70b 0.72b – 0.26 0.01

– 0.87b 0.70b 0.45 –0.42a

Hg total n = 50

DOC Hg total MeHg Cd pH

0.42a 0.56a 0.56a 0.58a –0.51a

0.87b

Hg P Hg P Hg Au

0.10 0.67b 0.25 0.54a –0.29 –0.58a

0.30 0.69a 0.39 0.18 0.03 –0.16

0.28 0.54a 0.32 0.32 –0.36 –0.43

0.14 0.65b 0.50a 0.17 –0.11 –0.24

Hg Au P

0.17 –0.16 0.25

0.22 –0.62 0.18

0.41 –0.24 0.31

0.24 –0.26 0.07

Hg Au P Hg Au P

0.05 0.06 0.29 0.14 –0.06 0.41

0.22 –0.35 0.17 0.40 –0.19 0.57

0.09 0.03 0.56a 0.13 0.09 0.77b

Hg Au P Hg Au P

0.38 0.03 0.51 –0.06 –0.23 0.48

0.77b –0.17 0.81b 0.45 0.23 0.79b

0.67a 0.22 0.79b 0.45 –0.09 0.80b

–

a Correlation is significant at the 0.05 level (2-tailed). b Correlation is significant at the 0.01 level (2-tailed).

0.15 –0.09 0.18 0.31 –0.04 0.37 0.72b 0.07 0.80b 0.51 0 0.72b


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Figure 2. Relationship between mercury in lake water and in yellow perch (5 yr old) for 24 lakes in Kejimkujik National Park, Nova Scotia). Numbers above symbols are DOC in µg L−1 .

linear over the range of total mercury measured (i.e. there was no threshold for total mercury concentrations in perch at concentrations observed in this study). Significant correlations with mercury in yellow perch were also observed for DOC and pH of lake water (r = 0.42 and –0.51 respectively, Table II). Yellow perch is a useful indicator of many contaminant levels in water. Ion et al. (1997) found that yellow perch was a useful species for monitoring levels of PCB’s and mercury concentrations in the St. Lawrence River. It should be noted that while significant correlations were observed between mercury, DOC, pH, and mercury content in fish tissue, the mechanism of methylation and bioaccumulation could not be surmised from these results. Figure 2 illustrates that variation around the regression line of total mercury in lake water versus mercury in perch is strongly related to the level of DOC in the waters. Surprisingly, values that fall below the regression line (higher mercury in yellow perch than expected for a given mercury level in lake water) have ‘low’ DOC values; whereas those data that plot above the regression line (lower mercury in yellow perch than expected) have ‘high’ DOC values. Clearly there is a complex interrelationship between mercury and DOC. The explanation may be linked to the photo oxidation of mercury and the control of factors such as light penetration, DOC, temperature and oxygen content on methylation and demethylation (Lean et al., 1999). Alternatively, this discrepancy may be related to the fact that MeHg bound up in high DOC waters is not available to bioaccumulate. If this

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TABLE III Correlation between Hg concentrations in leaf tissue of red maple and white pine versus elements in various soil horizons and texture classes for 39 samples at Kejimkujik Park, Nova Scotia Soil Hg

Humus Ah > 0.063 mm Ah < 0.063 mm C > 0.063 mm Au Hg P Au Hg P Au Hg P Au Hg P

Red – maple White – pine Humus –

0.48a – –

–

–

–

0.44a – –

0.34a –

–

–

0.70b –

–

– –

0.25 – · 0.33a – · 0.44a –

C < 0.063 mm Au Hg P

0.51b – – – · 0.48a – 0.43a – · – 0.48a – –

–

–

–

0.40a · 0.41a

–

a Correlation is significant at the 0.05 level (2-tailed). b Correlation is significant at the 0.01 level (2-tailed.

interpretation is true it illustrates the separation between DOC- mercury transport and DOC-mercury binding effects on the food chain. There were weak correlations between the concentration of mercury in vegetation and mercury in various soil horizons (Table III). As shown in Table III, significant correlations are evident between mercury in the leaf tissue of red maple and white pine and the mercury content of the humus (O-horizon) (r2 = 0.48 and 0.44, respectively). The Ah-horizon ( > 0.63 mm) was also, significantly correlated with mercury in white pine (r2 = 0.34). There were correlations with other elements in the soil: a strong correlation between the mercury content in leaf tissue and the value of Au in the < 0.063 mm fraction (Table III). The high correlation between Au and mercury is undoubtedly related to the geological affinity between the elements (Levinson, 1980). Many factors may contribute to the levels of mercury in leaf tissue. St Louis et al. (2001) indicated that a forest canopy could receive mercury from several inputs: (i) atmospheric deposition onto a leaf surface (ii) adsorption of atmospheric gases (iii) assimilation of elemental mercury through stomatal uptake. These factors combined with root uptake determine the levels in tree foliage. While other researchers have suggested that root uptake is important only for high levels of mercury in soil, the correlation observed in this study suggests otherwise. While no significant correlations were found between mercury in soil and vegetation with mercury in perch, there were significant correlations between the levels of P in vegetation (white pine and red maple) and levels of mercury in yellow perch. Phosphorous also correlated strongly between several media (Table II). For example, there were significant positive correlations between levels of P in the soil (Ah and C-horizon) and levels of mercury in lake waters (Table II). High concentrations of P have been linked to increased MeHg production through its affect on eutrophication. Eutrophciation may enhance the level of MeHg through a variety of factors including increased microbial activity and fulvic acid concentrations (Vaithiyanathan et al., 1996). However, Vaithiyanathan (1996) noted that the


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correlation between mercury and P was associated with enhanced peat accretion rates and not a change in the mobilization of mercury. Therefore phosphorous may play a role in the amounts of peat present in the wetlands surrounding the lakes in Kejimkujik Park. This may result in an increase in DOC export and a resulting increase in mercury transport from wetlands to lakes. There is no evident correlation between mercury in Usnea sp. and soil chemistry, which may simply be a result of the small number of samples. An alternative explanation would be that since epiphytic lichens derive the majority of their nutrients and moisture from atmospheric aerosols, and not by adsorption from their host tree, they would not be expected to have a significant correlation with soil chemistry (Getty et al., 1999). 4.3. S PATIAL ASSOCIATIONS Figure 3 illustrates the spatial distributions of mercury concentrations in various sample media. In several, but not all cases, there is agreement between the locations of anomalies as measured by the various media. The highest mercury levels in yellow perch (Figure 3) are found in Big Red Lake and in several of the surrounding lakes such as Luxton and Little Red Lake (all of which are headwater lakes). Concentrations of 0.72 µg g−1 mercury at Big Red Lake and 0.54 µg g−1 at Luxton Lake represent the highest yellow perch concentrations and values 3 to 4 times higher than Pebbleloggitch, which is < 10 kms away (Figure 3). Coincident anomalous levels are also found in vegetation and in soils around Big Red Lake (Figure 3). Mercury concentrations in red maple from around Big Red Lake represent the highest mercury values (76 ng g−1 ) and again concentrations decrease over a short distance to ‘background’ levels of around 10 ng g−1 in the watershed basin for Kejimkujik Lake (Figure 3). Mercury concentrations in the soil are also high in the Big Red Lake area. Values in the Ah horizon (< 0.063 mm) are in excess of 400 ng g−1 . The vegetation and soil around Big Red Lake also show high levels of several other metals notably Au and Zn. There are also coincident anomalies in mercury for all media around North Cranberry Lake. While the mercury content in yellow perch at North Cranberry Lake and George Lake are similar (0.4997 and 0.4686 µg g−1 , respectively) the mercury concentrations in the lake waters are elevated at George Lake relative to North Cranberry (4.4 ng L−1 and 1.93 ng L−1 respectively). Similarly, mercury concentrations in red maple and the soil, particularly the Ah horizon is also high in the area (Figure 3). Also of interest are areas where there are high levels of mercury in one media but not in other media. For example, it was observed that the area around Pebbleloggitch Lake has relatively high concentrations of mercury in the soils and red maple but concentrations in the fish were the lowest in the 24 lakes sampled (0.1854 µg g−1 ). Pebbleloggitch Lake was also characterized by relatively high levels of

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Figure 3. Concentration of mercury (total) in various media at Kejimkujik National Park a:) in yellow perch (5 yr old)- b:) in lake water- 50 sample points c:) in C-horizon > 63 micron – 47 samples and d:) in red maple leaf tissue –125 samples. BRD=Big Red Lake, LUX=Luxton Lake, PEB=Pebbleloggitch Lake=Beaverskin Lake, PUZ=Puzzle Lake, CRN=Cranberry Lake, LOO=Loon Lake, FRZ=Frozen Ocean Lake, GRE=Grafton Lake and KEJI=Kejimkujik Lake.


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mercury (4.75 ng L−1 ) in the lake waters and moderate DOC (7.06 µg g−1 ). This ‘exception’ to the pattern illustrates the complexity of mercury cycling in the area.

5. Conclusions The elemental concentrations from a variety of media at Kejimkujik National Park, Nova Scotia illustrate that the levels of mercury in various components of the ecosystem (vascular plants, soils and rocks) have a broad concentration range of values but the maximum values are not unusually higher than other ecosystems (Vaidya et al., 1999). However, the level of mercury in the fish (Perca flavescens) and in particular the loons (Gavia immer) are among the highest in North America (Burgess et al., 1998a). This suggests that in situ processes affecting mercury methylation and retention are important to controlling the final levels. The occurrence of background levels of mercury in yellow perch (despite the presence of relatively high values of mercury (total) in lake waters, soils and red maple leaf tissue) for several lakes may indicate that in certain lakes mercury is not in a bioavailable form and therefore is not readily available to enter the aquatic food chain. This emphasizes dual role of DOC in acting both as a transporter of mercury species from wetland but also a ligand for mercury species in lakes. It is possible that the methyl mercury is bound to DOC (O’Driscoll and Evans, 2000) and not bioavailable. DOC and pH play fundamental roles in the control of mercury levels in Kejimkujik National Park. The importance of DOC and pH in mercury cycling has been observed in other wetland environments (Rudd, 1995). The results of this study provide further evidence that wetland environments will typically be areas where mercury has the potential to bioaccumulate. In these areas the combination of low pH, and high DOC provide an environment conducive to retention of mercury and transport to lakes. The importance of the terrestrial ecosystem in mercury cycling and its interaction with wetland dominated ecosystems is a growing area of interest in mercury research, and this study suggests several areas of new research. Although concentrations of mercury in yellow perch are unrelated to mercury levels in terrestrial vegetation and soil, phosphorous levels in vegetation and in the soil were strongly correlated (positive) with mercury in fish. While there is no known link between P in vegetation and mercury in fish there are several possible explanations. Phosphorous and mercury may be linked through a third parameter such as the oxygen content of the lake and surrounding wetland, which will affect microbial activity and MeHg production. It is also possible that soil characteristics such as buffering capacity may play a role in phosphorous dynamics and affect the vegetation-perch correlation. While this requires more study before any conclusions can be drawn, it is clear that multidisciplinary work (such as this) is essential to understanding the mercury cycle and links between terrestrial and aquatic processes.

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Acknowledgements The project has been funded through the Toxic Substance Research Initiative (TSRI), Health Canada and through the Metals in the Environment (MITE) project at the Geological Survey of Canada. The cooperation of Parks Canada personnel, particularly Cliff Drysdale, Peter Hope, Ian Morrison, Sally O’Grady and Bob Thexton, from Kejimkujik National Park is highly appreciated.

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