Environ. Sci. Technol. 2001, 35, 1736-1741
Mercury Accumulation Rates and Spatial Patterns in Lake Sediments from West Greenland: A Coast to Ice Margin Transect RICHARD BINDLER* AND INGEMAR RENBERG Department of Ecology and Environmental Science, Umea˚ University, SE-901 87 Umea˚, Sweden PETER G. APPLEBY Environmental Radioactivity Research Centre, University of Liverpool, Liverpool L69 3BX, UK N. JOHN ANDERSON Department of Geography, University of Copenhagen, DK-1350 Copenhagen K, Denmark NEIL L. ROSE Environmental Change Research Centre, University College London, London WC1H 0AP, UK
The Arctic is recognized as an important focus for longrange transport of contaminants, such as mercury (Hg), from industrial regions at lower latitudes. In addition to large geographic gaps, there are few long-term retrospective time trends in arctic research, besides the Greenland ice record, to assess the onset of atmospheric pollution as well as to establish the rates of change in the terrestrial environment. In a study of sediments from 21 lakes along a 150 km transect from the coast to the ice sheet margin in the Søndre Strømfjord (Kangerlussuaq) region, we present stratigraphic evidence for elevated Hg inputs to this icefree region on Greenland’s west coast. Nineteen study lakes showed Hg concentration enrichments (HgEFconc) in surface compared to deeper sediments, with a mean HgEFconc of 3. Higher HgEFconc are found in lakes closest to the ice margin. The existence of this Hg gradient is supported by pollution Hg inventories in three 210Pb-dated cores. While 210Pb inventories and Pb pollution are higher at the coast, pollution Hg inventories are nearly 3-fold higher at the ice margin (570 µg m-2) than at the coast (210 µg m-2). These dated cores also indicate an onset of Hg pollution in the region beginning at least by the late 19th century but possibly as early as the 17th century.
Introduction The Arctic is recognized as an important focus for long-range transport of contaminants, which are carried from industrial regions at lower latitudes. Since antiquity pollutants such as lead (Pb) and copper (Cu) have been carried to the remote Arctic (1, 2). A diverse range of pollutants is found in the contemporary arctic environment (3, 4), among these are mercury (Hg) and persistent organic pollutants (POPs), which * Corresponding author phone: (+46) 90-786 9784; fax: (+46) 90-786 6705; e-mail:
[email protected]. 1736
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present a risk to native fauna and the inhabitants of the region. It is hypothesized for some volatile organic compounds, as well as mercury, that there may be a latitudinal fractionation, which contributes to the continued mobilization of these compounds from warmer to colder climates (i.e. “cold condensation”), where they are ultimately deposited and stored (5-7). The Arctic represents a huge area with generally few inhabitants and limited infrastructure, which contributes to logistical difficulties for monitoring and research programs. Many areas of the Arctic are poorly represented in the scattered sampling programs that have occurred. Time-series data, both contemporary and long-term retrospective data, are even more limited, resulting in great uncertainty over the temporal trends of environmental contamination, both in terms of its onset and the rates of change. Lake sediments and other environmental archives, e.g. peat deposits and glacial ice and snow, permit reconstruction of past atmospheric deposition trends. Based on a summary of Hg accumulation rates in lake sediments in the arctic and boreal regions (8) and a tops-bottoms concentration approach across the Norwegian and Russian Arctic (9), the minimum sediment enrichment rate for Hg pollution in the Arctic is about 1.5-fold over background, although some lakes exhibit as much as a 4-7-fold increase in Hg accumulation. While these data are significant for their evidence of a widespread contamination of high latitude lakes, the data also point to severe gaps in the geographic availability of analyses. Much of the Greenland coast is ice free, and particularly along the west coast the region contains thousands of lakes, which can provide sediment data on past and present pollution in this region. Given the vastness of the region, recent research in Greenland has been restricted to a generally broad assessment of pollutants without temporal resolution in the terrestrial environment (10). Here, we present results on temporal trends in Hg pollution in dated lake sediment cores and an assessment of the spatial distribution of Hg in lake sediments from the Søndre Strømfjord (Kangerlussuaq) region, West Greenland. The sampling was conducted along a transect from the coast to the Inland Ice margin.
Materials and Methods Søndre Strømfjord (Greenlandic, Kangerlussuaq) is a fjord extending ca. 170 km inland on the west coast of Greenland (Figure 1). At the head of the fjord is the village (population ca. 325) and airport (formerly Sondrestrom airbase) of Kangerlussuaq (67°01’N, 50°41’E). The margin of the Inland Ice is a further 25 km beyond the head of the fjord. The Søndre Strømfjord region represents a major climatic gradient, from a maritime-influenced coastal zone to more continental conditions close to the ice sheet (11). Annual precipitation ranges from 500 to 1000 mm at the coast to
