FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

and porewaters were expressed by hand for subsequent chemical analyses.
Chemical analyses of porewaters and the trophic status of the mires
Pore water samples were kept cool. Upon returning to the lab, all water samples were
filtered to exclude material greater than 0.2 :m using polysulfone membrane filters (Acrodisc,
Gelman), and refrigerated. Anions (Cl - and Br - ) and cations (Na + , K + , Mg 2+ , Ca 2+ ) in the waters
were measured using chemically suppressed ion chromatography with conductivity detection
(Steinmann and Shotyk, 1997). Each of the porewater samples was analyzed in duplicate both
for anions and for cations.
The pH of the surface waters at GL is neutral to alkaline and the porewaters typically
contain ca. 20 mg/l Ca 2+ ; this is typical of minerotrophic fens and indicates the importance of
mineral dissolution reactions, both within the peatland and in the surrounding basin, which
control the composition of the waters (Shotyk, 1988). In contrast to the GL fen, the pH of the bog
waters from DK is acidic (pH 4) and the porewaters contain only ca. 2 mg/l Ca 2+ ; this is typical
of ombrotrophic bogs, and shows that mineral dissolution reactions are quantitatively
insignificant: this is true because of the limited supply of minerals for reaction with the surface
waters of the bog. The low pH value and low concentrations of Ca 2+ in the porewaters, therefore,
indicates that mineral matter is supplied to the DK core only from the atmosphere, and this must
be true also of trace metals such as Hg and Pb.
Measurement of Pb and other trace element analyses using XRF
Peat cores were frozen within one day of sample collection, and shipped frozen to the
lab in Berne. Individual slices from the “A” cores were partially thawed and a plexiglass
template (10 x 10 cm) was used to allow the outer 2.5 cm of each slice to be trimmed away using
an acid rinsed ceramic knife on a plastic cutting board; clean lab procedures were followed,
cleaning the cutting board and knife with deionized water three times between each slice. The
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