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

132 F. Roos-Barraclough et al. / The Science of the Total Environment 292 (2002) 129–139
2.3. Effects of sample preparation: grinding
samples
Five samples of an in-house peat reference
material were ground using a coffee mill.These
samples were analysed for Hg using the Leco
AMA-254 and the values obtained were compared
to those obtained using five unground samples of
the same material.
2.4. Effects of sample preparation: water content
in air-dried plugs
The EGR2A core (co-ordinates CH 570.525,
232.150) was collected on 26 August 1991.The
core was taken using a Livingston corer (Aaby
and Digerfeldt, 1986).The cylindrical core was
initially taken in 1-m sections (total length 692
cm, ds8 cm).The core was then sliced, frozen,
into 2-cm slices.The slices were stored in individual
airtight plastic bags at y18 8C until analysis.
Slices from 46 to 592 cm were thawed before
plugs were taken.Four plugs were taken from
each slice.One plug from each slice was weighed
wet.All the plugs were allowed to air dry in a
class 100 clean air cabinet for 20 h.The air-dried
plugs, which had been weighed wet, were reweighed
after 20 h and then placed in an oven at
105 8C until constant weight was obtained.The
percentage water remaining in the air-dried plugs
was then calculated from the air-dried weight and
the constant dry weight of the plugs.This value
for water content of air-dried samples was used to
calculate the theoretical dry weight of the remaining
air-dried plugs, which were subsequently analysed
for Hg.
2.5. Effects of peat properties: Hg concentrations
in different bog plant species
Twenty-three plant species were collected from
the surface of the ombrotrophic bog at Etang de
la Gruere ` in the Swiss Jura Mountains (1005 m)
between July 1997 and September 2000.The
samples were stored in air-tight plastic bags immediately
after collection and were kept frozen until
analysis.Samples were then air dried in a class
100 laminar flow cabinet overnight and analysed
for Hg content by AAS, using the Leco AMA
254.
2.6. Bulk density and water content in a peat
monolith
A peat monolith was collected at SWM (coordinates
CH 631.250, 177.000) on 28 August,
1991, using a Wardenaar corer (Wardenaar, 1987).
The monolith obtained (10=10=100 cm) was
stored at y18 8C after collection.It was then cut
(frozen) into 1-cm slices, using a stainless steel
band saw and the individual slices were again
stored at y18 8C until analysis.The top 17 slices
were used in the following analyses.A stainless
steel tube with a sharpened end, of diameter 16mm
was used to remove three plugs of known
volume from each 1-cm slice.The wet weight of
each plug was recorded and the plugs were then
dried to constant weight in an oven at 105 8C.The
dry weights were recorded and the plugs were then
stored in air-tight plastic boxes, which had been
soaked for 1 h in 10% HNO and rinsed six times
3
with water (R G18 V).
H O
2
2.7. Effects of peat properties: variation in Hg
concentrations within one 10=10=1 cm slice
The slice 15 cm from the surface of SWM core
was used to investigate the diversity of Hg concentrations
within a single 10=10=1 cm slice of
peat.The slice appeared to be homogenous in
terms of composition of plant material.However,
wood was removed from the samples before analysis.Sixteen
plugs (four rows of four) were
extracted as described above, at even distance
from one another.The samples were analysed for
Hg using the Leco AMA 254.The theoretical dry
weight of the samples was calculated using their
wet weights and the average water content of slice
15, previously determined to be 93.0"0.4%. The
Hg concentration was calculated and expressed as
y1 ng g in dry weight of peat.
3. Results
3.1. Suitable peat analysis program using the Leco
AMA 254
Increasing the drying time from 9 to 500 s only
increased the blank value from 0.020 Hg (ns2)