appearance of the particle and the surrounding
sediment sample using an 18.9-mm-diameter
polypropylene corer (produced by cutting off the
sediment was noted, and the particle and sedi-
tapered end of a 20-cm3 syringe). One P4 particle
ment were shaken separately in isooctane prior to
was quickly transferred into the center of the hole
gas chromatographic analysis.
in the sediment sample, and the core was quickly
If P4 particles were not located by examining
replaced. The sediment surrounding the core was
the samples, three additional samples were ana-
gently compacted to fill in the voids around the
lyzed by solvent extraction followed by gas chro-
core. An additional 5 g of water was added so that
matography (Walsh and Taylor 1993). The sedi-
the wet sediment was sufficiently fluid to flow
ment surrounding the residual particle was ob-
into the voids surrounding the core; this addition-
tained using a 26.5-mm-diameter polypropylene
al water increased the initial moisture content by
corer (produced by cutting off the tapered end of
a 50-cm3 syringe). The corer was centered over
1.7%.
At the three higher moisture contents, a 2-mm-
the area where the P4 particle was placed and
diameter hole was made using a wooden dowel,
pushed to the bottom of the container. The sedi-
and the particle was pushed down to a depth of 3
ment was transferred to a 120-mL glass jar
cm. Then the sides of the sample were gently
equipped with a Teflon-lined cap, and the P4 was
squeezed to seal the hole.
extracted with isooctane and analyzed by gas
chromatography using the procedure outlined in
the analytical method. Fifteen additional samples
INCUBATION OF SEDIMENT SAMPLES
were prepared (three replicates at each moisture
Samples incubated at 15 and 20C were placed
content) and extracted immediately to establish
the day 0 mass of P4.
in a Labline Biotronette plant growth chamber.
Since only one growth chamber was available, one
experimental treatment was completed before the
DETERMINATION OF
next one was initiated. Samples incubated at 4C
SAMPLING INTERVALS
were placed in a coldroom at CRREL. Samples at
each temperature were placed in random order
A rigid sampling interval was not set initially.
and were rearranged on each working day. To
Because the vapor pressure of P4 is an exponen-
maintain the moisture content, samples were
tial function of temperature, the rate of loss of P4
was expected to be significantly higher at 20C
weighed, and any water lost by evaporation was
then at 4C, so the sampling intervals were short-
replaced with reagent-grade water. To prevent ex-
er for the higher temperatures. In addition, subli-
cessive loss of moisture overnight and over week-
mation of P4 depends on the diffusion coefficient
ends, sample containers were placed in larger
plastic containers (66 46 15 cm) and loosely
of P4 vapor. The diffusion coefficient of P4 in sed-
iment is unknown but can be assumed to be less
covered with a plastic lid. This procedure main-
than in air. In sediment the effective diffusion co-
tained the relative humidity close to 100% and
efficient decreases as moisture content increases.
slowed evaporative losses.
Thus the sampling interval for the high-moisture-
content samples was longer than the lower-mois-
RECOVERY OF PARTICLES
ture-content samples.
The residual P4 was measured periodically dur-
Based on a previous experiment in which ERF
sediments were air-dried at 20C, samples below
ing incubation. At each sampling interval, two
saturation at or above 20C were sampled inten-
samples were taken for microscopic examination.
The sediment sample was placed on the stage of a
sively within the first two weeks of incubation.
Cambridge Instruments dissecting scope, and at a
magnification of 10, the sediment overlying the
ANALYSIS OF DATA
residual particle was gently removed and placed
on a 30-mesh sieve. The material on the mesh was
Moisture content was expressed as degree of
rinsed with distilled water to remove fine-grained
saturation. Residual particle masses were nor-
sediment. Sediment was removed in 1-mm depth
malized to the day 0 mass (M/Mo) and plotted
increments down to a depth of 4 cm or until the P4
vs. time. Regression analyses were performed if
particle was found. If the particle was found, its
appropriate to see if significant changes in mass
diameter was measured using a micrometer, the
occurred as a function of time.
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