40
C Pond
BT Pond
S7
S3
S9
30
S8
S5
20
S6
10
Figure 52. Fall 1995 measurements of
accumulation at sedimentation stations
established in 1992.
0
be such that, in another 6 to 9 years, the upper
during this study and the generally random na-
uncontaminated sediment should provide a bar-
ture of WP occurrence.
rier deep enough to keep dabbling ducks from
We gauged WP migration by analyzing mate-
reaching contaminated material beneath it.
rial in sediment traps within contaminated per-
manent ponds, and by analyzing the materials
collected in plankton nets from the bedload and
WHITE PHOSPHORUS FATE,
suspended load of gully runoff from the ponds
TRANSPORT AND MIGRATION
during ebb tide. Plankton nets in the centers of
gullies provide the only data available on trans-
WP-contaminated sediment is eroded and
port and migration of WP into the Eagle River
transported from the ponds, mudflats and gully
and Knik Arm. The sediment traps in ponds pro-
walls by a variety of processes operating through-
vide data on localized WP movement by resus-
out the year (Tables 2 and 3). The processes are
pension. Sediment trap and surface samples,
primarily wind, river and tidal currents, and vari-
which were taken in previous years (Lawson et
ous types of slope erosion. Animals, waterfowl
al. 1995, 1996), provide data on mudflat scour of
and humans may likewise disturb and mobilize
WP during runoff. Ice samples were obtained in
WP in ponds.
1994, but weather conditions in late 1995 and early
Both ice and water entrain and transport WP-
1996 did not produce ice conditions suitable to
contaminated sediments. Wind and water cur-
floe analyses. Previous work indicated that ice
rents in ponds can resuspend WP-contaminated
floes cause WP erosion and transport (Lawson et
sediments, as evidenced by analyses of resus-
al. 1996).
pended materials in sediment traps. Gully trans-
Plankton nets in four gullies draining contami-
port during ebb moves these sediments into the
nated ponds and mudflats were used to trap sedi-
Eagle River. Samples of material trapped by plank-
ments during the monthly tidal flooding events
ton nets record WP-contaminated sediment trans-
of May through October (Fig. 17 and 21b). Of 138
port during ebb tide. Analyses of samples from
samples, WP was detected in 44 (32%), indicating
sediments adhering to ice floes are evidence that
WP transport during ebb tide in all tidal flooding
ice can erode and transport WP-contaminated
events exceeding 5.1 m elevation (Fig. 53). This
sediments.
relationship to elevation is consistent with the
Field sampling of sediment in transport in a
more limited 1994 results (Lawson et al. 1996).
natural setting, rather than in a controlled labora-
The quantities detected in these samples were
typically less than 0.1 g/g. The B-Gully site is
tory, is difficult in the intertidal environment and
was not possible in Eagle River or Knik Arm dur-
the only exception to this trend, with values rang-
ing from less than 0.1 to about 0.9 g/g. The
ing tidal ebb. Given the fine particle size of both
the suspended and bed loads, it is likely that these
reasons for this difference are not clear; however,
sediments are transported into Knik Arm where
the upper reaches of B-Gully are undergoing lat-
their fate is unknown. Whether WP erosion, trans-
eral and headward erosion into a heavily cratered
port and redeposition constitute a quantitatively
and highly contaminated part of the mudflats (Fig.
important biologic hazard cannot be assessed be-
27) (Racine et al. 1993, Racine and Brouillette
cause of the limited number of samples acquired
1995b). It is therefore possible that the plankton
59
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