water flowed from the direction of C/D to Pond
would desaturate, and based on the output of mois-
146 along the border of ERF, the water does not
ture sensors in Area C, was quite successful at
seem to originate from C/D, but rather as inflow
achieving this goal (Fig. 13). Even the station
from the uplands adjacent to ERF between C and
(C 200 m) that is located adjacent to the bulrush
C/D. The hydrologic separation of these two areas
marsh dried.
was previously surmised, but has now been dem-
The relationship between groundwater eleva-
onstrated. Isolation of these areas results in faster
tion and tension in the surface sediments is
drawdown times and more effective drying.
revealed in data from our 1998 piezometer data
station. When groundwater elevations dropped to
Sublimation/oxidation conditions
50 cm below the sediment surface, tension rises
A major factor in the wetness of the areas
above 5 cbars, the estimated air entry point for
drained is the weather. The summer of 1998 was
sediment in this part of ERF (Walsh et al. 1995b).
one of the wettest on record, with especially heavy
The groundwater elevation dropped below the
rainfall in the months of May and June. These are
bottom of the piezometer well (77 cm depth) on 26
normally the driest months of the core season. The
June (Fig. 14), and did not rise into the well again
late flooding tides of May eliminated any drying
until 6 August, following heavy rainfall, then a
that month, and June was one of the wettest on
flooding tide on 9 August. While the sediment was
record, with almost twice the normal rainfall. In
unsaturated, frequent rewetting by precipitation is
addition, temperatures were below normal for
shown by the wide fluctuations in tension.
July and August, and skies were cloudy for almost
Sediment temperatures during desaturation
the entire three months from June through Aug-
were sufficiently high for slow sublimation. Sedi-
ust. Table 4 is a synopsis of the relevant climatic
ment temperatures were considerably lower in
conditions for June, July, and August.
1998 than in 1997. During the time that sediments
Sediment temperature and moisture conditions
were unsaturated at the C 100-m station, maxi-
were monitored within Area C at three sites in
mum 24-hour average temperatures at 5-cm depth
were 21.72 and 18.34C for 1997 and 1998, respec-
1997 and at two sites in 1998 (Fig. 12). The most
important condition for attenuation of white phos-
tively. Mean temperatures at 5-cm depth were
17.53 and 15.79C, for 1997 and 1998, respectively.
phorus particles in ERF is the desaturation of the
sediments, which takes place naturally in inter-
Lack of sunshine probably accounted for the lower
mittently wetted areas of ERF in summer during
temperatures in 1998.
long periods between flooding tides. Pumping of
Sublimation was confirmed by loss of mass
permanent ponds was tested to see if sediments
from the planted particles. For particles planted
Table 4. 1998 climatic data for ERF (normals are for
Anchorage).
Temperature (C)
Rainfall (mm)
Clear skies or
Month
Normal
1998
Normal 1998 scattered clouds
June
29.0
48.7
12.4
12.0
4 days
July
43.4
33.3
14.7
13.2
5 days
August
62.0
82.2
13.5
11.0
2 days
C Piezometer
Miller's Hole
Site 883
Pen 5
C 100-m Grid Composite
Figure 12. Data station locations, Pond 183, Area C.
16
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