Environmental Engineering Reference
In-Depth Information
Fig. 7.4 Schematic of
collected mesocosm with
approximately 40 cm of soil
within a 7.5 cm diameter,
schedule 40 PVC pipe, 50 cm
in length. A piece of
geotextile fabric is taped to
the bottom to prevent the soil
from sliding out. Marks
should be placed on the
outside of the PVC at depths
of 10 and 25 cm below the
soil surface
Top of the Soil
10 cm
25 cm
Geotextile
Fabric
4.
Installing the deep electrodes
. Note that the three deep Pt electrodes will be
placed in an equally spaced arrangement around the mesocosm, optimizing
the distance between the edge of the mesocosm and the future location of the
salt bridge (see Fig.
7.5
).Usingcoloredtape,placeamarkoneachelectrode
that is 25 cm above the Pt point. Then, using a narrow sharpened stainless
steel rod (slightly larger than the electrode), carefully make a VERTICAL
pilot hole that is approximately ½ cm shallower than the depth where you will
place the Pt electrode. Remove the rod and carefully slide a straight Pt
electrode into the hole, and push the electrode to the exact depth where
measurements are to be made (25 cm). Carefully install two additional deep
electrodes in the same manner being sure to distribute them around the
mesocosm (Fig.
7.5
). Label these electrodes 25A, 25B, and 25C (for 25 cm
below the soil surface).
5.
Installing the salt bridge
. The salt bridge is made from a piece of PVC pipe that
has an OD of approximately 22 mm. It is filled with an agar which is saturated
with KCl (similar to the calomel electrode itself) (Veneman and Pickering
1983
). Prepare to use the salt bridge by inserting your previously selected (and
tested) calomel reference electrode into the agar at the top of the salt bridge
until the electrode is approximately 2-3 cm into the tube and the agar has
encompassed the end of the electrode. Wipe any agar or salt from the electrode
and PVC tube and carefully wrap with parafilm to produce a water tight seal
that will hold the electrode in place. This will help to keep the electrode from
drying out over time.
A pilot hole approximately 5-10 cm deep should be made using a section of
sharpened 2.5 cm dia. pipe, and the soil should be removed to make room for
