Environmental Engineering Reference
In-Depth Information
10 cm
10 cm
10 cm
15 cm
25
25 cm
25 cm
25 cm
10 cm
Fig. 7.7 On
left
, distilled water is added to the bucket until it reaches a level 15 cm below the soil
surface. The tips of shallow and deep Pt electrodes should be located 5 cm above the water level
and 10 cm below the water level, respectively. Water should be added periodically to preserve the
desired level. An alternate arrangement (shown on
right
) is to use a taller bucket and to saturate the
mesocosm to the soil surface. This can be especially informative if soil horizons with contrasting
properties (such as OM content) occur at depths of 10 and 25 cm
to break open and expose the fresh soil surface (rather than a knife-cut soil
surface). Note that you will need to test the freshly exposed and broken soil
surface with the
d is detected
from where the low valence Fe from the steel in a knife blade or shovel has
contacted the soil.)
Placeafewdropsof
αα
d (sometimes a false positive reaction to
αα
d(Childs
1981
)onone-halfofthecoreatvarious
depths along the length of the mesocosm and note whether there is a reaction.
Look for a pink color to develop. (If there is a lot of Fe
2+
in the soil solution,
this can sometimes occur quite rapidly. Other times, if there is very little Fe
2+
in solution, it may take a few minutes for a subtle reaction to be observed.)
In particular, pay attention to whether there is a reaction in the vicinity of
where you had placed the electrodes (10 and 25 cm below the soil surface).
Also keep in mind, the depth at which the water table was maintained in your
mesocosm.
αα
