Characteristics of the Environment - Field Sampling: Principles and Practices in Environmental Analysis - page 43

centimeters of soil should be taken from each layer so that the same amount
of soil is obtained for analysis?
Answer: The first step is to remember that bulk density can also be
represented as g/cm 3 , thus for this soil the bulk densities for this unit are
1.2 and 1.5 g/cm 3 (which is the same as g/cc.) The next step is to decide
how many grams of soil are needed in the sample. If each sample is to
contain
50 g the equation to make the required calculation is:
Bulk density×area×depth=50 g
rearranging the equation
Carrying out the calculation for the soil with a bulk density of 1.2g/cc the
depth of the sample taken would be 8.3 cm and the sample with bulk density
of 1.5 g/cc would be 6.6 cm.
The bulk density of soil horizons and underlying layers is important in determining the
volume of soil needed during the sampling process. In addition, knowing the bulk density
of the horizons can indicate the likely path of water and contamination through the soil
(see Figure 2.8) [19].
2.5. WATER MOVEMENT OVER AND THROUGH SOIL
Water is the great mover in the environment. Air and ice also move soil; however, air
cannot directly move particles larger than sand, while water and ice can. Although ice can
move large boulders, it is not a major component of most of the environment. Water and
ice move very large rocks and boulders, and in this process they are reduced to gravel,
sand, and silt, and clay may be released if present in the rock. Ground rock is deposited
on banks along rivers and streams and at the mouth of rivers and the end of glaciers.
FIGURE 2.8 Water moving downward and horizontally in soil containing
compacted layers.