Page 320 - Soil and water contamination, 2nd edition

Patterns in the soil and in the vadose zone 307

c. why the pH in soil pore water is generally lower near a forest edge than in the centre
of a forest;
d. why heavy metals are usually more mobile in sandy soils than in loamy soils;
e. why heavy metal concentrations correlate positively with the Al O concentration in
2 3
soil;
f. why preferential flow paths promotes the leaching of contaminants from the soil root
zone.;
g. why tillage causes a net loss of soil material and associated contaminants on convex
parts of the landscape and a net gain on concave parts;
h. why the topsoil of floodplains along the river Rhine is less contaminated at locations
with high sediment deposition rates than at locations with low deposition rates;
i. why the 137 Cs deposition density in soil is greater on concave parts than on convex
parts of a slope.

2. Spijker (2005) studied the anthropogenic metal enrichment in the topsoil in the Province
of Zeeland, the Netherlands, by collecting soil samples from two depths (0–5 cm
and 40–80 cm) at each sampling location. These samples were analysed for several
parameters, including Cd and Al O . The figure below shows the Cd concentration (in
3
2
-1
mg kg ) plotted against the Al O concentration (in %) for both the topsoil samples (Δ)
2 3
°
and the deeper samples ( ).
a. What is probably the reason for the topsoil samples containing more Cd than the
deeper samples?
6642 6642 6642
0.5
0.4

Cd (mg kg -1 ) 0.3

0.2

0.1

0
4 6 8 10 12
Al O (%weight)
2 3
b. In a topsoil sample the Cd concentration is 0.43 mg/kg and the Al O concentration
2 3
is 11 percent. Estimate the anthropogenic enrichment of Cd in this topsoil sample
using the information from the graph below.
c. What are the two critical assumptions in this method for calculating the
anthropogenic Cd enrichment?

3. A vineyard soil was sampled at intervals of 10 cm depth. The soil sample for each interval
was bulked, homogenised, and analysed for Cu concentrations (Cu is a constituent of
Bordeaux mixture, a widely used fungicide in viniculture). The table below gives the
-2
resulting data. Calculate the Cu deposition density in g m for the top 40 cm of the soil,
-3
given that the bulk density of the soil is 1350 kg m .

10/1/2013 6:45:35 PM
Soil and Water.indd 319
Soil and Water.indd 319 10/1/2013 6:45:35 PM