Environmental Engineering Reference
In-Depth Information
of the three points, show a significant difference for Pb (decrease from 0.33 mg/l to 0.13
mg/l) and for Cr
+6
, which increased from 0.05 mg/l to 0.11 mg/l. Cr
+6
is the only
measured metal, which shows significant increase of concentrations during February.
Leaching of heavy metals from soils, irrigated with effluents and sludge, depends on
the characteristics of the soil, application rates and the period of application, and the
availability of water movement to transport them to ground or surface water bodies.
Under a proper managerial practice, metals are accumulated in the soil surface and
immobilized in the humus layer by adsorption on the surface of particulate organic
matter. The leaching of metals from soil horizons is enhanced by a low pH, reduced
organic matter, low cation exchange capacity of the soil, water movement (which is
likely to occur when hydraulic application rates exceed evaporation rates), and is more
likely in sandy soils (Roy & Couillard 1998).
Figure 8.9. Spatial and seasonal
variations of Cd and Ni.
Mean values between the time series in
Oct., Nov., and Feb. at each sampling
point denominated by the same letter,
and values within each time group
followed by the same number are not
significantly different at the 0.05 level.
