Geoscience Reference
In-Depth Information
5
Solute Transport in Soil
5.1 Introduction
At the soil surface, nutrients, pesticides and salts dissolved in water iniltrate the soil.
The residence time of these solutes in the vadose zone may have a large effect on soil
and groundwater pollution:
•
Organic compounds are mainly decomposed in the unsaturated zone, where the main
biological activity is concentrated.
Many plants have no active roots below the groundwater level and therefore extract water
•
and nutrients only from the soil in the unsaturated zone.
Whereas in the unsaturated zone the transport of solutes is predominantly vertical, in the
•
saturated zone solutes may disperse in any direction, threatening groundwater extrac-
tions and surface water systems.
Therefore, to manage soil and water related environmental problems effectively,
proper quantiication of the transport processes in the unsaturated zone is important
(Beltman et al.,
1995
). For a number of reasons in delta areas relatively much atten-
tion is paid to solute transport in soils. In delta areas like the Netherlands the popula-
tion density is high, the chemical industry is intensive, the agrochemical input in the
agriculture is huge, the sedimented soils are very permeable, the groundwater levels
are shallow and the groundwater recharge luxes are large due to the humid climate.
Question 5.1:
Why are the aforementioned factors a reason to pay more attention to
solute transport in soils?
At ield scale level, low and transport processes can be described in a physical
way, as weather conditions, vegetation, soil characteristics, drainage situation and
cultivation are well deined for individual ields. For regional analysis, model simula-
tions at ield scale level may form the basic unit, which are combined with geographic
information systems (Singh,
2005
). However, also within a ield spatial variability of
soil characteristics may cause a large variation of solute luxes (Biggar and Nielsen,
177
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