Geoscience Reference
In-Depth Information
These relations have been established to try to simplify the work of
characterization of soils. For example, a very high conductivity implies a
very high salinity. But these links are statistical and empirical, and vary
considerably from one situation to another. The numbers given here are
only examples.
Electrical
conductivity
2
Osmotic
potential
1
3
Content of
salts and ions
Fig. 13.2
Relations between parameters expressing salinity.
Relations of conductivity and quantities of ions (Servant
and Servat 1966)
￿ First, we have
k CE = S anions = S cations
S anions = Cl - + SO 4 2 - + HCO 3
- + CO 3 2 -
S cations = Ca 2 + + Mg 2 + + Na + + K + + NH 4
Actually, the contents of Ca 2+ and of CO 3 2- have no importance
considering the low solubility of CaCO 3 , which precipitates before the
salinity threshold of the water is reached.
The coefficient k is close to 10 or 12 for salinity dominated by
chlorides. Hence,
where
NaCl ] mmol/l ≈ 10 · EC dS/m
Or, in terms of conductivity:
1 mmho/cm 58 ◊ (10 or 12)
____________
10 3
g NaCl / l
￿ Again:
TDS mg/l (Total Dissolved Solids) (0.64 to 0.72)·10 3 ·EC mmhos / cm , if the
electrical conductivity is below 10 mmhos/cm. Zhang et al . (2009) also
give numbers of the same order of magnitude.
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