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.