L1 /
13
CH3041
IONIC STRENGTH
• The 20 largest
rivers carry 40% of the continental
runoff. The Amazon carries 15%.
• Ionic
strength
I = 1/2 S ci zi 2
c = concentration, z = ion charge
Freshwater 10-3 - 10-4
Seawater 0.7 mol l-1
• Conductivity (mSiemens/cm
or mho/cm) µ I
distilled 1 mS freshwater 100 mS, sea 50 mS
• An indication of the sources of river water may be made by comparing the:
weight ratio Na / (Na + Ca) vs Ionic Strength
weight ratio Na / (Na + Ca) vs Ionic Strength
• Ca indicates mineral weathering (CaCO3).
• Na indicates rain as an ion source.(evaporites)
