70
Chemical Oceanography, 4th Edition
rivers entering the oceans on various continents is shown in Figure 2.5. The composition
of average world water is compared with normal sea water in Figure 2.6. Although the total
dissolved solids varies from 70 to 200 ppm, the equivalent fractions of the major components of most rivers are similar. The major cations are Ca 2+ , Mg 2+ , and Na + , and the major
anions are HCO 3
– , SO 4
2– , and Cl – . Most of the NaCl is recycled from sea salt aerosols. The
SiO 2 is predominantly in the un- ionized form Si(OH) 4 at the pH of most rivers (7.3 to 8.0).
The major constituents of world river water are Ca 2+ and HCO 3
– (from weathering of CaCO 3 ).
Australia
S. America
N. America
Ca 2+
Asia
Ca
2+
Ca
2+
Ca
2+
Ca 2+
Ca 2+
Mg
2+
Mg
2+
HCO 3
–
HCO 3
–
HCO 3
–
HCO 3
–
Cl
–
Cl
–
Cl
–
Cl
–
SiO 2
SiO 2
SiO 2
SiO 2
K
+
K
+
NO 3
–
NO 3
–
Africa
Mg
2+
Mg
2+
Mg
2+
HCO 3
–
HCO 3
–
Cl
–
Cl
–
SiO 2
SiO 2
Europe
Mg
2+
K
+
K
+
K
+
Figure 2.5
The major components of various rivers on the continents of the world.
Na
+
Na
+
K
+
HCO 3
– , Br
– , B(OH) 3 ,
CO 3
2– , F
–
Si(OH) 4
HCO 3
–
NO 3
–
Cl
–
(a)
(b)
Cl –
Ca
2+
Ca 2+
Mg
2+
Mg
2+
SO 4
2–
SO 4
2–
K
+
Figure 2.6
The equivalent fraction of the major constituents of the average world river and seawater.