The average composition of river water is very different from that of sea water. The pH varies greatly from areas of high organic activity, e.g. the equatorial rain forests, to zones of little activity around the poles; the average is usually between 6.0 and 8.0. Large rivers, e.g. the Amazon, remove about 105 kg of material per km2 of catchment area every year. Of this, 2 × 104 kg is dissolved and the rest is carried as solid particles of colloidal debris. The composition of typical river water is:
Ion | Parts per thousand | Percentage of dissolved material |
|---|
bicarbonate HCO3− | 58.5 | 48.6 |
calcium Ca2+ | 15.0 | 12.5 |
silicate SiO2− | 13.1 | 11.0 |
sulphate SO42− | 11.2 | 9.3 |
chloride Cl− | 7.8 | 6.5 |
sodium Na+ | 6.3 | 5.3 |
magnesium Mg2+ | 4.1 | 3.4 |
potassium K+ | 2.3 | 2.0 |
nitrate NO32+ | 1.0 | 0.8 |
iron Fe2+ or Fe3+ | 0.7 | 0.6 |
TOTAL | 120.0 | 100.0 |
See also sea water, major constituents.