Fundamentals

Sources of salt-related ions in water

Soil minerals and their effects on water quality

Soil minerals such as calcite (CaCO₃) and feldspars (sodium-, calcium-, or potassium-rich silicates) have low solubilities and contribute to water only small increases in salinity.

Highly soluble minerals such as gypsum (CaSO₄•2H₂O) have higher solubility and may contribute significant concentrations of Ca²⁺ and SO₄^2- ions. (The solubility of gypsum in pure water is about 2,600 mg/L; in the presence of sodium and magnesium ions, it can range even higher.)

Other highly soluble minerals may be found in severely salt-affected soils: sodium chloride, sodium sulfate, and magnesium sulfate. Such salts are readily leached by rainfall or irrigation water, migrating further down in the soil profile. Often such a migration of salts is beneficial to plants, because the cations and anions end up beneath, and out of the reach of, plant roots. (Many plants are adversely affected by high concentrations of salt ions.)

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