Carbonation

A chemical weathering process whereby the action of acid rain reacts with calcium carbonate containing minerals (e.g. chalk). The carbonation process starts with carbon dioxide in the atmosphere dissolving in water (rain or groundwater), which forms carbonic acid (H2O + CO2 = H2CO3). When dissolved in water carbonic acid it breaks down into hydrogen ions (H+) and bicarbonate ions (HCO3-), increasing soil acidity.

This weak acid reacts with minerals in the soil that contain calcium carbonate (CaCO3). This reaction gradually dissolves the mineral to produce calcium bicarbonate (Ca(HCO3)2), which is released into the soil solution and is readily leached from a soil profile.

The removal of these neutral / alkaline compounds reduces the buffering capacity of these soils, potentially increasing the acidity of the soil pH, although the extent of any increase towards acidity will depend on the initial extent of calcium carbonate within a soil.

Carbonation can affect the structure of a soil, as well as making nutrients available due to the dissolution of minerals for plant uptake.