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In the environment, bulk calcium carbonate will dissociate into calcium and carbonate ions.

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In the environment, calcium carbonate will dissociate into calcium and carbonate ions. These ions are naturally ubiquitous in the environment; calcium will be assimilated by species present in the water and is necessary to maintain a good chemical balance in soils, water and plants and carbonate will become part of the carbon cycle.

Data from Allan DJ (1995) indicate that most natural waters contain various bicarbonate and carbonate compounds, originating from dissolution of sedimentary rocks. Streamwater usually contains bicarbonates and carbonates and carbonic acid readily dissolves CaCO3 rocks, forming Ca(HCO3)2. The resulting streamwater is a solution of CO2, H2CO3, HCO3- and CO3^2- ions forming an effective buffer system that resists change in pH. The relative proportions of CO2, H2CO3, HCO3-and CO3^2- are pH dependent. At a pH below 4.5, only CO2 and H2CO3 are present and almost no HCO3- or CO3^2- is found. At higher pH values dissociation of H2CO3 occurs, HCO3-and CO3^2- are present and CO2 and H2CO3 are no longer detectable. At intermediate pH values, HCO3- predominates. Above a pH of about 8.3, HCO3- also declines with formation of CO3^2-. The dissociation dynamics are influenced by both temperature and ionic concentrations.

Therefore, the chemistry of carbonate in water is clearly understood.

References: Allan DJ (1995), Stream Ecology: Structure and function of running waters, Published by Chapman and Hall.