Alkalinity is divisible into bicarbonate alkalinity and carbonate alkalinity and in some cases hydroxide alkalinity. Total titrable bases in a water expressed as equivalent CaCO3 are referred to as total alkalinity. In most waters bicarbonates (HCO3-) and carbonates (CO3=) are the major bases, but others can also be important under particular conditions. (see instructions given for estimation of alkalinity - under practicals). Total alkalinity of natural waters may range from 5 mg to several hundreds per litre (as CaCO3). The alkalinity often reflects the carbonate contents of the rocks and soils of the water shed and bottom muds. Water of arid regions may also have highly alkaline waters. For biological purposes a total alkalinity over 40 mg of CaCO3/litre is considered to indicate hard waters (see also discussion under “CO2”).
It is suggested that hard waters are usually more productive than soft, but this is more due to higher phosphorus levels associated with it rather than high alkalinity per se (Boyd, 1979, see also our discussion on “Productivity”). Regarding buffering alkalinity system see under “Carbon dioxide”.
