the charge balance of ions in a solution. Certain ions, including Na+, K+, Ca2+, Mg2+, Cl−, , and are "conservative" such that they are unaffected by changes in temperature, pressure or pH. Others such as are affected by changes in pH, temperature, and pressure. By isolating the conservative ions on one side of this charge balance equation, the nonconservative ions which accept or donate protons and thus define alkalinity are clustered on the other side of the equation. This combined charge balance and proton balance is called total alkalinity. Total alkalinity is not (much) affected by temperature, pressure, or pH, and is thus itself a conservative measurement, which increases its usefulness in aquatic systems. All anions except and have low concentrations in Earth's surface water (streams, rivers, and lakes). Thus carbonate alkalinity, which is equal to is also approximately equal to the total alkalinity in surface water. Detailed description Alkalinity or measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate, defined as pH 4.5 for oceanographic/limnological studies. The alkalinity is equal to the stoichiometric sum of the bases in solution. In most Earth surface waters carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and presence of carbon dioxide in the atmosphere. Other common natural components that can contribute to alkalinity include borate, hydroxide, phosphate, silicate, dissolved ammonia, the conjugate bases of some organic acids (e.g., acetate), and sulfate. Solutions produced in a laboratory may contain a virtually limitless number of bases that contribute to alkalinity. Alkalinity is usually given as molar equivalents per liter or kilogram of solution. Commercially, as in the swimming pool industry, alkalinity might also be given in parts per million of equivalent calcium carbonate (ppm CaCO3). Alkalinity is sometimes incorrectly used interchangeably with basicity. For example, the addition of CO2 lowers the pH of a solution, thus reducing basicity while alkalinity remains unchanged (see example below). A variety of titrants, endpoints, and indicators are specified for various alkalinity measurement methods. Hydrochloric and sulfuric acids are common acid titrants, while phenolpthalein, methyl red, and bromocresol green are common indicators. Theoretical treatment In typical groundwater or seawater, the measured total alkalinity is set equal to: AT = []T + 2[]T + []T + [OH−]T + 2[]T + []T + []T − [H+]sws − [] (Subscript T indicates