is typically reported as mg/L as CaCO3. (The conjunction "as" is appropriate in this case because the alkalinity results from a mixture of ions but is reported "as if" all of this is due to CaCO3.) This can be converted into milliequivalents per Liter (meq/L) by dividing by 50 (the approximate MW of CaCO3 divided by 2). Example problems Sum of contributing species The following equations demonstrate the relative contributions of each component to the alkalinity of a typical seawater sample. Contributions are in μmol.kg−soln−1 and are obtained from A Handbook of Methods for the analysis of carbon dioxide parameters in seawater " ," salinity = 35 g/kg, pH = 8.1, temperature = 25 °C. AT = []T + 2[]T + []T + [OH−]T + 2[]T + []T + []T − [H+] − [] − [HF] Phosphates and silicate, being nutrients, are typically negligible. At pH = 8.1, [] and [HF] are also negligible. So, {| |AT || = []T + 2[]T + []T + [OH−]T − [H+] |- | || = 1830 + 2 × 270 + 100 + 10 − 0.01 |- | || = 2480 μmol.kg−soln−1 |} Addition of CO2 Addition (or removal) of CO2 to a solution does not change its alkalinity, since the net reaction produces the same number of equivalents of positively contributing species (H+) as negative contributing species ( and/or ). Adding CO2 to the solution lowers its pH, but does not affect alkalinity. At all pH values: CO2 + H2O ⇌ + H+ Only at high (basic) pH values: + H+ ⇌ + 2 H+ Dissolution of carbonate rock Addition of CO2 to a solution in contact with a solid can (over time) affect the alkalinity, especially for carbonate minerals in contact with groundwater or seawater . The dissolution (or precipitation) of carbonate rock has a strong influence on the alkalinity. This is because carbonate rock is composed of CaCO3 and its dissociation will add Ca2+ and into solution. Ca2+ will not influence alkalinity, but will increase alkalinity by 2 units. Increased dissolution of carbonate rock by acidification from acid rain and mining has contributed to increased alkalinity concentrations in some major rivers throughout the eastern U.S. The following reaction shows how acid rain, containing sulfuric acid, can have the effect of increasing river alkalinity by increasing the amount of bicarbonate ion: 2 CaCO3 + H2SO4 → 2 Ca2+ + 2 +