Alkalinity
In the ocean, on the other hand, alkalinity is completely dominated by carbonate and bicarbonate plus a small contribution from borate.
Moreover, measuring alkalinity is important in determining a stream's ability to neutralize acidic pollution from rainfall or wastewater.
[6] There can be long-term changes in the alkalinity of streams and rivers in response to human disturbances such as acid rain generated by SOx and NOx emissions.
[7] In 1884, Professor Wilhelm (William) Dittmar of Anderson College, now the University of Strathclyde, analysed 77 pristine seawater samples from around the world brought back by the Challenger expedition.
He found that in seawater the major ions were in a fixed ratio, confirming the hypothesis of Johan Georg Forchhammer, that is now known as the Principle of Constant Proportions.
Dittmar found that the concentration of calcium was slightly greater in the deep ocean, and named this increase alkalinity.
Alkalinity roughly refers to the molar amount of bases in a solution that can be converted to uncharged species by a strong acid.
[9] 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 HCO−3 and CO2−3 have low concentrations in Earth's surface water (streams, rivers, and lakes).
[8] Alkalinity measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate, defined as pH 4.5 for many oceanographic/limnological studies.
Other common natural components that can contribute to alkalinity include borate, hydroxide, phosphate, silicate, dissolved ammonia, and the conjugate bases of organic acids (e.g., acetate).
In commercial (e.g. the swimming pool industry) and regulatory contexts, alkalinity might also be given in parts per million of equivalent calcium carbonate (ppm CaCO3)[citation needed].
This is opposed to the free concentration, which takes into account the significant amount of ion pair interactions that occur in seawater.)
Alkalinity can be measured by titrating a sample with a strong acid until all the buffering capacity of the aforementioned ions above the pH of bicarbonate or carbonate is consumed.
This pH is also called the CO2 equivalence point where the major component in water is dissolved CO2 which is converted to H2CO3 in an aqueous solution.
In this case, the higher the pH, the more bicarbonate and carbonate ion there will be, in contrast to the paradoxical situation described above, where one does not have equilibrium with the atmosphere.
[16]: 181 Biological processes have a much greater impact on oceanic alkalinity on short (minutes to centuries) timescales.
Both of these processes consume hydrogen ions (thus increasing alkalinity) and release gases (N2 or H2S), which eventually escape into the atmosphere.
As a result, upwelling areas (where water from the deep ocean is pushed to the surface) also have higher alkalinity values.
[22] There are many programs to measure, record, and study oceanic alkalinity, together with many of the other characteristics of seawater, like temperature and salinity.
