Alkalinity (water)

Alkalinity is the concentration of ions in the water that neutralize the hydrogen ion[1] and is a combination of the chemicals dissolved in water, such as bicarbonates, carbonates, hydroxides, borates, phosphates and silicates that will react to neutralise added acid and buffer the pH of the water[2]. Natural fresh water typically has either no or very low levels of alkalinity due to very low levels of dissolved chemical species present, whereas highly saline and/or sea waters typically contain high levels of alkalinity[5].

Quick facts

The ocean's average pH is now around 8.1

which is alkaline, but as the ocean continues to absorb more CO2, the pH decreases and the ocean will become more acidic[3].

Alkalinity is a measure of how basic, or not acidic, water or substrate is. It is the amount of chemical substances in the water that can help buffer or keep the pH stable when acid substances are added. Alkalinity can only buffer acids to a certain point, at which stage the pH will move from being alkaline to being acidic.

The levels of alkalinity are critical to the functioning of healthy wetlands. Wetlands may naturally be acidic or alkaline. Organisms in wetlands have evolved coexist in aquatic environments within certain ranges of alkalinity or acidity. A decrease in the alkalinity may result in a change in the species composition of the wetland. Over time, a decrease the alkalinity of the water will make it less resilient and more susceptible to a drop in pH.

Marine or sea waters typically have a pH of ~ 8 and alkalinity levels ranging between 100-130 mg CaCO₃/L[4], whereas the alkalinity of fresh waters are typically lower and span a much wider range. Alkalinity is a reflection of the various salts and nutrients present in waters which are used by aquatic species for growth.

Links and references

pH (Lacustrine and palustrine)

pH - Water

ANZECC-ARMCANZ Water Quality Guidelines.

References

1. ^ Hydrogen Ion - an overview | ScienceDirect Topics. [online] Available at: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/hydrogen-ion [Accessed 22 October 2023].
2. ^ (27 April 2016). Monitoring alkalinity and hardness. [online] Available at: https://www.dpi.nsw.gov.au/fishing/aquaculture/publications/water-quality-management/monitoring-alkalinity-and-hardness [Accessed 11 September 2023].
3. ^ Ocean acidification. [online] Available at: https://www.noaa.gov/education/resource-collections/ocean-coasts/ocean-acidification [Accessed 10 October 2023].
4. ^ pH of coastal waterways - OzCoasts. [online] Available at: https://ozcoasts.org.au/indicators/biophysical-indicators/ph_coastal_waterways/ [Accessed 11 September 2023].
5. ^ Standard methods for the examination of water and wastewater (1998), American Public Health Association: Washington, DC, eds. L S Clesceri, A E Greenberg & A D Eaton.

Last updated: 23 October 2023