Award: OCE-2042935

The world's oceans, lakes, rivers, and estuaries are experiencing accelerating chemical changes driven by rising atmospheric carbon dioxide (CO₂). As waters absorb more CO₂, their pH declines. This process is known as ocean acidification in marine environments, with analogous changes occurring in freshwater systems. These shifts in water chemistry have far-reaching consequences for aquatic life, from shellfish and corals that struggle to build their shells and skeletons in more acidic waters, to the microscopic plankton that form the base of aquatic food webs. Accurately tracking and predicting these changes requires precise knowledge of the underlying chemistry.

 

At the heart of this chemistry is the carbonate system, which has a set of chemical reactions that determine how simple chemicals, dissolved CO₂, bicarbonate ions (HCO₃^-), and carbonate ions (CO₃^2-), are distributed in water at any given acidity level. The accuracy of any calculation involving this system depends critically on a set of fundamental chemical constants, including the bicarbonate dissociation constant (K₂) which relates the relative concentrations of bicarbonate and carbonate to the acidity of a solution. Prior to this work, the mathematical formulas used to describe K₂ were well-established for open ocean waters but were relatively poorly characterized in low-salinity environments, such as rivers and estuaries.

 

The goal of this project was to address that gap by using a highly precise pH measurement method known as spectrophotometry. We conducted hundreds of careful laboratory measurements across a wide range of salinities and temperatures, covering conditions from freshwater rivers through estuaries to fully marine waters. These measurements were used to develop a new, improved formula for K₂ that is accurate across a wide environmental range. This new formula shows substantially better agreement between measured and predicted values.

 

The findings have been published in two open-source peer-reviewed journals, ensuring that scientists, resource managers, and policymakers worldwide can freely access and apply the results. Results were also presented at scientific conferences, reaching an international audience of researchers working across freshwater, estuarine, and marine environments.

 

Beyond the scientific community, this work has importance to society in several ways. Acidification assessments can be used to make informed decisions about resource management using this work. Because many ecologically and commercially important species spend critical life stages in low-salinity estuarine and coastal environments that were previously poorly constrained by existing K₂ equations, the improvements created by our investigations are quite relevant to understanding organism-level and ecosystem-level responses to changes in acidification. Also, this work is relevant to emerging efforts to remove CO₂ from the atmosphere by artificially altering ocean chemistry (i.e., marine carbon dioxide removal). Such work, called ocean alkalinity enhancement, requires accurate knowledge of carbonate chemistry across a wide range of salinity and temperature conditions.

 

Last Modified: 05/18/2026
Modified by: Robert H Byrne