Freshwater carbonate buffering revisited

Abstract

Concentrations of total dissolved inorganic carbon (DIC) in freshwater ecosystems are controlled by terrestrial inputs and a myriad of in situ processes, such as aquatic metabolism. Dissolved CO₂ is one of the components of DIC, and its dynamics are also regulated by chemical equilibrium with the DIC pool, so-called carbonate buffering. Although its importance is generally recognized, carbonate buffering is still not consistently accounted for in freshwater studies. Here, we review key concepts in freshwater carbonate buffering, perform simulation experiments, and provide a case study of an alkaline river to illustrate calculations of DIC from CO₂. These analyses demonstrate that carbonate buffering can alter common interpretations of CO₂ data, including carbon–oxygen coupling through production and respiration. As direct measurements of dissolved CO₂ are increasingly common, accounting for CO₂ equilibria with DIC is critical to understanding its role in carbon cycling within most freshwater systems.