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Abstract Rivers and streams play an important role within the global carbon cycle, in part through emissions of carbon dioxide (CO2) to the atmosphere. However, the sources of this CO2and their spatiotemporal variability are difficult to constrain. Recent work has highlighted the role of carbonate buffering reactions that may serve as a source of CO2in high alkalinity systems. In this study, we seek to develop a quantitative framework for the role of carbonate buffering in the fluxes and spatiotemporal patterns of CO2and the stable and radio‐ isotope composition of dissolved inorganic carbon (DIC). We incorporate DIC speciation calculations of carbon isotopologues into a stream network CO2model and perform a series of simulations, ranging from the degassing of a groundwater seep to a hydrologically‐coupled 5th‐order stream network. We find that carbonate buffering reactions contribute >60% of emissions in high‐alkalinity, moderate groundwater‐CO2environments. However, atmosphere equilibration timescales of CO2are minimally affected, which contradicts hypotheses that carbonate buffering maintains high CO2across Strahler orders in high alkalinity systems. In contrast, alkalinity dramatically increases isotope equilibration timescales, which acts to decouple CO2and DIC variations from the isotopic composition even under low alkalinity. This significantly complicates a common method for carbon source identification. Based on similar impacts on atmospheric equilibration for stable and radio‐ carbon isotopologues, we develop a quantitative method for partitioning groundwater and stream corridor carbon sources in carbonate‐dominated watersheds. Together, these results provide a framework to guide fieldwork and interpretations of stream network CO2patterns across variable alkalinities.
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This content will become publicly available on July 16, 2026
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 CO2is 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 CO2data, including carbon–oxygen coupling through production and respiration. As direct measurements of dissolved CO2are increasingly common, accounting for CO2equilibria with DIC is critical to understanding its role in carbon cycling within most freshwater systems.
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- PAR ID:
- 10635908
- Publisher / Repository:
- Associated Sciences of Limnology and Oceanography
- Date Published:
- Journal Name:
- Limnology and Oceanography Letters
- ISSN:
- 2378-2242
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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