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Author ORCID Identifier
https://orcid.org/0000-0001-8061-4560
https://orcid.org/0000-0002-5894-6240
https://orcid.org/0000-0003-2896-3063
https://orcid.org/0000-0003-0726-0131
Abstract
The capacity of aquatic systems to buffer acidification depends on the sum contributions of various chemical species to total alkalinity (TA). Major TA contributors are inorganic, with carbonate and bicarbonate considered the most important. However, growing evidence shows that many rivers, estuaries, and coastal waters contain dissolved organic molecules with charge sites that create organic alkalinity (OrgAlk). This study describes the first comparison of (1) OrgAlk distributions and (2) acid–base properties in contrasting estuary-plume systems: the Pleasant (Maine, USA) and the St. John (New Brunswick, CA). The substantial concentrations of OrgAlk in each estuary were sometimes not conservative with salinity and typically associated with very low pH. Two approaches to OrgAlk measurement showed consistent differences, indicating acid–base characteristics inconsistent with the TA definition. The OrgAlk fraction of TA ranged from 78% at low salinity to less than 0.4% in the coastal ocean endmember. Modeling of titration data identified three groups of organic charge sites, with mean acid–base dissociation constants (pKa) of 4.2 (+/- 0.5), 5.9 (+/- 0.7) and 8.5 (+/- 0.2). These represented 21% (+/- 9%), 8% (+/- 5%), and 71% (+/- 11%) of titrated organic charge groups. Including OrgAlk, pKa, and titrated organic charge groups in carbonate system calculations improved estimates of pH. However, low and medium salinity, organic-rich samples demonstrated persistent offsets in calculated pH, even using dissolved inorganic carbon and CO2 partial pressure as inputs. These offsets show the ongoing challenge of carbonate system intercomparisons in organic rich systems whereby new techniques and further investigations are needed to fully account for OrgAlk in TA titrations.
Date Created
December 16, 2024
Department
Ocean Process Analysis Laboratory
Publication Date
12-16-2024
Subject
organic acid-base biogeochemistry
Grant/Award Number and Agency
NSF Awards 1658377 and 1658321
Journal Title
Limnology and Oceanography
Language
English
Publisher
Wiley
Digital Object Identifier (DOI)
https://doi.org/10.1002/lno.12761
Document Type
Article
Recommended Citation
Hunt, C. W., J. E. Salisbury, X. Liu, and R. H. Byrne. Organic alkalinity distributions, characteristics, and application to carbonate system calculations in estuarine and coastal systems. Limnology and Oceanography n/a. doi:10.1002/lno.12761
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Biogeochemistry Commons, Chemistry Commons, Oceanography Commons