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The Ecosystem Science and Modeling lab has been collecting water samples from five stations in the Mission-Aransas Estuary (MAE, Northwest Gulf of Mexico, Texas coast) for carbonate system characterization on a monthly to twice monthly basis since May 2014. This dataset includes temperature, salinity, dissolved inorganic carbon (DIC), total alkalinity (TA), calcium, and pH measurements from surface and bottom water samples in MAE from May 2014 – Feb 2017 and Dec 2018 – Feb 2020. Additional data for this estuary to fill in the Feb 2017 – Dec 2018 gap are also archived with BCO-DMO (http://www.bco-dmo.org/dataset/784673, doi:10.1575/1912/bco-dmo.784673.1).
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Organic alkalinity distributions, characteristics, and application to carbonate system calculations in estuarine and coastal systems
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 CO2partial 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.
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- Award ID(s):
- 1658377
- PAR ID:
- 10573217
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 70
- Issue:
- 2
- ISSN:
- 0024-3590
- Format(s):
- Medium: X Size: p. 319-333
- Size(s):
- p. 319-333
- Sponsoring Org:
- National Science Foundation
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