Organic Alkalinity as an Important Constituent of Total Alkalinity and the Buffering System in River-To-Coast Transition Zones

Shuzhen Song, Richard Garth James Bellerby, Zhaohui Aleck Wang, Eyal Wurgaft, Daoji Li

Research output: Contribution to journalArticlepeer-review

Abstract

Organic acid-base species in the dissolved organic carbon pool have been shown to make an important contribution (i.e., organic alkalinity; OrgAlk) to the total alkalinity (TA) in many coastal systems. This study documents an intensive investigation of OrgAlk characteristics in the river-to-coast transition zones of six southeast Chinese rivers. OrgAlk, mainly originating from river input, accounted for an important proportion of TA (0.3%–12%) in six estuaries. Carboxylic acid groups were commonly present in all estuaries. Notable differences in the TA values (1–18 μmol kg−1) determined by several established TA measurement approaches were identified in estuaries where organic acids with pKa <5.2 were abundant. The most widely used open-cell titration method, in comparison with closed-cell titration and single-step titration, is the best approach to incorporate OrgAlk in titrated TA when the pKa values of organic acids were >5 in the study estuaries. Across our study sites, OrgAlk might modify H+ concentrations by 3%–69% (i.e., pH by 0.01–0.78) and aragonite saturation states by 1%–72%, indicating that OrgAlk can play a significant role in the coastal carbonate buffering system. It is essential to improve current TA measurement approaches to more accurately represent OrgAlk in the coastal system and assess impacts of OrgAlk on coastal carbonate chemistry.

Original languageEnglish
Article numbere2022JC019270
JournalJournal of Geophysical Research: Oceans
Volume128
Issue number8
DOIs
StatePublished - Aug 2023

Bibliographical note

Funding Information:
We thank Sophie Kuhl, Kate Morkeski, Siyuan Chang, Changjun Li, Feng Zhang, Changxing Zong for sampling assistance and language improvement. The study was supported by National Natural Science Foundation of China (42106039), China postdoctoral science foundation (2020M681229), Norwegian Research Council project CE2COAST through the 2019 “Joint Transnational Call on Next Generation Climate Science in Europe for Oceans” (321890), and National Thousand Talents Program for Foreign Experts (WQ20133100150).

Publisher Copyright:
© 2023 The Authors.

Keywords

  • aragonite saturation state
  • carbonate system
  • coastal system
  • estuaries
  • organic alkalinity
  • total alkalinity

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