Decoupling of Estuarine Hypoxia and Acidification as Revealed by Historical Water Quality Data

Hypoxia and acidification are commonly coupled in eutrophic aquatic environments because aerobic respiration is usually dominant in bottom waters and can lower dissolved oxygen (DO) and pH simultaneously. However, the degree of coupling, which can be weakened by non-aerobic respiration and CaCO3 cycling, has not been adequately assessed. In this study, we applied a box model to 20 years of water quality monitoring data to explore the relationship between hypoxia and acidification along the mainstem of Chesapeake Bay. In the early summer, dissolved inorganic carbon (DIC) production in mid-bay bottom waters was dominated by aerobic respiration, contributing to DO and pH declines. In contrast, late-summer DIC production was higher than that expected from aerobic respiration, suggesting potential buffering processes, such as calcium carbonate dissolution, which would elevate pH in hypoxic waters. These findings are consistent with contrasting seasonal relationships between riverine nitrogen (N) loads and hypoxic and acidified volumes. The N loads were associated with increased hypoxic and acidified volumes in June, but only increased hypoxic volumes in August, when acidified volume declines instead. Our study reveals that the magnitude of this decoupling varies interannually with watershed nutrient inputs, which has implications for the management of co-stressors in estuarine systems.



Work Title Decoupling of Estuarine Hypoxia and Acidification as Revealed by Historical Water Quality Data
Open Access
  1. Chunqi Shen
  2. Jeremy M. Testa
  3. Maria Herrmann
  4. Raymond G. Najjar
  1. Hypoxia
  2. Acidification
  3. Box model
  4. Chesapeake Bay
  5. Estuary
  6. Carbonate chemistry
License In Copyright (Rights Reserved)
Work Type Article
  1. Environmental Science & Technology
Publication Date January 10, 2023
Publisher Identifier (DOI)
Deposited February 28, 2023




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Work History

Version 1

  • Created
  • Added Shen_etal_box_model_resubmit_revision3.pdf
  • Added Creator Chunqi Shen
  • Added Creator Jeremy M. Testa
  • Added Creator Maria Herrmann
  • Added Creator Raymond G. Najjar
  • Published
  • Updated Keyword Show Changes
    • Hypoxia, Acidification, Box model, Chesapeake Bay, Estuary, Carbonate chemistry
  • Updated