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The Benthic Exchange of O2, N2 and Dissolved Nutrients Using Small Core Incubations
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Hypoxia Decreases Nitrogen Removal in Coastal Marine Sediments
Jing Sun1, Xingyu Yang1, Liuqian Yu2,3
1Department of Ocean Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR 999077, P. R. China.
Environmental Science & Technology
|March 30, 2026
Summary
Hypoxia, or low oxygen, intensifies sediment nitrogen cycling and ammonium release in coastal zones. This reduces overall nitrogen removal, potentially worsening eutrophication in nitrogen-limited waters.
Area of Science:
- Environmental Science
- Marine Chemistry
- Geochemistry
Background:
- Hypoxia significantly influences nitrogen cycling in sediments, but its effects vary across different aquatic systems.
- Understanding these impacts is crucial for managing coastal water quality and eutrophication.
Purpose of the Study:
- To investigate the mechanisms by which hypoxia affects nitrogen cycling in sediments.
- To quantify the impact of hypoxia on ammonium efflux, nitrification, and denitrification.
Main Methods:
- Observations and mass-balance analysis were conducted in the Pearl River Estuary.
- Sediment nitrogen cycling processes were quantified under varying oxygen conditions.
Main Results:
- Low-oxygen conditions increased sediment ammonium efflux.
- Hypoxia reduced nitrification rates, decreasing nitrate availability for denitrification.
- Denitrification efficiency was significantly lower under hypoxic conditions compared to well-oxygenated conditions.
Conclusions:
- Bottom-water hypoxia enhances sediment nitrogen recycling and diminishes nitrogen removal in coastal systems.
- This mechanism can amplify eutrophication in nitrogen-limited coastal environments.
- The findings are applicable to many coastal systems with low-to-moderate nitrate levels.
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