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Nitrogen loss process in hypoxic seawater based on the culture experiment
Dongfan Tian1, Yueqi Wang1, Jianwei Xing1
1CAS Key Laboratory of Marine Ecology and Environmental Science, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Function Laboratory of Marine Ecology and Environmental Sciences, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; University of Chinese Academy of Sciences, Beijing 100049, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China.
Oxygen minimum zones (OMZs) are key oceanic nitrogen loss areas. This study reveals nitrogen loss processes in hypoxic waters, dominated by anammox in later stages, balancing sediment inputs.
Area of Science:
- Marine Biogeochemistry
- Oceanography
- Microbial Ecology
Background:
- Oxygen minimum zones (OMZs) and hypoxic seawaters are critical sites for oceanic nitrogen loss.
- Understanding nitrogen cycling in these environments is crucial for marine ecosystem health.
Purpose of the Study:
- To investigate the primary reactions, rates, and proportions of dissolved inorganic nitrogen (DIN) transformations under varying dissolved oxygen concentrations.
- To elucidate the nitrogen loss processes occurring in hypoxic marine environments.
Main Methods:
- Laboratory simulation cultures were employed to mimic hypoxic seawater conditions.
- Dissolved inorganic nitrogen (DIN) concentrations and transformations were monitored across different oxygen levels.
Main Results:
- Nitrogen loss in hypoxic waters proceeded through three distinct stages.
- Stage 1: Dissimilatory nitrate reduction to ammonium (DNRA) and denitrification were dominant.
- Stage 2: Anaerobic ammonium oxidation (anammox) and denitrification became key.
- Stage 3: Anammox was the primary nitrogen loss pathway, reaching equilibrium with sediment mineralization inputs.
Conclusions:
- Anammox plays a significant role in nitrogen loss within OMZs, particularly in later stages of hypoxia.
- Estimated annual nitrogen loss in global OMZs ranges from 240-260 Tg, highlighting the global impact of these processes.