Exploration of nitrogen sources and transformation processes in eutrophic estuarine zones based on DOM and stable isotope compositions

• Published in: Marine pollution bulletin 2024-12, Vol.209 (Pt B), p.117256, Article 117256
• Main Authors: Hu, Xiujian, Cao, Shengwei, Wen, Mengtuo, Zhang, Yuanjing, Zhao, Yuewen, Liu, Yaci, Kong, Xiangke, Li, Yasong
• Format: Article
• Language: English
• Subjects: Bayes Theorem; Bayesian model; Biogeochemical processes; Dissolved organic matter (DOM); Environmental Monitoring; Estuaries; Eutrophication; Fresh Water - chemistry; Nitrate isotope; Nitrates - analysis; Nitrogen - analysis; Nitrogen cycling; Nitrogen Isotopes - analysis; Salinity; Seawater - chemistry; Water Pollutants, Chemical - analysis
• ISSN: 0025-326X; 1879-3363; 1879-3363
• DOI: 10.1016/j.marpolbul.2024.117256

Our study examines nitrogen sources and transformations in Xiamen Bay, where eutrophication has increased due to higher nitrogen levels. By analyzing dissolved organic matter (DOM) and nitrate stable isotopes (δ15N-NO3−and δ18O-NO3−), the study finds that nitrate in low salinity areas is influenced by freshwater-seawater mixing and biogeochemical processes, while in high salinity areas, it is mainly affected by physical mixing. Bayesian mixing model (MixSIAR) results show that the primary nitrate sources are fecal matter and sewage, followed by atmospheric deposition. During the high flow period, DOM may facilitate nitrogen transformation and release through processes such as degradation or mineralization. In contrast, during the low flow period, the system is mainly influenced by the physical mixing of saline and freshwater. Studies have shown that DOM can indicate the biogeochemical intensity in water bodies, further identifying the main factors influencing the distribution and transformation processes of nitrate content, providing a basis for mitigating eutrophication in estuarine areas. [Display omitted] •Manure and sewage were the main NO3- sources of Xiamen Bay.•The main sources of DOM are domestic wastewater and algal activity.•Different seasons affect the dominant processes between DOM and nitrogen cycling.