Nitrate transformation and source tracking of rivers draining into the Bohai Sea using a multi-tracer approach combined with an optimized Bayesian stable isotope mixing model

Xinwei Ren; Fu-Jun Yue; Jianhui Tang; Cai Li; Si-Liang Li

doi:10.1016/j.jhazmat.2023.132901

Nitrate transformation and source tracking of rivers draining into the Bohai Sea using a multi-tracer approach combined with an optimized Bayesian stable isotope mixing model

J Hazard Mater. 2024 Feb 5:463:132901. doi: 10.1016/j.jhazmat.2023.132901. Epub 2023 Nov 2.

Authors

Xinwei Ren¹, Fu-Jun Yue², Jianhui Tang³, Cai Li⁴, Si-Liang Li⁵

Affiliations

¹ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
² Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; Tianjin Bohai Rim Coastal Earth Critical Zone National Observation and Research Station, Tianjin University, Tianjin 300072, China; Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin 300072, China. Electronic address: fujun_yue@tju.edu.cn.
³ Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China.
⁴ School of Urban and Environment Science, Huaiyin Normal University, Huaian 223300, China.
⁵ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; Tianjin Bohai Rim Coastal Earth Critical Zone National Observation and Research Station, Tianjin University, Tianjin 300072, China; Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin 300072, China; Haihe Laboratory of Sustainable Chemical Transformations, Tianjin 300192, China. Electronic address: siliang.li@tju.edu.cn.

PMID: 37931340
DOI: 10.1016/j.jhazmat.2023.132901

Abstract

Excessive levels of NO₃^- can result in multiple eco-environmental issues due to potential toxicity, especially in coastal areas. Accurate source tracing is crucial for effective pollutant control and policy development. Bayesian models have been widely employed to trace NO₃^- sources, while limited studies have utilized optimized Bayesian models for NO₃^- tracing in the coastal rivers. The Bohai Rim is highly susceptible to ecological disturbances, particularly N pollution, and has emerged as a critical area. Therefore, identification the N fate and understanding their sources contribution is urgent for pollution mitigation efforts. In addition, understanding the influenced key driven factors to source dynamic in the past ten years is also implication to environmental management. In this study, water samples were collected from 36 major river estuaries that drain into the Bohai Sea of North China. The main transformation processes were analyzed and quantified the sources of NO₃^- using a Bayesian stable isotope mixing model (MixSIAR) with isotopic approach (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-). The overall isotopic composition of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- in estuary waters ranged from -0.8-19.3‰ (9.3 ± 4.6‰) and from -7.1-10.5‰ (5.0 ± 4.3‰), respectively. The main sources of nitrate in most river estuaries were manure & sewage, and chemical fertilizer, while weak denitrification and mixed processes were observed in Bohai Rim region. A temporal decrease in the nitrogen load entering the Bohai Sea indicates an improvement in water quality in recent years. By incorporating informative priors and utilizing the calculated coefficients, the accuracy of sourcing results was significantly improved. This study highlighted the optimized MixSIAR model enhanced its accuracy for sourcing analysis and providing valuable insights for policy formulation. Future efforts should focus on improving management strategies to reduce nitrogen into the bay.

Keywords: Dual stable isotope; MixSIAR; Nitrate appointment; Nitrogen load; Parameter optimization.