Source apportionment of nitrate in the Pearl River Estuary based on dual stable isotope

Lin Qiaoyun; Wang Xin; Chen Zhonghan; Han Lili; Yang Jing; Zhao Zhuangming

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Lin Qiaoyun，Wang Xin，Chen Zhonghan, et al. Source apportionment of nitrate in the Pearl River Estuary based on dual stable isotope[J]. Haiyang Xuebao，2025, 47(x)：1–12

Citation:

Lin Qiaoyun，Wang Xin，Chen Zhonghan, et al. Source apportionment of nitrate in the Pearl River Estuary based on dual stable isotope[J]. Haiyang Xuebao，2025, 47(x)：1–12

Citation:

Lin Qiaoyun，Wang Xin，Chen Zhonghan, et al. Source apportionment of nitrate in the Pearl River Estuary based on dual stable isotope[J]. Haiyang Xuebao，2025, 47(x)：1–12

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Source apportionment of nitrate in the Pearl River Estuary based on dual stable isotope

1.
South China Institute of Environmental Science, Ministry of Ecology and Environment, Guangzhou 510530, China
2.
State Key Laboratory of Marine Resources Utilization in the South China Sea, Hainan University, Haikou 570228, China

Available Online: 2025-07-07

Abstract

Abstract

To elucidate nitrogen cycling processes and identify dominant nitrogen pollution sources in the Pearl River Estuary (PRE), seawater samples were systematically collected from 40 stations in coastal waters (the western of Lingdingyang, Modaomen and Huangmaohai) during July 2020. By integrating hydrochemistry parameters and nitrogen-oxygen dual stable isotope (δ¹⁵N-${\mathrm{NO}}_3^- $ and δ¹⁸O-${\mathrm{NO}}_3^- $), we quantitatively analyzed the main sources of nitrate pollution and elucidated spatial gradient variation and transformation mechanism. The results showed an average nitrate concentration of 44.05 ± 27.85 μmol/L in the PRE, with the nitrogen-oxygen isotope value of 10.8 ± 2.6‰ and 6.1 ± 4.5‰, respectively. ${\mathrm{NO}}_3^- $, δ¹⁵N-${\mathrm{NO}}_3^- $ and δ¹⁸O-${\mathrm{NO}}_3^- $ values in the three areas deviated from conservative mixing behavior, with regression slopes between δ¹⁵N-${\mathrm{NO}}_3^- $ and δ¹⁸O-${\mathrm{NO}}_3^- $ indicating phytoplankton assimilation and nitrification are the dominant processes governing isotopic variations in the PRE. Additionally, incomplete sedimentary denitrification also significantly contributes to nitrogen reservoir dynamics. The Bayesian mixing model results revealed that domestic sewage represents the largest nitrate source in Lingdingyang, Modaomen and Huangmaohai, accounting for an average of 51.97% + 25.1%. Aquaculture emerged as the secondary source, which may linked to extensive aquaculture activities along the Pearl River Delta (PRD). These findings provide scientific basis for integrated nitrogen pollution control and water quality management in coastal ecosystems.
- Nitrogen and oxygen isotopic composition of nitrate,
- Nitrogen cycling,
- Source tracking,
- Pearl River Estuary

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