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<p>The quantitative identification of nitrate sources is of great significance for water resources management. Stable isotopes combined with Bayesian isotope mixing model (SIAR) model were widely used to identify nitrogen sources. However, limited attention has been paid to how variations in the isotopic composition of nitrate sources affect the estimated source contributions in isotope mixing models. Here, the δ<sup>15</sup>N-NO<sub>3</sub><sup>−</sup> and δ<sup>18</sup>O-NO<sub>3</sub><sup>−</sup> isotopes, the SIAR model, and the uncertainty and sensitivity analysis were used to quantify the contributions and uncertainties of nitrate sources in Huashan watershed. 60 surface water (SW) samples and 82 groundwater (GW)samples were collected from November 2021 to October 2022, and atmospheric deposition (AD), chemical nitrogen fertilizer (NF), soil nitrogen (SN), and manure and sewage (M&amp;S) were determined as the potential nitrate sources. Source identification by SIAR indicated that in November 2021 the M&amp;S was the main contributor of nitrate to SW, while NF was the main contributor to nitrate in groundwater. In April 2022, NF contributed the most to nitrate in surface water, while nitrate in groundwater mainly originated from SN and MS. The variation between November 2021 and April 2022 sources is due to spring fertilization and rainfall. The uncertainty analysis showed that the greatest uncertainties were in SN and NF. Sensitivity analysis showed that the changes in the nitrate isotopic composition of M&amp;S had the greatest effect on the results for δ<sup>15</sup>N, whereas only the mean values of oxygen isotope values of AD had a greater effect on the results for δ<sup>18</sup>O. Fertilizer application and changes in soil fertility due to agricultural rotations and cropping practices are intrinsic to the high level of uncertainty in SN. Sensitivity analysis highlighted the necessity of accurately measuring the isotopic end-members of potential nitrate sources to reduce the uncertainty in SIAR-based nitrate source apportionment results. Management strategies for the Huashan watershed should focus on domestic sewage treatment, optimization of agricultural practices, and integrated management of strongly connected surface water–groundwater systems to proactively prevent nitrogen pollution risks.</p>

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Quantitative identification, uncertainty and sensitivity analysis of nitrate sources using stable isotopes in a drinking water source watershed of Eastern China

  • 期刊论文

  • 发表日期：

    2026年2月11日

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  • Lu Zhang,
  • Jiangbo Han,
  • Yunfeng Dai,
  • Jin Lin,
  • Xue Li,
  • Wei Li,
  • Peng liu

摘要

The quantitative identification of nitrate sources is of great significance for water resources management. Stable isotopes combined with Bayesian isotope mixing model (SIAR) model were widely used to identify nitrogen sources. However, limited attention has been paid to how variations in the isotopic composition of nitrate sources affect the estimated source contributions in isotope mixing models. Here, the δ15N-NO3− and δ18O-NO3− isotopes, the SIAR model, and the uncertainty and sensitivity analysis were used to quantify the contributions and uncertainties of nitrate sources in Huashan watershed. 60 surface water (SW) samples and 82 groundwater (GW)samples were collected from November 2021 to October 2022, and atmospheric deposition (AD), chemical nitrogen fertilizer (NF), soil nitrogen (SN), and manure and sewage (M&S) were determined as the potential nitrate sources. Source identification by SIAR indicated that in November 2021 the M&S was the main contributor of nitrate to SW, while NF was the main contributor to nitrate in groundwater. In April 2022, NF contributed the most to nitrate in surface water, while nitrate in groundwater mainly originated from SN and MS. The variation between November 2021 and April 2022 sources is due to spring fertilization and rainfall. The uncertainty analysis showed that the greatest uncertainties were in SN and NF. Sensitivity analysis showed that the changes in the nitrate isotopic composition of M&S had the greatest effect on the results for δ15N, whereas only the mean values of oxygen isotope values of AD had a greater effect on the results for δ18O. Fertilizer application and changes in soil fertility due to agricultural rotations and cropping practices are intrinsic to the high level of uncertainty in SN. Sensitivity analysis highlighted the necessity of accurately measuring the isotopic end-members of potential nitrate sources to reduce the uncertainty in SIAR-based nitrate source apportionment results. Management strategies for the Huashan watershed should focus on domestic sewage treatment, optimization of agricultural practices, and integrated management of strongly connected surface water–groundwater systems to proactively prevent nitrogen pollution risks.