Purpose Accurately tracing nitrogen (N) sources and clarifying their migration-transformation processes is essential for mitigating riverine N pollution, yet the mechanisms across media and land-use contexts remain unclear. Materials and methods In this study, we assessed and compared the differences in the nitrate content and isotopic compositions (δ15N-NO3− and δ18O-NO3−) of surface water, as well as the carbon (C) and N content and their isotope values (δ13C and δ15N, respectively) in the suspended particulate matter (SPM) and surface sediments (SSM) of the Wei River, with respect to various land-use types [i.e. construction land (CL), agricultural land (AL), and forest land (FL)]. Moreover, the N sources in the different media were quantitatively assessed, and the transformation processes were clarified. Results The nitrate content, δ15N-NO3−, δ15N and N content of SPM in the FL were significantly lower than those in AL and CL (P < 0.001). Manure and sewage were the dominant nitrate sources in CL (58.1 ± 8.5%) and AL (53.3 ± 19.0%). The SPM found in CL and AL were mainly derived from terrestrial soil (46.7 ± 21.8% and 44.1 ± 30.4%, respectively) and effluent detritus (28.2 ± 15.6% and 24.4 ± 16.5%, respectively), whereas that in FL primarily originated from terrestrial leaf litter (50.4 ± 24.8%) and terrestrial soil (26.9 ± 22.2%). Note that terrestrial soil was the dominant source for the SSM observed across all land-uses types (56.4%–87.2%). Significant positive correlations were observed between δ15N-NO3− and δ15N-SPM (P < 0.001) and between δ15N-NO3− and δ18O-NO3− (P < 0.001), indicating that the nitrate transformation was mainly influenced by assimilation. However, no significant correlations were observed between SPM and SSM (δ13C, δ15N, and C and N contents), suggesting weak vertical mixing in the water column. Conclusions Overall, this study underscores the strong coupling between land-use patterns and N cycling, indicating that effective regulation requires management strategies tailored to specific land-use conditions.

Nitrogen sources and transformation processes across different media under various land-use types in the Wei River watershed

期刊论文
发表日期：

2026年4月14日

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Jun Zhang,
Zongtian Zhang,
Manyao Yang,
Pengtao Wang,
Ganggang Zhang,
Ziteng Wang,
Fei Yu

摘要

Purpose

Accurately tracing nitrogen (N) sources and clarifying their migration-transformation processes is essential for mitigating riverine N pollution, yet the mechanisms across media and land-use contexts remain unclear.

Materials and methods

In this study, we assessed and compared the differences in the nitrate content and isotopic compositions (δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻) of surface water, as well as the carbon (C) and N content and their isotope values (δ¹³C and δ¹⁵N, respectively) in the suspended particulate matter (SPM) and surface sediments (SSM) of the Wei River, with respect to various land-use types [i.e. construction land (CL), agricultural land (AL), and forest land (FL)]. Moreover, the N sources in the different media were quantitatively assessed, and the transformation processes were clarified.

Results

The nitrate content, δ¹⁵N-NO₃⁻, δ¹⁵N and N content of SPM in the FL were significantly lower than those in AL and CL (P < 0.001). Manure and sewage were the dominant nitrate sources in CL (58.1 ± 8.5%) and AL (53.3 ± 19.0%). The SPM found in CL and AL were mainly derived from terrestrial soil (46.7 ± 21.8% and 44.1 ± 30.4%, respectively) and effluent detritus (28.2 ± 15.6% and 24.4 ± 16.5%, respectively), whereas that in FL primarily originated from terrestrial leaf litter (50.4 ± 24.8%) and terrestrial soil (26.9 ± 22.2%). Note that terrestrial soil was the dominant source for the SSM observed across all land-uses types (56.4%–87.2%). Significant positive correlations were observed between δ¹⁵N-NO₃⁻ and δ¹⁵N-SPM (P < 0.001) and between δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ (P < 0.001), indicating that the nitrate transformation was mainly influenced by assimilation. However, no significant correlations were observed between SPM and SSM (δ¹³C, δ¹⁵N, and C and N contents), suggesting weak vertical mixing in the water column.

Conclusions

Overall, this study underscores the strong coupling between land-use patterns and N cycling, indicating that effective regulation requires management strategies tailored to specific land-use conditions.