Anthropogenic impacts and quantitative sources of nitrate in a rural-urban canal using a combined PMF, δ15N/δ18O-NO3-, and MixSIAR approach

Chi Zhang; Wenbo Rao; Zhihua Wu; Fangwen Zheng; Tianning Li; Chao Li; Xiang Lei; Hengwang Xie; Xiaodong Chu

doi:10.1016/j.envres.2024.118587

Anthropogenic impacts and quantitative sources of nitrate in a rural-urban canal using a combined PMF, δ¹⁵N/δ¹⁸O-NO₃^-, and MixSIAR approach

Environ Res. 2024 Mar 2;251(Pt 1):118587. doi: 10.1016/j.envres.2024.118587. Online ahead of print.

Authors

Chi Zhang¹, Wenbo Rao², Zhihua Wu³, Fangwen Zheng⁴, Tianning Li¹, Chao Li¹, Xiang Lei¹, Hengwang Xie³, Xiaodong Chu⁵

Affiliations

¹ College of Earth Sciences and Engineering, Jiangning Campus of Hohai University, No. 8, Fochengxi Road, Jiangning District, Nanjing 211100, China.
² College of Earth Sciences and Engineering, Jiangning Campus of Hohai University, No. 8, Fochengxi Road, Jiangning District, Nanjing 211100, China. Electronic address: raowenbo@163.com.
³ Jiangxi Authority of Water Conservancy Project of the Ganfu Plain, No. 2, Fazhan Road, High-Tech Development District, Nanchang 330096, China.
⁴ School of Hydraulic and Ecological Engineering, Nanchang Institute of Technology, Qingshanhu District, No. 59, Beijingdong Road, Nanchang 330099, China.
⁵ Jiangxi Institute of Geo-Environment Monitoring, Nanchang 330095, China.

PMID: 38437903
DOI: 10.1016/j.envres.2024.118587

Abstract

Nitrate (NO₃^-) pollution in irrigation canals is of great concern because it threatens canal water use; however, little is known about it at present. Herein, a combination of positive matrix factorization (PMF), isotope tracers, and Mixing Stable Isotope Analysis in R (MixSIAR) was developed to identify anthropogenic impacts and quantitative sources of NO₃^- in a rural-urban canal in China. The NO₃^- concentration (0.99-1.93 mg/L) of canal water increased along the flow direction and was higher than the internationally recognized eutrophication risk value in autumn and spring. The inputs of the Fuhe River, NH₄⁺ fertilizer, soil nitrogen, manure & sewage, and rainfall were the main driving factors of canal water NO₃^- based on principal component analysis and PMF, which was supported by evidence from δ¹⁵N/δ¹⁸O-NO₃^-. According to the chemical and isotopic analyses, nitrogen transformation was weak, highlighting the potential of δ¹⁵N/δ¹⁸O-NO₃^- to trace NO₃^- sources in canal water. The MixSIAR and PMF results with a <15% divergence emphasized the predominance of the Fuhe River (contributing >50%) and anthropogenic impacts (NH₄⁺ fertilizer plus manure & sewage, >37%) on NO₃^- in the entire canal, reflecting the effectiveness of the model analysis. According to the MixSIAR model, (1) higher NO₃^- concentration in canal water was caused by the general enhancement of human activities in spring and (2) NO₃^- source contributions were associated with land-use patterns. The high contributions of NH₄⁺ fertilizer and manure & sewage showed inverse spatial variations, suggesting the necessity of reducing excessive fertilizer use in the agricultural area and controlling blind wastewater release in the urban area. These findings provide valuable insights into NO₃^- dynamics and fate for sustainable management of canal water resources. Nevertheless, long-term chemical and isotopic monitoring with alternative modeling should be strengthened for the accurate evaluation of canal NO₃^- pollution in future studies.

Keywords: Anthropogenic impact; Nitrate (NO(3)(−)) isotope; Nitrification-denitrification; Source contribution; West main canal.