Abstract Identifying the sources and characteristics of water pollution is essential for the protection and management of water environments. Nitrate (NO 3 − ) is a key pollutant affecting water quality in the Qingshui River, a typical semi‐arid tributary in the upper Yellow River basin. This study aimed to investigate the spatiotemporal patterns and sources of NO 3 − in the basin using an integrated analysis of hydrochemistry, stable isotopes, and dissolved organic matter (DOM) fluorescence. Hydrochemical results revealed that the water quality exhibited distinct seasonal variations, influenced by the unique hydrological and climatic conditions of the upper Yellow River. The surface water showed elevated concentrations of NO 3 − with limited denitrification, and NO 3 − accumulation was driven by multiple sources. Based on the dual isotopes ( δ 15 N and δ 18 O) and the MixSIAR model, it was quantitatively determined that allochthonous inputs—including chemical nitrogen fertilizer, soil nitrogen, domestic sewage, and manure—constituted the primary sources of NO 3 − . DOM fluorescence analysis revealed active biological or microbial metabolic activities, while allochthonous DOM significantly contributed to NO 3 − contamination. Both the MixSIAR model and DOM fluorescence results confirmed that protein‐like substances were mainly derived from domestic sewage, whereas humic‐like substances originated from non‐point source pollution in the study area. These findings demonstrate the feasibility of combining isotopic and DOM fluorescence approaches to trace NO 3 − sources in surface water. This integrated methodology can support the design of targeted zonal management strategies to protect the surface water environment and maintain sustainable socioeconomic systems in semi‐arid regions.
A Wed, study studied this question.
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