无定河流域地表水硝酸盐浓度的时空分布特征及来源解析

无定河流域作为黄河的一级支流，其水生态环境质量深刻影响着黄河流域生态保护与高质量发展.为识别无定河流域硝酸盐污染来源，对2019～2021年期间无定河的地表水样品进行了采集，探究了流域地表水体硝酸盐浓度的时空分布特征及影响因素，借助水化学方法、氮氧同位素示踪技术以及MixSIAR模型定性和定量地确定了地表水硝酸盐各来源及其贡献率.结果表明，无定河流域硝酸盐浓度存在显著时空差异.时间上，丰水期地表水NO^-₃-N浓度均值高于平水期；空间上，下游地表水NO^-₃-N浓度均值高于上游.地表水硝酸盐浓度的时空差异主要受降雨径流、土壤类型以及土地利用类型的影响.无定河流域地表水丰水期硝酸盐的主要来源是生活污水及粪肥、化学肥料和土壤有机氮，其贡献率分别为43.3%、 27.6%和22.1%,降水的贡献率仅占7.0%.不同河段地表水硝酸盐污染源贡献率存在差异，上游土壤氮贡献率明显高于下游，为26.5%;而下游生活污水及粪肥的贡献率明显高于上游，为48.9%.可为无定河乃至干旱及半干旱地区的河流硝酸盐来源解析和污染治理...

Temporal and Spatial Distribution Characteristics and Source Analysis of Nitrate in Surface Water of Wuding River Basin

The Wuding River Basin is a first-class tributary of the Yellow River, and the quality of its water ecological environment has a profound impact on the ecological protection and high-quality development of the Yellow River Basin. In order to identify the source of nitrate pollution in the Wuding River Basin, surface water samples of the Wuding River were collected from 2019 to 2021, and the temporal and spatial distribution characteristics and influencing factors of nitrate concentration in surface water in the basin were explored. Nitrogen and oxygen isotope tracer technology and the MixSIAR model were used to qualitatively and quantitatively determine the sources of surface water nitrate and their contribution rates. The results showed that there were significant spatial and temporal differences in nitrate concentrations in the Wuding River Basin. In terms of time, the mean concentration of NO^-₃-N in surface water in the wet season was higher than that in the flat-water period; spatially, the mean concentration of NO^-₃-N in the downstream surface water was higher than that in the upstream. The spatial and temporal differences in surface water nitrate concentrations were mainly affected by rainfall runoff, soil types, and land use types. The main sources of nitrates in the surface water of the Wuding River Basin during the wet season were domestic sewage, manure, chemical fertilizers, and soil organic nitrogen, whose contribution rates were 43.3%, 27.6%, and 22.1%, respectively, and the contribution rate of precipitation was only 7.0%. There were differences in the contribution rate of nitrate pollution sources in surface water of different river sections. The contribution rate of soil nitrogen in the upstream was significantly higher than that in the downstream, which was 26.5%. The contribution rate of domestic sewage and manure in the downstream was significantly higher than that in the upstream, which was 48.9%. To provide a basis for the analysis of nitrate sources and pollution control in Wuding River and even rivers in arid and semi-arid regions.