黄土高塬沟壑区典型城郊流域地表水硝酸盐来源示踪

随着工农业的快速发展，地表水硝酸盐污染已成为黄土高原地区严重的环境问题之一.以黄土高塬沟壑区典型城郊流域砚瓦川为研究区，采用水化学分析方法和氮氧双稳定同位素技术，并结合SIAR模型，定量识别旱季和雨季研究区地表水硝酸盐不同污染源的贡献率，阐明不同污染源季节性差异的主要原因.结果表明，流域地表水无机氮主要以NO₃^--N和NO₂^--N形态存在，NO₃^--N和NO₂^--N雨季浓度平均值均高于旱季，而NH₄⁺-N则呈现相反特征；流域内地表水硝酸盐的转化过程主要以硝化作用为主，雨季其主要来源是粪肥污水，而旱季主要为粪肥污水和土壤氮淋溶，铵肥次之；不同污染源对流域地表水硝酸盐的贡献比例具有显著的季节性差异，旱季与雨季城镇污水排放的贡献比例均为最高，分别为31.40%和65.66%，且雨季污水排放对NO₃^-的影响远高于旱季，夏季居民用水增加导致大量污水排放至流域内是引起这一现象的主要原因.

Identification of Nitrate Source of Surface Water in a Typical Peri-urban Watershed in the Tableland of the Loess Plateau, China

With the rapid development of industry and agriculture, nitrate pollution in surface water has become one of the serious environmental problems in the Loess Plateau region. In this study, Yanwachuan watershed, a typical suburban watershed in the gully region of a loess plateau, was selected as the research area. Using hydrochemical data and nitrogen and oxygen bistable isotopes, combined with the SIAR model, the contribution rates of different pollution sources of nitrate in surface water in the dry season and wet season were quantitatively identified, and the main reasons for seasonal differences in different pollution sources were clarified. The results showed that inorganic nitrogen mainly existed in the form of NO₃^--N and NO₂^--N, and the average concentration of NO₃^--N and NO₂^--N in the wet season was higher than that in the dry season, whereas NH₄⁺-N showed the opposite characteristics. Nitrification was the main process of nitrate transformation in the surface water of the basin. In the wet season, the main sources of nitrate were manure and sewage, whereas in the dry season, manure, sewage, and soil N leaching were the dominant sources, followed by ammonium fertilizer. The contribution proportion of different pollution sources to nitrate in surface water of the watershed showed significant seasonal differences. The sewage had the highest contribution, accounting for 31.40% and 65.66% in the dry season and rainy season, respectively, and the contribution of sewage to NO₃^- in the wet season was much higher than that in the dry season. The increase in residential water consumption in summer led to a large amount of sewage discharge into the watershed.