Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China.
School of Scientific Research, China University of Geosciences (Beijing), Beijing 100083, China.
Sci Total Environ. 2021 Mar 15;760:143938. doi: 10.1016/j.scitotenv.2020.143938. Epub 2020 Dec 13.
Environmental issues triggered by increasing nitrate in agricultural river has become global concern. Identifying nitrate sources and transformation are crucial for water sources protection and eliminating nitrate contamination in an agricultural watershed. In this study, chemical and dual isotopic compositions of nitrate were employed to trace the nitrate sources and transformation processes, and proportional contribution of NO source were estimated by SIAR based on Bayesian model. NH concentrations in middle Mun and lower Mun in wet season were significantly higher than NO, suggesting enhanced runoff processes by flood promote agricultural fertilized NH leaching into the river. Higher Cl concentration and NO/Cl indicated that manure and sewage was the dominate nitrate source in the Lam Takhong River and the upper Mun. The overall values of δN-NO and δO-NO ranged from -3.9‰ to +16.6‰ and from -5.2‰ to +40.0‰, respectively. The results of nitrate isotopes indicated that NO mainly originated from soil N nitrogen, chemical fertilizer, and manure and sewage wastes. Spatially, soil N and chemical fertilizer contributed the most nitrate in the mainstream of lower Mun, middle Mun, and the Lam Takhong River; whereas over 60% of nitrate was derived from manure and sewage in the upper Mun. The spatial variation of water discharge and rainfall, together with the nitrate concentration and isotopes inferred that the nitrate sources and transformations in rain-fed river in tropical zone were distinguished from other rivers. High water discharge driven by rainfall events accelerated the nitrate export and the contribution of atmospheric deposition in wet season, and enlarged the contribution of manure and sewage in dry season. This study provided an example for further researches and approaches to assess the effects of tropical climate and agriculture on nitrate accumulation in watershed.
农业河流中硝酸盐增加引发的环境问题已成为全球关注的焦点。确定硝酸盐的来源和转化对于水源保护和消除农业流域的硝酸盐污染至关重要。在本研究中，采用硝酸盐的化学和双重同位素组成来追踪硝酸盐的来源和转化过程，并通过基于贝叶斯模型的 SIAR 估计 NO 源的比例贡献。雨季中 Mun 河中游和下游的 NH 浓度明显高于 NO，表明洪水增强的径流过程促进了农业施肥 NH 向河流中的淋溶。较高的 Cl 浓度和 NO/Cl 表明，在 Lam Takhong 河和 Mun 河上游，粪肥和污水是硝酸盐的主要来源。δN-NO 和 δO-NO 的总体值分别在-3.9‰至+16.6‰和-5.2‰至+40.0‰之间。硝酸盐同位素的结果表明，NO 主要来源于土壤 N 氮、化肥和粪肥和污水废物。从空间上看，在 Mun 河下游、中游和 Lam Takhong 河的主流中，土壤 N 和化肥对硝酸盐的贡献最大；而在上游 Mun，超过 60%的硝酸盐来自粪肥和污水。径流量和降雨量的空间变化以及硝酸盐浓度和同位素推断表明，热带地区雨养河流的硝酸盐来源和转化与其他河流不同。降雨事件驱动的高径流量加速了硝酸盐的输出，并增加了雨季大气沉降的贡献，同时扩大了旱季粪肥和污水的贡献。本研究为进一步研究和评估热带气候和农业对流域硝酸盐积累的影响提供了一个范例。
