National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Institute of Lake Ecological Environment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; State Environmental Protection Key Laboratory for Lake Pollution Control, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; College of Water Conservancy, Shenyang Agricultural University, Shenyang 110866, China.
National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Institute of Lake Ecological Environment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; State Environmental Protection Key Laboratory for Lake Pollution Control, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Sci Total Environ. 2022 Sep 1;837:155674. doi: 10.1016/j.scitotenv.2022.155674. Epub 2022 May 17.
The control of agricultural nitrogen through inflow rivers is crucial for lake aquatic environment conservation, while nitrate is the main form of non-point source pollution of agricultural nitrogen in watersheds. Therefore, understanding the nitrate sources and transformation in the intensive-agricultural region was particularly concerned. Nitrate sources and transformation varied largely during some crucial periods or events. However, low-resolution sampling campaigns increased some uncertainties due to without considering the effect of key driving factors for identifying nitrate transformations and sources. In our study, high-frequency sampling and analysis of nitrogen and oxygen isotope, hydrochemical and Bayesian model was conducted at the Dagang River to capture nitrate sources and transformations and identify its response to rainfall-runoff process at the event scale. In addition, the N cycle process was refined by comparing the variation and relationship of water quality factors and isotopes before, during, and after rainfall. We found that nitrate and major ions derived from similar agricultural activities caused by anthropogenic factors, such as domestic sewage from rural residents and livestock waste, through field survey and principal component analysis. The δN-NO and δO-NO in Dagang River ranged from +0.05‰ to +9.94‰ and + 1.49‰ to +11.64‰, respectively. The spatio-temporal variations of nitrate isotopes and hydrochemical compositions of river water suggested that nitrification was the dominant nitrate transformation process although the mixing effect occurred in some periods, especially during, and after the rainfall. The relationship between NO/Cl and Cl ratios suggested the occurrence of denitrification in downstream of the river basin after the rainfall. The results of Bayesian model showed that livestock manure and groundwater contributed to the most (66.4 ± 31.9%) nitrate, which indicated the necessity to establish its regulatory policy to avoid the overuse of livestock manure and groundwater in Dagang River. This study benefit for developing concrete and legible management and conservation strategies for decreasing the effect of anthropogenic nitrogen loading on lake eutrophication.
农业氮素通过入流河流的控制对湖泊水环境保护至关重要，而硝酸盐是流域农业氮素非点源污染的主要形式。因此，特别关注集约化农业区的硝酸盐来源和转化。硝酸盐的来源和转化在某些关键时期或事件中差异很大。然而，由于没有考虑到确定硝酸盐转化和来源的关键驱动因素的影响，低分辨率的采样活动增加了一些不确定性。在我们的研究中，在大港河进行了高频采样和氮氧同位素、水化学和贝叶斯模型分析，以捕捉硝酸盐的来源和转化，并在事件尺度上识别其对降雨径流过程的响应。此外，通过比较降雨前后水质因素和同位素的变化和关系，细化了氮循环过程。我们发现，硝酸盐和主要离子来源于类似的农业活动，这些活动是由人为因素引起的，例如农村居民的生活污水和牲畜废物。通过野外调查和主成分分析发现，大港河的 δN-NO 和 δO-NO 分别在+0.05‰到+9.94‰和+1.49‰到+11.64‰之间变化。硝酸盐同位素和河水水化学组成的时空变化表明，尽管在某些时期，特别是在降雨期间和之后，混合作用发生，硝化作用是硝酸盐转化的主要过程。NO/Cl 和 Cl 比值之间的关系表明，降雨后流域下游发生了反硝化作用。贝叶斯模型的结果表明，牲畜粪便和地下水对硝酸盐的贡献最大（66.4±31.9%），这表明有必要制定其监管政策，以避免在大港河过度使用牲畜粪便和地下水。本研究有助于制定具体和明确的管理和保护策略，以减少人为氮负荷对湖泊富营养化的影响。
