Key Laboratory of Marine Environment Science and Ecology, Ministry of Education, Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China.
Key Laboratory of Marine Environment Science and Ecology, Ministry of Education, Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China.
Sci Total Environ. 2020 Jun 25;723:137928. doi: 10.1016/j.scitotenv.2020.137928. Epub 2020 Mar 14.
Nitrogen (N) pollution in groundwater has become a worldwide environmental geological issue due to the excessive N application into the vadose zone and furthered N leaching. Dissolved organic nitrogen (DON) are proposed as an overlooked pathway of N loss from agricultural systems to groundwater recently. Here, we collected soil (0-320 cm) and groundwater samples in a historic agricultural area to characterize the distribution and chemodiversity of DON in the vadose zone-groundwater system, and identified specific linkages between DON traits and the bacterial community. The results showed that DON and NO-N were the main forms of dissolved N in the vadose zone-groundwater system. The deep vadose zone (> 100 cm) was an important storage area for DON (44.9%), having implications for long-term groundwater quality degradation. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that the DON was dominated by condensed aromatics and lignins (57.2%) in the vadose zone, whereas amino sugars, proteins, peptides and lignins (72.5%) were dominant in groundwater. By analyzing shared and ubiquitous DON molecular formulas detected among different layers, it was found that < 2.52% of DONs could be leached from surface soil to groundwater directly, and most DONs went through biological conversion during the whole leaching path. It was identified that bacterial community played an important role in DONs transformation. The most active bacteria in the transformation were Nitrospira, Bacillus, and Sphingomonas and they tended to interact with DON of high N/C and H/C ratios, causing molecules with high unsaturation, high aromaticity and high oxidation to accumulate. The results would be helpful to elucidate DON occurrence in groundwater and track the key processes governing DON transport from the surface soil to groundwater.
地下水的氮（N）污染由于过度的 N 施用于包气带和进一步的 N 淋失，已成为一个全球性的环境地质问题。最近，溶解有机氮（DON）被认为是农业系统中 N 损失到地下水的一个被忽视的途径。在这里，我们在一个历史悠久的农业区收集了土壤（0-320cm）和地下水样本，以表征包气带-地下水系统中 DON 的分布和化学多样性，并确定 DON 特征与细菌群落之间的具体联系。结果表明，DON 和 NO-N 是包气带-地下水系统中溶解 N 的主要形式。深包气带（>100cm）是 DON 的一个重要储存区（44.9%），这对地下水质量的长期退化有影响。傅里叶变换离子回旋共振质谱（FT-ICR MS）表明，DON 在包气带中以缩合芳烃和木质素（57.2%）为主，而在地下水中以氨基糖、蛋白质、肽和木质素（72.5%）为主。通过分析不同层之间检测到的共享和普遍存在的 DON 分子公式，发现<2.52%的 DON 可以直接从表土淋滤到地下水，并且大多数 DON 在整个淋滤过程中都经过了生物转化。研究表明，细菌群落对 DON 的转化起着重要作用。在转化过程中最活跃的细菌是硝化螺旋菌、芽孢杆菌和鞘氨醇单胞菌，它们倾向于与高 N/C 和 H/C 比的 DON 相互作用，导致具有高不饱和、高芳香度和高氧化的分子积累。研究结果将有助于阐明地下水 DON 的发生，并追踪从表土到地下水的 DON 迁移的关键过程。
