Nutrient Management and Water Quality Group, Department of Environmental Science and Technology, University of Maryland, College Park, MD 20742, United States.
Department of Environmental Science, University of Arizona, Tucson, AZ 85721, United States.
Water Res. 2022 Jul 1;219:118533. doi: 10.1016/j.watres.2022.118533. Epub 2022 Apr 30.
Agricultural runoff is a significant contributor to nitrogen (N) and phosphorus (P) pollution in water bodies. Limited information is available about the molecular characteristics of the dissolved organic N (DON) and P (DOP) species in the agricultural runoff and surface waters. We employed Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry (FT-ICR-MS) to investigate the changes in the molecular characteristics of DON and DOP at three watershed positions (upstream water, runoff from agricultural fields, and downstream waters). Across three watershed locations, more-bioavailable compounds (such as amino sugars, carbohydrates, lipids, and proteins) accounted for <5% of DON and 4-31% of DOP molecules, whereas less-bioavailable compounds (such as lignin, tannins, condensed hydrocarbons, and unsaturated hydrocarbons) were >95% of DON and 69-96% of DOP. Of the dissolved organic matter, runoff waters from agricultural fields contained the greatest proportion of DON formulas (20-25%) than upstream (18%) and downstream (13-14%) waters, indicating the presence of a greater diversity of DON species in the runoff. Various nutrient sources present in agricultural fields such as crop residues, soil organic matter, and transformed fertilizers likely contributed to the diverse composition of DON and DOP in the runoff, which were likely altered as the surface water traversed along the flow pathways in the watershed. The presence of more-bioavailable molecules detected in upstream compared to agricultural runoff and downstream waters suggests that photochemical and/or microbial processes likely altered the characteristics of DON and DOP compounds. The findings of this study increase our understanding of DON and DOP compounds lability and transformations in runoff and surface waters , which may be useful in quantifying the contribution of organic N and P sources to water quality impairment in aquatic ecosystems.
农业径流是水体中氮（N）和磷（P）污染的重要贡献者。关于农业径流和地表水溶解有机氮（DON）和磷（DOP）物种的分子特征，信息有限。我们采用傅里叶变换-离子回旋共振-质谱（FT-ICR-MS）研究了三个流域位置（上游水、农业田径流和下游水）中 DON 和 DOP 分子特征的变化。在三个流域位置，更具生物可利用性的化合物（如氨基酸糖、碳水化合物、脂质和蛋白质）占 DON 的<5%和 DOP 分子的 4-31%，而生物利用性较低的化合物（如木质素、单宁、浓缩烃和不饱和烃）占 DON 的>95%和 DOP 的 69-96%。在溶解有机质中，农业田径流水中所含的 DON 公式比例（20-25%）高于上游（18%）和下游（13-14%）水，表明径流中 DON 物种的多样性更大。农业田中的各种养分来源，如作物残体、土壤有机质和转化肥料，可能导致径流中 DON 和 DOP 的组成多样化，这些物质在地表水沿着流域的流动路径迁移时可能会发生变化。与农业径流和下游水相比，上游水中检测到更多具有生物利用性的分子，这表明光化学和/或微生物过程可能改变了 DON 和 DOP 化合物的特性。本研究的结果增加了我们对径流和地表水 DON 和 DOP 化合物的不稳定性和转化的理解，这可能有助于量化有机氮和磷源对水生生态系统水质恶化的贡献。
