Helmholtz-Centre for Environmental Research - UFZ, Department of River Ecology, Brückstraße 3a, D-39114, Magdeburg, Germany.
Helmholtz-Centre Munich, German Research Center for Environmental Health, Research Unit Analytical Biogeochemistry (BGC), Ingolstädter Landstraße 1, P. O. Box 1129, D-85758 Neuherberg, Germany.
Water Res. 2019 Nov 1;164:114919. doi: 10.1016/j.watres.2019.114919. Epub 2019 Jul 27.
Fluvial networks are globally relevant for the processing of dissolved organic matter (DOM). To investigate the change in molecular DOM diversity along the river course, high-field FTICR mass spectrometry and NMR spectroscopy of riverine DOM as well as bacterial abundance and activity were measured in a third order stream along a land-use gradient from pristine, agricultural to urban landscapes. DOM composition showed a clear evolution along the river course with an initial decrease of average oxidation and unsaturation followed by an increased relative abundance of CHNO and CHOS compounds introduced by agriculture and waste water, respectively. DOM composition was dominated by rather unsaturated CHO compounds (H/C ≤ 1) in headwaters and by more aliphatic molecules at downstream sites. Oxygenated functional groups shifted from aromatic ethers and hydroxyl groups to aliphatic carboxylic acids and aliphatic hydroxyl groups. This massive dislocation of oxygen significantly increased the diversity of atomic environments in branched aliphatic groups from headwater to downstream DOM. Mass spectra of DOM enabled the detection of compositional relationships to bacterial abundance and activity which was positively related to more aliphatic components (H/C > 1) and negatively related to unsaturated components. FTICR mass and NMR spectra corroborated the initial decline in DOM molecular diversity predicted by the River Continuum Concept (RCC) but demonstrated an anthropogenic increase in the molecular diversity of DOM further downstream. While the high DOM molecular diversity in first order headwater streams was the result of small scale ecosystem plurality, agriculture and waste water treatment introduced many components in the lower reaches. These anthropogenic influences together with massive bacterial oxidation of DOM contributed to a growth of molecular diversity of downstream DOM whose composition and structure differed entirely from those found in pristine headwaters.
河流网络在全球范围内对溶解有机质（DOM）的处理具有重要意义。为了研究分子 DOM 多样性沿河道的变化，我们在一条三级溪流中测量了沿土地利用梯度从原始、农业到城市景观的河流水体 DOM 以及细菌丰度和活性的高场傅里叶变换离子回旋共振质谱（FTICR-MS）和 NMR 光谱。DOM 组成沿河道呈现出明显的演化，平均氧化和不饱和度最初降低，随后农业和废水分别引入的 CHNO 和 CHOS 化合物的相对丰度增加。DOM 组成在源头以相当不饱和的 CHO 化合物（H/C ≤ 1）为主，在下游以更多的脂肪族分子为主。含氧官能团从芳基醚和羟基转移到脂肪族羧酸和脂肪族羟基。这种氧的大量位移显著增加了从源头到下游 DOM 中支化脂肪族基团中原子环境的多样性。DOM 的质谱能够检测到与细菌丰度和活性的组成关系，这些关系与更多的脂肪族成分（H/C > 1）呈正相关，与不饱和成分呈负相关。FTICR-MS 和 NMR 光谱证实了河流连续体概念（RCC）预测的 DOM 分子多样性的初始下降，但也证明了下游 DOM 分子多样性的人为增加。虽然一级源头溪流中 DOM 的高分子多样性是小规模生态多样性的结果，但农业和废水处理在下游引入了许多成分。这些人为影响以及 DOM 的大规模细菌氧化共同导致下游 DOM 的分子多样性增加，其组成和结构与原始源头完全不同。
