Streams and rivers are important components of the carbon cycle as they transport and transform dissolved organic matter (DOM). Using high‐resolution Fourier‐transform ion cyclotron resonance mass spectrometry, we studied the spatial distribution of DOM at the molecular level at more than 100 sites across a stream network during summer and winter baseflow. We developed a model approximating the time DOM spent in the fluvial network, a key constraint on the biogeochemical processing of DOM. Discharge‐weighted travel time explained the compositional changes of DOM, which differed markedly in summer and winter. We attribute these seasonal differences to variation in source material, putatively reflecting the dynamics of freshly produced DOM in summer and DOM with an imprint of leaf litter in winter. Hydrological mixing was an important driver of the spatial dynamics of DOM. From the convergence rate of DOM compound intensities to the network‐wide average, we inferred the spatial distribution of sources within the catchment. Finally, we estimated network‐wide apparent mass transfer coefficients (v_{f app}) of individual DOM compounds, which describe the vertical velocity at which DOM compounds are removed by biotic and abiotic processes. We identified the oxidative state of carbon as an important factor explaining v_{f app}, which we consequently attribute to biological uptake of thermodynamically favorable DOM compounds. This work contributes to our understanding of the spatial processes, temporal constraints, and chemical properties of DOM that regulate the transformation and diagenesis of DOM at the fluvial network scale.

中文翻译：

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传播时间和源变化解释了高山流网中溶解有机物的分子转化

溪流是碳循环的重要组成部分，因为它们运输和转化溶解有机物（DOM）。使用高分辨率傅里叶变换离子回旋共振质谱，我们研究了夏季和冬季基流中整个网络中100多个站点在分子水平上DOM的空间分布。我们开发了一个模型，估算了DOM在河流网络中所花费的时间，这是DOM生物地球化学处理的关键约束。出院加权旅行时间解释了DOM的组成变化，夏季和冬季明显不同。我们将这些季节差异归因于源物质的变化，推测是反映了夏季新鲜生产的DOM的动态以及冬季有叶子凋落物的DOM的动态。水文混合是DOM空间动力学的重要驱动力。从DOM复合强度的收敛速度到全网平均水平，我们推断出流域内源的空间分布。最后，我们估算了整个网络的表观传质系数（v _{f app}）中的各个DOM化合物，它们描述了通过生物和非生物过程去除DOM化合物的垂直速度。我们确定碳的氧化状态是解释v _{f app}的重要因素，因此我们将其归因于对热力学有利的DOM化合物的生物摄取。这项工作有助于我们了解DOM的空间过程，时间限制和化学性质，这些作用在河流网络规模上调控DOM的转化和成岩作用。