This study focuses on characterizing the contributions of key terrestrial pathways that deliver dissolved organic carbon (DOC) to streams during hydrological events and on elucidating factors governing variation in water and DOC fluxes from these pathways. We made high-frequency measurements of discharge, specific conductance (SC), and fluorescent dissolved organic matter (FDOM) during 221 events recorded over 2 years within four Vermont (USA) watersheds that range in area from 0.4 to 139 km². Using the SC measurements, together with statistical information on discharge, we separated the event hydrographs into contributions from three terrestrial pathways, which we refer to as riparian quickflow, subsurface quickflow, and slow-flow groundwater. The pathway discharges were used as input to a mixing model that closely approximated sub-hourly streamwater DOC concentrations as measured with the FDOM sensors. Subsurface quickflow, comprised of pre-event water, was the leading contributor to streamwater DOC fluxes, while riparian quickflow, comprised of event water, was the second-leading contributor to streamwater DOC fluxes, despite comprising the smallest proportion of streamflow yield among the three end-member pathways. Fixed-effects regression analysis revealed that the relationship between DOC fluxes from the end-member pathways and event magnitude was consistent across the four watersheds. This analysis also showed that DOC fluxes from the quickflow pathways increased significantly with temperature and varied inversely, but weakly, with catchment antecedent wetness. We believe that our approach, which leverages in-stream sensors that enable high-frequency measurements over extended periods, may be applicable for evaluating controls on DOC export from other watersheds within and beyond our study region.

中文翻译：

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使用基于示踪剂的混合模型在可变流路贡献的背景下评估溪流溶解的有机碳动力学

这项研究的重点是表征在水文事件期间将溶解有机碳 (DOC) 输送到溪流的关键陆地途径的贡献，并阐明控制这些途径中水和 DOC 通量变化的因素。我们对面积从 0.4 到 139 km ^{2 的}四个佛蒙特州（美国）流域内 2 年内记录的 221 次事件中的放电、比电导 (SC) 和荧光溶解有机物 (FDOM) 进行了高频测量. 使用 SC 测量值以及有关排放的统计信息，我们将事件水文过程线分为来自三个陆地路径的贡献，我们将其称为河岸快速流、地下快速流和慢流地下水。路径排放被用作混合模型的输入，该模型非常接近使用 FDOM 传感器测量的亚小时河流水 DOC 浓度。由事件前水组成的地下快速流是河流 DOC 通量的主要贡献者，而由事件水组成的河岸快速流是河流 DOC 通量的第二大贡献者，尽管在三者中占河流产量的比例最小终端成员途径。固定效应回归分析表明，来自端元通路的 DOC 通量与事件强度之间的关系在四个流域中是一致的。该分析还表明，来自快流路径的 DOC 通量随温度显着增加，并与集水区先行湿度呈负向变化，但变化较弱。我们相信，我们的方法利用能够长时间进行高频测量的河内传感器，可能适用于评估对我们研究区域内外其他流域的 DOC 出口控制。