Sunlight can oxidize dissolved organic carbon (DOC) to dissolved inorganic carbon (DIC) in freshwaters. The importance of complete photooxidation, or photomineralization, as a sink for DOC remains unclear in temperate rivers, as most estimates are restricted to lakes, high latitude rivers, and coastal river plumes. In this study, we construct a model representing over 75,000 river reaches in the Connecticut River Watershed (CRW), USA, to calculate spectrally resolved photomineralization. We test the hypothesis that photomineralization is a negligible DOC sink across all reaches and flow conditions relative to DOC fluxes. Our model quantifies reaction rates and transport drivers within the river reaches for the ranges of flow conditions, incoming solar irradiance, and canopy cover shading observed throughout the year. Our model predicts average daily areal photomineralization rates ranging from 1.16 mg-C m⁻² day⁻¹ in low flow river reaches in the winter, to 18.33 mg-C m⁻² day⁻¹ in high flow river reaches during the summer. Even for high photomineralization fluxes, corresponding photomineralization uptake velocities are typically at least an order of magnitude smaller than those reported for other instream processes. We calculate DOC elimination by photomineralization relative to DOC fluxes through individual stream reaches as well as the entire riverine portion of the CRW. We find that relative photomineralization fluxes are highest in summer drought conditions in low order streams. In median flows and mean light intensities, for an average watershed travel distance, 3%–5% of the DOC fluxes are eliminated, indicating that photomineralization is a minor DOC sink in temperate rivers.

中文翻译：

---

温带河流中溶解有机物的光矿化是否重要？

阳光可以将淡水中溶解的有机碳 (DOC) 氧化为溶解的无机碳 (DIC)。在温带河流中，完全光氧化或光矿化作为 DOC 汇的重要性仍不清楚，因为大多数估计仅限于湖泊、高纬度河流和沿海河流羽流。在这项研究中，我们构建了一个代表美国康涅狄格河流域 (CRW) 超过 75,000 条河段的模型，以计算光谱分辨光矿化。我们测试了这样一个假设，即相对于 DOC 通量，光矿化在所有河段和流动条件下都是一个可以忽略不计的 DOC 汇。我们的模型根据全年观察到的流量条件、入射太阳辐照度和树冠遮蔽，量化了河段内的反应速率和运输驱动因素。^-2 天^-1在冬季低流量河段，达到 18.33 mg-C m ^-2 天^-1在夏季高流量河流到达。即使对于高光矿化通量，相应的光矿化吸收速度通常至少比其他流程中报告的速度小一个数量级。我们通过光矿化计算 DOC 消除，相对于通过单个河流河段以及 CRW 的整个河流部分的 DOC 通量。我们发现，在夏季干旱条件下，低阶河流的相对光矿化通量最高。在中值流量和平均光强度中，对于平均流域移动距离，消除了 3%–5% 的 DOC 通量，表明光矿化是温带河流中的次要 DOC 汇。