Sources of dissolved and particulate carbon to the Fraser River system vary significantly in space and time. Tributaries in the northern interior of the basin consistently deliver higher concentrations of dissolved organic carbon (DOC) to the main stem than other tributaries. Based on samples collected near the Fraser River mouth throughout 2013, the radiocarbon age of DOC exported from the Fraser River does not change significantly across seasons despite a spike in DOC concentration during the freshet, suggesting modulation of heterogeneous upstream chemical and isotopic signals during transit through the river basin. Dissolved inorganic carbon (DIC) concentrations are highest in the Rocky Mountain headwater region where carbonate weathering is evident, but also in tributaries with high DOC concentrations, suggesting that DOC respiration may be responsible for a significant portion of DIC in this basin. Using an isotope and major ion mass balance approach to constrain the contributions of carbonate and silicate weathering and DOC respiration, we estimate that up to 33 ± 11% of DIC is derived from DOC respiration in some parts of the Fraser River basin. Overall, these results indicate close coupling between the cycling of DOC and DIC, and that carbon is actively processed and transformed during transport through the river network.

弗雷泽河系统的溶解碳和颗粒碳的来源在空间和时间上差异很大。与其他支流相比，盆地北部内陆的支流向主干输送更高浓度的溶解有机碳 (DOC)。根据 2013 年全年在弗雷泽河河口附近采集的样本，尽管新鲜期间 DOC 浓度出现峰值，但从弗雷泽河输出的 DOC 的放射性碳年龄并未随季节发生显着变化，这表明在运输过程中对上游化学和同位素信号的异质性进行了调制流域。溶解无机碳 (DIC) 浓度在碳酸盐风化明显的落基山源头地区最高，但在 DOC 浓度高的支流中，表明 DOC 呼吸可能是该盆地 DIC 的重要组成部分。使用同位素和主要离子质量平衡方法来限制碳酸盐和硅酸盐风化和 DOC 呼吸的贡献，我们估计高达 33 ± 11% 的 DIC 来自弗雷泽河流域某些地区的 DOC 呼吸。总体而言，这些结果表明 DOC 和 DIC 的循环密切耦合，并且碳在通过河网的运输过程中被积极处理和转化。