Riverine export of carbon (C) is an important part of the global C cycle; however, most riverine C budgets focus on individual forms of C and fail to comprehensively measure both organic and inorganic C species in concert. To address this knowledge gap, we conducted high frequency sampling of multiple C forms, including dissolved organic C (DOC), inorganic carbon (as alkalinity), particulate organic C (POC), coarse particulate organic C (CPOC), and invertebrate biomass C across the main run-off season in a predominantly rain-fed watershed in Southeast Alaska. Streamwater concentrations were used to model daily watershed C export from May through October. Concentration and modeled yield data indicated that DOC was the primary form of riverine C export (8708 kg C/km²), except during low flow periods when alkalinity (3125 kg C/km²) was the dominant form of C export. Relative to DOC and alkalinity, export of particulate organic C (POC: 992 kg C/km²; CPOC: 313 kg C/km²) and invertebrates (40 kg C/km²) was small, but these forms of organic matter could disproportionately impact downstream food webs because of their higher quality, assessed via C to nitrogen ratios. These seasonal and flow driven changes to C form and export likely provide subsidies to downstream and nearshore ecosystems such that predicted shifts in regional hydroclimate could substantially impact C transfer and incorporation into aquatic food webs.

河流碳（C）输出是全球碳循环的重要组成部分；然而，大多数河流碳预算侧重于碳的个体形式，未能同时综合衡量有机和无机碳形态。为了解决这一知识差距，我们对多种碳形式进行了高频采样，包括溶解有机碳（DOC）、无机碳（碱度）、颗粒有机碳（POC）、粗颗粒有机碳（CPOC）和无脊椎动物生物质碳阿拉斯加东南部一个主要靠雨水灌溉的流域的主要径流季节。溪流浓度用于模拟 5 月至 10 月的每日流域碳输出。浓度和模拟产量数据表明，DOC 是河流 C 输出的主要形式（8708 kg C/km ² ），但在低流量期间，碱度（3125 kg C/km ² ）是 C 输出的主要形式。相对于 DOC 和碱度，颗粒有机 C（POC：992 kg C/km ² ；CPOC：313 kg C/km ² ）和无脊椎动物（40 kg C/km ² ）的输出量较小，但这些形式的有机物可以由于其较高的质量（通过碳氮比评估），对下游食物网产生了不成比例的影响。这些季节性和流量驱动的碳形式和出口变化可能会为下游和近岸生态系统提供补贴，因此预测的区域水文气候变化可能会严重影响碳转移和纳入水生食物网。