The coupled carbon (C) cycle across terrestrial and aquatic environments at the watershed scale has been identified as an important, but poorly constrained component of the global carbon budget. Here, we extended Soil and Water Assessment Tool (SWAT) with coupled riverine particulate organic carbon (POC) and dissolved organic carbon (DOC) modules (referred to as SWAT-C hereafter). Results show that SWAT-C reproduced daily POC and DOC fluxes well in two watersheds in the Northeastern United States. We found that SWAT-C tended to underestimate high flows and peak DOC and POC fluxes. Uncertainty analysis indicated flux uncertainties associated with POC and DOC simulations were larger than those for flow simulation. Sensitive parameters controlling POC and DOC biogeochemical processes were identified along with how these parameters influence mechanisms underlying C cycling. We anticipate that the tool developed and applied here will inform C related ecosystem services in watershed assessment and planning.

分水岭规模上跨陆地和水生环境的耦合碳（C）循环已被确定为全球碳预算的重要组成部分，但受其制约较小。在这里，我们扩展了土壤和水评估工具（SWAT），并结合了河流颗粒有机碳（POC）和溶解性有机碳（DOC）模块（以下称为SWAT-C）。结果表明，SWAT-C在美国东北部的两个流域中很好地复制了每日POC和DOC通量。我们发现，SWAT-C倾向于低估高流量以及DOC和POC峰值流量。不确定性分析表明，与POC和DOC模拟相关的通量不确定性大于流量模拟的不确定性。确定了控制POC和DOC生物地球化学过程的敏感参数，以及这些参数如何影响碳循环的机理。我们预计，此处开发和应用的工具将为流域评估和规划中与C相关的生态系统服务提供信息。