Despite the widely recognized importance of aquatic processes for bridging gaps in the global carbon cycle, there is still a lack of understanding of the role of riverbed processes for carbon flows and stocks in aquatic environments. Here, we added a sediment diagenesis and sediment carbon (C) resuspension module into the SWAT-C model and tested it for simulating both particulate organic C (POC) and dissolved organic C (DOC) fluxes using 4 years of monthly observations (2014–2017) in the Tuckahoe watershed (TW) in the U.S. Mid-Atlantic region. Sensitivity analyses show that parameters that regulate POC deposition in river networks are more sensitive than those that determine C resuspension from sediments. Further analyses indicate that allochthonous contributions to POC and DOC are about 36.6 and 46 kgC ha−1 year−1, respectively, while autochthonous contributions are less than 0.72 kgC ha−1 year−1 for both POC and DOC (less than 2% of allochthonous sources). The net deposition of POC on the riverbed (i.e., 11.4 kgC ha−1 year−1) retained ca. 31% of terrestrial inputs of POC. In addition, average annual buried C was 0.34 kgC ha−1 year−1, accounting for only 1% of terrestrial POC inputs or 3% of net POC deposition. The results indicate that about 79% of deposited organic C was converted to inorganic C (CH4 and CO2) in the sediment and eventually released into the overlying water column. This study serves as an exploratory study on estimation of C fluxes from terrestrial to aquatic environments at the watershed scale. We demonstrated capabilities of the SWAT-C model to simulate C cycling from uplands to riverine ecosystems and estimated C sinks and sources in aquatic environments. Overall, the results highlight the importance of including carbon cycle dynamics within the riverbed in order to accurately estimate aquatic carbon fluxes and stocks. The new capabilities of SWAT-C are expected to serve as a useful tool to account for those processes in watershed C balance assessment.

中文翻译：

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对河床上的沉积物成岩过程进行建模，以更好地量化中大西洋地区小流域的水生碳通量和储量。

尽管人们普遍认识到水生过程对于弥合全球碳循环中的差距的重要性，但仍然缺乏对河床过程对水生环境中碳流量和库存量的作用的了解。在这里，我们在SWAT-C模型中添加了沉积物成岩作用和沉积物碳（C）重悬浮模块，并使用4年的每月观测值对其进行了模拟颗粒有机C（POC）和溶解有机C（DOC）通量的测试（2014年– 2017年）在美国中大西洋地区的塔克霍（Tuckahoe）分水岭（TW）。敏感性分析表明，调节河流网络中POC沉积的参数比确定沉积物中C重悬的参数更为敏感。进一步的分析表明，POC和DOC的异源贡献分别约为ha-1 year-1和36.6 kgC ha-1，而POC和DOC的土生土贡献均低于0.72 kgC ha-1年-1（少于异源来源的2％）。POC在河床上的净沉积量（即11.4 kgC ha-1 year-1）保留了大约。POC地面输入的31％。此外，年平均埋藏碳为0.34 kgC ha-1 year-1，仅占地面POC输入的1％或净POC沉积的3％。结果表明，沉积物中约79％的有机碳转化为无机碳（CH4和CO2），并最终释放到上覆水柱中。这项研究是在流域尺度上估算从陆地到水生环境的碳通量的探索性研究。我们展示了SWAT-C模型的功能，可以模拟从高地到河流生态系统的碳循环，以及在水生环境中估算的碳汇和碳源。总的来说，这些结果突出了在河床中包括碳循环动态的重要性，以便准确估算水生碳通量和储量。预计SWAT-C的新功能将成为在流域C平衡评估中考虑这些流程的有用工具。