Drought is becoming increasingly prevalent globally, stimulating research into its effects on river ecosystems. However, our understanding of how droughts affect riverine CO2 dynamics on a daily scale remains limited, particularly considering the likelihood of future drought occurrence. Here, we seize the opportunity to compare daily CO2 cycles between a non-drought summer and an unprecedented drought summer. We developed a new diel CO2 process model to examine how droughts affect diel change in riverine CO2. Our findings reveal that summer drought amplifies diurnal CO2 fluctuations and the pattern holds true across rivers of varying sizes, with increases of 62% for the stream and 24% for the river during drought conditions. We demonstrate that, in comparison to higher radiation and temperature induced by droughts, diel amplitude is more sensitive to low water depths. A decrease in water depth by 43% and 44% corresponded to 13% and 25% less gas exchange in the studied stream and river, respectively, while decreasing ecosystem respiration by 26% and 57%. Our model effectively captures diel CO2 variations driven by drought considering river size, contributing valuable insights into aquatic ecosystem behavior and refining CO2 emission estimates. We emphasize the vulnerability of shallow rivers to drought, and carbon emissions from shallower waters should be explicitly assessed at sub-daily scales to improve the estimates of daily CO2 emissions.

中文翻译：

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夏季干旱增加了德国两条不同大小的河流的 CO2 昼夜波动率


干旱在全球范围内变得越来越普遍，这促使人们研究其对河流生态系统的影响。然而，我们对干旱如何在日常尺度上影响河流 CO2 动态的理解仍然有限，特别是考虑到未来发生干旱的可能性。在这里，我们抓住机会比较了非干旱夏季和前所未有的干旱夏季之间的每日 CO2 循环。我们开发了一个新的 diel CO2 过程模型来研究干旱如何影响河流 CO2 的 diel 变化。我们的研究结果表明，夏季干旱放大了 CO2 的昼夜波动，这种模式适用于不同大小的河流，在干旱条件下，溪流增加了 62%，河流增加了 24%。我们证明，与干旱引起的较高辐射和温度相比，Diel 振幅对低水深更敏感。水深减少 43% 和 44% 分别对应于所研究的溪流和河流中的气体交换减少 13% 和 25%，同时生态系统呼吸减少 26% 和 57%。考虑到河流大小，我们的模型有效地捕获了干旱驱动的 diel CO2 变化，为水生生态系统行为提供了有价值的见解并完善了 CO2 排放估计。我们强调浅水河流对干旱的脆弱性，应在次日尺度上明确评估浅水区的碳排放量，以改进对每日 CO2 排放量的估计。