Droughts lead to falling river water levels and consequently expose river sediments. It is well known that from these exposed aquatic sediments, CO₂ emits to the atmosphere, but upscaling of CO₂ measurements from discrete point measurements to an entire river system remains challenging. Naturally occurring heterogeneous processes must be accounted for to obtain an overall CO₂ flux and to assess its significance. We contribute to this challenge by incorporating a two stage scaling approach using in situ CO₂ fluxes and remote sensing data. First, by combining optical airborne data with closed chamber measurements at a representative model site during a first scaling stage, we derive land cover type specific CO₂ fluxes and identify distance to the water as the most suitable proxy for further upscaling. Second, we upscale derived spatial relations from the first scaling stage to the entire river system of the Elbe River using a satellite‐based analysis. In this way, we derived area‐weighted CO₂ emissions from exposed river sediments of 56.6 ± 64.8 tC day⁻¹ (corrected distance proxy) and 52.9 ± 44.6 tC day⁻¹ (land cover proxy), respectively, for 1 day during the 2018 extreme drought. Given the intensification of droughts in terms of length and reoccurrence frequency, this result not only highlights the importance of drought‐induced exposition of river sediment as a source of atmospheric CO₂ but also underscores the ability to monitor CO₂ emissions over an entire river system on a regular basis using remote sensing.

中文翻译：

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极端干旱期间易北河裸露的河流沉积物中二氧化碳排放量的空间上升

干旱导致河流水位下降，因此使河流沉积物暴露出来。众所周知，从这些暴露的水生沉积物中，CO ₂排放到大气中，但是将CO ₂测量值从离散点测量扩展到整个河流系统仍然具有挑战性。必须考虑自然发生的异质过程，以获得总的CO ₂通量并评估其重要性。通过结合使用原位CO ₂通量和遥感数据的两阶段缩放方法，我们为这一挑战做出了贡献。首先，在第一个缩放阶段，通过将光学机载数据与代表性模型站点的密闭舱室测量结果相结合，得出特定于土地覆盖类型的CO ₂流量并确定距水的距离，作为进一步放大的最合适的替代方法。其次，我们使用基于卫星的分析方法，对从第一个比例缩放阶段到易北河整个河流系统的空间关系进行了上调。通过这种方式，我们得出了在干旱期间1天，暴露的河流沉积物在16.6天内的面积加权CO ₂排放量分别为56.6±64.8 tC day ^-1（校正距离代理）和52.9±44.6 tC day ^-1（土地覆盖代理）。 2018年极端干旱。鉴于干旱的持续时间和复发频率的加剧，这一结果不仅突出了干旱诱发的河流沉积物作为大气CO ₂来源的重要性，而且强调了监测CO的能力。使用遥感定期在整个河流系统中产生_2种排放。