Carbon dioxide (CO₂) emission from fluvial systems represents a substantial flux in the global carbon cycle. However, variation in fluvial CO₂ fluxes at the air–water interface as well as its drivers are poorly understood, especially in non-forested headwaters. Here, we measured CO₂ concentration and fluxes in 14 lowland open-canopy streams (Pampean region, Argentina) that cover a wide range of land use and water quality. We also analyzed drivers of CO₂ concentration and fluxes, including factors related to metabolism, gas solubility, alkalinity, and gas transfer. Metabolic rates varied considerably among the study sites, but most streams (i.e., 8 out of the 11 where we were able to estimate ecosystem metabolism) were net heterotrophic. Metabolic differences among sites were mostly driven by the aromatic carbon content and the percent of the stream reach covered by primary producers. All streams, even those that were not net heterotrophic were CO₂ supersaturated. Alkalinity combined with in-stream primary production explained 52.3% of the variance in the partial pressure of CO₂ (pCO₂), but our observations suggest that pCO₂ might be controlled by external groundwater inputs of dissolved inorganic carbon rather than by internal metabolism. All streams were net emitters of CO₂ to the atmosphere. Significantly more variance in CO₂ flux was explained by gas transfer velocity (63.7%) than by pCO₂ (21.9%). We also observed high spatial heterogeneity in CO₂ fluxes within each stream, which was associated with flow variation and the presence of different macrophyte and algae patches. Overall, our results indicate that CO₂ emission in these extremely low turbulence streams is controlled by a combination of external and internal biogeochemical processes and limited atmospheric exchange.

河流系统排放的二氧化碳 (CO ₂ ) 代表了全球碳循环中的大量通量。然而，人们对空气-水界面处河流 CO ₂通量的变化及其驱动因素知之甚少，尤其是在非森林源头。在这里，我们测量了 14 条低地开放树冠溪流（阿根廷潘佩恩地区）中的 CO ₂浓度和通量，这些溪流涵盖了广泛的土地利用和水质。我们还分析了 CO _{2的驱动因素}浓度和通量，包括与代谢、气体溶解度、碱度和气体转移有关的因素。研究地点之间的代谢率差异很大，但大多数溪流（即，我们能够估计生态系统代谢的 11 个溪流中的 8 个）是净异养的。地点之间的代谢差异主要由芳香碳含量和初级生产者覆盖的河流范围百分比驱动。所有的流，甚至那些不是净异养的流都是CO ₂过饱和的。碱度与流内初级生产相结合，解释了 CO ₂ ( p CO ₂ ) 分压变化的 52.3%，但我们的观察表明p CO ₂可能由溶解的无机碳的外部地下水输入控制，而不是由内部代谢控制。所有的流都是CO ₂到大气的净排放物。气体传输速度 (63.7%) 比p CO ₂ (21.9%)解释了CO _{2通量的显着变化。}我们还观察到每条流中 CO ₂通量的高度空间异质性，这与流量变化以及不同大型植物和藻类斑块的存在有关。总体而言，我们的结果表明，这些极低湍流流中的CO _{2排放受外部和内部生物地球化学过程以及有限的大气交换的组合控制。}