The partial pressure of CO₂ in rivers regulates the intensity and direction of carbon dioxide (CO₂) exchange at the water–air interface. Environmental, nutrient factors, and their stoichiometric ratios within the watershed may affect the level of carbon dioxide partial pressure in rivers. However, the relationship between pCO₂ responses to the environment, nutrient factors, and their stoichiometric ratios at a large watershed scale was not well understood. In this study, water samples from 20 locations in the mainstream and 16 tributaries of the middle reaches of the Yellow River were collected to study the spatial characteristics of pCO₂ and its influencing factors. pCO₂ vales showed spatial heterogeneity ranging from 45.57 to 3631.48 μatm, and an average of 1341.87 μatm. Relative to the atmospheric equilibrium value (415 μatm), 90% of the samples were supersaturated. During the study period, higher pCO₂ appeared in the Wanjiazhai Reservoir at the northernmost part of the mainstream in the middle reaches, and in the tributaries of the Fen, Wei, and Beiluo Rivers. Overall, the transition from carbon sink to carbon source was experienced in the middle reaches of the Yellow River from north to south. River pCO₂ exhibited a significant correlation with phosphorus concentrations and their associated stoichiometric ratio, suggesting that microbial metabolism drove CO₂ saturation in rivers. In addition, different land use proportions contributed significantly to changes in river pCO₂.

中文翻译：

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夏季黄河中游CO2分压空间变化特征及影响因素

_{河流中CO 2}的分压调节水-空气界面处二氧化碳(CO _{2 )交换的强度和方向。}流域内的环境、营养因素及其化学计量比可能会影响河流中的二氧化碳分压水平。_{然而，在大流域范围内，pCO 2}对环境、营养因子及其化学计量比的响应之间的关系尚不清楚。本研究采集了黄河中游干流20个地点和16条支流的水样，研究了pCO ₂的空间特征及其影响因素。pCO ₂值表现出空间异质性，范围为45.57至3631.48μatm，平均值为1341.87μatm。相对于大气平衡值（415μatm），90%的样品处于过饱和状态。研究期间，中游干流最北端的万家寨水库以及汾河、渭河、北洛河支流出现了较高的pCO _2值。总体而言，黄河中游自北向南经历了碳汇向碳源的转变。河流pCO ₂与磷浓度及其相关的化学计量比显着相关，表明微生物代谢驱动河流中CO ₂饱和度。此外，不同的土地利用比例对河流pCO ₂的变化贡献显着。