Abstract：
Anthropogenic influences significantly modify the hydrochemical properties and material flow in riverine ecosystems across Asia, potentially accounting for 40-50% of global emissions. Despite the pervasive impact on Asian rivers, there is a paucity of studies investigating their correlation with carbon dioxide (CO2) emissions. In this study, we computed the partial pressure of CO2 (pCO2) using the carbonate equilibria-based model (pCO2SYS) and examined its correlation with hydrochemical parameters from historical records at 91 stations spanning 2013-2021 in the Ganga River. The investigation unveiled substantial spatial heterogeneity in the pCO2 across the Ganga River. The pCO2 concentration varied from 1321.76 μatm, 1130.98 μatm, and 1174.33 μatm in the upper, middle, and lower stretch, respectively, with a mean of 1185.29 μatm. Interestingly, the upper stretch exhibited elevated mean pCO2 and FCO2 levels (fugacity of CO2: 3.63 gm2d-1) compared to the middle and lower stretch, underscoring the intricate interplay between hydrochemistry and CO2 dynamics. In the context of pCO2 fluctuations, nitrate concentrations in the upper segment and levels of biological oxygen demand (BOD) and dissolved oxygen (DO) in the middle and lower segments are emerging as crucial explanatory factors. Furthermore, regression tree (RT) and importance analyses pinpointed biochemical oxygen demand (BOD) as the paramount factor influencing pCO2 variations across the Ganga River (n = 91). A robust negative correlation between BOD and FCO2 was also observed. The distinct longitudinal patterns of both parameters may induce a negative correlation between BOD and pCO2. Therefore, comprehensive studies are necessitated to decipher the underlying mechanisms governing this relationship. The present insights are instrumental in comprehending the potential of CO2 emissions in the Ganga River and facilitating riverine restoration and management. Our findings underscore the significance of incorporating South Asian rivers in the evaluation of the global carbon budget.
摘要：
人为影响显着改变了整个亚洲河流生态系统的水化学特性和物质流，可能占全球排放量的40-50%。尽管亚洲河流受到普遍影响，缺乏调查它们与二氧化碳(CO2)排放的相关性的研究。在这项研究中,我们使用基于碳酸盐平衡的模型（pCO2SYS）计算了CO2分压（pCO2），并根据2013-2021年恒河91个站点的历史记录检查了其与水化学参数的相关性。调查揭示了整个恒河中pCO2的巨大空间异质性。pCO2浓度从1321.76μatm变化，1130.98μatm,上部为1174.33μatm，中间,和较低的拉伸，分别,平均值为1185.29μatm。有趣的是,与中段和下段相比，上段拉伸表现出升高的平均pCO2和FCO2水平（CO2逸度：3.63gm2d-1），强调水化学和CO2动力学之间复杂的相互作用。在二氧化碳波动的背景下，上段的硝酸盐浓度以及中段和下段的生物需氧量（BOD）和溶解氧（DO）水平正在成为关键的解释因素。此外，回归树（RT）和重要性分析指出生化需氧量（BOD）是影响恒河pCO2变化的最重要因素（n=91）。还观察到BOD和FCO2之间存在强烈的负相关。这两个参数的不同纵向模式可能会导致BOD和pCO2之间的负相关。因此,有必要进行全面的研究，以破译管理这种关系的潜在机制。目前的见解有助于理解恒河中二氧化碳排放的潜力，并促进河流的恢复和管理。我们的发现强调了将南亚河流纳入全球碳预算评估的重要性。
