Deciphering carbon dioxide fluxes and interactions in the Ganga river Basin of South Asia

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.