Urbanization Drives Carbon Dioxide Supersaturation in South Asian River Networks: Insights from the Krishna River Basin, India

Abstract

Rivers are globally significant sources of atmospheric carbon dioxide (CO₂). However, the processes governing supersaturation of CO₂ in large tropical fluvial networks are poorly understood. In particular, strikingly little is known about the role of land use in shaping CO₂ variability in South Asian river basins, which are undergoing rapid urbanization. Here, we show that the wide variability in the partial pressure of CO₂ (pCO₂: 246.3–21271.2 μatm) in an agriculture-dominated river basin (Krishna River basin, India) is primarily shaped by the extent of urbanization. Specifically, a strong positive correlation between pCO₂ and built-up area (%) was observed when the built-up area exceeded 2%. Furthermore, machine learning analysis showed that pCO₂ variability was predicted by built-up area (%), Strahler order, and altitude, together explaining ∼77% of the spatial variability. Additionally, a strong negative correlation between excess CO₂ and oxygen relative to atmospheric equilibrium indicates that in-stream metabolism, fueled by organic matter inputs from urbanized areas, is the primary cause of CO₂ supersaturation, establishing a mechanistic link between pCO₂ and the built-up area. Given that pCO₂ increases with urbanization, limiting urban inputs is crucial for reducing fluvial CO₂ emissions from South Asian river basins.