Spatiotemporal variation in pCO₂, CH₄, N₂O, DOM, and ancillary water quality measured in the Ganges, Mekong, and Yellow River during 2016 to 2019

Despite growing research on greenhouse gas (GHG) emissions from inland waters, few systematic efforts have been made to assess the regional-scale GHG emissions from Asian rivers under increasing anthropogenic stress. We examined factors controlling longitudinal and seasonal variations in the partial pressure of CO₂ (pCO₂), and CH₄ and N₂O concentrations in the Ganges, Mekong, and Yellow River (Huang He) by simultaneously measuring gas concentrations and stable C isotopes, and optical properties of dissolved organic matter (DOM) from 2016 to 2019. The levels of pCO₂ and CH₄ were distinctively higher in polluted tributaries and affected reaches of the Ganges and Mekong than in the Yellow River. The highest levels of N₂O were found in the Ganges, followed by Yellow River and Mekong. Across these basins, dry-season mean concentrations of CO₂, CH₄, and N₂O were 1.6, 2, and 7 times higher than those measured in the monsoon season, respectively. This seasonality was consistent with that of δ¹³C-CO₂, while δ¹³C-CH₄ showed an opposite pattern. The overall results suggest that neglecting localized pollution impacts on GHG emissions from increasingly urbanized river basins can result in inaccurate estimates of global riverine GHG emissions.