Land use and urbanization indirectly control riverine CH and CO emissions by altering nutrient input.

Urban rivers are recognized as significant sources of methane (CH) and carbon dioxide (CO) emissions. Despite this, the influence of land use and urbanization on carbon emissions across rural-urban rivers at the watershed scale has been insufficiently explored. This study utilized in-situ surveys of the Liao River in northern China to investigate the spatial and temporal variations of CH and CO emissions and their relationship with urbanization and its potential controlling factors. The findings revealed that CH emissions peaked in fall, whereas CO emissions were highest in summer. The average fluxes of CH and CO at the water-gas interface were 1387.22 ± 2474.98 µmol·m·d and 52.78 ± 54.44 mmol·m·d, respectively. Water quality parameters accounted for 80.49 % of the total variation in CH and CO concentrations and fluxes. Structural equation modeling indicated that TN, TP, DTC, and conductivity had direct effects on riverine CH and CO emissions, with standardized direct effects of 0.50 and 0.49, respectively. Nutrient input emerged as the primary driver, increasing CH and CO concentrations and fluxes, particularly in urban-adjacent river sections likely receiving higher nutrient loads. This study underscores that land use and urbanization indirectly influence riverine CH and CO emissions by modifying nutrient inputs. Effective land use management and nutrient input control are recommended strategies to mitigate riverine CH and CO emissions.