Greenhouse gases concentrations and emissions from a small subtropical cascaded river-reservoir system

•Partial pressure and fluxes of CO2 and CH4 in a subtropical cascaded damming river were measured.•Cascade damming decreased riverine CO2 emissions, while promoted CH4 fluxes.•Cascade damming altered the spatial patterns of riverine pCO2, pCH4 and “pCO2/pCH4”.•Released waters from reservoirs were C gas emission hotspots in the cascade damming river.•pCO2 and pCH4 and fluxes were affected by autotrophic production and carbon trapping.