Intensive human disturbances have led to complex internal variations in the riverine CO2 system, especially in the urbanized rivers in semi-arid areas. This study examines the factors controlling carbonate system in a river draining an urban ecological restoration area on the Loess Plateau, North China, where riverine dissolved inorganic carbon (DIC) and CO2 partial pressure (pCO2) exhibited pronounced variations influenced by land use changes. The most notable changes included a decrease in DIC (24.0 mg L-1) and pCO2 (280 mu atm) in the urban restored area with damming, driven by strong aquatic photosynthesis, and a sharp increase in DIC (55.7 mg L-1) and pCO2 (6,222 mu atm) in the urban downstream, attributed to sewage input. In contrast, in the upstream of the urban restored area, DIC (33.8 mg L-1) and pCO2 (723 mu atm) were mainly controlled by carbonate weathering. Overall, this river acted as a strong atmospheric CO2 source, with an average CO2 emission of 450.1 mmol m-2 d-1, slightly higher than the global riverine average (359.4 mmol m-2 d-1), and exhibited pronounced spatial variability. A CO2 sink (-11.2 mmol m- 2 d-1) developed in the urban restoration area, whereas sewage input at urban downstream transformed the river into a strong CO2 source (1,668.5 mmol m- 2 d-1), highlighting the impact of anthropogenic perturbations on riverine CO2 source - sink dynamics. Therefore, enhancing urban ecological restoration while effectively reducing CO2 emission from sewage is crucial for achieving CO2 neutrality in urban rivers, particularly in arid and semi-arid climates.