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Gradual riparian wetland drying is increasingly sensitive to global warming and contributes to climate change. Riparian wetlands play a significant role in regulating carbon and nitrogen cycles. In this study, we analyzed the emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from riparian wetlands in the Xilin River basin to understand the role of these ecosystems in greenhouse gas (GHG) emissions. Moreover, the impact of the catchment hydrology and soil property variations on GHG emissions over time and space was evaluated. Our results demonstrate that riparian wetlands emit larger amounts of CO2 (335–2790 mgm-2h-1 in the wet season and 72–387 mgm-2h-1 in the dry season) than CH4 and N2O to the atmosphere due to high plant and soil respiration. The results also reveal clear seasonal variations and spatial patterns along the transects in the longitudinal direction. N2O emissions showed a spatiotemporal pattern similar to that of CO2 emissions. Near-stream sites were the only sources of CH4 emissions, while the other sites served as sinks for these emissions. Soil moisture content and soil temperature were the essential factors controlling GHG emissions, and abundant aboveground biomass promoted the CO2 , CH4 , and N2O emissions. Moreover, compared to different types of grasslands, riparian wetlands were the potential hotspots of GHG emissions in the Inner Mongolian region. Degradation of downstream wetlands has reduced the soil carbon pool by approximately 60 %, decreased CO2 emissions by approximately 35 %, and converted the wetland from a CH4 and N2O source to a sink. Our study showed that anthropogenic activities have extensively changed the hydrological characteristics of the riparian wetlands and might accelerate carbon loss, which could further affect GHG emissions. [ABSTRACT FROM AUTHOR]

• Reservoir drawdown zone was a hotspot of GHG emissions. • CH 4 fluxes went to zero due to dam decommissioning. • Soil volumetric moisture content and soil bulk density were the major factors contributing to GHG emissions. • The desiccation of reservoir sediments can result in loss of C from reservoir. Reservoirs are a category of artificial ecosystem that play a key role in the global carbon cycle. However, there has been limited research on the impacts of dam decommissioning (DD) on greenhouse gas (GHG) emissions over a reservoir life cycle. This study analyzed the effects of DD on CO 2 and CH 4 fluxes emitted from impounded water zone (area of inundated sediments), the drawdown zone (area of sediment exposure during DD), and the margin zone (area of long-term sediment exposure) before, during, and after the drawdown of a retired reservoir in Inner Mongolia. The margin zone encompassed ± 90 % of the total reservoir area over the study period, whereas the impounded water and drawdown zones accounted for the remainder. CO 2 emissions decreased during DD process in the margin zone (325.24 ± 313.80–128.81 ± 128.78 mg m−2h−1) and impounded water zones (286.00 ± 242.00–0.00 ± 0.00 mg m−2h−1), whereas they increased in the drawdown zone (0.00 ± 0.00–239.52 ± 104.35 mg m−2h−1). CH 4 emissions gradually declined over time after DD in the impounded water zone and this zone was the main contributor of CH 4 fluxes before DD (57.36 ± 12.77 mg m−2h−1), and finally emissions went to zero. Exposure of sediments gradually resulted in a significant increase in CO 2 emissions. The major factors affecting GHG emissions were soil volumetric moisture content (SMC) and soil bulk density (ρb). The CO 2 -eq of the reservoir ecosystem decreased after DD. This happened despite CO 2 emissions increasing because CH 4 , which has a higher global warming potential, decreased following DD. The consideration of DD in the carbon footprint of reservoirs for understanding of reservoir carbon dynamics and the global carbon balance requires further study of the long-term effects of DD on carbon fluxes. [ABSTRACT FROM AUTHOR]