Greenhouse gas emissions from river riparian wetlands: An example from the Inner Mongolia grassland region in China

Abstract. Riparian wetlands play a significant role in regulating carbon and nitrogen cycles. Gradual riparian wetland drying is increasingly sensitive to global warming and contributes to climate change. 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 were evaluated. Our results demonstrate that riparian wetlands emit larger amounts of CO2 (335–2790 mg m−2 h−1 in August and 72–387 mg m−2 h−1 in October) 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 and 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 the 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 resulted in the loss of the soil carbon pool by approximately 60 %, reducing CO  emissions by approximately 35 %, and shifting the CH4 and N2O emissions from the source to the 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 the GHG emissions.