Emission dynamics of greenhouse gases regulated by fluctuation of water level in river-connected wetland.

The application of reservoirs in the upper reaches of rivers will change the hydrological rhythm of river-connected wetlands in the lower reaches, causing changes in the distribution of wetland vegetation. The differences of carbon and nitrogen sequestration and emission potential in different vegetations may lead to the dynamics of greenhouse gas emissions from wetlands during hydrological periods. For a wetland connected to the Yangzi River, China, the dynamic changes of vegetation and water areas were identified by remote sensing, and the water level, the emission fluxes of greenhouse gases and the functional bacteria of carbon and nitrogen in soil were measured in-situ. Compared with drought period, the area of phragmites zone in flooding period increased by 28.2%, while the areas of carex and phalaris zones decreased by 42.9%. The carbon and nitrogen accumulation in the soil of phragmites zone is the highest, while the cumulative amount of phalaris is the lowest. The emission fluxes of CH4 and N2O in mud/water and various vegetations were positively correlated with water level and reached the maximum during flooding period. Although the global warming potential of mud/water was highest than that of vegetations, carex zone had the highest warming potential among vegetation zones. CH4 contributes 8-37 times as much as N2O to global warming potential in the wetland. The increase of flooding time promoted the emissions of CH4 and N2O in the wetland. The anaerobic condition caused by flooding stimulated the activities of denitrifying and methanogenic bacteria, thus increasing the emission of greenhouse gases. The sequestrations and emissions of carbon and nitrogen regulated by a reservoir in the upstream suggest that the operation of water conservancies should be considered to alleviate the greenhouse gas emission from river-connected wetland.