Study On The Methane Emission And Its Impacting Factors In Riparian Restored Wetlands

Riparian wetland ecosystems play an important role in the global cycling of carbon, acting as both sources and sinks for this element. As a greenhouse gas, methane is currently recognized as contributing20-39%of global warming. During the last centuries, riparian wetlands are being created and restored at great frequency around the world to replace or compensate for wetland habitat loss. Created and restored riparian wetlands have been well-studied in water purification and non-point source pollution control, however, few studies on methane flux from created and restored riparian wetlands.The objective of our study is to estimate temporal and spatial patterns of methane emissions from restored riparian wetlands with different vegetation stypes, hydroperiods and exogenous organic materials; to filter out the environmental parameters controlling CH4emissions; to provide scientific basis for design and management of created and restored riparian wetlands. The main results were as follows:(1) P. australi and S.validus which have advanced aerenchyma show lower methane emission rates. Aerenchyma may have inhibitory effect on methane emissions. Vegetations with high density produce more litter and secretion to increase soil organic carbon accumulation, and provide more transmission path for methane, which may promote methane emissions.(2) Methane emissions had a significant relationship with water tables within-20-+20cm, increasing exponentially as water levels rise. Few methane emissions were observed under water levels within-20-0cm (P>0.05), while there were significant high rates of methane under water levels within10-20cm. The results show that drowned condition is a requirement to promote methane emissions.(3) Inundation duration time shows significant influence on methane emissions in restored riparian wetlands. Methane emission rates increased gradually with the longer inundation duration above the water level of0cm. While decreasing trend occurred after a peak appeared at more than the20th day.(4) Methane fulxes in wetlands with additive carbon of130and260g/kg respectively show higher rates than blank control group, and increased significantly with more amount of additive carbon. Addition of organic carbon to soils can promote methane fluxes, and the stimulation effect relies on its quantity.(5) It is advised that the following measures should be taken to reduce methane emissions in created and restored riparian wetlands:choose vegetations with advanced aerenchyma; lower water level; reduce inundation duration time or inundate intermittently and inhibit organic carbon accumulation in soils.