Effects Of Restoration And Utilization Of Saline-alkali Wetlands In Western Songnen Plain On CO₂ And CH₄ Emission Fluxes

The western part of the Songnen Plain is one of the three major concentrated distribution areas of soda saline-alkali soil in the world,located in the semi-arid area of agriculture and animal husbandry and ecological fragile zone,which has an important strategic position in China’s ecological environmental protection and is currently the key governance area of national concern.As an important ecosystem type,CO₂and CH₄emissions of Soda saline wetland in the western Songnen Plain not only have an important impact on the atmospheric environment,but also affect the stability and health of the wetland ecosystem.In order to better understand the flux characteristics of CO₂and CH₄in the soda saline-alkali wetland system and their key influencing factors,this study took alkali spot,degraded reed wetland,reed wetland reed restoration and rational use of wetland（reed restoration+fish and crab culture,rice field,rice field+crab culture）in the western part of the Songnen Plain as the research object,based on field in situ observation experiments,the characteristics of CO₂and CH₄fluxes and the seasonal changes of CO₂and CH₄dissolution concentrations in water under the restoration and rational utilization mode of soda saline-alkali wetland were discussed.The"source/sink"functions of CO₂and CH₄in soda saline wetlands were evaluated,and key impact factors were analyzed.The main conclusions are as follows:（1）The CO₂and CH₄emission fluxes of ecosystems under the restoration and rational utilization of saline-alkali wetlands have obvious characteristics of temporal and spatial changes.In terms of CH₄flux,in terms of time,the CH₄flux in alkali spot land was more consistent in summer and autumn(0.14 mg·m^-2·h^-1),and the CH₄flux of degraded reed wetland,reed restoration wetland and rice field+crab culture was shown as summer(0.002,0.70 and 0.28 mg·m^-2·h^-1)>autumn(0.0002,0.27 and-0.0006 mg·m^-2·h^-1),while the CH₄flux of reed wetland+fish and crab culture and rice fields were shown in autumn(0.22 and0.24 mg·m^-2·h^-1)>summer(-0.03 and 0.06 mg·m^-2·h^-1).Spatially,the CH₄emission fluxes were generally manifested as rice field+crab culture(2.67 mg·m^-2·h^-1)>alkaline spot land(2.31 mg·m^-2·h^-1)>restoration of reed wetland+fish and crab culture(0.97 mg·m^-2·h^-1)>degraded reed wetland(0.63 mg·m^-2·h^-1)>natural restoration of reed wetland(-0.21mg·m^-2·h^-1)>rice field(-0.95 mg·m^-2·h^-1).In terms of CO₂fluxes,in terms of time,CH₄fluxes of alkaline spotted land,degraded reed wetlands and restored reed wetlands were shown as summer(2.43 0.70 and 1.75mg·m^-2·h^-1)>autumn(-0.12,-0.08 and-1.96 mg·m^-2·h^-1),while the CH₄fluxes of reed wetlands+fish and crab culture,paddy fields and paddy fields+crab culture were shown as autumn(0.87,0.12 and 3.05 mg·m^-2·h^-1)>summer(0.10,-1.07 and-0.38 mg·m^-2·h^-1);Spatially,natural restoration of reed wetlands(0.98 mg·m^-2·h^-1)>rice fields(0.30mg·m^-2·h^-1)>rice paddy+crab culture(0.28 mg·m^-2·h^-1)>restoration of reed wetlands+fish and crab culture(0.19 mg·m^-2·h^-1)>alkali spotted land(0.14 mg·m^-2·h^-1)>degraded reed wetlands(0.002 mg·m^-2·h^-1).（2）The overall concentration of CH₄in water dissolved in different saline-alkali wetlands was as rice field+crab culture(149.80μmol·L^-1)>natural restoration of reed wetlands(41.11μmol·L^-1)>rice fields(39.90μmol·L^-1)>restoration of reed wetland+fish and crab culture 20 cm(16.52μmol·L^-1)>restoration of reed wetlands+fish and crab culture 10 cm(6.65μmol·L^-1);the overall concentration of dissolved CO₂in water in different saline-alkali wetlands was as follows:rice field+crab culture(8363.29μmol·L^-1)>rice fields(7978.75μmol·L^-1)>salt restoration reed wetland+fish and crab culture 20 cm(7159.24μmol·L^-1)>natural restoration of reed wetlands(6680.94μmol·L^-1)>restoration of reed wetland+fish and crab culture 10 cm(4441.02μmol·L^-1).（3）In the restoration of saline-alkali wetlands and under different utilization modes,temperature was the main factor affecting the seasonal variation of CO₂emission flux in different wetlands,but the variation characteristics of temperature and CH₄flux lacked consistency,indicating that other factors other than temperature had a large influence on CH₄flux.The influence of water on CO₂flux in saline-alkali wetlands was greater than that on CH₄flux.Salinity is not an important factor affecting the difference of CO₂and CH₄emission fluxes in different saline-alkali wetlands.Temperature was negatively correlated with the dissolution concentration of CH₄and CO₂in water（p<0.01）.p H was significantly negatively correlated with the concentration of CO₂dissolution in water（p<0.01）.DOC was positively correlated with the concentration of CH₄dissolution in water（p<0.05）.