Effects Of Agricultural Reclamation On Greenhouse Gases Emission From Farml And Surrounding Wetlands In Sanjiang Plain

Sanjiang Plain is one of the largest and concentrated distributed wetland in China.It is the most important regions of the wetland biodiversity protection in the world.In addition,it is also the main grain production base and reserve base in China.Recently,the typical natural wetland landscape of Sanjiang Plain has been fragmented into a farmland which isolated wetland patches.The land use changing mainly caused by human activities,such as reclamation,grazing and excessive use etc.All of these lead to change the ecological structure and function of wetland in Sanjiang Plain.This study was conducted to analyze the impacts of farming activity to greenhouse gases emissions and environmental factors in different reclamation intensity.The periods were divided into three stages,from 1 to 5 years,6 to 15 years and more than 16 years.The purposes of this study were to understand the role of farmland surrounding wetlands in maintaining regional environment;to analyze the ecological function of carbon sink or carbon source;to provide a scientific basis to protect and restore wetlands,and to promote the sustainable development of the regional ecological environment.The main results of this study were as follows:（1）There were a significant seasonal variation of TER and soil CO₂ fluxes in natural wetland and farmland surrounding wetland,which showed a single peak mode.Reclamation leads to increase TER and soil respiration rate,which increasing with reclamation time.The single peak mode of ecosystem CH₄ emissions flux was showed in the farmland surrounding wetland.However,it’s showed the double peak mode in natural wetland.Reclamation leads to the decreasing of CH₄ emissions sharply.The ecosystem N₂O emissions flux showed the double peak mode both in natural wetland and the farmland surrounding wetland,but the single peak mode in soil N₂O emissions flux.The peak time of N₂O emissions flux in the farmland surrounding wetland is earlier than the natural wetland.Reclamation leads to the increasing of N₂O emissions flux.（2）Reclamation also leads to the increasing of soil temperature,declining soil moisture content and soil pH.The content of SOC,total nitrogen,available nitrogen,nitrate nitrogen in farmland surrounding wetland which showed natural>moderate disturbance>light disturbance>heavy disturbace.The content of ammonium nitrogen which showed moderate disturbance>light disturbance>heavy disturbace>natural,but the differences were not significant.The content of MBC which showed light disturbance>natural>heavy disturbace>moderate disturbance.The content of MBN which showed light disturbance>heavy disturbace>natural>moderate disturbance.Vegetation aboveground biomass in farmland surrounding wetland declined with the disturbance intensity.Vegetation underground biomass declined with the disturbance intensity also,except the moderate disturbance.（3）Three greenhouse gas emissions fluxes are significantly related to soil temperature,CO₂ emission fluxes has the highest correlation with soil temperature of-5cm,CH₄ emission fluxes has the highest correlation with soil temperature of-20cm,N₂O emission fluxes has the highest correlation with soil temperature of-5cm.Changes of environment factors effected the greenhouse gas emissions deeply.The content of MBN has the highest correlation with CO₂emission.The content of SOC,total nitrogen,available nitrogen and MBC/MBN have the highest correlation with N₂O emission.Three greenhouse gas emissions fluxes increased with the increasing of vegetation aboveground biomass.（4）With the increase of disturbance intensity,the amount of net carbon exchange and NEE in ecosystem gradually increased,changed from the negative value to positive value,the farmland surrounding wetlands changed from carbon sink to carbon source,global warming potential gradually transformed into enhanced global warming potential.