Spatial Heterogeneity And Influencing Factors Of Nitrogen Content Of Wetlands In Northeast Frozen Areas

Swamp wetlands are the most dominant global natural wetland types,which play an important ecological role.Swamp wetland soil nitrogen content affects the global nitrogen cycle,not only maintain soil fertility,but also protect the material and energy balance of the swamp wetland ecosystem.The Northeast frozen area is an important swamp wetland distribution area in the high latitudes.The cold and wet climate is suitable for the storage of soil nitrogen in swamp wetlands.With the gradual warming of the world,the environment of the Northeast frozen areas has changed,which affects soil nitrogen content.By predicting the soil nitrogen content of swamp wetlands in the Northeast frozen area,the spatial distribution pattern of soil nitrogen in swamp wetlands at different soil depths and in different frozen regions are revealed,and the influence of environmental factors on the nitrogen content of swamp wetland soil are analyzed.It can protect natural wetlands,maintain biodiversity and develop and implement effective wetland management practices,which provides basic data and scientific basis for the development and utilization of swamp wetlands and the protection and management of wetland ecosystems.To further explore the spatial heterogeneity of nitrogen content in swamp wetlands in Northeast permafrost region.This study uses geographic information system（GIS）technology and remote sensing（RS）technology,spatial distribution of nitrogen content in swamp wetland is simulated based on random forest algorithm and spatial heterogeneity of soil nitrogen content in vertical and horizontal marsh wetlands gets accounted,the effects of environmental factors on the spatial heterogeneity of soil nitrogen content in swamp wetlands are analyzed.The main conclusions of the study are as follows:（1）The mean soil nitrogen content of swamp wetlands in the Northeast frozen areas is 5.91g/kg,3.70g/kg and 2.58g/kg,respectively.The mean soil nitrogen density is 1.26kg/m~2、1.15kg/m~2and0.83kg/m~2,respectively.The soil nitrogen storage in the Northeast frozen area at depth of 0-100 cm is 1.64×10~8t.From the vertical distribution,soil nitrogen content in top layer>soil nitrogen content in middle layer>soil nitrogen content in bottom layer.Wetland soil nitrogen content decreases with depth,the trend of increase and decrease of soil nitrogen density in swamp wetlands is the same as that of soil nitrogen content.（2）The average nitrogen content of the surface,middle and bottom soils in the continuous permafrost area is 8.39g/kg,5.51g/kg and 3.55g/kg.The average nitrogen content of the surface,middle and bottom soils in the mostly continuous permafrost area is 6.90 g/kg,4.04 g/kg and 2.69g/kg.The average nitrogen contents of the surface,middle and bottom soils in the island-shaped permafrost area is 5.39 g/kg,3.18 g/kg and 2.47 g/kg.The average nitrogen content of the surface,middle and bottom soils in the seasonally frozen soil area is 4.46g/kg,3.16g/kg and 2.12g/kg.From a horizontal distribution,soil nitrogen content of continuous permafrost area>soil nitrogen content of mostly continuous permafrost area>soil nitrogen content of island-shaped permafrost area>soil nitrogen content of seasonally frozen soil area.（3）The nitrogen content of the swamp wetlands in the northeast permafrost region is highly heterogeneous.From the vertical direction,the self-variation coefficients of nitrogen content in the surface,middle and bottom soil layers are 34.01%,34.59%and 37.98%,respectively,which are moderate variation,the coefficient of variation increases gradually with depth.From the horizontal direction,the self-variation coefficients of nitrogen content in continuous permafrost area,mostly continuous permafrost area,island-shaped permafrost area,seasonally frozen soil area are less than10%,which are weak variation.The coefficients of variation of continuous permafrost,large permafrost,island permafrost and seasonal frozen soil are 14.85%,13.02%and 11.41%,respectively,which are moderate variation.The coefficient of variation among other permafrost regions is less than 10%,which are weak variation.（4）Different environmental factors have different effects on soil nitrogen content in wetlands.In the top layer,the relative importance of mean annual temperature,land surface temperature and mean annual humidity to the soil nitrogen content of wetlands is higher.In the middle layer,he relative importance of mean annual temperature,land surface temperature and mean annual humidity to the soil nitrogen content of wetlands is higher.In the bottom layer,the relative importance of mean annual humidity,elevation and mean annual precipitation to the soil nitrogen content of wetlands is higher.The soil nitrogen content is positively and significantly positively correlated with the mean annual humidity and elevation,and significantly negatively correlated with the surface temperature and the mean annual temperature in the three-layer soil.