Research On Ecological Function Evolution Of Water And Soil Conservation,Wind Prevention And Sand Fixation In Dumeng County

Ecological environment is the basic condition for survival,production and life of humans.With the rapid development of society and leap progress of science,humans have exerted more influences on natural ecological environment to a larger scope.The regional ecological environmental problems caused thereby emerge one after another.In the beginning of 21^st century,excessive pasturing and wasteland reclaiming in Dumeng County caused very serious land desertification and fragility of the ecological environment.Hence,Dumeng County became a national key county for prevention and control of desertification.In order to ensure sustainable social and economic development of the region,the green ecological project of“Northwest Wind Gap”was carried forward all across the county.Through large-area afforestation,the ecological environment in Dumeng County was preliminarily improved.Till 2013,the prairie grazing banning policy was popularized in the whole county.1.03 million mu of grasslands with“deterioration,desertification and salinization”were governed and thus the grassland ecosystem was recovered.The prerequisite for ecological environment management is to find functions of the ecological environment and its evolution trends.At present,service functions of ecological systems are mainly evaluated by model evaluation method and NPP quantitative index evaluation method.Specifically,the model evaluation method requires a lot of parameters and demands a lot of data.The quantitative index method is mainly based on NPP data,only requires a few of parameters and can be cooperated easily.Hence,the paper collected LandSat remote sensing images of three phases in 2000,2009 and 2016 and space data such as 30m DEM and soil diagrams.By the NPP quantitative index method and software such as ArcGIS and ENVI,the paper researches conservation of water and soil,wind prevention and sand fixation and their time-space changing characteristics in Dumeng County during 2000,2009 and 2016,expecting to support decision making for regional ecological environment governance and sustainable social and economic development.?1?Net Primary Productivity NPP denotes the net first productivity subtracted by photosynthetic products consumed by heterotrophic respiration.It could deeply reflect environmental changes.It is a basic computation parameter of ecological functions including conservation of water and soil,and wind prevention and sand fixation.According to relevant materials,the method for estimating local effective solar radiation was found.The gross solar radiation SOL was estimated.Based on relevant local meteorological materials in 2000,2009 and2016,the local temperature stress factors were obtained.On this basis,the Thornthwait method was used to solve moisture stress factors of Dumeng County in these three years.Results were substituted into the CASA model.Through computation,three-phase NPP time-space changing characteristics of Dumeng County were obtained.Results show that:As for NPP of Dumeng County in 2000,the NPP values of vegetation areas in the whole county were low,wherein the NPP mean value was 17.85 in the county;NPP values of over 65%areas of the county were lower than 26;NPP values of only 83.58 km² of lands were over 46.In 2009,the NPP mean value of the whole county increased from 17.85 to 22.15.Area of lands with NPP values ranging between 46and 78 was nearly doubled.In 2016,the NPP mean value of Dumeng County slightly increased to23.6,while the area of lands with NPP value ranging between 26 and 46 increased by about 300km².?2?Function of Conservation of Water and Soil:The paper uses 30 m DEM data to extract a gradient grid map of Dumeng County.Through min-max normalization,results were substituted into NPP index computation.Hence,three-phase time-space changing characteristics of the function of conservation of water and soil in Dumeng County were obtained.Results show:the service ability indexes of conservation of water and soil in Dumeng County were low in 2000,wherein the mean value of service ability indexes of conservation of water and soil was 16.63;most lands in the whole research area had the service ability indexes of conservation of water and soil ranging between 0 and 9,which accounted for 29.01%.In 2009,lands with the ability indexes of conservation of water and soil ranging between 44 and 76 were doubled;the mean value of service ability indexes of conservation of water and soil in the whole research area increased to20.65;the proportion of lands with the service ability indexes of conservation of water and soil ranging between 0 and 9 decreased to 14.75%.In 2016,the average service ability index of conservation of water and soil in the research area slightly increased to 21.99.The change was mainly caused by that the area lands with the service ability indexes of conservation of water and soil ranging between 22 and 33 increased from 586.90 km² in 2000 to 723.48 km² in 2016.?3?Function of wind prevention and sand fixation:With the gradient grid map of Dumeng County,roughness factors of Dumeng County computed by grid computation were substituted into NPP indexes.Through computation,the three-phase time-space changing characteristics of service ability indexes of wind prevention and sand fixation in Dumeng County were obtained through computation.Results show:ability indexes of wind prevention and sand fixation in Dumeng County were relatively low in 2000,wherein ability indexes of nearly 31.22%of lands ranged within 0-0.22;the ability indexes of wind prevention and sand fixation of only 75.77 km² of lands ranged within 1.14-2.05,while their area only accounted for 1.25%of the total area of county.In2009,the land service ability of wind prevention and sand fixation all across Dumeng County was obviously strengthened.The average ability index of wind prevention and sand fixation of the whole county increased from 0.44 in 2000 to 0.54 in 2009.The area of lands with the ability indexes of wind prevention and sand fixation ranging within 0.22-191 increased to different extends at different stages.The area of lands with the ability indexes of wind prevention and sand fixation ranging within 0.51-0.83 increased most quickly,with the increase of 264.93 km² in total.In 2016,the ability of wind prevention and sand fixation in Dumeng County was not enhanced obviously in comparison with 2009,while the average ability index of wind prevention and sand fixation only increased by 0.58.