| In recent decades,due to the influence of climate factors and human activities,the vegetation ecosystem in northern China has been degraded for a time,such as the decline of productivity,the decrease of vegetation coverage and the increase of desertified land.Not only the supply and service capacity has been reduced,but also the regulation and service capacity of soil conservation,wind prevention and sand fixation,and water conservation has been reduced,Dust weather occurs frequently,and 12 dust storms spread to Beijing and Tianjin in a month from March to April in 2000,which has a great impact on the local and surrounding economic and social development and the health of residents.Therefore,since 2001,China began to implement the Beijing Tianjin sandstorm source control project.Its main purpose is to restore the damaged and degraded ecosystem,slow down and reduce the impact of the deterioration of the ecological environment on Beijing Tianjin and its surrounding areas through artificial afforestation and grass planting,returning farmland to forest and grass,small watershed management and other measures.After nearly 20 years of treatment,the Beijing Tianjin sandstorm source treatment project has achieved certain results.In order to scientifically and accurately evaluate the ecological effect of the project area,this paper selected 2001-2015 as the research period,and revealed the objective situation of ecosystem services in the project area through quantitative calculation of ecosystem services,driving force research and spatial flow analysis of wind prevention and sand fixation services.The main contents and conclusions are as follows:(1)Assessment results and spatial and temporal distribution characteristics of ecosystem services in the project areaBased on meteorological data,remote sensing data,land use data,soil attributes and other data,combined with multiple models,this paper evaluated the ecosystem services of the project area from 2001to 2015.The results of quantitative evaluation showed that the annual average total NPP was 1.19×10~8 t;The annual average value of vegetation coverage is 59.20%;The annual average total amount of water conservation is 166.43×10~8 m~3;The annual average total amount of soil conservation was 11.89×10~8 t;The annual average total amount of wind break and sand fixation is 35.34×10~8 t;The annual average total amount of carbon sequestration is 0.54×10~8 t.The annual average total amount of oxygen release is1.45×10~8 t.In this paper,the study period is divided into three periods:2001-2005,2006-2010 and 2011-2015.From the time point of view,NPP,vegetation coverage,water conservation,soil conservation,carbon fixation and oxygen release show a trend of first decrease and then increase in the three periods,and the trend of wind prevention and sand fixation is first increase and then decrease;From the perspective of spatial distribution,NPP,water conservation,soil conservation,carbon sequestration and oxygen release showed a decreasing trend from southeast to northwest,while vegetation coverage and sand fixation showed a decreasing trend from east to west.From the perspective of different regions and stages,in the three time stages,except for the trend of water conservation decreasing at first and then increasing,the remaining ecosystem service indicators show a trend of continuous increase,which is the region where the ecosystem services continue to improve in the past 15 years.(2)Analysis on driving forces of ecosystem services in engineering areaDriving force analysis adopts the method of geographic detector,selects three factors to analyze the driving force of water conservation,soil conservation,wind protection and sand fixation calculated by the model,and concludes that different ecosystem service indicators have different main influencing factors,among which the main influencing factor of water conservation is precipitation,and the influence changes little with time and is relatively stable;The main influence factor of soil conservation is topographic relief,but the influence of topographic relief on soil conservation gradually decreases with time;As far as windbreak and sand fixation are concerned,the three factors are very small,and they are not the main factors affecting windbreak and sand fixation.The results show that there are significant differences among the five zones according to precipitation and topographic relief.With the increase of precipitation,the average values of water conservation and soil conservation show an increasing trend,while the characteristics of wind break and sand fixation with precipitation are not obvious;According to the population density,too low or too high population density is not conducive to the increase of water conservation and soil conservation.In addition,in the area of land use change,the dominant factors of water conservation and soil conservation are analyzed.The dominant factor of water conservation change is the change of land use,so water conservation is more sensitive to human activities;Soil conservation is more sensitive to climate change.For the improvement of regional soil conservation,we should adjust the corresponding measures according to the climate change in different years.(3)Analysis on flow path of windbreak and sand fixation serviceAccording to the results of air mass trajectory simulated by hysplit model,combined with the wind speed value of sand,a total of 545 flow paths of wind prevention and sand fixation service were simulated,including 174 from 2001 to 2005,179 from 2006 to 2010 and 192 from 2011 to 2015.Most of them came from the Northwest and entered the central and western regions of the project area through Mongolia.Combined with the distribution frequency of the flow path of wind prevention and sand fixation in three time periods,taking the county as the unit,the wind sand source control project in Beijing and Tianjin is divided into five levels:slightly affected area,generally affected area,moderately affected area,seriously affected area and seriously affected area.At the same time,according to the statistical results of regional ecosystem services,it can be seen that the amount of ecosystem services in the area seriously affected by sandstorm is the lowest,so it is recommended to strengthen ecological management in this area. |
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