| Ecological risk assessment is an important theoretical basis for regional land use optimization,resource management,construction and rehabilitation of ecological environment.With the development of urbanization,the implementation of the immigrant's relocation in southern Shaanxi and the harsh natural environment in the mountains,the structure of regional land use has greatly changed,and spatially presented the regional characteristics.Natural factors and human activities have changed the structure and process of the ecosystem through different land utilizing,have also affected the ability of the regional ecosystem to provide products and services to the society,and have caused the simultaneous change in the possible process of harm or adverse effect to the ecological environment.In this study,the SouthernShaanxi is taken as study area,which located in Qinba mountainous.Based on the remote sensing data,meteorological data and soil data,the characteristics of land use change,landscape pattern and ecological processes are studied and four ecosystem services quality of NPP,carbon-sequestration-oxygen-release,soil conservation and water conservationand and their values in southern Shaanxi were assessed and evaluated,using remote sensing interpretation method,GIS spatial analysis,landscape pattern index of Fragstats method and a variety of mathematical models.Ultimately,the three factors of the ecological risk of land landscape,soil carbon storage and the total value of ecosystem are introduced to evaluate the comprehensive ecological risk in southern Shaanxi,using entropy method,and spatio-temporal change of the comprehensive ecological risk is studied under multidimensional conditions.The specific results are as follows:(1)During the period of 1990?2015,the comprehensive dynamic degree of land use in southern Shaanxi was 0.2403%,and the single dynamic degree of different land use types is obvious difference.Thereinto the construction land is obviously increasing,and the reduction of grassland is fastest.The degree index of land use quantitatively showed a rising trend,spatially taking on the features of high level in the middle and low level in brim area,high in the south and low in the north.The annual rate of land use degree greatly changed in 2000-2005 and it was small in 2005?2010.The dynamic degree of land use transfer in the south Shaanxi was spatially between 0.23%-10.01%and the transfer intensity is distinct difference in space.The farmland was mainly transferred to the construction land on the low terrain niche.The grassland was transferred to the farmland in the low-and-middle terrain niche.The competition appears among grassland,woodland and farmland in the middle-and-high terrain niche.The dynamic degree of land use transfer was highest in water conservation ecological function area of the eastern section of the southern Qinling Mountains and weakest in the alpine area and the mid-west section of the southern Qinling Mountains.(2)From 1990 to 2015,Patch density index of different land use types showed an increasing trend.Thereinto patch density of farmland was the largest and the unused land was the smallest.There are obvious variations of landscape shape index before and after 2000.Since 2000,The aggregation index and contiguity index of various landscape types both declined.The diversity index increased but the dominance index declined,which shows the fragmentation of landscape increased.From vertical direction,water area and built-up land expand to the region of a little steep slope and high altitude.The transfer between woodland and grassland was the most significant on mid-high terrain niche,and human activities gradually expand from low terrain niche to the mid-high terrain niche.From the perspective of the pattern,the stable pattern occupies the largest area,especially "grassland-grassland-grassland-grassland".From the perspective of landscape scale,with the increase of terrain niche,the patch density presents an inverted "U" type,and the average area of the patch shows a trend of "U",which shows smaller landscape scale in low terrain niche and high terrain niche.The landscape has a certain correlation with elevation and topography,but no reliable relationships was found between it and slope.(3)The annual average of net primary productivity,carbon sequestration and oxygen release,soil conservation quantity and water conservation quantity in southern Shaanxi were 619.73gC · m-2 · a-1,88.28 t·hm2,17.54t·hm2 and 4800.81t·hm2 respectively.The four kinds of ecosystem service qualities show the decreasing-increasing-lower trend in 1990-2015,and spatially low value in basins and high in mountain area.All kinds of mass per unit area was the highest in the slope of 8°?15 °and at the altitude of 1500-2000m.The total quality was highest in the slope of 15°?25 °and at the altitude of 500?1000m.For years,the average of net primary productivity value,carbon-sequestration-and-oxygen-release value,soil conservation value and water conservation value Cere 1436.67 yuan/hm2,5260.19 yuan/hm2,5335.97 yuan/hm2 and 3283.54 yuan/hm2 respectively.In 1990?2015,The location of high ecosystem service value per unit area concentrated in mountainous counties of Qinling Mountains and Bashan mountains,the location of low value were mainly concentrated in the city and its surrounding cities,and the lowest value was in the northeast of south Shaanxi.In addition,the value of ecosystem services was degraded in hilly counties and the value of ecosystem services was improving in the counties of Hanjiang River's fountainhead.(4)From 1990 to 2015,the multi-year average value of the comprehensive value per unit area was 15318.6 yuan/hm2.The variation coefficient of the comprehensive value of the unit area was 33.34%.From the administrative point of view,the location of high value were mainly concentrated in the eastern section of Daba Mountains and the middle section of South Qinling mountains.The location low value areas were mainly concentrated in the northeast of south Shaanxi and the eastern section of south Qinling Mountains.The total comprehensive value was highest in the slope of 15°?25° and the altitude of 1000?1500m.From the point of view of spatial aggregation,the spatial distribution of value per unit was homogeneous,but the state of such spatial similarity was decreased.(5)For years,the average ecological risk intensity index of landscape was 0.1654 in southern Shaanxi.In 1990-2015,the ecological risk intensity index of landscape showed a slight drop and then continuous increase.Spatially there were high value in the middle and low value in the north and south.Ecological risk intensity index was low in mountainous counties and high in flatland and basin area of low mountains.The multi-year average value of comprehensive ecological risk was 0.6739.In 1990?2015,the comprehensive ecological risk intensity showed a decreasing trend.Spatially there were high in the middle and low in the north and south.From spatially global autocorrelation,the spatial distribution of comprehensive ecological risk was homogeneous,which shows the spatial aggregation of spatial similarity values.At the same time,H-H type of high ecological risk was mainly distributed in the hilly area of slope farmland and L-L type of low ecological risk mainly distributed in slope of more than 15°.In short,the ecological environment quality has improved from 1990 to 2015,but there were spatially great differences in southern Shaanxi.Due to strong interference by human activities in flatland and basin areas,there are small landscape scale,eco-environmental quality declines and the landscape ecological risk increases.The future should be paid attention to strengthen the optimization of land use and to improve the ecological management of land use in the counties of flatland and basin area.Major research innovation:Based on long time series and multidimensional spatial scale,the paper has analyzed the spatiotemporal dynamics of land use pattern and its ecosystem service values in southern Shaanxi.The landscape features and ecosystem service process are vertically studied in depth by using the compound topographic factors.The comprehensive value of ecosystem services and soil carbon storage is introduced into the index system of ecological risk assessment,which makes comprehensive ecological risk closely related to the complex ecosystem structure and process.The specific innovation points are as follows:(1)Research content highlights topographic features.There are many mountain areas in southern Shaanxi,and the vertical landscape types are typical.This paper not only uses elevation and slope of simple topographic factors,but also uses terrain niche of complex topographic factor to study spatiotemporal dynamics of land use and landscape pattern on different terrain niche and topographical features of ecosystem service quality and its continuous change in elevation.Based on the above research,the local spatial autocorrelation of the ecological risk on the terrain is studied,which beneficially and horizontally break through the ecological environment governance with administrative division or land use type as unit,so as to enhance the ecological space control in the vertical direction.(2)Ecological risk assessment index introduces ecosystem service value and soil carbon storage,highlighting the exposure characterization of risk assessment and the ecological endpoint of monetization.the comprehensive value of ecosystem services can highlight the comprehensive effect of ecosystem services and enhance the comprehensive thinking of geography research than single ecosystem service value.The research results are conducive to the overall consideration of ecosystem services optimization and the follow-up management measures of ecological risk,and also provide theoretical support for ecosystem risk assessment based on ecosystem services.(3)From micro to macro multidimensional dynamic,the paper studies dynamics of landscape and the change of ecological risk not only from the pixel of micro scale,but also from land use types,topography and administrative divisions of the macro scale.The research period is from 1990 to 2015.Systematic analysis of spatiotemporal dynamics is conducive to grasp the process and pattern of regional land use and ecological risk,and lay the foundation for future coupling research and analysis of driving mechanism. |
PDF Full Text Request