| With the rapid development of social economy and the continuous expansion of the city,the breadth and depth of human land use continues to deepen, it caused great changes in land cover, and it is causing more and more resource and environment problems, and it is also triggered a series of social, economic and ecological problems. Therefore the land using is gradually widely concerned by authorities and academia. Tianjin is located in the Bohai lake, is an important port city in china. In the process of development of Tianjin, the land use problems gradually, such as unreasonable structure of land use, land use intensity difference. At the same time, the land use change will cause the change of ecological landscape, which triggered a series of ecological problems.This study selected Tianjin remote sensing images in1999,2009 and 2013 as the basic data,classified the remote sensing images by ENVI software;combined with Arc GIS spatial analysis technology, obtaining the land use transfer matrix from 1999 to 2009 and from 2009 to 2013.Using the FRAGSTATS software to calculate the 10 landscape pattern indexes which selected to characterize landscape quantity area features, landscape component shape and landscape composition diversity characteristics in study area, quantitatively analyzed the dynamic changes of landscape from landscape level and class level. Then studied the evolution of landscape pattern from the central area to the boundary region by gradient analysis method. According to the equal interval sampling method, divided the research area into 161 risk areas. The regional ecological risk of the entire study area constructed by the ecological risk index of each risk area. The quantitative analysis on the evolution rule of regional ecological risk can provide scientific basis for the land use and regional development of Tianjin. This thesis made some main research results:1. Change in the number and space of land use typesThe study show that, under the interference of human activities, in the period from 1999 to2013, greatly changed between the types of land use in the study area. Cultivated land and construction land as the main land use types of study area, have changed largest. The area of construction land increased significantly, and the area of cultivated land decreased significantly. For other types of land use such as forest land, garden land, water and water facilities land and unused land, change is small, and showed a decreased trend. From 1999 to2013 the comprehensive dynamic degree is high, and the transfer between land use type is large, land out of cultivated land, land into construction, and the balance between water and water facilities land import and export are the major transformation. The dynamic degree of land use between 2009 and 2013 is far higher than that between 1999 and 2009, the dynamic transformation between types of land use from 2009 to 2013 is more activity.2. Analysis of land use patterns changesLandscape pattern impacted by the land use dynamic changes. At landscape aspect, from1999 to 2013, the landscape diversity increased, various types of distribution, dominant type weakened, fragmentation degree increased, border shape of landscape patch is regular and became more complicated. At the landscape type aspect, from 1999 to 2013,fragmentationdegree of cultivated land is increase, landscape dominance decreased, the patch shape became complex. According to the construction land, the degree of landscape fragmentation reduced,connectivity enhanced, landscape dominance increased, patch shape relatively regular. Other types of landscape, like water and water facilities land landscape and garden landscape, the landscape fragmentation degree increased; the forest landscape fragmentation in the landscape in the first study period increased, in the second study period the landscape fragmentation is greatly reduced, the landscape patch shape became complex. Unused land landscape fragmentation degree is low, the patch shape became regular.3. Analysis of landscape gradient changesAt the landscape level, the gradient near the city, landscape type is rich, and there is no more dominant landscape types, the fragmentation degree is high, the landscape patch shape is more complicated. In gradually away from the city, the cultivated landscape became the dominant landscape types, the relative abundance degree decreased, the distribution of landscape is not uniform, the degree of fragmentation reduced gradually. And near the northern mountains, cultivated landscape dominance decreased gradually, the forest landscape dominance increased, component proportion of the difference became smaller gradually,uniform distribution, fragmentation degree increased, patch shape complexity.At the landscape type level, the cultivated landscape in 2 gradient belt get the highest degree of landscape fragmentation, with the increase of landscape gradient the degree of landscape fragmentation decrease. In the 18-20 gradient belts, affected by natural conditions,the cultivated landscape fragmentation degree increased. Patch shape is complex, and in14-17 gradient belts reach a maximum. In the 0 gradient belt, the area of construction land landscape is constantly increasing, landscape connectivity gradually increased, landscape fragmentation degree is low. Construction landscape shape is more structured, and with the change of gradient, in 18-19 gradient belts, due to a nearby with the mountain and the influence of geographical environment, landscape shape became complex. In 0-1 gradient belts water and water facilities landscape fragmentation degree, landscape shape gradually ordered, in 20 gradient belt landscape fragmentation degree is low, and landscape shape serious deviation square. From 1999 to 2013, the forest landscape connectivity degree increased, fragmentation degree of landscape is reduce. In 5-7 gradient belts, the distribution of garden landscape is loose, the landscape fragmentation degree and the complexity of patch shape are high. The unused land of study area was mainly distributed in the 4-9 gradient belts,from 1999 to 2013, land landscape fragmentation degree of unused increased. The shape of patch with the exploitation intensity increases and the time tends to be regular.According to the characteristics of gradient distribution of landscape pattern, the study area is divided into four landscape gradient zone: the city urban landscape area(0 gradient belt);transitional landscape area(1-7 gradient belts); Township landscape area(8-18 gradient belts);landscape in the mountainous area(19-24 gradient belts).4. Analysis of regional ecological risk assessmentRegional ecological risk value of the study area in 1999 ranged between 0.07-0.37, in 2009 ranged between 0.11-0.55, in 2013 ranged between 0.09-0.42.The overall tend is the high-riskareas expanded, the low-risk area reduced. The foremost ecological risk in the study area is middle ecological risk in 1999, followed by a low ecological risk, the second highest ecological risk is the least. In 2009 the overall ecological risk level is higher, with high ecological risk level primarily, high ecological risk region is the second types of risk in this year. The high ecological risk significantly reduced in 2013. From 1999 to 2009, the ecological risk level transformed 92.4% from low to high in the total area of the study area,from high to low is 2.65%; From 2009 to 2013, the ecological risk level transformed 0.02%from low to high in the total area of the study area, from high to low is 78.24%. During the period between 1999 and 2009, ecological risk of deterioration is serious condition. From2009 to 2013, the ecological environment is restored. Overall, from 1999 to 2013 ecological risk showed an increasing trend in Tianjin.Land use change is an important driver of the increase of regional ecological risk. |
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