The Study Of Landscape Ecological Evolution Characteristics And Ecosystem Health In Bahe Middle-up River Basin

The Bahe River is a river originating from the Blue Valley of the Qinling Mountains.It is one of the eight rivers in the “Eight River around Chang’an.” Bahe River is not only an important ecological river,a cultural corridor,but also an ecological barrier in the east of Xi’an.As a city river in Guanzhong,Shaanxi Province,the ecological health of the Bahe River Basin is closely related to humans.In recent years,with the rapid economic development and population increase,the pressure on the Bahe River Bas in has also gradually increased.Especially in Bahe Middle-up River basin,the ecological sensitivity is high,which directly affects the ecological security of the downstream areas and even the Weihe River basin.Therefore,this topic took the Bahe Middle-up River Basin as the research object,and analyzed the landscape pattern evolution characteristics and development trends at the landscape scale,the basin landscape-scale ecosystem health assessment system was established based on relevant theories and experiences,the ecosystem health of Bahe Middle-up River Basin was evaluated,so the existing ecological environment problems were discussed,and corresponding suggestions were put forward.The research results have positive s ignificance for basin ecology and landscape ecology.The findings are as follows:With the support of ENVI software and Arc GIS software,NDVI,NDWI and PVI were extracted based on the two remote sensing images from 2007 and 2016,and were combined with the original wavebands of remote sensing images as multi-source data.The remote sensing interpretation was performed using the decision tree c lassification method.Finally,six types of landscapes were acquired: grassland,woodland,cultivated land,construction land,water areas,and unused land.The total accuracy of the two-stage classification was above 83%.By analyzing the evolution characteristics of the class level and landscape level of Bahe Middle-up River Bas in,it can be concluded that from 2007 to 2016,the woodland occupied a dominant position in the entire landscape,and the fragmentation was relatively low,which was healthier than other landscape types.The area of the grassland decreased 4368 hm2,and the landscape clustered and regularized.The area of construction land increased by 18%,and the degree of fragmentation deepened.The area of cultivated land reduced 6869 hm2,the structure was relatively loose,there was a trend of small land area and a large number of plaques.The area of unused land decreases and the shape tended to be complicated;the water area base was small,and the change of area and landscape index was not large,but it had a fragmentation trend.In terms of the overall landscape,the connectivity of the patches became higher,the pattern distribution was more reasonable,the proportion of landscape types was greater,and the degree of fragmentation of the landscape became lower.The overall landscape pattern was moving towards a state of aggregation and health.Using GIS spatial analysis techniques,the reduction of grassland area was mainly due to the conversion to woodland.The reduction of cultivated land was mainly due to the conversion to woodland and construction land.Most of the unused land was converted into arable land and construction land.Based on Markov predictions,grassland,cultivated land and unused land were reduced by 3756 hm2,3590 hm2 and 81 hm2,respectively,from 2025 to 2043.The area of woodland increased significantly with a change of 7958 hm2.The water area was slowly declining,the area of woodland was increasing significantly,and the area of construction land was increasing.Based on the PSR model,a comprehensive assessment of the ecosystem health of the Bahe Middle-up River Basin can be obtained.In 2007 and 2016,the comprehensive health was 0.5208,0.6138,and the health level was raised from three to two levels.This showed that the 2016 basin ecosystem had relatively strong vitality and a relatively reasonable structure,so the ecosys tem was relatively stable.However,the ecological health value of 2016 just reached the secondary standard(0.4~0.6),so the ecology didn’t fully recover to health.Therefore,we still need to pay attention to the protection and restoration of the ecological function of the upper reaches of the Weihe River.