Research On Spatio-temporal Dynamic Changes Of Hydrological Ecology In The Mainstream Of Tarim River Based On 3S Technology

The Tarim River basin is the most concentrated and well-preserved area of Populus euphratica forest in China.However,for a long time,under the influence of human activities,the vegetation gradually declined,and the water environment of the basin continued to deteriorate.In order to explore the effective measures for ecological restoration of the Tarim River,protect the hydrological ecosystem of the basin and protect the good environment for vegetation growth,this paper based on 3S technology,using remote sensing data and hydrological data of the Tarim River,the method of remote sensing quantitative inversion combined with the field investigation and verification was used to carry out the hydrological ecological change monitoring and surface water chemical analysis of the Tarim River.The main conclusions are as follows:（1）In the past 20 years（2000-2019）,the vegetation coverage in the mainstream of the Tarim River has changed slightly,but it has shown an overall increasing trend.The vegetation coverage is basically 19%～30%.During the 20 years,the vegetation coverage of the mainstream has increased by 48%,with an average annual growth rate of 2.09%.The results show that a series of treatment and protection measures have played a role and improved the current situation of hydrology and ecology in the basin to a certain extent.（2）On the time scale,the vegetation coverage of the main stream of the Tarim River changes significantly with the seasons,which is related to the growth cycle of vegetation.Spring is the period of plant growth,so the vegetation grows rapidly in April and May,and reaches the most exuberant period in summer,with a maximum vegetation coverage of29.54%.In September,it gradually entered a period of vegetation decline,and the vegetation coverage began to decrease.The minimum vegetation coverage during the year appeared in winter,and the vegetation coverage of the mainstream of the Tarim River in 2019 was as low as 13.07%.（3）On the spatial scale,the vegetation coverage of the mainstream of the Tarim River has a large spatial difference,generally showing a decreasing trend from upstream to downstream.In the same period,the vegetation coverage of the upper reaches is significantly higher than that of the middle and lower reaches.In the past 20 years,the vegetation coverage of the upper reaches was about 1.87 times that of the middle reaches and about 3.23 times that of the lower reaches.The forest area is gradually sparse along the river section.In 2017,the vegetation coverage of the upstream section was 3.77 times that of the downstream section.At this time,the vegetation coverage gap of the different sections of the Tarim River reached the largest.（4）The growth of vegetation is closely related to the hydrochemical characteristics of the mainstream.Through the hydrochemical analysis,it is found that all the surface water samples collected in the study area are weakly alkaline,and the water bodies are generally dominated by chlorinated（Cl）water.Most of the water samples have high salinity,poor water quality,so they belong to mixed water.In general,the hydrochemical type in the upper and middle reaches of Tarim River is Ca-Mg-HCO₃-Cl type,and that in the lower reaches of Tarim River is Ca-Mg-Cl-SO₄ type,and the content of HCO₃^-decreased to a certain extent in the lower reaches of the river.（5）Water is the most important environmental factor for vegetation growth.The spatio-temporal change of hydroecology have important effects on the growth of desert riparian forest.The upstream has a large amount of water and good water quality,and the vegetation has a good growth environment;the lower reaches of the river has less recharge and low groundwater level,which exceeds the range of water absorption by vegetation roots,and strong evaporation leads to the increase of salinity of water body and the deterioration of soil and water environment,which threatens the growth of vegetation and further affects the ecological restoration of the mainstream.In order to change the hydrological and ecological status of the basin to the maximum extent,we should make a comprehensive plan to restore the hydrological and ecological environment according to local conditions,and explore effective methods and measures for vegetation rejuvenation.At the same time,we should also accurately assess the ecological water demand,carry out ecological water transfer projects continuously and efficiently,maximize the conservation of water resources and the restoration of natural vegetation,and jointly build a good hydrological and ecological environment.