| The lower reaches of Tarim River is one of the representative ecological weak areas in the world.To save the degraded ecological environment in the lower reaches of the Tarim River since the 1960 s,the Chinese government implemented the Tarim River governance project in 2000 with emergency ecological water delivery as a representative measure.Understanding and monitoring the ecological hydrological process of vegetation in the lower reaches of the Tarim River plays an important role in the planning of water delivery strategies,the evaluation of watershed ecology,the understanding of the rules of environmental evolution in arid areas,and the promotion of sustainable economic development in the river basin.This article uses multi-source remote sensing data through multi-scale remote sensing coordinated monitoring to realize the extraction,mapping and change process analysis of different spatial and temporal dimensions of the downstream vegetation,combined with groundwater monitoring station data to study the downstream surface and underground key hydrological environment parameters change process,and finally analyze the regional vegetation ecology Hydrological process response to artificial water delivery.The main conclusions are as follows:(1)The integrated monitoring of multi-scale vegetation remote sensing shows that the ecological environment of vegetation in the study area has been significantly improved since the artificial ecological water delivery.Object-oriented monitoring of small-scale high-resolution images shows that nearly 60% of Populus euphratica in the study area disappeared nearly half a century before the water was delivered,and the area of the sparse Populus euphratica below the Daxihaizi Reservoir basically recovered to the area of the sparse Populus euphratica before the flow was not cut off,Mainly located on the river bank 0.5～3km.Meso-scale Landsat time trajectory and coverage frequency monitoring showed that the vegetation in the study area was generally good but fluctuating strongly,The constant vegetation area and non-vegetation conversion vegetation area decreased longitudinally along the river,and the vegetation of various trend types was mainly located at the river bank 1.5km Within the area,the vegetation area with unsteady fluctuations and the coverage frequency of 1 to 8 times accounted for89% and 66% of the vegetation area of the riverbank,respectively.The vegetation coverage area expanded more significantly after 2013.Large-scale MODIS intensive time-series remote sensing monitoring shows that the vegetation environment in the study area has experienced a steady rise from 2000 to 2005,a decline in fluctuations from 2006 to 2009,a rapid rise from 2010 to 2013 to a rise in fluctuations from 2014 to 2020.Since2013,the vegetation environment in the study area has become more obvious,and the seasonal differences have gradually become apparent.The environmental conditions near Daxihaizi Reservoir is the best,and the vegetation restoration efficiency near Taitma Lake is the highest.(2)Monitoring of the water body of Tail-end Taitma Lake and the buried depth process of the river bank groundwater has shown that the hydrological environment conditions in the study area have obvious differences in time and space but have all been improved.The water bodies of Taitma Lake are mainly distributed 6km west of National Highway 218 and low-lying places along the route,showing a fragmented spatial pattern.The water area is more obvious after 2010.In the past 20 years,the groundwater depth in the study area has experienced steady uplift(2001～2004),steady decline(2005～2008),fluctuating uplift(2009～2013),fluctuating decline(2014～2015),steady uplift(2016～2017).From 2000 to 2017,the groundwater depth of each section fluctuated as a whole,Among them,Yingsu groundwater fluctuated slightly,Kaerdayi groundwater rising rate was 0.03m/a,and the groundwater rising rate of Alagan was 0.17m/a,The groundwater in Yiganbuma has risen by 4.65 m at a rate of 0.22m/a in 18 years,The Kuergan groundwater rises more obviously but fluctuates more drastically.The farther away from the Daxihaizi Reservoir,the more obvious the groundwater rise,and the closer to the river bank,the more obvious the groundwater rise.The improvement of the hydrological environment in the study area is a long and slow process.(3)The vegetation ecological hydrological changes process and the artificial water delivery process in in the study area show strong spatial dependence and time lag.The waters of Taitma Lake are directly affected by the amount of water discharged from Daxihaizi and fluctuate frequently,and the waters are obvious when the water is more than 400 million m3/time.The temporal and spatial variation of groundwater depth in the study area is closely related to the upstream incoming water,From 2009 to 2017,the correlation coefficient between the change of groundwater level and the amount of ecological water delivery was 0.51,and the correlation coefficient with the number of days of water delivery was 0.44.The horizontal spatial response distance of groundwater in Yingsu,Kaerdayi,Alagan,Yiganbujima and Kurgan is about 1370 m,1190m,2651 m,1462m,1301 m.The vegetation ecological hydrological process in the study area is a typical arid area vegetation ecological hydrological process,The response mechanism is Changes in water delivery elements—changes in groundwater depth—changes in the ecological environment of vegetation,The response to groundwater depth in one year is the most obvious,Groundwater changes in the current year and the next year have the most significant impact on vegetation growth,Water delivery during vegetation growth season can promote the ecological environment,Once the study area has no upstream water for 2 consecutive years,The downstream ecological environment will be significantly degraded.The buried depth of 7m groundwater determines the direction of the ecological environment change in the basin.The normal growth of trees in the basin with groundwater greater than 6m will be affected,and the groundwater depth less than5 m can promote the benign growth of trees and shrubs in the downstream. |
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