Study On Water Regulation In Tarim River Basin Based On The Change Of Ecological Indicators

Ecological indicators are the important indicator for evaluating the health of ecosystems,and their changes indirectly reflect the ability of ecosystems to provide materials and services for human survival and development.Water resources are in short supply in arid areas,and the contradiction between water use for the national economy and for ecology is prominent.In the context of ecological civilization construction,rational and efficient use of limited water resources is an important issue facing arid regions.On a long-term scale,a systematic analysis of the changing laws of ecological indicators and a comprehensive grasp of the driving mechanism of changes in ecological indicators are an important prerequisite for the scientific deployment and efficient use of water resources,and is of great significance to the realization of the sustainable development of the regional ecological environment.In this study,Tarim River Basin in the arid region of Northwest China was selected as the research area.With the support of remote sensing image data,meteorological and hydrological data and GIS spatial analysis technology,firstly,the temporal and spatial change law of ecological environment in the cut-off area of the lower reaches of Tarim River from 2000 to 2018 was analyzed by using univariate linear regression method and Mann Kendall trend test method,and its ecological security was comprehensively evaluated.The differences in the ecological environment between the dry-up area and the water conveyance area were also compared.Aiming at the two scientific problems of the change patterns ecological indicators and their driving mechanism in the mainstream region,an integrated function that coupled a logistic function and an asymmetric Gaussian function was adopted,and the time trajectory fitting method,sensitivity analysis method and structural equation model were integrated.A novel framework model that could comprehensively detect the gradual change of ecological indicators and quantitatively analyze the response relationship between changes in ecological indicators and changes in environmental conditions was constructed,and the change pattern of ecological indicators in the mainstream of the Tarim River was systematically analyzed,and driving mechanism of the change of ecological indicators was deeply explored.Then,according to the law and driving mechanism of the change of ecological indicators,the corresponding water regulation countermeasures were put forward.The main conclusions of the study are as follows:（1）Affected by the increase of ecological water delivery and precipitation in the lower reaches of the Tarim River,although the vegetation coverage and productivity in the cut-off area increased,their level was still low as a whole.Under the condition of scarce water supply,the extremely significant increase of air temperature（p<0.01）exacerbated the degree of soil drought in the dry-up area.When the number of windy days decreased significantly（p<0.01）,the number of sandstorm days increased,and the protection function of ecosystem continued to decline.The ecological security of the entire dry-up area was at the level of early warning and moderate early warning.Compared with the cut-off area,the soil moisture degree in the downstream water transfer area was increasing,and the increase of vegetation coverage and vegetation productivity was also significantly higher than that in the cut-off area.In view of this,it was suggested to learn from the successful experience of ecological restoration in the downstream water conveyance area and carry out ecological management of Karanqi River and Nashen River,so as to restore the original river network pattern of the connection of the Kongque River,Nashen River and Tarim River,change the limited ecological function of the existing single river and improve the overall ecological function of the region.（2）The analysis of change pattern showed that the Gross Primary Productivity（GPP）,Evapotranspiration（ET）and Water Use Efficiency（WUE）of vegetation in the mainstream of Tarim River were all increasing,and could be expected to continue to rise or to remain at a high-level stable state.The longest continuous period of GPP change was 15 years,showing that ecological restoration was a long-term process.The years of GPP mutation were consistent with the implementation periods of major measures in the Tarim River Basin（1990,2001,and 2011）,indicating the reliability of this framework.Among the three ecological indicators studied,GPP was most sensitive to environmental change,and was the most sensitive to the Leaf Area Index（LAI）,and also had the strongest correlation with it（p<0.001）.Therefore,LAI could be used as the main control factor for judging plant growth.In addition,when GPP increased to216.44g·C·m^-2,WUE reached the maximum threshold of 0.93 g·C·m^-2·mm^-1,which could be used as the critical value to judge the ecological water use efficiency of the mainstream of Tarim River.（3）For the water allocation in the cut-off area and water conveyance area in the lower reaches of the Tarim River,under the condition of meeting the water demand of vegetation and riverbank ecological environment in the water conveyance area and ensuring the appropriate water surface area of Taitema lake,it was calculated that the annual water demand below Daxihaizi Reservoir is 300～318 million m³.The annual average discharge of Daxihaizi Reservior was required to be 350 million m³,so the average annual surplus water volume was 32～50 million m³.The surplus water volume could fully meet the annual demand of 2,255.36～2,991.37×10⁴m³ of Nashen River.The annual ecological water demand of Karanqi river was 3,474.95～4,330.72×10⁴m³,which could be met by water diversion from the mainstream of Tarim River or Bosten Lake.