Evaluation Of Ecological Restoration Effects Based On GIS/RS For Northwest Inland River Basin,China

Ecological degradation has become a global common problem,seriously threatening the survival of humankind.Ecological restoration – kind of solution to the degradation is by using the human efforts to restore the structure,function,biodiversity and sustainability of degraded ecosystems close to their pre-disturbed(or self-sustaining)state.This is an effective way for mitigating ecological degradation,addressing environmental problems and restoring the ecological function.Furthermore,this is an important part of ecological restoration research of understanding the current state and the recovery degree,which can ensure the ecosystem restoration in accordance with established goals and trajectories.Correctly evaluating the effects of ecological restoration is of great practical significance for mitigating the process of ecological degradation and promoting the sustainable development of regional ecological environment.The Minqin oasis is a non-zonal landscape that extends from the Shiyang River to the Tengger Desert and the Baden Jaran Desert.It is a typical desert oasis as an important part of the ecologically fragile zone in the northwest of China,because of its important role in ecological barrier and has attracted worldwide attention.As the modern human activities continuously enhance and the water supply in upstream sharply decline,over-exploitation of groundwater and unreasonable irrigation and wastage of water resources occurred and causes a series of serious ecological and environmental problems,such as the decline of groundwater level,the increase of groundwater mineralization,vegetation degradation,desertification and salinization.In order to control the continuous decline of the groundwater level in Minqin Basin and to repair the seriously degraded ecological environment of Shiyang River Basin,the Chinese government launched the Comprehensive Treatment Program of the Shiyang River Basin(CTSRB)in January 2006.It aimed to increase the surface water supply and reduce groundwater mining through a series of ecological restoration measures such as adjustments to the structure of the planting industry,enforcement of water resources allocation and guarantee projects,water-saving irrigation reconstruction projects,ecological construction and protection projects,water resources protection and management system construction and so on.Eventually achieve the goal of "never allow Minqin to become the second Lop Nor".This paper takes Minqin Basin as the study area,and uses the GIS and RS techniques to establish the temporal and spatial patterns and evolution sequences of the three ecological factors of water,soil and biology in the Minqin Basin before and after the implementation of CTSRB(2001-2015).The recovery conditions of groundwater depth and groundwater mineralization as the “water” factors and fractional vegetation coverage and vegetation growth as the “biology” factors were quantitatively analyzed and mainly compared for the pre-CTSRB(2001-2006),CTSRB I(2006-2010),and CTSRB II(2010-2015)periods throughout the six regions,involving the entire study area,whole irrigated region,periphery of irrigated regions,Ba,Quanshan and Hu.On this basis,soil moisture and soil temperature as the “soil” factors were introduced for constructing the comprehensive ecological restoration evaluation index system by using the principal component analysis.Furthermore,a comprehensive evaluation model of ecological environment was established to make a comprehensive assessment of the ecological restoration effects in the Minqin Basin during the past 10 years from the implementation of the CTSRB through the contrast of all-round and multi-angle analysis.Finally,further countermeasures and measures for ecological restoration were discussed.This study aims to explore and discover the changing rules of ecological factors and the direction of ecosystem development under various evaluation indexes and their combined effects so as to establish a set of effective evaluation index system and evaluation model of ecological restoration effect.It can provide a scientific basis and decision support for the implementation and management of the following ecological restoration measures in Minqin Basin and the whole Shiyang River Basin,and provide a reference for the ecological restoration and the corresponding evaluation for global arid and semi-arid desert-oasis ecosystem.The main conclusions of this study are as follows:(1)The CTSRB has a significant effect on the restoration of groundwater level in Minqin Basin,and the restoration effects at the periphery of irrigated regions was better than that in the whole irrigated region,and the downstream of the basin was better than the upstream.The groundwater level in Hu,the periphery of the irrigated regions and the entire study area began to gradually rise with the rate of 0.38 m/year,0.27 m/year and 0.18 m/year,respectively,which basically suppressed the groundwater declining.During the CTSRB period,the area with groundwater depth >-20 m in six regions gradually decreased with varied rate.Four obvious "groundwater depletion cones" exhibited the continuous growth fusion during the CTSRB period and even began to shrink after 2013.The groundwater level in the study area was gradually becoming more and more balanced under constant changes.The areas with groundwater level increasing expanded to 65.03% during the CTSRB I period based on 0.31% during the pre-CTSRB period,and then decreased to 37.09% during the CTSRB II period.The surface water supply(i.e.increased surface runoff and inter-basin water transfer),and the reduced groundwater exploitation(i.e.the quotas of per capita water resource and reduced well density)and other relevant ancillary measures(e.g.repairing the lining,promoting water saving in the irrigation area,adjusting the industrial structure and the implementating WUAs water management system,etc.)were the main reasons that caused the restoration of groundwater level in the study area.(2)The CTSRB has a certain effect in the restoration of groundwater mineralization,but its effect was not significant.The increasing rate of groundwater mineralization has slowed down and the seasonal variation has been changed.The restoration effects in the upstream were better than downstream.The areas with decreased mineralization content also increased from 5.48% during the pre-CTSRB period to 30.69% during the CTSRB I period and further increased to 69.29% during the CTSRB II period.The change of groundwater level and its flow from southwest to northeast determines the mineralization of groundwater gradually from Ba to Quanshan and then to Hu,southwest low northeast high characteristics.The gradual recovery of the groundwater level in Minqin Basin was the main reason for the restoration of the mineralization of the groundwater.The increase in the proportion of surface water in agricultural irrigation and the reduction of groundwater exploitation during the CTSRB period were indirect causes.(3)The implementation of the CTSRB promoted the restoration of natural vegetation at the periphery of irrigated regions,although the area of artificial oases decreased due to the implementation of the "close the pumping-wells and transform the land" strategies.The no vegetation areas at the periphery of irrigated regions were gradually shifting to the vegetation areas,the desert vegetation gradually grows better,the coverage gradually increases,and the area gradually expands.The percentage of area increased at the periphery of irrigated regions were increased from 17.10% during the pre-CTSRB period to 52.31% during the CTSRB I period,and then to 71.47% during the CTSRB II period;the area of the vegetation coverage <5% reduced at the rate of 4.55%/year during the CTSRB II period,while the area with vegetation coverage at 5%-20% expanded at 4.29%/year.The main reason resulting in the restoration of surface vegetation is the result of the implementation of measures such as the artificial afforestation,transforming the land to forest,enclosure,compaction and afforestation.(4)The implementation of CTSRB has restored the ecological environment of Minqin Basin,but the overall restoration effects were still not obvious enough,and the performances of the CTSRB were different in different regions.The implementation of this ecological project has effectively contained the further degradation and greatly accelerated the restoration process of the ecological environment in Minqin Basin.The recovery effects were the result of the combined effects of the implementation of the CTSRB.From the period of pre-CTSRB to CTSRB I,and then to CTSRB II,both the eco-environmental index and the areas of "good" and "better" state of ecological environment first decreased and then increased;the area regarded as the ecological restoration region expanded from 18.75% to 43.48%,and further expanded to 72.42%.Thus,it is believed that with the continued implementation of the CTSRB,its ecological restoration effects of Minqin Basin will become more and more significant.(5)Groundwater depth,groundwater mineralization and fractional vegetation coverage are the three major ecological factors affecting the ecological environment of Minqin Basin,which the average weight were 33.32%,33.05% and 24.37%,respectively.In the follow-up process of ecological management,according to the regional differences in the restoration of the above three major ecological elements,we should make the right remedy,increase the proportion of surface water supply and reduce the groundwater mining to make a reasonable "on diet" plan for groundwater depletion cones in Ba and Quanshan;plant the anti-wind and anti-sand plants at the periphery of Ba and Quanshan and anti-salinity plants at the periphery of Hu,respectively.Finally,achieve the regional-social-economic harmonious development.