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Tarim River is located in south Xinjiang,northwest China.With a length of 1321 km,it is one of the longest inland rivers in the world.The name translates to "Water of Life",and certainly the river plays a key role in the development of the local society and the health of the ecosystem.Water resource development driven by irrational exploitation and increases in water utilization at the upper reaches over the past five decades has greatly disturbed the natural distribution of water resources within the valley.One major consequence is that more than 321 km of the watercourse has been drained after the Daxihaizi Reservoir was built in the 1970s.Consequently,groundwater depths along the dry watercourse increased leading to continual deterioration of groundwater quality.Along with fall in groundwater level and deterioration of groundwater quality,was the deterioration of the desert riparian system at the lower reaches of Tarim River.The desert riparian system reached a state of collapse: the area of Populus euphratica forest,the main tree species of the region,declined from 5.4 × 104—0.523 × 104 hm2 along the lower reaches of Tarim River,while the area covered by shrub and meadow decreased by 200 km2.In addition,a total area of 12,300 km2 experienced desertification.To prevent the continued deterioration of the ecosystem along the dried-up watercourse and to prevent further desertification,a water delivery project has been carried out.Starting from May 2000,the water in Boston Lake was intermittently supplied to the dry watercourse.By December 2006,11 intermittent water releases had been carried out.The released water played a critical role in vegetation recovery.However,from December 2006—June 2010,the ecological water delivery ceased.This provided a research opportunity for studying the stability of the ecosystem at the lower Tarim River after seven years of introduced water deliveries.The aims of this study were to 1) describe the variations in groundwater depths and the quality of groundwater during the four year long interval of no water delivery,2) depict the variations in vegetation species diversity during the interval,3) explain the relationships between groundwater and species diversity.Based on the monitoring data of groundwater depths,groundwater chemistry and species of vegetation,the variations in species diversity and related factors were analyzed.It was found that the average of groundwater depths in 2006 was approximately 5 m,while they were 6.5 m in 2010.The Shannon-Weiner,Simpson,Margalef and Pattrick and Cody indexes expressed a decreased change.In contrast,the Peilou Index showed an increased change,indicating that the ecosystem in the lower Tarim River is in a compromised state,even though seven years of introduced water delivery had been carried out.Both Non-Parameter Analysis and Redundancy Analysis confirmed that in the year 2006,species diversity had close relationships to total dissolved solids(TDS) of groundwater,while the relationship of species diversity to the depths of groundwater was not significant.In contrast,species diversity had a close relationship to the depths of groundwater in 2010 rather than TDS.Therefore,considering the relationship between variations in groundwater level and species diversity,it can be deduced that the rational groundwater depth in the lower Tarim River under the situation of water delivery is 5 m and the intimidated groundwater depth is 6.5 m.

Based on monitoring data collected from 2006 to 2009 at the lower reaches of the Tarim River, tempo-spatial variations in groundwater depth and chemistry during an approximately 3-year interval of intermittent water delivery were studied. Results indicate that as the groundwater depth increased at the upper sector of the river's lower reaches from March 2007 to September 2009, so too did the main chemical composition of groundwater. Groundwater depth at the intermediate sector also increased, but major ions in groundwater declined. The groundwater depth at the lower sector started to decrease in August 2008, and the concentrations of main ions in the groundwater generally rose and fell along with the variations in groundwater depth. The groundwater depth and chemistry in the monitoring wells located at a distance from the aqueduct expressed complex changes at different sections. For instance, at the section near the Daxihaizi Reservoir Section B, groundwater depth increased gradually, but chemical composition changed little. In contrast, the groundwater depth of monitoring wells far from the Daxihaizi Reservoir (Section I) decreased and salt content in the groundwater increased. In sectors at a moderate distance from the reservoir, groundwater depth decreased and concentrations of main ions significantly increased.

The water of Bosten Lake was released to lower reaches of the Tarim River for 5 times from 2000 to 2002. The changes of total dissolved solid (TDS) and the major ions (SO42−, Cl−, Na+, Ca2+, Mg2+ and HCO3−) were analyzed during this period. It was found out that TDS and the concentrations of the major ions initially and quickly increased and then decreased, but finally increased again. These changes were different at different distances from the river, which indicated that the groundwater changes relied on the distance from the river. In addition, the salt in groundwater was only diluted but not removed by the water. It was suggested that ecological measures should be sought to really promote the quality of the groundwater at the lower reaches of the Tarim River.