Quantitative classification and analysis on plant communities in the middle reaches of the Tarim River

Plant communities were sampled in the lower reaches of the Tarim River, Xinjiang. The results showed that there are 23 species belonging to 21 genera in 11 families, most of which have low occurrence frequency in quadrats. The most common species is Tamarix ramosissima, which occurred in 17 sites accounting for 89.47% of the total 19 sites. Quantitative classification (TWINSPAN) and ordination (CCA) methods were used to study the distribution patterns of 23 plant species in 19 sites in this valley. TWINSPAN results showed that the plant communities in the middle reaches of the Tarim River could be divided into 3 groups and the sampling sites could be divided into 7 types in 3 groups. CCA results were consistent with TWINSPAN results, and showed species distribution patterns correlated with major environmental variables of groundwater level and soil moisture.

Evaluation of oasis stability in the lower reaches of the Tarim River

Oasis stability in the lower reaches of the Tarim River was assessed at the landscape scale（including changes in landscape pattern and land use in the oasis） and at the regional scale（including the cold-island effect and NDVI of the oasis） based on the methods of landscape ecology,GIS and Remote Sensing（RS）.Thematic Mapping（TM） remote sensing images from 1990,2000 and 2009 were employed along with the related meteorological and hydrological data pertaining to the reclamation area of the oasis in the lower reaches of the Tarim River.The results indicated that landscape heterogeneity and oasis complexity increased between 1990 and 2000.The comprehensive index of the degree of land use,the average index of the cold-island effect,NDVI value and oasis stability all decreased.However,the change trends in the indices referred to above were opposite between 2000 and 2009,and oasis stability was enhanced to some extent.

Dynamical variations in groundwater chemistry influenced by intermittent water delivery at the lower reaches of the Tarim River

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 (SO2-4, Cl-, Na+, Ca2+, Mg2+ and HCO-3) 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.

Eco-water conveyances applied to control desertification at the lower reaches of the Tarim River

The lower reaches of the Tarim River are one of the areas suffering from most severe sandy desertification in Xinjiang, Northwest China. Irrational utilization of water and land resources results in eco-environmental deterioration in the Tarim River. In May 2000, the local government carried out the water conveyances project in the Tarim River. The influence of water conveyance on desertification reversion is analyzed and discussed according to the monitoring data in the past three years. Based on monitored data of the nine observed sections, along the channel of conveyance, the intensity and scope of desertification reversion in the upper reaches are larger than those in the lower reaches. Dynamic changes of desertification reversion are more obvious from the channel of conveyance to its two sides. However, the range of influence and intensity of desertification reversion is limited at present. It is suggested that the way and range of water conveyances should be adjusted in the future.

A quantitative assessment on groundwater salinization in the Tarim River lower reaches,Northwest China

Based on monitored data from 840 samples, we assessed the spatial and temporal variability of groundwater salinization in the Tarim River lower reaches combining classical statistics and geostatistics. Results show that total dissolved solids （TDS） is significantly correlated with other related ions, such as Na＋, Mg2＋, Ca2-, C1- and K＋. TDS and underground water level have characteristics of spatial autocorrelation, both of which present the isotropic characteristic and con- form to the spherical model in each year from 2001-2009. TDS is basically greater than 1 g/L but less than 2 g/L in the Tarim River lower reaches, which indicates that salt stagnation pollution is more serious. The most serious salinization （3 g/L 〈 TDS _〈 35 g/L） contaminated area is mainly in the middle and lower part of the study area.

Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River Basin

Evapotranspiration(ET) and its controlling mechanism over the desert riparian forests in arid regions are the important scientific basis for the water resources managements of the lower reaches of the inland rivers of China. Nearly three years of continuous measurements of surface ET, soil water content at different depths and groundwater table over a typical Tamarix spp. stand and a typical Populus euphratica stand were conducted in the lower reach of the Tarim River. The ET seasonal trends in the growing season were controlled by plant phenology, and ET in non-growing season was weak. The diurnal variations of ET resulting from the comprehensive effects of all atmospheric factors were significantly related with reference ET. The spatial pattern of ET was determined by vegetation LAI, more vegetation coverage, more ET amount. Groundwater is the water source of surface ET, and the soil water in shallow layers hardly took part in the water exchange in the groundwatersoil-plant-air system. The temporal processes of ET over the Tamarix stand and the Populus stand were similar, but the water consumption of the well-grown Populus euphratica was higher than that of the well-grown Tamarix spp. Further analysis indicates that plant transpiration accounts for most of the surface ET, with soil evaporation weak and negligible; groundwater table is a crucial factor influencing ET over the desert riparian forests, groundwater influences the processes and amounts of ET by controlling the growth and spatial distribution of desert riparian forests; quantifying the water stress of desert riparian forests using groundwater table is more appropriate, rather than soil water content. Based on the understanding of ET and water movements in the groundwater-soil-plant-air system, a generalized framework expressing the water cycling and its key controlling mechanism in the lower reaches of the inland rivers of China is described, and a simple model to estimate water requirements of the desert riparian forests is presented.