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Water resources are essential for desert oases and are key drivers of local ecological processes critical to the growth of desert vegetation. In this study, the oasis in the hinterland of the Taklamakan Desert, China, was selected as the research subject. Using high-precision classification of oasis vegetation through machine learning, surface water within the oasis was identified and extracted from multi-year Landsat remote sensing data. The spatial distribution patterns of the main community-building species, Populus euphratica and Tamarix ramosissima, were studied under different moisture gradients using environmental covariates and measured groundwater depth to invert its spatial distribution and K-mean clustering to construct surface water and groundwater moisture gradients. The results indicated that the classification accuracy for the two species reached 0.917. Gradients 1-5 were used to categorize the water resources, dividing surface water and groundwater into five gradients. Gradient 3 exhibited the optimal moisture conditions, with a high surface water distribution frequency (0.017) and shallow groundwater depth (3.158 m), while Gradient 4 showed the least optimal moisture conditions, characterized by a low surface water distribution frequency (0.008) and deep groundwater depth (4.820 m). The water gradient decreased in the following order: Gradient 3 > Gradient 5 > Gradient 1 > Gradient 2 > Gradient 4. The optimum gradients for growth of P. euphratica and T. ramosissima were gradients 5, 1, and 2. The normalized vegetation index spatial distribution patterns of the two species were consistent with that of the moisture gradient. Tamarix ramosissima was found to be more tolerant to salinity and drought than P. euphratica. Overall, this study provides valuable information on the effect of the spatial distribution of water resource gradients on oasis vegetation and can guide future water delivery policies in oases., Competing Interests: Declaration of competing interest The authors declare that they have no competing financial interests or personal relationships that may have influenced the work reported in this study., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Understanding vegetation water utilization can provide scientific basis for vegetation protection and rational distribution of water resources in arid desert oasis area. In this study, sapling (DBH≤10 cm), mature (10 cm40 cm) Populus euphratica were chosen as sample trees in natural oasis of Dariaboui. We measured oxygen isotopes of xylem water and potential water sources (surface water, soil water in 0-3 m soil layer and groundwater) of P. euphratica with different tree ages. The IsoSource model was used to study water sources of P. euphratica . The results showed that soil water content increased with increasing soil depth, while the δ 18 O value of soil water decreased firstly and then stabilized. When groundwater depth was 2 m, the δ 18 O value of xylem water increased with increasing tree ages. When the depths of groundwater were 4.2 and 8 m, the δ 18 O values of xylem water decreased with increasing tree ages. Water sources of P. euphratica varied across tree age. When the depth of underground water was 2 m, the main water source for young trees was surface water, and the contribution proportion was 64.7%. For mature and overmature trees, it was deep soil water and ground-water, with a contribution of about 30%. When the depth of groundwater was 4.2 m, the main water sources of P. euphratica of different tree ages were deep soil water and groundwater, and the contribution proportion was about 30%. The lowest contribution of P. euphratica of different tree ages was shallow soil water, accounting for about 10%.

Water use efficiency of plants in arid regions plays a key role in affecting the distribution and water use of plants. We analyzed the responses of water use efficiency of Populus euphratica and Tamarix sp. to different groundwater depths by measuring foliar δ 13 C of the two dominant species in a desert hinterland. The results showed that as the groundwater depth increased from 2.1 m to 4.3 m, foliar δ 13 C of Tamarix sp. increased slightly and remained relatively stable. Tamarix sp. had a more stable water use efficiency to adapt to the arid environment. Foliar δ 13 C of P. euphratica first slightly decreased and then increased. P. euphratica improved its water use efficiency to adapt to drought stress. At the same groundwater depth, foliar δ 13 C of Tamarix sp. was higher than that of P. euphratica, indicating that water use efficiency of Tamarix sp. was higher than that of P. euphratica.

Understanding the effect of flooding on groundwater quality is imperative for oasis vegetation protection and local ecological environment development. We used geochemical and remote sensing inversion methods to evaluate the effects of flood recharge on the groundwater hydrochemical and geochemical processes in the Daliyaboy Oasis. Groundwater samples were collected from 30 ecological observation wells in the study area before (PRF) and after (POF) the flood. Except for small changes in HCO3− and K+ and a decrease in pH, ion levels were higher POF than PRF, and the water chemistry was essentially unchanged. In the POF groundwater, HCO3− was correlated with Cl−, Na+, Mg2+, total soluble solids (TDS), and electrical conductivity (EC), but not with SO42−, Ca2+, K+, or pH, and was positively correlated with all other variables, while the remaining variables, except for pH, were strongly positively correlated with each other. PRF water chemistry was controlled by silicate and evaporite mineral weathering and evaporation processes, resulting in high groundwater TDS, EC, and a major ion content, while POF major groundwater ions were regulated by mineral weathering and flood recharge. We demonstrated the high accuracy of remote sensing inversion, confirming this as a reliable method for evaluating groundwater chemistry. The results of the study help to reshape and predict the history of the regional hydrogeological environment and hydrogeochemical development, and provide a theoretical basis for assessing the rational use of local water resources and protecting the ecological environment. [ABSTRACT FROM AUTHOR]

Irrigation salinity is a common environmental threat for sustainable development in the Keriya Oasis, arid Northwest China. It is mainly caused by unreasonable land management and excessive irrigation. The aim of this study was to assess and map the salinity risk distribution by developing a composite risk index (CRI) for seventeen risk parameters from traditional and scientific fields, based on maximizing deviation method and analytic hierarchy process, the grey relational analysis and the Pressure-State-Response (PSR) sustainability framework. The results demonstrated that the northern part of the Shewol and Yeghebagh village has a very high salinity risk, which might be caused by flat and low terrain, high subsoil total soluble salt, high groundwater salinity and shallow groundwater depth. In contrast, the southern part of the Oasis has a low risk of salinity because of high elevation, proper drainage conditions and a suitable groundwater table. This achievement has shown that southern parts of the Oasis are suitable for irrigation agriculture; for the northern area, there is no economically feasible solution but other areas at higher risk can be restored by artificial measures. Therefore, this study provides policy makers with baseline data for restoring the soil salinity within the Oasis. [ABSTRACT FROM AUTHOR]

• Stable hydrogen and oxygen isotope method was used to research size-dependent water use pattern of Haloxylon ammodendron woodland. • Both development stage and groundwater depth had significant effect on water use pattern of H. ammodendron. • H. ammodendron used water from increasingly deeper soil layers throughout its development. • Water absorption depth decreased for seedlings but increased for mature trees with increasing groundwater depth. Haloxylon ammodendron is one of the major dominant woody species in Central Asian desert, and the size-dependent water use pattern of this species significantly affects the functioning of the local ecosystem. Here, we investigated the water-use responses of H. ammodendron to groundwater depth from seedling to mature tree in the Gurbantunggut Desert, China. Three sites were selected along a groundwater depth gradient, with 4.6 m, 7.4 m, and 11.0 m, respectively. Based on basal stem diameter, H. ammodendron plants were grouped into three development stages, namely seedling, sapling, and mature tree. Hydrogen isotope ratios (δ 2H) and oxygen isotope ratios (δ 18O) were measured for xylem water at different basal stem diameter (BSD) values, soil water in different soil layers, and groundwater. The water sources used by the seedlings, saplings, and mature trees were determined by applying the IsoSource model. The relationship between δ 18O value of xylem for H. ammodendron and basal stem diameter reflected changes in the water source from upper soil water to deeper soil water as H. ammodendron grows. With the decline in groundwater depth, seedlings decreased their water uptake depth, whereas saplings increased at mid depth but decreased at maximum depth. However, mature trees constantly increased their water absorption depth across sites. Tree height, crown width, and BSD presented a decreasing trend as the groundwater depth declined. The above study promotes the evaluation of the impact of groundwater retrogression on H. ammodendron population in its natural habitat. [ABSTRACT FROM AUTHOR]