Ecological risk assessment of landscape in arid area watersheds under ecological water conveyance: A case study of Taitema Lake.

The Taitema Lake Basin serves as an ecological barrier in the south of the Tarim Basin, connecting with the Qiemo, Ruoqiang, and Milan oases, collectively preventing the expansion and merging of the desert, specifically inhibiting the convergence of the Taklamakan Desert and Lop Nur. In recent years, with changes in the natural environment and an increase in water usage, the downstream flow of the Tarim River has decreased, leading to the gradual drying up of Taitema Lake and exacerbating desertification, resulting in frequent sandstorms. Subsequently, under the influence of ecological water transfer projects, Taitema Lake has gradually recovered, and the ecological environment has improved. This study focuses on Taitema Lake and its nearby regions, constructing the Regional Landscape Ecological Risk Index (ERI) to assess landscape ecological risks before and after ecological engineering and determine ecological benefits. The results indicate that the EWC (Ecological Water Conveyance) project effectively supplements water in the intermediate and lower courses of the Tarim River and the terminal lakes, significantly bolstering ecological conditions in the lake basin and reducing risks. However, the current EWC project is relatively extensive, and the water reaching the Tarim River and Taitema Lake depends entirely on the surplus water from upstream production and daily life. Additionally, the distribution of downstream water depends entirely on natural topography, leading to uneven spatiotemporal distribution of water resources and significant evaporation losses. Rational hydraulic engineering measures should be taken to re-plan the distribution of rivers and lakes, achieving the maximum ecological benefits of the EWC project.

Aeolian disaster risk evaluation in the African Sahel.

The Sahel is facing a serious environmental crisis due to aeolian disaster that has seriously affected the local development and survival of residents. Thus, evaluating the aeolian disaster risk levels and their variation in the Sahel is important. This study established an optimal model by evaluating the applicability of different models in the aeolian disaster risk determination in the Sahel. Using this model, the spatiotemporal changes in the risk subsystem of aeolian disaster (hazard, sensitivity, vulnerability, and restorability) and the aeolian disaster risk in the Sahel from 2000 to 2020 were analyzed. Based on this analysis, the impact of climate change and human activities on the aeolian disaster risk in the Sahel was evaluated. Results revealed that the variable fuzzy recognition (VFR) based on the aeolian disaster risk index (ADRI) model had the highest accuracy, reaching 89.72 %. The middle of the Sahel, located in the desert-grassland transition zone, exhibited a high hazard, sensitivity, and vulnerability, rendering it highly susceptible to aeolian disaster. The proportion of areas with very low and very high aeolian disaster risk levels decreased from 2000 to 2020, while those with low and high levels increased, and the change in moderate risk level areas remained relatively stable. Areas of low, moderate, and high risk are more sensitive to climate change and human activities and are subjected to greater pressure for change. Human activities were the main factor for the change of ADRI in the Sahel, accounting for 69.74 and 58.19 % of the increased and decreased areas of ADRI, respectively. This study evaluated the level of aeolian disaster risk in the Sahel and identified the main driving factors, providing a reference for Sahel countries to better implement the Green Great Wall (GGW) program in Africa, thereby mitigating the adverse effects of aeolian disaster.

Windblown sediment transport and loss in a desert-oasis ecotone in the Tarim Basin.

The Tarim Basin is regarded as one of the most highly erodible areas in China. Desert comprises 64% of the land use in the Basin, but the desert-oasis ecotone plays a prominent role in maintaining oasis ecological security and stability. Yet, little is known concerning the magnitude of windblown sediment transport in a desert-oasis ecotone. Therefore, aeolian sediment transport and loss was assessed from a desert-oasis experimental site located near Alaer City in the northwestern Tarim Basin. Sediment transport and factors governing transport were measured during three high wind events in 2012 and four events in 2013. Sediment transport was measured to a height of 10 m using passive aeolian airborne sediment samplers. The mass flux profile over the eroding surface was well represented by the power-law (R2 > 0.77). Sediment loss from the site ranged from 118 g m-2 for the 20-24Apr 2012 wind event to 2925 g m-2 for the 31Mar-11Apr 2012 event. Suspension accounted for 67.4 to 84.8% of sediment loss across all high wind events. Our results indicate the severity of wind erosion in a desert-oasis ecotone and thus encourage adoption of management practices that will enhance oasis ecological security.

Life span and structure of ephemeral root modules of different functional groups from a desert system.

The terminal branch orders of plant root systems have been proposed as short-lived 'ephemeral' modules specialized for resource absorption. The occurrence of ephemeral root modules has so far only been reported for a temperate tree species and it is unclear if the concept also applies to other woody (shrub, tree) and herb species. Fine roots of 12 perennial dicotyledonous herb, shrub and tree species were monitored for two growing seasons using a branch-order classification, sequential sampling and rhizotrons in the Taklamakan desert. Two root modules existed in all three plant functional groups. Among the first five branch orders, the first two (perennial herbs, shrubs) or three (trees) root orders were ephemeral and had a primary anatomical structure, high nitrogen (N) concentrations, high respiration rates and very short life spans of 1-4 months, whereas the last two branch orders in all functional groups were perennial, with thicker diameters, no or collapsed cortex, distinct secondary growth, low N concentrations, low respiration rates, but much longer life spans. Ephemeral, short-lived root modules and long-lived, persistent root modules seem to be a general feature across many plant functional groups and could represent a basic root system design.

[Three-dimension temporal and spatial dynamics of soil water for the artificial vegetation in the center of Taklimakan desert under saline water drip-irrigation].

Three-dimension temporal and spatial dynamics of the soil water characteristics during four irrigating cycles of months from April to July for the artificial vegetation in the center of Taklimakan Desert under saline water drip-irrigation had been analyzed by timely measuring the soil water content in horizontal and vertical distances 60 cm and 120 cm away from the irrigating drips, respectively. Periodic spatial and temporal variations of soil water content were observed. When the precipitation effect was not considered, there were no significant differences in the characteristics of soil water among the irrigation intervals in different months, while discrepancies were obvious in the temporal and spatial changes of soil moisture content under the conditions of rainfall and non-rainfall. When it referred to the temporal changes of soil water, it was a little higher in April but a bit lower in July, and the soil water content in June was the highest among four months because some remarkable events of precipitation happened in this month. However, as a whole, the content of soil moisture was reduced as months (from April to July) went on and it took a decreasing tendency along with days (1-15 d) following a power function. Meanwhile, the characteristics of soil water content displayed three changeable stages in an irrigation interval. When it referred to the spatial distributions of soil water, the average content of soil moisture was reduced along with the horizontal distance following a linear regression function, and varied with double peaks along with the vertical distance. In addition, the spatial distribution characteristics of the soil water were not influenced by the factors of precipitation and irrigating time but the physical properties of soil.

[Effect of shifting sand burial on evaporation reduction and salt restraint under saline water irrigation in extremely arid region].

The Taklimakan Desert Highway Shelterbelt is drip-irrigated with high saline groundwater (2.58-29.70 g x L(-1)), and shifting sand burial and water-salt stress are most common and serious problems in this region. So it is of great importance to study the effect of shifting sand burial on soil moisture evaporation, salt accumulation and their distribution for water saving, salinity restraint, and suitable utilization of local land and water resources. In this study, Micro-Lysimeters (MLS) were used to investigate dynamics of soil moisture and salt under different thicknesses of sand burial (1, 2, 3, 4, and 5 cm), and field control experiments of drip-irrigation were also carried out to investigate soil moisture and salt distribution under different thicknesses of shifting sand burial (5, 10, 15, 20, 25, 30, 35, and 40 cm). The soil daily and cumulative evaporation decreased with the increase of sand burial thickness in MLS, cumulative evaporation decreased by 2.5%-13.7% compared with control. And evaporative inhibiting efficiency increased with sand burial thickness, evaporative inhibiting efficiency of 1-5 cm sand burial was 16.7%-79.0%. Final soil moisture content beneath the interface of sand burial increased with sand burial thickness, and it increased by 2.5%-13.7% than control. The topsoil EC of shifting sand in MLS decreased by 1.19-6.00 mS x cm(-1) with the increasing sand burial thickness, whereas soil salt content beneath the interface in MLS increased and amplitude of the topsoil salt content was higher than that of the subsoil. Under drip-irrigation with saline groundwater, average soil moisture beneath the interface of shifting sand burial increased by 0.4% -2.0% compare with control, and the highest value of EC was 7.77 mS x cm(-1) when the sand burial thickness was 10 cm. The trend of salt accumulation content at shifting sand surface increased firstly, and then decreased with the increasing sand burial thickness. Soil salt contents beneath the interface of shifting sand burial were much lower than that of shifting sand surface. 35 cm was the critical sand burial thickness for water-saving and salt restraint. In summary, sand burial had obvious inhibition effects on soil evaporation and salt accumulation, so maybe it could be used to save water and reduce salt accumulation in arid shifting desert areas.

[Effects of salt stress on Nitraria roborowskii growth and physiological characteristics of stress resistance].

A pot experiment was conducted to study the influences of different NaCl concentrations (0, 50, 100, 200, 400 mmol x L(-1)) on the growth, leaf hydrogen peroxide (H2O2), malonaldehyde (MDA) content, superoxide dismutases (SOD), catalases (CAT), peroxidase (POD), ascorbate peroxidase (APX) enzymes activity, water potential, soluble sugar and proline contents of Nitraria roborowskii. The results showed that the growth of N. roborowskii was not affected at lower NaCl concentrations (< or = 50 mmol L(-1)), while the SOD, POD, CAT and APX activities in leaves of N. roborowskii were increased. However, higher NaCl concentrations (> 50 mmol x L(-1)) restrained the growth parameters of crown area, number of branches, dry mass of leaf, branch and lateral root, and remarkably reduced the SOD, POD and CAT activities, soluble sugar and proline contents in leaves of N. roborowskii. H2O2 and MDA contents in leaves were increased and water potential was reduced with increasing NaCl concentrations.

Soil microbial diversity, site conditions, shelter forest land, saline water drip-irrigation, drift desert.

Soil microbes in forest land are crucial to soil development in extreme areas. In this study, methods of conventional culture, PLFA and PCR-DGGE were utilized to analyze soil microbial quantity, fatty acids and microbial DNA segments of soils subjected to different site conditions in the Tarim Desert Highway forest land. The main results were as follows: the soil microbial amount, diversity indexes of fatty acid and DNA segment differed significantly among sites with different conditions (F < F0.05 ). Specifically, the values were higher in the middle and base of dunes than the top part of dunes and hardened flat sand, but all values for dunes were higher than for drift sand. Bacteria was dominant in the soil microbial community (>84%), followed by actinomycetes and then fungi (<0.05%). Vertical differences in the soil microbial diversity were insignificant at 0-35 cm. Correlation analysis indicated that the forest trees grew better as the soil microbial diversity index increased. Therefore, construction of the Tarim Desert Highway shelter-forest promoted soil biological development; however, for enhancing sand control efficiency and promoting sand development, we should consider the effects of site condition in the construction and regeneration of shelter-forest ecological projects.

[Variation characteristics of soil microbial activities in the Tarim Desert Highway shelter forests, Xinjiang of Northwast China].

By the methods of Biolog, fumigation extraction, and colorimetric titration, this paper determined the soil carbon sources metabolic intensities, microbial biomass, and enzyme activities in the Tarim Desert Highway shelter-forests with different plantation times, and analyzed the variation characteristics of soil microbial activities in these shelter forests. With the increasing planting years of the shelter forests, the soil microbial metabolic activities (AWCD) and microbial diversity indices enhanced obviously, but the AWCD values in different soil layers had no significant differences. The soil catalase activity among the forests had no significant difference, but the soil cellulase and sucrase activities varied significantly. The soil microbial biomass carbon and nitrogen increased with the increasing planting years of the shelter forests, having a significant difference among the forests, but the microbial biomass phosphorus had no significant difference. The AWCD values had significant correlations with soil available nutrient contents, but less correlations with soil bulk density and moisture content. It was suggested that under the present management patterns and climate conditions, the soil metabolic activities in the Tarim Desert Highway shelter forests would be improved continuously with the increasing planting years of the forests.

Research on chemical characteristics of soil salt crusts with saline groundwater drip-irrigation in the Tarim Desert Highway Shelterbelt.

Soil salt crusts are special layers at soil surface which are widely distributed in the Trim Desert Highway Shelterbelt under drip-irrigation with high salinity groundwater. In order to reveal annual variation of their chemical characteristics, soil salt crusts in shelterbelt of different ages in hinterland of the Taklimakan Desert were sampled. SOM, total salt, inions and pH were analyzed. Following results were obtained. SOM of salt crusts increased with the shelterbelt ages, but increasing trend became lower gradually. Total salt, ions, and pH of salt crusts reduced gradually with the shelterbelt ages. Total salt of salt crusts in shelterbelt of different ages was much higher than shifting sandy land. Ions were higher than shifting sandy land, Cl(-), Na(+), and SO4 (2-) increased more obvious, then Mg(2+), K(+), Ca(2+) and HCO3 (-), CO3 (2-) was little and nearly had no change. pH was all alkaline, pH of salt crusts in shelterbelt of 11 years was even lower than shifting sandy land. We can include that the quality of shallow soil (0~30 cm) in the Trim Desert Highway Shelterbelt becomes better gradually.

[Effects of stumping on Calligonum mongolicum shelterbelt growth and soil moisture and salt distribution along Tarim Desert Highway, Xinjiang of Northwest China].

In order to ensure the stability and sustainability of the Calligonum mongolicum shelterbelt along Tarim Desert Highway, the aged C. mongolicum was stumped to investigate its growth and soil moisture and salt distribution. After stumping twice, C. mongolicum grew rapidly in its height, crown width, maximum basal diameter, and sprout number. Three years after stumping, the average height of the sprouts exceeded the control (no stumping), and the crown width and maximum basal diameter was 92.0% and 73.0% of the control, respectively. The fresh mass of the branches and assimilating branches, their dry mass, and the total fresh mass and dry mass of the aboveground parts reached 80.0%, 115.0%, 80.0%, 116.0%, 93.5%, and 88.0% of the control, respectively. Four years after stumping, the aboveground biomass surpassed the control. Comparing with the control, stumping increased the soil moisture content significantly and decreased the soil salt concentration. It was suggested that, to stump the aged C. mongolicum repeatedly could increase the soil moisture content and decrease the soil salt concentration in root zone, and effectively promote the rejuvenation and renewing of C. mongolicum.

[Effects of thinning on Calligonum arborescens growth and soil water-salt distribution in Tarim Desert Highway shelterbelt, Xinjiang of Northwest China].

In order to understand the effects of thinning on the growth of Calligonum arborescens and the soil water-salt distribution in Tarim Desert Highway shelterbelt, a thinning experiment was conducted on an aged and declined C. arborescens woodland in a demonstration section of the shelterbelt, with the growth of C. arborescens and the soil water-salt distribution monitored. Thinning had no effects on the phenophase of C. arborescens, but after thinning, the growth of the current year plant height, crown width, ground diameter, and new branch length of reserved trees was larger than that of the control, and the increment was in the order of planting space 2 mx 1 m > 1 m x 1 m > the control, with significant differences among the treatments. The assimilation branch surface area in treatments 2 mx 1 m and 1 m x 1 m were 5.97 m2 and 5.22 m2 per plant, respectively, being significantly larger than the control (3.1 m2 per plant). The soil moisture content in 0-160 cm layer was significantly higher in treatments 2 m x 1 m and 1 mx 1 m than in the control, and increased obviously with thinning intensity. The soil salt content was in the order of control > planting space 1 m x 1 m > 2 m x 1 m, and the differences among the treatments were significant. It was suggested that the best reserved plant density after thinning was planting space 2 m x 1 m.

[Changes and analysis of soil quality under different land use types in oasis rim].

The aggravation process of oasisization leads to changes of land use type in oasis rim. In order to discuss the effects of different land use types on soil properties and soil quality, the four land use types located Cele oasis rim in south margin of Tarim Basin, which are the cotton field, orchard, and Caligonum mongolicum Turcz land use type reclaimed by people and nature state land use type covered by Alhagi sparsifolia SHAP, were selected as study object. The relative soil quality index (RI) and the soil quality synthesis index (SQI) were used to analyse the changes of soil quality between four land use types within 0-20 cm, 2040 cm, 40-60 cm soil depth, respectively. Meantime, the fractal theory was used to analyse the particle-size distribution (PSD) property of top soil under different land use types. The results indicated that there was a significant difference in the soil organic matter and total nitrogen in same soil depth between four land use types; the order ranked according to RI was same to the order ranked according to SQI in each soil depth between four land use types. The cotton field and orchard have an obviously positive effect on soil quality of the top soil, however, the soil quality of Alhagi sparsifolia SHAP land use type was gradually increasing along with the increasing soil depth. The soil properties and soil quality of Caligonum mongolicum Turcz land use type were at the lowest level according to the comparison results among all land use types, and the calculation results of PSD fractal dimension also indicated the Caligonum mongolicum Turcz land use type had the worst ability on maintaining soil fine fractions.

[Assessment of farmland soil quality under different utilization intensity in arid area].

Based on the 2005-2007 experimental data in Cele oasis in the southern margin of Tarim Basin of Xinjiang, the soil quality of four typical types of farmland with different utilization intensity, i.e., farmland with high input, farmland with normal input, newly reclaimed farmland, and farmland in oasis' interior, was analyzed and assessed by using sustainable yield index, soil improvement index, and soil quality synthesis index. Among the farmlands, there were significant differences in the contents of soil organic matter, available nitrogen, and available phosphorus. Newly reclaimed farmland had the lowest level of soil quality, while the farmland in oasis' interior had relatively higher soil quality. This study could help the reasonable exploitation and utilization of farmlands in Cele oasis, and the protection of local farmland eco-environment.

[Relationships of soil microbial biomass with soil environmental factors in Tarim Desert highway shelter-forest].

By using correlation analysis, this paper studied the relationships of soil microbial quantity and biomass with soil physical and chemical factors and enzyme activities in highway shelter-forests of Tarim Desert, aimed to approach the interactions between microbes and environmental factors in aeolian sandy soil of extremely arid area. The results showed that soil microbial quantity and biomass in the shelter-forests had an increasing trend with the decrease of soil bulk density and particle size (R < -0.84) and the increase of soil moisture content and porosity (R > 0.85), with the correlation between soil microbial biomass and soil bulk density as the key. Soil microbial quantity and biomass were positively correlated with soil nutrient contents, mainly caused by the correlations of soil actinomycetes and microbial biomass C and P with soil available nutrients. Greater differences (R = 0.51-0.91) were observed in the correlations of soil enzyme activities with soil microbial quantity and biomass, which was mainly determined by the correlations of soil invertase and phosphatase activities with soil actinomycetes and microbial biomass C. The increase of soil salt content was not favorable to the accumulation of soil microbial biomass (R < -0.71), and there was a higher positive correlation (R > 0.63) between soil microbial amount and biomass. In practice, good soil condition should be established in the forestlands of arid area for the development of soil microbes and the promotion of soil matter cycling.

[Relationship between ephemeral plants distribution and soil moisture on longitudinal dune surface in Gurbantonggut desert].

Ephemeral plant is a particular group of desert flora only distributed in northern Xinjiang, China. In this study, field surveys of vegetation and soil moisture were conducted in the southern area of the Gurbantonggut desert from March to August 2002. The species number, coverage and growth of ephemerals and soil moisture were measured in 7 quadrats at different geomorphic positions on the longitudinal dune surface. The results showed that soil moisture in a depth of 0-30 cm affected ephemeral plants distribution significantly. In early spring, the soil moisture was 4.62% on the intredune, 3.98% on the plinth, and 2.01% on the crest. Consequently, the average coverage of ephemeral plants reached 51.8%, 38.2% and 4.4%, respectively. The existence of ephemeral plants distribution influenced soil moisture as well. In later May, there was an increase of surface soil moisture from the interdune to the crest. The soil moisture was 1.00% on the intredune, 1.90% on the plinth, and 2.45% on the crest.