Hexi Corridor Region Research Articles

Development and Application of a New QuEChERS Method in UHPLC-QqQ-MS/MS to Detect Seven Biogenic Amines in Chinese Wines.

The aim of this study was to develop and validate an improved, simple, and sensitive method for the simultaneous determination of seven types (cadaverine, CAD; hexylamine, HEX; histamine, HIS; phenylethylamine, PEA; putrescine, PUT; tyramine, TYR) of biogenic amines (BAs) in wine matrices. For this reason, a modified QuEChERS combined with ultra-performance liquid chromatography coupled to a triple quadrupole mass spectrometry (UHPLC-QqQ-MS/MS) method was investigated. The optimization of UHPLC-QqQ-MS/MS separation and QuEChERS procedure was performed. Under optimum conditions, the excellent chromatographic performance of the whole separation was accomplished within 6.3 min analyzing time. Meanwhile, the recoveries ranged from 77.2% to 101.7%, while relative standard deviation (RSD) remained between 0.0% and 9.4%. The limit of detection (LOD, 0.50–1.00 µg/L) and the limit of quantification (LOQ, 1.65–3.30 µg/L) were lower than those permitted by legislation in food matrices, which demonstrated the high sensitivity and applicability of this efficient method. This validated method was also applied in a pilot study to analyze BAs in 81 wine samples from Hexi Corridor Region (Gansu Province, Northwest China), CAD, HEX, HIS, PEA, PUT, and TYR were detected to varying degrees in the samples. However, when compared with the existing standards, the BAs in all 81 wine samples did not exceed the prescribed limit value or toxic dose (2–40 mg/L). Moreover, a statistical approach was also conducted using Pearson correlation analysis, and to evaluate their concentrations in terms of wine parameters (storage time, grape variety, wine type, and basic physicochemical index). The results showed that, among the seven kinds of BAs, the concentration of HIS had a certain correlation with alcoholic degree and grape variety. In addition, the level of PEA had a certain correlation with the wine pH and wine storage time. It is worth noting that this seems to be the first report regarding the application of QuEChERS-UHPLC-QqQ-MS/MS in the analysis of BAs in wine in this region.

Evaluation of urban-rural difference and integration based on quality of life

The relationship between urban and rural areas must be properly handled in regional development. With the implementation of rural revitalization strategy, China has entered a critical period of change of urban-rural relationship and rural development mode. Urban-rural integration is an urgent problem to be solved. Taking the 87 counties of Gansu Province as evaluation units, this paper constructed an index system of quality of urban and rural life involving economic, social and environmental aspects and established a model for evaluating quality of urban and rural life. Then, importance-performance analysis (IPA), information entropy, equalization index and model of urban-rural integration degree were used to analyze the spatial patterns of quality of urban and rural life as well as urban-rural integration degree. Results show: (1) Quality of urban and rural life presented consistent spatial patterns. Both presented significant spatial variation, positive spatial autocorrelation and relatively strong spatial agglomeration. (2) There was a close correlation between quality of urban and rural life. Evaluation units with high quality of urban life also showed high quality of rural life, and evaluation units with low quality of urban life also showed low quality of rural life, suggesting polarization effect. (3) The urban-rural integration in Gansu Province was mainly of medium or lower degree. Hexi Corridor region presented high degree of urban-rural integration, Longzhong region presented medium degree of urban-rural integration, Longdong region presented different degrees of urban-rural integration, and Longdongnan and Gannan regions presented medium or lower degree of urban-rural integration. In the background of rural revitalization and urban-rural integration, Gansu Province should establish or improve the institutional mechanism and policy system for urban-rural integration from the perspective of factor-industry-function. This can help solve the problems in urban-rural integration and promote the progression of urban-rural integration in Gansu Province.

Simultaneous Analysis of 20 Mycotoxins in Grapes and Wines from Hexi Corridor Region (China): Based on a QuEChERS⁻UHPLC⁻MS/MS Method.

The aim of this study is to develop and validate an improved analytical method for the simultaneous quantification of 20 types of mycotoxins in grapes and wines. In this research, the optimization of tandem mass spectrometer (MS/MS) parameter, ultra-high pressure liquid chromatography (UHPLC) separation, and QuEChERS procedure, which includes wine/water ratio, the amount and type of salt, clean-up sorbent, were performed, and the whole separation of mycotoxins was accomplished within 7 min analyzing time. Under optimum conditions, recoveries ranged from 85.6% to 117.8%, while relative standard deviation (RSD) remained between 6.0% and 17.5%. The limit of detection (LOD, 0.06–10 μg/L) and the limit of quantification (LOQ, 0.18–30 μg/L) were lower than those permitted by legislation in food matrices, which demonstrated the high sensitivity and applicability of this efficient method. Finally, 36 grapes and 42 wine samples from the Hexi Corridor region were analyzed. Penicillic acid (PCA), mycophenolic acid (MPA), cyclopiazonic acid (CPA), fumonisin B1 (FB1) and zearalenone (ZEN) were detected in a small number of grape samples with lower concentrations between 0.10 μg/L and 81.26 μg/L. Meanwhile, ochratoxin A (OTA), aflatoxin B2 (AFB2), MPA, CPA, and ZEN were detected in some wine counterparts with concentrations ranged from 0.10 μg/L to 4.62 μg/L. However, the concentrations of the detected mycotoxins were much lower than the maximum legal limits set of other products.

Spatial and temporal characteristics of droughts in Central Asia during 1966–2015

In drought-prone regions like Central Asia, drought monitoring studies are paramount to provide valuable information for drought risk mitigation. In this paper, the spatiotemporal drought characteristics in Central Asia are analyzed from 1966 to 2015 using the Climatic Research Unit (CRU) dataset. Drought events, as well as their frequency, duration, severity, intensity and preferred season, are studied by using the Run theory and the Standardized Precipitation Evapotranspiration Index (SPEI) at 3-month, 6-month, and 12-month timescales. The Principle Components Analysis (PCA) and the Varimax rotation method, the Sen's slope and the Modified Mann-Kendall method (MMK), as well as the wavelet analysis are adopted to identify the sub-regional drought patterns and to study the drought trend, periodicity and the possible links between drought variation and large-scale climate patterns, respectively. Results show that the drought characteristics in Central Asia vary considerably. The Hexi Corridor region and the southeastern part suffered from more short-term drought occurrences which mostly occurred in summer while the northeastern part experienced fewer droughts with longer duration and higher severity. Central Asia showed an overall wetting trend with a switch to drying trend since 2003. Regionally, the continuous wetting trend is found in north Kazakhstan while a consistent drying in the Aral Sea and Hexi Corridor region is observed in the last half-century. For 2003–2015, a significant drying pattern is detected in most Central Asia, except the northern Kazakhstan. A common significant 16–64-month periodical oscillation can be detected over the six sub-regions. The drought changes in Central Asia are highly associated with ENSO but less related to the Tibetan Plateau pressure. The North Atlantic Oscillation has an influence on drought change in most Central Asia but less for the Hexi Corridor and the drought variation in eastern Central Asia is affected by the strength of the Siberian High.

Cannabis in Eurasia: origin of human use and Bronze Age trans-continental connections

A systematic review of archaeological and palaeoenvironmental records of cannabis (fibres, pollen, achenes and imprints of achenes) reveals its complex history in Eurasia. A multiregional origin of human use of the plant is proposed, considering the more or less contemporaneous appearance of cannabis records in two distal parts (Europe and East Asia) of the continent. A marked increase in cannabis achene records from East Asia between ca. 5,000 and 4,000 cal bp might be associated with the establishment of a trans-Eurasian exchange/migration network through the steppe zone, influenced by the more intensive exploitation of cannabis achenes popular in Eastern Europe pastoralist communities. The role of the Hexi Corridor region as a hub for an East Asian spread of domesticated plants, animals and cultural elements originally from Southwest Asia and Europe is highlighted. More systematic, interdisciplinary and well-dated data, especially from South Russia and Central Asia, are necessary to address the unresolved issues in understanding the complex history of human cannabis utilisation.

Changes in soil and vegetation with stabilization of dunes in a desert–oasis ecotone

AbstractRevegetation of indigenous plants in a desert–oasis ecotone is an effective way of maintaining the stability of oases. Understanding the changes in vegetation and soil is crucial for restoration management. The properties of soil and vegetation at stabilized sites of different ages were investigated in a typical desert–oasis ecotone, located in the Hexi Corridor region in arid northwestern China, over a period of 40 years. The results indicated that after 40 years the organic matter, total‐N and available‐P at 0–2 cm soil depth increased from 0.1, 0.1 g kg−1, 7 mg kg−1 to 2.0, 0.9 g kg−1, and 75 mg kg−1, respectively. At 2–5 cm the organic matter, total‐N and available‐P increased from 0.4, 0.1 g kg−1, and 7 mg kg−1 to 2.3, 0.4 g kg−1, and 38 mg kg−1, respectively. The number of herbaceous species increased from 4 to 9 and the herbaceous cover increased from 6 to 28 % after 40 years. The height and cover of the sand‐binding vegetation Haloxylon ammodendron (H. ammodendron) reached the highest levels of 446 cm and 68 % after 25 years. After 35 years H. ammodendron dwindled and its belowground and aboveground biomass both decreased significantly. With effective natural regeneration, after 40 years the population of H. ammodendron remained stable and its cover and density remained at 38 % and 1870 ha−1 respectively. The positive mutual feedback between vegetation and soil permitted the sand‐binding vegetation community to become stable over time.

Temporal variations of ground-dwelling arthropods in relation to grassland salinization

The richness and abundance of ground-dwelling arthropods were investigated by a space-for-time substitution approach from spring to autumn of 2012 in the Hexi Corridor region, Gansu Province, to understand the effects of grassland salinization on the temporal distribution of the ground-dwelling arthropod community. The results showed that: 1) grassland salinization had a serious damage to the ground-dwelling arthropod community. The magnitude of the decrease was spring > summer > autumn, resulting in obvious change on seasonal distribution pattern of the ground-dwelling arthropod community; 2) the abundance of predators, herbivores and decomposers decreased significantly in all three seasons with salinization development, with greater effects in spring than in summer and autumn; 3) with salinization development, the most abundant taxon was Formicidae. However, the second dominant family changed over the time of the study. For example, in the lightly salinized grassland, the second dominant families were Lycosidae in spring and autumn, they were gradually replaced by Tenebrionidae in spring and Gnaphosidae in autumn in the severely salinized grassland; and 4) changes in the ground-dwelling arthropod community were largely related to changes in the physical environment and resource availability during the process of grassland salinization. Our results suggest that plant density, vegetation cover and fine particles content played important roles in structuring the ground-dwelling arthropods during the process of grassland salinization.

Soil texture controls vegetation biomass and organic carbon storage in arid desert grassland in the middle of Hexi Corridor region in Northwest China

Soil texture plays an important role in controlling vegetation production and soil organic carbon (SOC) concentration in arid desert grassland ecosystems. However, little is known about the occurrence and extent of these textural effects in the arid desert grasslands of Northwest China. This study used 160 soil profiles taken from 32 desert grassland sites in similar topographical units (alluvial–diluvial fans) in the middle of Hexi Corridor region of Northwest China to investigate vegetation biomass, SOC storage, and soil texture of seven layers in the top 100 cm of soil. The mean aboveground biomass, below-ground biomass, and total biomass in arid desert grassland were 155.3, 95.3, and 256.3 g m–2, respectively. More than 95% of the below-ground biomass was distributed in the top 30 cm of soil. Spatially, vegetation biomass was positively related to soil clay content and silt + clay content. The mean SOC density in the top 100 cm was 2.94 kg m–2 and ~46.8% of the storage was concentrated in the top 30 cm. SOC concentrations and stocks were positively and significantly related to clay content and silt + clay content in the seven soil layers sampled from the top 100 cm. The soil silt + clay content explained 42–79% of the variation in SOC stocks in the different soil depths. In conclusion, soil texture appears to be an important control on vegetation productivity and SOC capacity in arid Hexi Corridor desert grassland soils.

Desertification assessments in the Hexi corridor of northern China’s Gansu Province by remote sensing

The Hexi corridor region lies in the arid and semiarid regions of Gansu Province, China. The sensitive ecological environment has undergone severe desertification caused by natural environmental change and unsustainable exploitation of the region. Remote sensing and GIS are being used to study desertification in this region. In this paper, we used Landsat TM and HJ data between June and August in 2000, 2005, and 2010 to analyze the spatial and temporal patterns of the desertification using five indices: the modified soil-adjusted vegetation index, fractional vegetation cover, the surface albedo, land surface temperature, and the temperature–vegetation drought index. We normalized the indicators, determined their weights, and defined five grades of desertification: none, light, moderate, severe, and extremely severe. We found that desertification in the Hexi corridor covered more than 76 % of the total land area; the total area of desertified land was 22.02 × 104, 21.22 × 104, and 21.06 × 104 km2 in 2000, 2005, and 2010, respectively, which amounted to 79.8, 76.9, and 76.3 % of the total area. In both periods, the most spatial changes in desertification showed a stability or reversal of desertification from 2000 to 2005 and from 2005 to 2010. From 2000 to 2010, the area in which desertification reversed (1.00 × 104 km2) was a little more than the area of newly desertified land (0.96 × 104 km2). The reversal of desertification mainly involved a change from severely and moderately desertified land to non-desertified land. Natural factor and human activity controlled the desertification process, but the reversal of desertification mainly resulted from human activity.

Trade-off between leaf turnover and biochemical responses related to drought tolerance in desert woody plants

We describe differences in leaf photo-protection mechanisms in a group of arid adapted C3 and C4 shrubs that differ in their leaf life-span and compared these mechanisms to known differences in drought tolerance. The experiments were carried out in the field with fourteen woody species native to the Hexi Corridor region, northwestern China. We assessed water status, chlorophyll content, antioxidant enzymes activity, and solute content. We found that differences in photo-protection mechanism among species were not a consequence of differences in photosynthetic pathway, but they were related to leaf life-span. Further, we found evidence that supports the concept of a trade-off between leaf turnover and photo-protective mechanism: species with a longer leaf life-span (leaves with low turnover rate) had higher values of enzymatic (POD and CAT) and no-enzymatic (Chl a, Chl b, Car, and soluble sugars-SS) compounds, than species with a shorter life-span (high turnover rate). These different photoprotective strategies are in accordance with known differences in morphological and physiological leaf attributes that allow for rapid acquisition resources (i.e. acquisitive type) or permit conservation of resources within well protected tissues (i.e. conservative type).

Influences of two patterns of El Ni o on hydrological and meteorological elements in the Hexi Corridor region of China

Influences of two patterns of El Ni o on hydrological and meteorological elements in the Hexi Corridor region of China

Changes in Soil Aggregate, Carbon, and Nitrogen Storages Following the Conversion of Cropland to Alfalfa Forage Land in the Marginal Oasis of Northwest China

Maintenance of soil organic carbon (SOC) is important for sustainable use of soil resources due to the multiple effects of SOC on soil nutrient status and soil structural stability. The objective of this study was to identify the changes in soil aggregate distribution and stability, SOC, and nitrogen (N) concentrations after cropland was converted to perennial alfalfa (Medicago sativa L. Algonguin) grassland for 6 years in the marginal oasis of the middle of Hexi Corridor region, northwest China. Significant changes in the size distribution of dry-sieving aggregates and water-stable aggregates, SOC, and N concentrations occurred after the conversion from crop to alfalfa. SOC and N stocks increased by 20.2% and 18.5%, respectively, and the estimated C and N sequestration rates were 0.4 Mg C ha(-1) year(-1) and 0.04 Mg N ha(-1) year(-1) following the conversion. The large aggregate (>5 mm) was the most abundant dry aggregate size fraction in both crop and alfalfa soils, and significant difference in the distribution of dry aggregates between the two land use types occurred only in the >5 mm aggregate fraction. The percentage of water-stable macroaggregates (>2, 2-0.25 mm) and aggregate stability (mean weight diameter of water-stable aggregates, WMWD) were significantly higher in alfalfa soils than in crop soils. There was a significant linear relationship between total SOC concentration and aggregate parameters (mean weight diameter) for alfalfa soils, indicating that aggregate stability was closely associated with increased SOC concentration following the conversion of crops to alfalfa. The SOC and N concentrations and the C/N ratio were greatest in the >2 mm water-stable aggregates and the smallest in the 0.25-0.05 mm aggregates in crop and alfalfa soils. For the same aggregate, SOC and N concentrations in aggregate fractions increased with increasing total SOC and N concentrations. The result showed that the conversion of annual crops to alfalfa in the marginal land with coarse-texture soils can significantly increase SOC and N stocks, and improve soil structure.

How did the Alxa Block respond to the Indo-Eurasian collision?

The Cenozoic deformation of the Alxa Block resulted directly from the evolution of the northern Qinghai-Tibetan Plateau. However, many data show that the deformation occurred only in the Middle-Late Miocene. Our studies show that the Altyn Tagh fault did not pass through the Alxa Block; on the contrary it went along the southern boundary of the Jintai-Huahai Basin, linking with the Helishan—southern Longshoushan fault. Due to important tectonic events in the northern Qinghai-Tibetan plateau during the Middle-Late Miocene time, the northern plateau underwent rapid uplift and the plateau compressed the Hexi Corridor Region, resulting in a change from NS-trending to EW-trending structures in the Jinta-Huahai basin, and in the development of compressive structures in the Beishan. The southern Alxa fault underwent right lateral movement, and in the northern and central parts of the block, NS-trending Tertiary extensional structures formed. These basins controlled by Tertiary faults are similar to basins developed by lateral extrusion with a strong foreland and weak limited boundaries. The authors suggest that a regional “conjugate” fault system resulted from nearly NS-trending compression from the Qinghai-Tibetan Plateau during the Miocene and Pliocene in the Alxa Block and southern Mongolia. And due to the control of early structures in these regions, most brittle faults reactivated earlier ductile faults; NW–SE faults along the Altai Mountain and NE–SW faults to the southeast in Mongolia consist of a “conjugate” fault system to the north. The Altyn Tagh fault and southern Helishan-Longshoushan fault comprise a “conjugate” fault system to the south. The Beishan and Jinta-Huahai Basin occupied the convergent area between these two sets of faults; the compression controlled the Tertiary deposition and led to the development of the Cenozoic Jinta-Huahai Basin. The Alxa Block bounded by these two sets of faults moved eastwards, which resulted in the development of Cenozoic compressive structures to the west of Helan Shan, and superimposed early ductile shear zones along the northeastern and southwestern boundaries of the Alxa Block respectively. This model could explain the Cenozoic deformation occurring in and around the Alxa region.

Plant community characteristics and their relationships with climate in the Hexi Corridor region of northwestern China

Species, coverage, density, appearance, important values and above ground biomass of desert plant communities in the Hexi Corridor region in northwestern China were investigated. Data on the meteorological factors at the investigation sites were collected. Their relationships were statistically analyzed. The results show that the composition of plant species and total density in the Hexi Corridor region are positively correlated with elevation and longitude, but negatively with latitude. The relation decreases from the southeast to the northwest in this region. In the desert regions with an accumulated temperature of >10°C greater than 3200°C, the shrubs, including semi-shrubs, occupy dominant positions in the communities. Their importance values reach 100. When the accumulated temperature is about 3000°C, the communities are often in some type of transition, either with herbage being the dominant species, with some semishrubs or shrubs as companion species, or the dominant species being semi-shrubs with some perennial herbage as companion species. In desert communities with an annual precipitation of over 110 mm, the main life forms of plants are semi-shrubs or perennial herbs. When precipitation is less than 110 mm, the main life forms of the vegetation are dwarf shrub or annual herbs. In the extreme arid regions with annual precipitation of around 50 mm in the northwestern part of the Hexi Corridor, barely some annual herbage come to life during the rainy season. Desert ecosystems consist of sparse vegetation with small biomass. They change with climate factors and are especially sensitive to precipitation, which is particularly important for their conservation.

Shifts of dust source regions over central Asia and the Tibetan Plateau: Connections with the Arctic oscillation and the westerly jet

An analysis of dust storms and blowing sand records at 681 stations in China during 1961–2000 and in Mongolia during 1980–2000 reveals that the dust source regions in central Asia and the Tibetan Plateau have monthly and interannual northward shifts from the Tibetan Plateau to Mongolia. The monthly shift is closely related to the location of the 200 hPa westerly jet and to the location and intensity of the 500 hPa westerly jet over central Asia and the Tibetan Plateau. The causes for interannual shifts vary by region. The westerly jet appears to drive the shift on the Tibetan Plateau; the intensity of the central Asian mid-latitude westerly, the Arctic oscillation (AO) and the East Asian winter monsoon may be the drivers in the Hexi Corridor region to the north of the Tibetan Plateau; and the AO and the location of the westerly jet in the Mongolian region. All these causes are closely related to the AO variations, which may provide a connection between climatic changes in East Asia and the North Atlantic, and the long-distance transport of dust. This connection could explain the shifts of dust source regions at interannual and millennial timescales and the roughly synchronous climate changes recorded in the Chinese loess and deep-sea sediments in the North Atlantic Ocean.

Soil Properties and Characteristics of Soil Aggregate in Marginal Farmlands of Oasis in the Middle of Hexi Corridor Region, Northwest China

Abstract The composition and stability of soil aggregate are closely related to soil quality, soil erosion, and agricultural sustainability. In this study, 49 soil samples at the 0–10 cm surface layer were collected from four soil types (i.e., Ari-Sandic Primosols, Calci-Orthic Aridosols, Siltigi-Otrthic Anthrosols, and Ustic Cambosols) in the marginal farmland in the oasis of the middle Hexi Corridor region and was used to determine the characteristics of soil aggregates. The composition of dry- and wet- sieved aggregates and the physical and chemical properties (including soil particle distribution, soil organic carbon (SOC), calcium carbonate (CaCO 3), and oxides of Fe 3+ and Al 3+) of the selected soils were analyzed. The results show that soil particle size distribution is dominated by fine sand fraction in most of soils except Ustic Cambosols. Soil organic carbon concentration is 5.88±2.52 g kg −1 on average, ranging from 4.75 g kg −1 in Ari-Sandic Primosols to 10.51 g kg −1 in Ustic Cambosols. The soils have high calcium carbonate (CaCO 3) concentration, ranging from 84.7 to 164.8 g kg −1, which is increased with soil fine particle and organic carbon content. The percentage of >0.25 mm dry aggregates ranges from 65.2% in Ari-Sandic Primosols to 94.6% in Ustic Cambosols, and large dry blocky aggregates (>5 mm) is dominant in all soils. The mean weight diameter of dry aggregates (DMWD) ranges from 3.2 mm to 5.5 mm. The percentage of >0.25 mm water-stable aggregate is from 23.8% to 45.4%. The percentage of aggregate destruction (PAD) is from 52.4% to 66.8%, which shows a weak aggregate stability. Ari-Sandic Primosols has the highest PAD. The distribution and characteristics of soil aggregates are in favor of controlling soil wind erosion. However, the stability of aggregate of all soils is weak and soils are prone to disperse and harden after irrigation. The mass of macro-aggregates and DMWD are positively significantly correlated with the contents of soii clay and silt, soil organic carbon (SOC), CaCO 3, and oxides of Fe 3+ and Al 3+. Soil fine silt and clay, SOC and CaCO 3 are important agents of aggregation in this region, and the effect of SOC and CaCO 3 on aggregate stability is more significant than that of soil silt and clay. Converting cropland to alfalfa forage land can increase SOC concentration, and in turn, enhance the formation of aggregates and stability. For the marginal farmlands in this fragile ecological area, converting cropland to alfalfa grassland or performing crop-grass rotation is an effective and basic strategy to improve soil structure and quality, to mitigate soil wind erosion, and to enhance oasis agricultural sustainability.

Cultivation effects on temporal changes of organic carbon and aggregate stability in desert soils of Hexi Corridor region in China

Sustainable agricultural use of cultivated desert soils has become a concern in Hexi Corridor in Gansu Province of China, because loss of topsoil in dust storms has been recently intensified. We chose four desert sites to investigate the effects of cultivation (cropping) on (i) soil organic C and its size fractions and (ii) soil aggregate stability (as a measure of soil erodibility). These parameters are of vital importance for evaluating the sustainability of agricultural practices. Total organic C as well as organic C fractions in soil (coarse organic C, 0.1–2 mm; young organic C, 0.05–0.1 mm; stable organic C, <0.05 mm) generally increased with the duration of the cultivation period from 0 (virgin soil, non-cultivated) to more than 30 years ( p < 0.05). Compared to total organic C in virgin soils (2.3–3.5 g kg −1 soil), significantly greater values were found after 10 to >20 years of cultivation (6.2–7.1 g kg −1 soil). The increase in organic C in desert soils following prolonged cultivation was mainly the consequence of an increase in the coarse organic C. The increase in total organic C in soil was also dependent on clay content [total organic C = 0.96 + 0.249 clay content (%) + 0.05 cultivation year, R 2 = 0.48, n = 27, p < 0.001]. This indicates that clay protected soil organic C from mineralization, and also contributed to the increase in soil organic C as time of cultivation increased. There was a significant positive correlation between aggregate stability and total organic C across all field sites. The water stability of aggregates was low (with water-stable aggregate percentage ∼4% of dry-sieved aggregates of size 1–5 mm). There was no consistent pattern of increase in the soil aggregate stability with time of cultivation at different locations, suggesting that desert soils might remain prone to wind erosion even after 50 years of cultivation. Alternative management options, such as retaining harvested crop residues on soil surface and excluding or minimizing tillage, may permit sustainable agricultural use of desert soils.

Environmental degradation in the Hexi Corridor region of China over the last 50 years and comprehensive mitigation and rehabilitation strategies

The regional hydrology and ecosystems of the Hexi Corridor region of northwestern China have changed over the last half century under the driving force of intense human activity and regional climate changes. Streamflow issuing from mountains in the eastern section of the Corridor by way of the Shiyang River has decreased significantly. Annual mountain outflow from the Heihe and Shule Rivers in the central and western portions of the Corridor, respectively, have tended to increase; however, their downstream discharge has decreased sharply. These lower reaches clearly display anthropogenic hydrological features. Water salinization and pollution have worsened. Presently, up to 208 km of river courses exhibit the poorest water pollution grades of IV and V. Overall, the forested area in the south Qilian Mountain region has decreased by 16.5% in the last 50 years, but has recently begun to show a gradual increase. However, natural desert forests in the northern portion of the Hexi Corridor have continued in a trend of degradation and rapid disappearance, with 3431 km2 lost in Minqin and Ejin counties alone. Grasslands have been progressively degraded and their area decreased such that grasslands in the Hexi Corridor region only cover 46.86% of their former area. Desertification has been exacerbated and the grasslands' stock capacity reduced. In the Hexi Corridor region desertification has proceeded swiftly over the last 50 years, reaching, in the early 1980s, a maximum annual rate of 2.15% of total initial grassland area. However, from the late 1980s through the 1990s their desertification rate has dropped significantly. A unified watershed-scale plan for water use and management in different regions of the Hexi Corridor, considering water demands for economic development as well as ecosystem maintenance and remediation, must be implemented. The improved and ultimate sustainability of regional development for the Hexi Corridor is linked to following ecological criteria in exploiting land resources, and to systematically protect ecosystem function, allowing for sound ecosystem development.