Photosynthetically active radiation (PAR) is an important input parameter for estimating plant produc-tivity due to its key role in the growth and development of plants. However, a worldwide routine network for sys-tematic PAR measurements is not yet established, and PAR is often calculated as a constant fraction of total solar radiation (SR). Although the ratio of PAR to SR (PAR/SR) has been reported from many places, few studies have been performed for dry regions. The present study was therefore carried out in an arid region of Mongolia to obtain PAR/SR and examine its dependency on sky clearness (the clearness index), water vapor in the atmosphere and aeolian dust. Continuous measurements of PAR and SR were taken every one second using quantum and pyranometer sensors, respectively, and the readings were averaged and recorded at intervals of 30 minutes for a period of 12 months. The lowest monthly mean daily PAR/SR occurred in April (0.420), while the highest ratio was observed in July (0.459). Mean daily PAR/SR during plant growing season (May−August) was estimated to be 0.442, which could be useful for modeling plant productivity in the study area. The annual mean daily PAR/SR (0.435) was lower than the values reported in many previous studies. This difference could be explained with the regional variation in climate: i.e. drier climatic condition in the study area. PAR/SR was negatively correlated with the clearness index (r= –0.36, P<0.001), but positively with atmospheric water vapor pressure (r=0.47, P<0.001). The average PAR/SR was significantly lower (P=0.02) on the dusty days compared to the non-dust days. Water vapor in the atmosphere was shown to be the strongest factor in the variation of PAR/SR. This is the first study examining PAR/SR under a semi-arid condition in Mongolia.

The vertical distribution of aerosols in the troposphere is important for determining their effects on cli-mate. The vertical distribution of aerosols under different atmospheric conditions in the free troposphere was di-rectly observed using a surface micro-pulse LIDAR (MPL) and a TP/WVP-3000 microwave radiometer at the Semi-Arid Climate & Environment Observatory of Lanzhou University (SACOL, 35.95°N, 104.10°E) in the western Loess Plateau, China, in the spring of 2008. The results showed two possible transportation paths of a sandstorm from May 1 to May 4 in 2008. In one path, sand-dust aerosols were transported toward the east from the Taklimakan Desert to the Badain Jaran Desert and the Tengger Desert by a westerly wind and then toward the southeast to Jingtai and Lanzhou. A weak aerosol index (AI) indicated another possible transport path toward the east from the Taklimakan Desert to the Qaidam Basin and through the Tibetan Plateau eastward to SACOL. The aerosol profile of sandstorm processes over the SACOL area displayed three patterns: a single peak distribution under stable at-mospheric conditions, indicating urban aerosol distribution; an exponential decrease under unstable atmospheric conditions in the presence of a sandstorm; and a slight change in the mixed layer during the first and last stages of the sandstorm, indicative of thorough mixing during lifting and deposition stages. Analyses of the aerosol layer height (ALH) showed that there are two types of ALH diurnal variation. The ALH during the first sandstorm stage was complex and disordered, and affected by atmospheric circulation. While the ALH had obvious diurnal variation in the other stage, the ALH and aerosol extinction coefficient (AEC) had a single peak, and was higher in the af-ternoon and lower in the morning. In the second case the ALH was in agreement with the atmospheric boundary layer height (BLH) variation. As a result of the development of the atmospheric boundary layer (ABL) during day and maintenance at night, ALH during sandstorm-free days showed obvious diurnal variations. Multiple vertical distribu-tion patterns of sand-dust aerosols will result in different climate effects; therefore, the vertical distribution patterns can be used to parameterize climate and aerosol models.

To improve the level of meteorological service for the Oilfield region in the Taklimakan Desert, the Urumqi Institute of Desert Meteorology of the China Meteorological Administration (CMA) conducted a detection experiment by means of wind profiling radar (WPR) in Tazhong Oilfield region of Xinjiang, China in July 2010. By using the wind profiler data obtained during the rainfall process on 27 July, this paper analyzed the wind field fea-tures and some related scientific issues of this weather event. The results indicated that: (1) wind profiler data had high temporal resolution and vertical spatial resolution, and could be used to analyze detailed vertical structures of rainfall processes and the characteristics of meso-scale systems. Before and after the rain event on 27 July, the wind field showed multi-layer vertical structures, having an obvious meso-scale wind shear line and three airflows from different directions, speeding up the motion of updraft convergence in the lower atmosphere. Besides, the wind directions before and after the rainfall changed inversely with increasing height. Before the rain, the winds blew clockwise, but after the onset of the rain, the wind directions became counterclockwise mainly; (2) the temperature advection derived from wind profiler data can reproduce the characteristics of low-level thermodynamic evolution in the process of rainfall, which is capable to reflect the variation trend of hydrostatic stability in the atmosphere. In the early stage of the precipitation on 27 July, the lower atmosphere was mainly affected by warm advection which had accumulated unstable energy for the rainfall event and was beneficial for the occurrence of updraft motion and precipitation; (3) the “large-value zone” of the radar reflectivity factor Z was virtually consistent with the onset and end of the rainfall, the height for the formation of rain cloud particles, and precipitation intensity. The reflectivity factor Z during this event varied approximately in the range of 18–38 dBZ and the rain droplets formed mainly at the layer of 3,800–4,500 m.

This paper, based on the analysis and calculation of the groundwater resources in an arid region from 1980 to 2001, put forward the concept of ecological groundwater level threshold for either salinity control or the determination of ecological warning. The surveys suggest that soil moisture and soil salinity are the most important environmental factors in determining the distribution and changes in vegetation. The groundwater level threshold of ecological warning can be determined by using a network of groundwater depth observation sites that monitor the environmental moisture gradient as reflected by plant physiological characteristics. According to long-term field observations within the Ejin oases, the groundwater level threshold for salinity control varied between 0.5 m and 1.5 m, and the ecological warning threshold varied between 3.5 m and 4.0 m. The quantity of groundwater re-sources (renewable water resources, ecological water resources, and exploitable water resources) in arid areas can be calculated from regional groundwater level information, without localized hydrogeological data. The concept of groundwater level threshold of ecological warning was established according to water development and water re-sources supply, and available groundwater resources were calculated. The concept not only enriches and broadens the content of groundwater studies, but also helps in predicting the prospects for water resources development.

This study presented a simulation-based two-stage interval-stochastic programming (STIP) model to support water resources management in the Kaidu-Konqi watershed in Northwest China. The modeling system coupled a distributed hydrological model with an interval two-stage stochastic programing (ITSP). The distributed hydrological model was used for establishing a rainfall-runoff forecast system, while random parameters were pro-vided by the statistical analysis of simulation outcomes. The developed STIP model was applied to a real case of water resources management planning in Kaidu-Konqi watershed, where three scenarios with different water re-sources management policies were analyzed. The results indicated that water shortage mainly occurred in agri-culture, ecology and forestry sectors. In comparison, the water demand from municipality, industry and stock-breeding sectors can be satisfied due to their lower consumptions and higher economic values. Different policies for ecological water allocation can result in varied system benefits, and can help to identify desired water allocation plans with a maximum economic benefit and a minimum risk of system disruption under uncertainty.

Located in the south of Xinjiang Uygur autonomous region, the Tarim River is the longest inland river in China. Agricultural development, excessive exploitation and low surface water use efficiency in the headstream regions have led to a marked decrease in the water supply to the mainstream. This, in turn, has resulted in the drying-up of the watercourse in the lower reaches of the Tarim River and serious deterioration of the eco-environment. The Aksu River Basin, the most important headstream of the Tarim River, was selected as the research area in this study. Taking elastic coefficient, water demand coefficient and water utilization intensity as the indices, we studied the impact of agricultural development on decreasing surface runoff since the 1950s. The re-sults indicated that (1) the increasing rate of consumption of surface runoff outstripped the rate of increase meas-ured in the natural catchment discharge, resulting in ever diminishing stream discharge into the Tarim River. Agri-cultural irrigation and seepage loss in irrigation canal systems were the major sources for runoff consumption, tak-ing 63.72% of the overall runoff consumption. What’s more, agricultural water consumption took up more than 97% of the water used for long-term production; (2) the expansion of cultivated land, change of planting structure and comparatively low agricultural irrigation efficiency all contributed to the decrease in surface runoff of the Aksu River. The elasticity coefficient of surface runoff reduction corresponding to the increase in planted area was 0.34 in the 1950s, while in the 2000s it had increased to 7.87. This reflected a more sensitive response of runoff decrease to cultivated land expansion. The increase in cotton and fruit production, without widely-used scientific irrigation methods and water-saving technology, led to considerable waste of the water resources. Meanwhile, the irrigation efficiency was still quite low, characterized by the waste of water resources, and the decrease of surface runoff; (3) in different stages, cultivated land area, planting structure and agricultural water use efficiency exerted different effects on runoff decrease. In the early stage, agricultural development showed no obvious effect on runoff de-crease. Since the 1960s, the expansion in cultivated land resulted in large consumption of surface runoff; since the 1990s, not only expansion in cultivated land expansion, but also planting structure exerted significant impact on the consumption of surface runoff. Recently, though agricultural water use efficiency has improved in some regions to reduce the consumption of runoff to a certain extent, overall agricultural water use efficiency is still quite low; (4) during the investigation period, water consumption by agricultural development reflected the unbalanced relation-ship between human activities and water resources.

Horqin Sandy Land is a fragile, seriously desertified region located in Inner Mongolia of China. Over-grazing is one of the primary drivers of desertification in this region. We investigated whether the establishment of grazing exclosures in areas with active sand dunes enhances soil carbon (C) sequestration and benefits soil re-covery. The results showed that soil organic C storage was 1.4, 1.9, and 3.5 times, and light fraction C storage was 2.3, 3.2, and 4.4 times in the 100-cm topsoil after 7, 12, and 25 years of grazing exclusion, respectively, compared to the case in active sand dunes. The light fraction of soil played an important role in soil C sequestration, although it might not change rapidly to provide an early indication of how soil C is increasing in response to grazing exclusion. The results indicated that soils could potentially sequester up to 13.8 Mt C in 25 years if active sand dunes in the study area were to be protected by exclosures. This corresponds to 12.8% of the estimated carbon loss (107.53 Mt) that has been associated with desertification over the past century in the Horqin Sandy Land. Our results suggested that exclosures have the capacity to increase soil C sequestration; however, decades will be required for soil C to recover to historical grassland levels observed prior to desertification.

Land use change significantly influences soil properties. There is little information available on the long-term effects of post-reclamation from grassland to cropland on soil properties. We compared soil carbon (C) and nitrogen (N) storage and related soil properties in a 50-year cultivation chronosequence of grassland in the agro-pastoral ecotone of Inner Mongolia. Field surveys on land use changes during the period of 1955–2002 were conducted to build a chronosequence of cropland of different ages since the conversion from grassland. The results showed that soil C and N storage, soil texture, and soil nutrient contents varied with land use types and cropland ages (P<0.01). In the 0–30 cm soil layer, the soil organic carbon (SOC) density was significantly lower in the crop-lands (3.28 kg C/m² for C50 soil) than in the grasslands (6.32 kg C/m²). After 5, 10, 15, 20, 35, and 50 years of crop planting (years since the onset of cultivation), the SOC losses were 17%, 12%, 19%, 47%, 46%, and 48%, respec-tively, compared with the grasslands. The soil total nitrogen (TN) density of the grasslands was 65 g N/m², and TN density of the cropland soil was 35 g N/m² after 50 years of crop planting. Both the SOC and TN densities could be quantitatively determined by a negative exponential function of cropland age (P<0.0001, R²=0.8528; P<0.0001, R²=0.9637). The dissolved organic carbon (DOC) content, soil available potassium (AK) content, clay content, and pH value were decreased; and the soil bulk density and sand content were increased since the conversion of grassland into cropland during the 50-year period. Our results show soil nutrients were higher in grassland than in cropland. The conversion of grasslands to croplands induced a loss of soil C storage and changes of related soil properties. The reclamation time of cultivated soil (cropland age) had significant effects on soil properties in the study area.

Litter phosphorus (P) return is important to maintain the P cycle and balance in the sandy land of arid areas. In this study, we determined the loss and return of litter P in sand dune areas and elucidated their relation-ship. We investigated litter production and litter P amount, and simulated leaf litter moving dynamics to understand the relationships between the loss of litter P and the total litter P, and between the return of litter P and the total litter P in active (AD), semi-stabilized (SSD) and stabilized (SD) dunes in Inner Mongolia, northeastern China. The vegetation litter P was 12.6, 94.5, and 201.6 mg P/m² in AD, SSD, and SD, respectively. A significant movement and loss of leaf litter P with time occurred on the three types of sand dunes. As a result, the loss of P was 7.4, 46.9, and 69.8 mg P/m² and the return of P was 5.5, 47.6, and 131.8 mg P/m² in AD, SSD, and SD, respectively. The rela-tionship between both loss and return of P and total litter P in AD, SSD, and SD was revealed by linear regression. The slope of the regression line indicated the rate of loss or return of litter P. From AD to SD, the loss rate showed a declining slope (0.52, 0.32, and 0.17 for AD, SSD, and SD, respectively), and the return rate showed a rising slope (0.48, 0.67, and 0.83 for AD, SSD, and SD, respectively). The loss of litter P should be regarded in the local man-agement of vegetation and land in sand dune areas. Improved vegetation restoration measures are necessary to decrease litter P loss to maintain the stability of ecosystems in sand dune areas.

With the classical statistical and geostatistical methods, the study of the spatial distribution and its in-fluence factors of soil water, salinity and organic matter was carried out for 0–70 cm soil layers in Manas River watershed. The results showed that the soil moisture data from all soil layers exhibited a normal distribution, with average values of 14.08%–21.55%. Geostatistical analysis revealed that the content of soil moisture had a moder-ate spatial autocorrelation with the ratios of nugget/sill ranging from 0.500 to 0.718, which implies that the spatial pattern of soil moisture is influenced by the combined effects of structural factors and random factors. Remarkable spatial distributions with stripped and mottled features were found for soil moisture in all different soil layers. The landform and crop planting had a relatively big influence on the spatial distribution of soil moisture; total soil salinity was high in east but low in west, and non-salinized soil and lightly salinized soil appeared at the northwest and southwest of the study area. Under the effect of reservoir leakage, the heavily salinized soils are widely distributed in the middle of the study area. The areas of the non-salinized and lightly salinized soils decreased gradually with soil depth increment, which is contrary to the case for saline soils that reached a maximum of 245.67 km² at the layer of 50–70 cm. The types of soil salinization in Manas River watershed were classified into four classes: the sulfate, chloride-sulfate, sulfate-chloride and chloride. The sulfate salinized soil is most widely distributed in the surface layer. The areas of chloride-sulfate, sulfate-chloride, and chloride salinized soils increased gradually along with the increment of soil depth; the variation range of the average values of soil organic matter content was be-tween 7.48%–11.33%. The ratios of nugget/sill reduced gradually from 0.698 to 0.299 with soil depth increment, which shows that the content of soil organic matter has a moderate spatial autocorrelation. The soil organic matter in all soil layers met normal distribution after logarithmic transformation. The spatial distribution patterns of soil or-ganic matter and soil moisture were similar; the areas with high organic matter contents were mainly distributed in the south of the study area, with the lowest contents in the middle.

Soil organic matter (SOM) plays an important role in maintaining vegetation cover and thus mitigating land erosion of fragile terrestrial ecosystems such as in the Northern Ordos Plateau of China (NOPC). However, little information is available on whether and how SOM varies spatially as an intrinsic characteristic of landform in NOPC. The objective of this study was to examine the spatial associations of SOM with landform and vegetation cover. The study was conducted in a 23,000-km2 area within NOPC because this area has landforms of mobile dunes (MD), flat dunes (FD), grassy sandy land (GSL), flat sandy bedrocks (FSB), and swamps and salt lakes (SW), which are typical landforms in semiarid ecosystems. SOM was determined using a standard laboratory analysis method for 5 cm topsoil samples collected at 72 locations across the study area. In addition, the 250 m Multitem-poral Moderate Resolution Imaging Spectroradiometer (MODIS) imageries taken in the period from August 2006 to August 2010 were used to extract Normalized Difference Vegetation Index (NDVI) which in turn was used as the surrogate of vegetation cover. Classic and geostatistical methods were used to compare SOM concentration across different landforms. The results indicated that an area with a greater value for NDVI (i.e. better vegetation cover) tended to have a higher SOM concentration regardless of the landform types. However, the association between SOM and NDVI varied from one landform to another. The SW and GSL had a highest SOM concentration, while MD had a lowest concentration. For the study area as a whole and the FD, GSL, and MD, SOM was found to be the sole function of NDVI, whereas, for the FSB, SOM was influenced by several intrinsic variables, namely ground surface altitude, slope, and aspect, as well as NDVI. SOM for the SW landform was found to be a function of NDVI. Furthermore, SOM and NDVI exhibited a consistent spatial pattern of increasing from north to south and from west to east. The highest SOM concentration of 3.5% occurred along an east-westward belt, which is adjacent to water pathways, in the mid part of the study area.

 The spatial distribution of plant populations is an important feature of population structure and it de-termines the population’s ecological preferences, biological characteristics and relationships with environmental factors. The point pattern analysis method was adopted to study the distribution pattern of Picea schrenkiana indi-viduals of different size classes and the correlations between two size classes as well as the impact of topog-raphical attributes on the population distribution. With increasing diameter at breast height, the plant density of the P. schrenkiana population showed a declining trend. Old trees showed a random distribution at a small spatial scale (0–12 m), whereas saplings, small trees and big trees all had an aggregated distribution at all scales. With the increase of tree age, the scales at which maximal aggregation occurred gradually increased and the aggregation strength decreased. At a small scale (0–16 m), all size classes showed a negative correlation and the larger the difference between tree size, the more significant the negative correlation. The number of medium, big and old trees had a significantly positive correlation with elevations, whereas the number of saplings and small trees was not significantly correlated with elevations. The numbers of saplings, small and medium trees showed a significant positive correlation with slope gradient, whereas the number of big trees was not significantly correlated, and the number of old trees was negatively correlated with gradient. With the exception of old trees, saplings, small, me-dium and big trees showed negative correlations with convexity index. The study provides a theoretical basis for the conservation, rehabilitation and sustainable management of forest ecosystems in the Tianshan Mountains.

This paper focused on the water relations of two halophytes differing in photosynthetic pathway, phe-notype, and life cycle: Karelinia caspica (Pall.) Less. (C₃, deep-rooted perennial Asteraceae grass) and Atriplex tatarica L. (C₄, shallow-rooted annual Chenopodiaceae grass). Gas exchange, leaf water potential, and growth characteristics were investigated in two growing seasons in an arid area of Xinjiang to explore the physiological adaptability of the two halophytes. Both K. caspica and A. tatarica showed midday depression of transpiration, in-dicating that they were strong xerophytes and weak midday depression types. The roots of A. tatarica were con-centrated mainly in the 0–60 cm soil layer, and the leaf water potential (Y_L)) increased sharply in the 0–20 cm layer due to high soil water content, suggesting that the upper soil was the main water source. On the other hand, K. caspica had a rooting depth of about 1.5 m and a larger root/shoot ratio, which confirmed that this species uptakes water mainly from deeper soil layer. Although A. tatarica had lower transpiration water consumption, higher water use efficiency (WUE), and less water demand at the same leaf water potential, it showed larger water stress impact than K. caspica, indicating that the growth of A. tatarica was restricted more than that of K. caspica when there was no rainfall recharge. As a shallow-rooted C₄ species, A. tatarica displayed lower stomatal conductance, which could to some extent reduce transpiration water loss and maintain leaf water potential steadily. In contrast, the deep-rooted C₃ species K. caspica had a larger root/shoot ratio that was in favor of exploiting groundwater. We concluded that C₃ species (K. caspica) tapes water and C₄ species (A. tatarica) reduces water loss to survive in the arid and saline conditions. The results provided a case for the phenotype theory of Schwinning and Ehleringer on halophytic plants.