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Abstract: The effluent from a Chinese paper mill (pH 7.1) was concentrated, and the solid residue was dried and ground. Crude lignosulfonate was obtained as a brown powder, and a novel sand-fixation agent was synthesized by means of graft copolymerization of the lignosulfonate with acrylic acid and formaldehyde. The newly synthesized product had good water solubility, potentially good biodegradation, and produced no additional pollution. The crusts formed on shifting sands using this agent had higher crushing strength and better resistance to wind erosion than those produced with two other recently patented fixatives. [Copyright &y& Elsevier]

The interactive relationships between ecological and hydrological processes drive plant performance, community structure, and community succession in arid areas. Yet the nature of potential hydrologic thresholds for responses of vegetation remains poorly understood. In this paper, we report on hydrologic thresholds associated with aboveground net primary production (ANPP) of Haloxylon ammodendron (HA) and sand-fixation region (SFR) between 1987 and 2012 in the ecotone of desert and oasis in the northwest China. In particular, we focused on precipitation and soil moisture dynamics. Our results showed that 1) ANPP and soil moisture of both HA and SFR decreased from 1987 to 2005, and then reached a stable state; 2) nonlinear models provided a much better fit to the data than linear models, highlighting the presence of a discontinuity in vegetation ANPP changes along precipitation and soil moisture gradients; 3) precipitation, accumulated between preceding-year June to current-year August, of <160 mm, or soil moisture at < 1.4–1.5% may decrease ANPP. Our results provide insights into the thresholds of precipitation and soil moisture in a long-term sand-fixing ecosystem, and highlight the importance of legacy precipitation for the recovery of the sand-fixing ecosystem. Consequently, the findings provide useful references for further understanding of the mechanisms of ANPP changes in a sand-fixing ecosystem with changes in precipitation and soil moisture. [ABSTRACT FROM AUTHOR]

Urbanization has brought about dramatic changes in the urban environment in China and its associated human population and transportation systems in recent years. However, urbanization in the oases of arid regions of China has been little studied and remains poorly understood. This paper aims to analyze spatiotemporal changes in an urban landscape along major vehicular road transects and compare the relationship between urban growth and transportation in Jiuquan, an oasis city in an arid region of China. We integrated remote sensing images, landscape metrics, and urban-rural gradient analysis to address these questions. The results showed that major vehicular roads stimulated Jiuquan's urban expansion, especially with regard to built-up land containing urban green land areas. Oasis urbanization not only increased landscape fragmentation and structural complexity, but also followed a linear branching, leapfrogging growth pattern characterized by “axial clumps” extending from downtown into rural areas along the road network. The primary source of urban land was not agricultural land, but unused land. These results also indicated that the transect approach implemented along representative roads was effective for studying the urbanization of oasis cities. Such an approach could be applied to master planning in similar oasis cities throughout arid China. [ABSTRACT FROM AUTHOR]

The Alxa Desert in north-central China has a unique landscape that contains hundreds of lakes and the highest sand dunes in the world. To date, however, the explanation of the water source in this desert is still controversial. In this paper, continuous hydrometeorological observations, including precipitation, evaporation, water level and temperature, in the interior of the Alxa Desert are presented and the water balance of a typical desert lake is calculated. The moisture, Cl − concentration, δ 2 H and δ 18 O of several sand profiles, the hydrogeochemical characteristics of some lakes and groundwater, and the elemental composition of some travertine samples are analyzed to investigate the rainfall percolation and groundwater recharge. The results showed that local precipitation is not the major replenishment source of the lakes and groundwater in the Alxa Desert. It is supposed that the groundwater from deep strata in the adjacent fracture zone might recharge the desert lake group from the southeast along an altitudinal gradient. [ABSTRACT FROM AUTHOR]

The paper examines the role of mountain runoff in the seasonal growth of oasis vegetation in the hyper-arid region of northwest China. Central to this examination is the development of a simple hydrologic model that relates hydrologic inflows and outflows estimated from remote sensing data (e.g., evapotranspiration, precipitation, snow accumulation, and snowmelt) to the calculation of runoff over a ten-year period (2000–2009). Modeled runoff is shown to reproduce the seasonal trends in hydrometric data fairly well, yielding R 2 's of 0.75 and 0.66 for stations in the upper reaches of the Shiyang and Hei River systems. Greater than 90% of the runoff from the Qilian Mountains to the oases occurs during the May–September period. Considerable discrepancy between modeled and observed runoff exists in the lower reaches of the rivers, where significant amounts of river water (>45%) are routinely extracted for cropland irrigation. Along the river systems, where water extraction and inflow of glacial meltwater are minor, model calculations replicate observed water yields much more closely. Analysis of seasonal trends in the contribution of snowmelt and rainfall to the return flow, reveals snowmelt as having the greatest influence in initiating the oasis growing period during the March-to-May period of each year. [ABSTRACT FROM AUTHOR]

Abstract: Soil fauna are considered to be an important determinant of the litter decomposition in terrestrial ecosystems. However, the contributions of soil macrofauna and mesofauna to litter decomposition in semi-arid environments are not well-recognized. In this paper, litterbags with different mesh sizes (4.7 mm, 2 mm and 0.01 mm) were employed to examine the intraspecific differences in the decomposition of Stipa baicalensis, Achnatherum avinoides, Lespedeza davurica and Agropyron cristatum. In addition, the effects of soil macrofauna and mesofauna on litter decomposition were determined in Songnen sandy land. The results of this study showed that Prostigmata, Psocidae and Oribatida were dominant fauna in the litterbags. Significant intraspecific differences were found in litter decomposition rates, and the process of litter decomposition can be separated into two apparent stages. Ac. avinoides exhibited the highest contribution rate to litter decomposition, followed by Ag. cristatum, L. davurica and S. baicalensis. Contribution rates of macrofauna and mesofauna to litter decomposition were different. The rate of litter decomposition was positively correlated with the group density of fauna. Our results suggested that both macrofauna and mesofauna could accelerate litter decomposition and, consequently, nutrient cycling in semi-arid ecosystems, although their functional roles were different in litter decomposition. [Copyright &y& Elsevier]

Abstract: In arid lands, the shifts in dominant plant types from grasses to shrubs can significantly alter the ecosystem function and biogeochemistry cycles. However, the magnitude of these alterations and its inherent mechanisms are still poorly understood. In this study, we measured soil respiration and NPP over two growing seasons in 2006–2007 in the co-occurring perennial grass and desert shrub ecosystems at the Ordos Plateau of Inner Mongolia, China. Over the two growing seasons, the desert shrub site presented higher aboveground biomass and NPP while lower soil respiration relative to the grass site (p < 0.05). In this paper, we can not determine that whether vegetation conversion or soil texture change drive the site difference in soil respiration because we did not control for soil texture. We suppose that the site difference in pulse response of soil respiration might play an essential role in regulating this soil respiration gap. In all the growing seasons, surface soil moisture (0–10 cm) was identified as the major driver of soil respiration at both sites. Compared to the linear soil moisture model, the integrated model incorporating both surface soil moisture and air temperature was performed better in predicting the dynamics of soil respiration. [Copyright &y& Elsevier]

Abstract: In the Tarim River Basin, the desert riparian forest vegetation is under high-temperature and aridity stress. However, the vegetation can grow continuously because of deep rooting that can reach groundwater, which can thus redistribute water into the upper soil profile. This paper describes patterns of hydraulic lift by Populus euphratica Oliv. and discusses its ecological effects. Our results show that the tap root sap velocity of P. euphratica Oliv. is positive during the day and night. However, a reverse sap flow was observed in the lateral roots during the night. The soil water content of the subsoil was higher than that of the topsoil at depths of 0–120cm. When the sap flow of the lateral roots was reversed at night, the soil water content clearly increased. In particular, at depths of 60–120cm, the soil water content at 4:00 was 28–38% greater than that at 16:00. The vapor pressure deficit was a factor that predominantly affected the root sap velocity, and the smaller vapor pressure deficit often facilitated a reverse sap flow in the lateral roots. Our findings demonstrate the hydraulic lift characteristics and ecological effects that occur in the desert riparian forest in extremely arid regions of middle Asia [Copyright &y& Elsevier]

Abstract: Pollen concentration has been commonly used to indicate vegetation cover and moisture change. However, this practice may not always be justified in arid and semi-arid regions. This paper investigates potential problems with the approach based on modern pollen assemblages and fossil pollen data from arid and semi-arid China. The results show that pollen concentration has no direct relationship with vegetation cover and effective moisture in our study region. Pollen representation and sediment accumulation rate may have contributed to the complication. We conclude that pollen concentration cannot be used as a reliable index of effective moisture in arid and semi-arid regions. [Copyright &y& Elsevier]

Abstract: The nonparametric Mann–Kendall test was used to detect the trends of major hydroclimatic variables in the Tarim River Basin, the largest inland river basin in China for the period of 1960–2007. Results showed that both mean annual air temperature and precipitation experienced an increasing trend, while annual streamflow demonstrated a mixed trend of decreasing and increasing: The mountainous region upstream showed an increasing trend and the region downstream exhibited a decreasing trend. Impacts of the increased air temperature on streamflow have shown different characteristics depending on location and seasons: it has positive effect on the runoff at mountainous region due to snowmelt and glacier-melt in spring, but negative effect on the runoff at plain area due to the increase of actual evaporation in summer. In addition, human activity contributed to the declining of streamflow in the arid plain oases at downstream of the Tarim River Basin. The results obtained in this paper can be used as a reference for the planning and management of water resources to maintain the health of the river system. [Copyright &y& Elsevier]

Abstract: Results integrated from several data sources such as the vertical distribution characteristics of dust aerosols detected by aircraft, optical particle counter and Lidar measurements in the troposphere, dust devils, dry heat convection, and cloud parameter characteristics monitored by satellites, allow the identification of a new upwards dust transport mechanism. During non-dust storm periods, fine dust particles can be firstly carried into the atmosphere about 10–200m by dust devils. Next, they can be carried to the height of the boundary layer at about 1000–6000m by strong dry heat convection, so that a well-mixed dust layer dominates, which may even develop an elevated dust layer over the desert in the warm and sunny season. These processes lead to high dust aerosol concentrations in the desert troposphere, which results in an increase of condensation nuclei in clouds, a decrease of the effective radius of cloud droplets, and thus the formation of precipitation is suppressed. This paper develops a mechanism of positive feedback, which follows the following sequence: dust aerosol increases—effective radius of cloud droplet decreases—precipitation decreases—arid climate is strengthened. This new mechanism is a distinct factor in the development of an arid climate, especially desert in North China, and gradually becomes one of the most important factors maintaining an arid climate in North China. The positive feedback can accelerate desertification in this area. [Copyright &y& Elsevier]

Abstract: Over the last decade, remote-sensing products found their use in numerous public applications and scientific research. Frequent validation of remote-sensing products is necessary to ensure the quality and accuracy. An important step in this process is the upscaling from field measurements of leaf area index (LAI) or other biogeophysical variables to the scale of a high-resolution satellite image. Unlike other vegetation types, semi-arid woodlands are often characterized by a distinct vegetation pattern, a low vegetation cover and site variations in bare soil reflectance which influence the upscaling process. This paper focuses on the upscaling of LAI field measurements of a semi-arid woodland in northwest China and the uncertainties associated with it. The LAI measurements were scaled up using two different approaches. The first upscaling method uses an ordinary average of the LAI measurements. The alternative method uses an area-based weighted average. The vegetation characteristics showed abundant small vegetation patches which were not accurately reflected in the systematic LAI field measurements. Therefore, the alternative method which reflected the vegetation structure more accurately needs to be considered. We conclude that an area-weighted average based on the fractional green vegetation cover is to be preferred over a simple average. If possible destructive sampling of the LAI is be preferred over indirect LAI measurements to reduce the errors associated with vegetation clumping and the presence of abundant non-green biomass. [Copyright &y& Elsevier]

Abstract: Establishing forest cover in arid or drought-stricken regions is a challenging task facing countries with a high degree of desertification or risk of desertification. China''s Loess Plateau is one such area, an extremely dry climate, especially in spring, and that has a highly dissected topography. A new tree-planting technique to improve drought resistance, in which planting holes are lined with biodegradable plastic to reduce drainage and evaporation, was tested in an arid, erosion-prone, hilly area of the Loess Plateau between 1997 and 2006, during a period of lower-than-normal precipitation. In this paper, we report the survival and growth of 15 tree species grown with and without the new plastic lining. The new tree-planting technique promoted root growth in the topsoil by keeping the soil moisture than the surrounding soil evident during the first 4 months after planting. Tree survival rates, branch growth increment per year, tenth-year canopy area, and tenth-year canopy density in trees planted using the new method increased by an average of 41.4%, 29.0%, 16.9%, and 65.3%, respectively, compared with the values for the conventional planting technique. This suggests that the new planting technique is more suitable than the conventional method for the study area''s soil environment and climate, and may prove suitable for similar areas elsewhere in the world where survival and growth rates are low. The results of our study thus represent a potentially valuable alternative for forest restoration and soil conservation in arid zones. [Copyright &y& Elsevier]

This paper discusses the sources, spatial distribution, frequency and trend of dust storms in China. Most dust storms in China originate from one of three geographic areas: the Hexi (River West) Corridor and western Inner Mongolia Plateau, the Taklimakan Desert, and the central Inner Mongolia Plateau. Dust is most likely from deteriorated grasslands, Gobi, alluvial, lacustrine sediments and wadis at the outer edge of deserts. But deserts themselves contribute only slightly to the dust storm directly. Two geographic areas frequently have dust storms: one is in the western Tarim Basin, a ground surface of deteriorated land and wadi, but it only affects its neighboring areas, and the other one is in the western Inner Mongolia Plateau, a ground surface of Gobi, alluvial and lacustrine sediments, but it causes most of the dust storms in north China. Generally speaking, dust storms have reduced in most regions of China from the 1950 to 2000. Dust storms are highly correlated with human activities and climate changes. [Copyright &y& Elsevier]

Ammopiptanthus mongolicus (Maxim.ex Kom.) Cheng f., an ancient relic of the Tertiary Period, is a rare and endangered species of Fabaceae in Mid-Asia desert and has been listed as one of primary protection plants by the Chinese government. Because of its high value of study and ecological usefulness in defending desert, this plant has been called ‘live fossil’. Using the leaves of A. mongolicus derived from water-stressed and water-supplemented environments at Shapotou in the south-east edge of Tengger Desert, seasonal changes of caloric values and osmotica, including free amino acids, total soluble sugar (TSS), sucrose, glucose and inorganic cations have been studied in this paper. The results showed that the main substances involved in osmotic adjustment varied with growth periods and between samples. At the early period it was soluble sugar mainly, and at the late period, besides soluble sugar, potassium and free amino acid (especially proline) also functioned. The higher levels of osmotica content (especially concentrations of total soluble sugar, sucrose, proline and potassium) and caloric values have been found in water-stressed plants rather than in irrigated ones. [Copyright &y& Elsevier]

This paper analyses climate change in the Yuanmou dry-hot valley area since the 1950s and compares it with that on the Yunnan plateau (Chuxiong City, Wuding County and Dongchuan City). Annual average temperature, the coldest month average temperature, annual evaporation, annual sunshine hours and annual mean wind speed, all have declined, while the annual rainfall and the average relative humidity have slightly increased. The causes of climate change are chiefly the result of large-scale irrigation in the cultivated land and the restoration of vegetation, and also related to local environmental change. [Copyright &y& Elsevier]