Northern Tianshan Mountains Research Articles

Variation of the Relative Soil Moisture of Farmland in a Continental River Basin in China

The reduction of grain production caused by drought is one of the most serious problems caused by natural disasters. The relative soil moisture of farmland is the most important monitoring indicator for agricultural drought. This study investigated the relative soil moisture of farmland data from 38 agrometeorological stations in a continental river basin area in China from 1992 to 2012. Spatial and temporal variations of the relative soil moisture of farmland were studied using geostatistical analysis. The results show that, from 1992 to 2012, the average annual relative soil moisture of farmland in the continental river basin ranged from 62.5 to 86.1%, and the relative soil moisture of farmland was high in the marginal areas of basins and low in the central areas of basins and plateau areas. The relative soil moisture of farmland was high in the Tarim Basin and the Hexi Corridor, which are located in the northern Tianshan Mountains and the southern and northern Qilian Mountains, and was low from the northern Altun Mountains to the south of Lop Nor, the Turpan Depression, and the Tarbagatai Mountains. From 1992 to 2012, the annual average relative soil moisture of farmland in the continental river basins showed an increasing trend, with a growth rate of 0.57% yr−1. The variation tendency of the relative soil moisture of farmland was different in different river basins; the relative soil moisture showed a decreasing trend in the Mongolian Plateau and an increasing trend in other basin areas. The relative soil moisture of farmland increased in summer, spring, and winter, and decreased in autumn. The change in relative soil moisture of farmland was due to a combination of climatic factors, such as precipitation and temperature, as well as topography and glacial meltwater.

Cretaceous and Paleogene saline lacustrine source rocks discovered in the southern Junggar Basin, NW China

Saline lacustrine source rocks in China provide the resource basis for many giant oil fields. Here, we report the first discovery of such source rocks in the piedmont area of the northern Tianshan Mountains in the southern Junggar Basin of NW China. These source rocks are Cretaceous and Paleogene in age. Organic geochemistry and trace-element data suggest that these mudstones were formed in a brackish–saline lacustrine environment, characterized by deep-water and reducing conditions, and in a warm and dry paleoclimate. Evidence for this environment includes mudstone Pr/Ph values of <1.0, high gammacerane index ratios of >0.4, and negative Ce and Eu anomalies. The total organic carbon (TOC) contents of these Cretaceous and Paleogene mudstones are typically >0.5%, with maximum values of 1.45% and 2.22%, respectively, signifying moderate to high organic matter abundance. Rock-Eval and kerogen analyses suggest that the organic matter was dominated by type II kerogen. The mudstones are generally thermally mature, suggesting favorable conditions for hydrocarbon (particularly oil) generation. Oil–source correlation confirms the oil generation of these two sets of source rocks, whose development are controlled mainly by reducing environments. These Cretaceous and Paleogene mudstones should therefore be a target for regional exploration in the southern Junggar Basin in addition to the known gas-producing Jurassic rocks. This oil-bearing potential is unique amongst the Early Cretaceous and Eocene–Oligocene central Asian petroliferous basins, as the eastern portion of this realm is considered to host predominantly Jurassic coal-based source rocks, giving rise to numerous large gas fields rather than oil resources.

The relationships between urban landscape patterns and fine particulate pollution in China: A multiscale investigation using a geographically weighted regression model

Abstract Providing accurate assessments of the relationships between urban landscape patterns and PM2.5 pollution is essential for improving urban sustainability in China. Accordingly, this paper uses a geographically weighted regression model to reveal the relationships between urban landscape patterns and PM2.5 pollution at different scales in China. First, we identified the level of PM2.5 pollution in China and quantified the urban landscape patterns based on the landscape metrics in 2015. Then, we analyzed the relationships between urban landscape patterns and PM2.5 pollution using geographically weighted regression with the county as the basic analytical unit. Finally, the spatial characteristics of the relationships between urban landscape patterns and PM2.5 pollution were analyzed at the national, regional and provincial scales. We found that the PM2.5 pollution in China was closely related to urban landscape patterns, with obvious spatial heterogeneity. The total area with a significant correlation between the urban landscape patterns (which were measured using the percentage of urban landscape, edge density, and patch density) and PM2.5 pollution ranged from 2.07 × 106 km2 to 2.26 × 106 km2, accounting for 42.55%–46.59% of the total PM2.5-polluted area in China. The high correlations were concentrated mainly in five provinces, namely, Xinjiang, Shaanxi, Fujian, Chongqing and Guangdong. We also found that the relationships between urban landscape patterns and PM2.5 pollution were stronger in urban agglomerations. The total area with a significant correlation between the urban landscape patterns and PM2.5 pollution was 9.20 × 105 km2, occupying 65.55% of the entire urban agglomeration area; this percentage was nearly 14% higher than the national average level. The strongest relationship was observed in the Northern Tianshan Mountains urban agglomeration. Contrasting with previous studies, our study fully considered the spatial autocorrelation and spatial differences between variables by using geographically weighted regression and clarified the spatial heterogeneity of the relationships between urban landscape patterns and PM2.5 pollution in China. Our findings imply that special attention must be paid to the urban landscape patterns in urban agglomerations during future urban development in China. Furthermore, effective regulations must be implemented to reduce the impacts of urban landscape patterns on PM2.5 pollution by controlling urban expansion and optimizing the spatial patterns of urban landscapes.

Quantifying the contributions of snow/glacier meltwater to river runoff in the Tianshan Mountains, Central Asia

Abstract This study investigated the contributions of snow/glacier meltwater to river runoff in the northern and central Tianshan Mountains (Central Asia). Based on end- member mixing analysis (EMMA), the hydrograph separation was carried out in six benchmark catchments with different glacier area ratios (GARs) and snow area ratios (SARs) during a typical snow melt period (TSMP) and a typical glacier melt period (TGMP). The results indicate that the contribution of snow/glacier meltwater to river runoff is positively correlated with GARs or maximum SARs. The contribution ratios of snowmelt water vary from 22% to 49% in TSMP. The contribution ratios of glacier meltwater vary from 12% to 59% in TGMP. The contribution ratios of snow meltwater in the northern Tianshan Mountains (36%) are higher than central Tianshan Mountains (31%), while the contribution ratios of glacier meltwater in the northern Tianshan Mountains (36%) are lower than central Tianshan Mountains (42%). The contribution of rainfall to river runoff is higher in TGMP (9%–23%) than in TSMP (5%–9%). Baseflow is the most important recharge source to river runoff, with the contribution ratios vary from 44% to 73% in TSMP, and vary from 30% to 75% in TGMP. The spatial and temporal variations in tracer concentrations in streamflow components were found to be responsible to the uncertainties in hydrograph separation.

Snow depth reconstruction over last century: Trend and distribution in the Tianshan Mountains, China

Abstract Clarifying the long-term variations in snow depth is important for hydrological, meteorological and ecological implications. However, the short period of snow depth records in the mountains has made the assessment of regional long-term variation of snow depth difficult. Based on reanalysis datasets from 1901 to 2014 as well as observational data from 1961 to 2014, this study applied the artificial neural networks (ANN) method to reconstruct the historical snow depths in the Tianshan Mountains of China from 1901 to 1960. The variations in monthly snow depth were analyzed during the periods of 1901–1960, 1961–2014, and 1901–2014 as historical, observed, and overall periods, respectively. The results indicated that the reconstructed snow depths captured the long-term variation and spatial distribution in the study area. For temporal scale, increases in snow depth were detected in the southern and eastern Tianshan Mountains during all three periods. The trends in snow depth indicated an increase in the western, northern and overall Tianshan Mountains during the periods of 1901–1960 and 1961–2014, but showed a decrease during the overall period of 1901–2014. The difference in variation of snow depth trends in different temporal scales indicates that the time scale of snow depth increase is decadal rather than centennial. For spatial scale, higher values of snow depth occurred in the western and northern Tianshan Mountains, while lower ones appeared in the southern and eastern Tianshan Mountains. In addition, the increasing trend in the reconstructed snow depth was more profound with increased elevation in the Tianshan Mountains during 1901–1960, with the smallest increasing rate at the elevation of 1000 m–1500 m. Although some uncertainties exist within the reconstruction, this work proposed a method for developing historical snow depth for observation-limited areas, which provided additional data for hydrological and ecological simulation. The results also allow us to achieve a better understanding of regional climate change.

Improved Atmospheric Modelling of the Oasis-Desert System in Central Asia Using WRF with Actual Satellite Products

Because of the use of outdated terrestrial datasets, regional climate models (RCMs) have a limited ability to accurately simulate weather and climate conditions over heterogeneous oasis-desert systems, especially near large mountains. Using actual terrestrial datasets from satellite products for RCMs is the only possible solution to the limitation; however, it is impractical for long-period simulations due to the limited satellite products available before 2000 and the extremely time- and labor-consuming processes involved. In this study, we used the Weather Research and Forecasting (WRF) model with observed estimates of land use (LU), albedo, Leaf Area Index (LAI), and green Vegetation Fraction (VF) datasets from satellite products to examine which terrestrial datasets have a great impact on simulating water and heat conditions over heterogeneous oasis-desert systems in the northern Tianshan Mountains. Five simulations were conducted for 1–31 July in both 2010 and 2012. The decrease in the root mean squared error and increase in the coefficient of determination for the 2 m temperature (T2), humidity (RH), latent heat flux (LE), and wind speed (WS) suggest that these datasets improve the performance of WRF in both years; in particular, oasis effects are more realistically simulated. Using actual satellite-derived fractional vegetation coverage data has a much greater effect on the simulation of T2, RH, and LE than the other parameters, resulting in mean error correction values of 62%, 87%, and 92%, respectively. LU data is the primary parameter because it strongly influences other secondary land surface parameters, such as LAI and albedo. We conclude that actual LU and VF data should be used in the WRF for both weather and climate simulations.

Ecological Effects of Grazing in the Northern Tianshan Mountains

Identifying the effects of grazing is critical for the conservation, protection and sustainable use of arid grassland ecosystems. However, research regarding the ecological effects of grazing along mountainous elevation gradients is limited in arid areas, particularly at the regional scale. Using the Biome-BGC grazing model, we explored the effects of grazing on grassland net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE) from 1979 to 2012 along an elevation gradient in the northern Tianshan Mountains. The NPP, ET and WUE values were generally lower under the grazing scenario than under the ungrazed scenario; the differences between the grazing and ungrazed scenarios showed increasing trends over time; and distinct spatial heterogeneity in these differences was observed. Distinct decreases in NPP and WUE under the grazing scenario mainly occurred in regions with high livestock consumption. The decrease in ET was greater in mountainous areas with high grazing intensity due to decreased transpiration and increased surface runoff. This study contributes to a better understanding of the ecological effects of grazing along an elevation gradient in the northern Tianshan Mountains and provides data to support the scientific management of grassland ecosystems.

Numerical Simulations of the Impacts of Mountain on Oasis Effects in Arid Central Asia

The oases in the mountain-basin systems of Central Asia are extremely fragile. Investigating oasis effects and oasis-desert interactions is important for understanding the ecological stability of oases. However, previous studies have been performed only in oasis-desert environments and have not considered the impacts of mountains. In this study, oasis effects were explored in the context of mountain effects in the northern Tianshan Mountains (NTM) using the Weather Research and Forecasting (WRF) model. Four numerical simulations are performed. The def simulation uses the default terrestrial datasets provided by the WRF model. The mod simulation uses actual terrestrial datasets from satellite products. The non-oasis simulation is a scenario simulation in which oasis areas are replaced by desert conditions, while all other conditions are the same as the mod simulation. Finally, the non-mountain simulation is a scenario simulation in which the elevation values of all grids are set to a constant value of 300 m, while all other conditions are the same as in the mod simulation. The mod simulation agrees well with near-surface measurements of temperature, relative humidity and latent heat flux. The Tianshan Mountains exert a cooling and wetting effects in the NTM region. The oasis breeze circulation (OBC) between oases and the deserts is counteracted by the stronger background circulation. Thus, the self-supporting mechanism of oases originating from the OBC plays a limited role in maintaining the ecological stability of oases in this mountain-basin system. However, the mountain wind causes the “cold-wet’’ island effects of the oases to extend into the oasis-desert transition zone at night, which is beneficial for plants in the transition region.

Drought assessment in northwest China during 1960-2013 using the standardized precipitation index

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 72:73-82 (2017) - DOI: https://doi.org/10.3354/cr01451 Drought assessment in northwest China during 1960-2013 using the standardized precipitation index Peng Yang1,2, Jun Xia1,3,*, Yongyong Zhang1, Longfeng Wang1,2 1Key Laboratory of Water Cycle & Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, PR China 2University of Chinese Academy of Sciences, Beijing 100049, PR China 3State Key Laboratory of Water Resources & Hydropower Engineering Sciences, Wuhan University, Wuhan 430000, PR China *Corresponding author: xiaj@igsnrr.ac.cn ABSTRACT: The standardized precipitation index (SPI) can be used to analyze the spatiotemporal characteristics of regional water resources. Monthly precipitation data obtained from 96 weather stations in northwest China from 1960 to 2013 were used to calculate the SPI. Changes in the SPI were analyzed using the Mann-Kendall (MK) test and the Pettitt test. The results indicated that 50 stations had a significant increasing trend in the annual SPI series. Analysis of seasonal SPI trends revealed the prevalence of serious drought conditions in the spring, while most stations exhibited a wetting trend in the winter. Significant (at α = 0.05 level) abrupt changes in the annual and seasonal SPI series occurred mostly in 1981-1985. Additionally, a significant abrupt change occurred in the year 1986 in 5 sub-basins (the Turpan-Hami Basin, Gurbantunggut Desert Basin, Northern Tianshan Mountains, Northern Kunlun Mountains, and the Tarim Desert Basin). KEY WORDS: Standardized precipitation index · Pettitt test · Mann-Kendall · Northwest China Full text in pdf format PreviousCite this article as: Yang P, Xia J, Zhang Y, Wang L (2017) Drought assessment in northwest China during 1960-2013 using the standardized precipitation index. Clim Res 72:73-82. https://doi.org/10.3354/cr01451 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 72, No. 1. Online publication date: April 19, 2017 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2017 Inter-Research.

天山北坡雪岭云杉林地开垦的土壤有机碳损失估算

PDF HTML阅读 XML下载 导出引用 引用提醒 天山北坡雪岭云杉林地开垦的土壤有机碳损失估算 DOI: 10.5846/stxb201606191191 作者: 作者单位: 新疆大学资源与环境科学学院,新疆大学资源与环境科学学院,新疆大学资源与环境科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41361098，31500398） Estimation of soil organic carbon loss from Picea schrenkiana forest to farmland in the northern Tianshan Mountains Author: Affiliation: College of Resources and Environment Science, Xinjiang University,College of Resources and Environment Science, Xinjiang University,College of Resources and Environment Science, Xinjiang University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在全球变暖的背景下，由土地利用变化导致的土壤碳库的变化已经受到越来越多的关注。首先采用物种分布模型预测了天山北坡雪岭云杉林的潜在分布，其次估计了与被开垦为农田的雪岭云杉林面积（PSC）以及由林地开垦为农田造成的有机碳损失。PSC分别由雪岭云杉林的现实分布、潜在分布和农田的现实分布确定。云杉林地和农田的土壤有机碳含量由野外采样和实验室分析获得。研究发现，PSC面积为2.68×106hm2，被开垦为农田的雪岭云杉林土壤有机碳的损失为171.7 t/hm2；研究区总有机碳的损失为459.70Tg。结果表明，研究区的林地恢复和重建项目将会使土壤有机碳储量有所增加，且土壤表层的增加量多于深层。 Abstract:The effect of land-use changes on soil carbon stocks is an increasing concern in the context of global climate warming. In this study, we initially delineated the deforestation area of a Picea schrenkiana forest cultivated to cropland (PSC) at the north slope of the Tianshan Mountains. We then estimated the corresponding soil organic carbon (SOC) loss during the land-use change. The PSC was estimated by the potential, actual distributions of forest and cropland. The SOC content of the forest and cropland soils was obtained through field sampling and laboratory analysis. We found that the area of the PSC was 2.68×106 hm2, and the SOC loss (per unit area) caused by the cultivation of forest to cropland was 171.7 t/hm2, correspondingly. The total SOC loss in the study area was 459.70 Tg. This result implies that continuing the afforestation and reforestation programs currently implemented in the study area would increase the SOC. In addition, we found that the potential SOC sequestration is expected to increase to a greater extent in the upper soil layers than the lower layers. 参考文献 相似文献 引证文献

An ecology-oriented exploitation mode of groundwater resources in the northern Tianshan Mountains, China

In recent years, ecological degradation caused by irrational groundwater exploitation has been of growing concern in arid and semiarid regions. To address the groundwater-ecological issues, this paper proposes a groundwater-resource exploitation mode to evaluate the tradeoff between groundwater development and ecological environment in the northern Tianshan Mountains, northwest China’s Xinjiang Uygur Autonomous Region. Field surveys and remote sensing studies were conducted to analyze the relation between the distribution of hydrological conditions and the occurrence of ecological types. The results show that there is a good correlation between groundwater depth and the supergene ecological type. Numerical simulations and ecological assessment models were applied to develop an ecology-oriented exploitation mode of groundwater resources. The mode allows the groundwater levels in different zones to be regulated by optimizing groundwater exploitation modes. The prediction results show that the supergene ecological quality will be better in 2020 and even more groundwater can be exploited in this mode. This study provides guidance for regional groundwater management, especially in regions with an obvious water scarcity.

Effects of changes in vegetation on precipitation in the northern Tianshan Mountains evaluated using multiple time scales

This study used a combination of the wavelet cross-correlation technique and numerical analysis of vegetative feedback to study the role of climate–vegetation feedback from 1981 to 2009 in the northern Tianshan Mountains, Xinjiang Province, China. The study area included the Irtysh River, the Bortala and Ili River valleys, the northern slopes of the Tianshan Mountains, and the western Junggar Basin. The feedback effects of changes in vegetation on precipitation appeared to vary in these five regions when different time scales are used to examine them. The most useful time scale was generally found to be 4–6 months. Time lag was another characteristic of this process, and the optimal time lag was 3–4 months. Nevertheless, optimal time scale and time lag did not differ significantly in these five regions. In this way, the correct time scale of the effects of variations in vegetation on precipitation in this cold, arid area was found. This time scale and time lag can be assessed through wavelet cross-correlation analysis. Then numerical analysis can be used to improve the accuracy of the analysis.

Tree-Ring Response to Snow Cover and Reconstruction of Century annual Maximum Snow Depth for Northern Tianshan Mountains, China

Abstract Heavy snowfall and extreme snow depth cause serious losses of human life and property in the northern Tianshan Mountains almost every winter. Snow cover is an important indicator of climate change. In this study, we developed five tree-ring-width chronologies of Schrenk spruce (Picea schrenkiana Fisch. et Mey) from the northern Tianshan Mountains using standard dendrochronological methods. Correlation analyses indicated that radial growth of trees in the northern Tianshan Mountains is positively affected by annual maximum snow depth. This relationship was validated and models of annual maximum snow depth back to the 18th century were developed. The reconstruction explains 48.3% of the variance in the instrumental temperature records during the 1958/59–2003/04 calibration periods. It indicates that quasi-periodic changes exist on 2.0–4.0-yr, 5.3-yr, 14.0-yr, and 36.0-yr scales. The reconstructed series shows that maximum snow depth exhibits obvious stages change, the periods characterized by lower maximum snow depth were 1809/10–1840/41, 1873/74–1893/94, 1909/10–1929/30, 1964/65–1981/82, and the periods characterized by higher maximum snow depth were 1841/42–1872/73, 1894/95–1908/09, 1930/31–1963/64, and 1982/83–present. The lower period of annual maximum snow depth during the 1920s–1930s is consistent with the severe drought that occurred at this time in northern China. From the 1970s to the present, the maximum snow depth has increased clearly with the change to a warmer and wetter climate in Xinjiang. The reconstruction sheds new light on snow cover variability and change in a region where the climate history for the past several centuries is poorly understood.

Alkaline Basalts in the Bayingou Ophiolitic Mélange of Northern Tianshan Mountains: Origination from Seamounts?

Alkaline Basalts in the Bayingou Ophiolitic Mélange of Northern Tianshan Mountains: Origination from Seamounts?

Detection of vegetation abundance change in the alpine tree line using multitemporal Landsat Thematic Mapper imagery

Detection of alpine tree line change using pixel-based approaches on medium spatial resolution imagery is challenging because of very slow tree sprawl without obvious boundaries. However, vegetation abundance or density in the tree line zones may change over time and such a change may be detected using subpixel-based approaches. In this research, a linear spectral mixture analysis (LSMA)-based approach was used to examine alpine tree line change in the Northern Tianshan Mountains located in Northwestern China. Landsat Thematic Mapper (TM) imagery was unmixed into three fraction images (i.e. green vegetation – GV, shade, and soil) using the LSMA approach. The GV and soil fractions at different years were used to examine vegetation abundance change based on samples in the alpine tree line. The results show that Picea schrenkiana abundance around the top of the forested area increased approximately by 18.6% between 1990 and 2010, but remained stable in the central forest region over this period. Juniperus sabina abundance around the top of the forested area, in the central scrub region, and at the top of the scrub region increased approximately by 19.3%, 8.2%, and 15.6%, respectively. The increased vegetation abundance and decreased soil abundance of both P. schrenkiana and J. sabina indicate vegetation sprawl in the alpine tree line between 1990 and 2010. This research will be valuable for better understanding the impacts of climate change on vegetation change in the alpine tree line of central Asia.

The relationship between soil, climate and forest development in the mid-mountain zone of the Sangong River watershed in the northern Tianshan Mountains, China

The mountainous forests in arid regions, being sensitive to climate change, are one of the key research topics related to the mechanism of interaction between climate and the terrestrial ecosystem. In this study, the spatial distribution of a mid-mountain forest and its environmental factors were investigated by using a combination of remote sensing technology, field survey, climate indices and soil nutrient analysis in the Sangong River watershed of the northern Tianshan Mountains. The forest (Picea schrenkiana) was distributed between 1,510 and 2,720 m asl. Tree height and diameter at breast height (DBH) exhibited a bi-modal pattern with increasing elevation, and rested at 2,450 and 2,250 m asl, respectively. The two maxima of DBH appeared at 2,000 and 2,550 m asl, and the taller trees were observed at 2,100 and 2,600 m asl. For the annual mean temperature, the difference was approximately 5.8°C between the lowest and the highest limits of the forest, and the average decreasing rates per hundred meters were 0.49°C and 0.55°C with increasing altitude between 1,500 and 2,000 m asl and above 2,000 m asl, respectively. The annual precipitation in the forest zone first increased and then decreased with the increase of altitude, and the maximum value was at 2,000 m asl. For per hundred meters, the annual precipitation increased with the rate of 31 mm between 1,500 and 2,000 m asl and decreased by 7.8 mm above 2,000 m asl. The SOM, TN and TP were high between 2,000 and 2,700 m asl and low at the lower and upper forest limits. The minimum CaCO3 concentration, pH value and EC coincided with the maximum precipitation belt at 2,000 m asl. The SOM, TN and TP were high in the topsoil (0–10 cm) and differed significantly from the values observed in the deep soil layers (>10 cm). The soil nutrients exhibited spatial heterogeneity and higher aggregation in the topsoil. In conclusion, soil and climate are closely related to each other, working synergistically to determine the development and spatial distribution of the mid-mountain forest in the study area. The order of the importance of environmental factors to forest development in this study is as follows: soil nutrients>precipitation>elevation>temperature.

Effects of climate changes on vegetation cover in the northern Tianshan mountains using multiple time scales

This paper analyzes climate-vegetation correlations over 30 years in the northern Tianshan mountains in Xinjiang Province. The analysis combines the wavelet crosscorrelation technique with trend analysis and spline interpolation. The study areas include the Irtysh River, Bortala Valley, Ili River Valley, the northern slope of the Tianshan mountains and the western Junggar Basin. Daily meteorological data were acquired from 21 eligible weather stations between January 1, 1981 and December 31, 2009, inclusive. The satellite data comprise NOAA/AVHRR NDVI digital images (1981–2001) and SPOT-4 VEGETATION NDVI digital images (1998–2010). The results showed that (a) the correlation between early climate changes and subsequent vegetation had multiple-time-scale and time-lag characteristics. In all regions, the overall correlations were similar on different time scales; (b) The most useful time scale for evaluating precipitation effects was 15 tenday periods, while the optimal time lag was 5 ten-day periods. The exception was the western Junggar Basin (where the optimal time lag was 2 ten-day periods); (c) The most useful time scale for evaluating temperature effects was 15 ten-day periods, except in the western Junggar Basin (where the most useful time scale was 10 ten-day periods) and (d) Early changes in temperature were more correlated with subsequent vegetation than with early changes in precipitation.

Effect of Land Use History and Pattern on Soil Carbon Storage in Arid Region of Central Asia

The purpose of this study is to investigate variations in soil organic carbon (SOC) in arid areas due to differences in the cultivation history, land use, and soil salinization. The study area is the lower Sangong River basin on the piedmont of the northern TianShan mountains, which experiences heavy land-use activities. In 1982 and 2005,127(152) and 74 (161) samples in old (new) oasis were collected from each site at the surface soil (i.e., 0–20 cm). The data reveal that the mean value of the surface soil organic carbon content of the old oasis was higher than that of the new oasis by 4.01 g/kg in 1982 and 3.79 g/kg in 2005. Additionally, the soil organic carbon content decreased more rapidly in the newly reclaimed oasis than in the old oasis from 1982 to 2005. The spatial pattern of the SOC content was correlated with the exploitation time in the new oasis, the agricultural land use history, and the SOC content. The decreasing trend is clearer in the high SOC content area than in the low SOC content area. Farmland is the largest carbon pool in both the new and old oases. The carbon density of the old oasis was higher than that of the new oasis by 4.01 and 3.79 g/kg in 1982 and 2005 respectively. The loss of SOC in the agricultural watershed of the arid region in NW China is obvious. Improvements of land management practices, such as no tillage, straw returning to soil, and balanced fertilization techniques, should be adopted to increase the SOC content.

Modeling grassland net primary productivity and water-use efficiency along an elevational gradient of the Northern Tianshan Mountains

Mountainous ecosystems are considered highly sensitive and vulnerable to natural disasters and climatic changes. Therefore, quantifying the effects of elevation on grassland productivity to understand ecosystem-climate interactions is vital for mountainous ecosystems. Water-use efficiency (WUE) provides a useful index for understanding the metabolism of terrestrial ecosystems as well as for evaluating the degradation of grasslands. This paper explored net primary productivity (NPP) and WUE in grasslands along an elevational gradient ranging from 400 to 3,400 m asl in the northern Tianshan Mountains-southern Junggar Basin (TMJB), Xinjiang of China, using the Biome-BGC model. The results showed that: 1) the NPP increased by 0.05 g C/(m2·a) with every increase of 1-m elevation, reached the maximum at the mid-high elevation (1,600 m asl), and then decreased by 0.06 g C/(m2·a) per 1-m increase in elevation; 2) the grassland NPP was positively correlated with temperature in alpine meadow (AM, 2,700–3,500 m asl), mid-mountain forest meadow (MMFM, 1,650–2,700 m asl) and low-mountain dry grassland (LMDG, 650–1,650 m asl), while positive correlations were found between NPP and annual precipitation in plain desert grassland (PDG, lower than 650 m asl); 3) an increase (from 0.08 to 1.09 g C/(m2·a)) in mean NPP for the grassland in TMJB under a real climate change scenario was observed from 1959 to 2009; and 4) remarkable differences in WUE were found among different elevations. In general, WUE increased with decreasing elevation, because water availability is lower at lower elevations; however, at elevations lower than 540 m asl, we did observe a decreasing trend of WUE with decreasing elevation, which may be due to the sharp changes in canopy cover over this gradient. Our research suggests that the NPP simulated by Biome-BGC is consistent with field data, and the modeling provides an opportunity to further evaluate interactions between environmental factors and ecosystem productivity.

Synchronous drying and cooling in central Asia during late Oligocene

Aridification of central Asia during late Oligocene and Early Miocene has been documented by numerous eolian records from the North Pacific and central Asia. However, direct evidence of aridity from the interior of the arid zone is still rather scarce. To better reconstruct the climate history in central Asia during the late Oligocene, we have analyzed ostracod assemblages and gypsum content in the sediments from the lacustrine Jingou River section in the northern Tianshan Mountains. Our results show that the cold water species Candona cf. Neglecta and Pseudocandona albicans replaced the warm water species Ilyocypris bradyi and Ilyocypris sp. to become the dominant species at 23.8 Ma, indicating significant cooling in central Asia at that time. At the same time, a substantial increase in gypsum content indicates the intensification of central Asian drying. The synchronous cooling and drying approximately coincided with the Oi2b.1 and/or Mi1 events, implying a causal linkage between late Oligocene global cooling and central Asian aridity.