Remote sensing monitoring of the recent rapid increase in cultivation activities and its effects on desertification in the Mu Us Desert, China

The recent ecological improvement in the Mu Us Desert of China, largely attributed to large-scale afforestation projects, has created new opportunities for cultivation activities. However, the subsequent rapid increase in reclamation on desertification land and its impact on desertification have raised concerns. In this study, we first extracted data on cultivated land and desertification land in 1975,1990, 2000, 2005, 2010, 2015, and 2020 through the human-computer interaction visual interpretation method. By overlaying the cultivated land dynamics and desertification land, we subsequently explored the effect of cultivation activities on desertification in the Mu Us Desert during the six periods from 1975 to 2020(1975–1990, 1990–2000, 2000–2005, 2005–2010, 2010–2015, and 2015–2020). The results showed that cultivated land in the Mu Us Desert showed a fluctuating and increasing trend from 3769.26 km~2 in 1975 to 4865.73 km~2 in 2020, with 2010 as the turning point for the recent rapid increase. The main contributors included the large and regular patches distributed in Yuyang District and Shenmu of Shaanxi Province, and relatively smaller patches concentrated in Inner Mongolia Autonomous Region. The increased cultivated land from the reclamation on desertification land was dominated by moderate and severe desertification lands, and the decreased cultivated land that was transferred into desertification land as abandoned cultivated land was dominated by slight and moderate desertification lands. The effect of cultivation activities on desertification reversal(average area proportion of 10.61% for reversed desertification land) was greater than that of the development of desertification(average area proportion of 5.82% for developed desertification land). Nevertheless, compared to reversed desertification land,both the significant increase of developed desertification land during the periods of 2000–2005 and 2005–2010 and the insignificant decrease during the periods of 2005–2010, 2010–2015, and 2015–2020 implied a potential remobilization risk. Therefore, this study provides a significant theoretical reference for the formulation of ecological restoration projects and regional macroeconomic development policies by considering the influence of cultivation activities, to ensure the overall environmental stability and sustainability in desertification land where reclamation and abandonment activities have taken place.

Effects of aeolian processes on nutrient loss from surface soils and their significance for sandy desertification in Mu Us Desert, China: a wind tunnel approach

Mu Us Desert, a region with high aeolian activity, is at extremely high risk of sandy desertification. Using surface soil samples collected from Mu Us Desert of northern China, we evaluated the effects of aeolian processes on nutrient loss from surface soils by employing wind tunnel experiments. The experiments were conducted using free-stream wind velocities of 14, 16, 18 and 22 m/s. Our results showed that the fine particles （〈50 pm in diameter; 12.28% of all transported materials） carrying large nutrient Ioadings were exported outside the study area by ae- olian processes. After the erodible fine particles were transported away from the soil surfaces at low wind velocity （i.e. 14 m/s）, the following relatively high wind velocity （i.e. 22 m/s） did not have any significant effect on nutrient export, because the coefficients of variation for soil organic matter, total phosphorus, total nitrogen and available potassium were usually 〈5%. Our experimental results confirmed that aeolian processes result in a large amount of nutrient export, and consequently increase the risk of sandy desertification in arid and semi-arid ecosystems.

A late Holocene winter monsoon record inferred from the palaeo-aeolian sand dune in the southeastern Mu Us Desert, northern China

The variation of the Asian winter monsoonal strength has seriously affected the climate and environmental conditions in the Asian monsoonal region, and even in marginal islands and the ocean in the East Asian region. However, relevant under-standing remains unclear due to the lack of suitable geological materials and effective proxies in the key study areas. Here, we present a grain-size record derived from the palaeo-aeolian sand dune in the southeastern Mu Us Desert, together with other proxies and OSL dating, which reflect a relatively detailed history of the winter monsoon and abrupt environmental events during the past 4.2 ka. Our grain-size standard deviation model indicated that 〉224 μm content can be considered as an indicator of the intensity of Asian winter monsoon, and it shows declined around 4.2–2.1 ka, enhanced but unstable in 2.1–0.9 ka, and obviously stronger since then. In addition, several typical climate events were also documented, forced by the periodic variation of winter monsoonal intensity. These include the cold intervals of 4.2, 2.8, 1.4 ka, and the Little Ice Age （LIA）, and relatively warm sub-phases around 3.0, 2.1, 1.8 ka, and the Medieval Warm Period （MWP）, which were roughly accordant with the records of the aeolian materials, peat, stalagmites, ice cores, and sea sediments in various latitudes of the Northern Hemisphere. Combined with the previous progresses of the Asian summer monsoon, we prelimi-narily confirmed a millennial-scale anti-correlation of Asian winter and summer monsoons in the Late Holocene epoch. This study suggests that the evolution of the palaeo-aeolian sand dune has the potential for comprehending the history of Asian monsoon across the desert regions of the modern Asian monsoonal margin in northern China.

Relationships between Artemisia ordosica communities and environmental factors following sand-dune stabilization in the Mu Us desert,northwest China

Artemisia ordosica is an excellent sand-fixing shrub for sand stabilization in northwestern China. Sand dune stabilization, a critically important process, leads changes in abiotic factors, such as soil structure and nutrient contents. However, the effects of factors on an A. ordosica community following sand stabilization remain unclear. In this study, we used canonical correspondence analysis （CCA） to examine the relationships between A. ordosica communities and environmental factors at three habitats： semi-fixed dune （SF）, fixed dune with low-cov- erage biological soil crust （F）, and fixed dune with high- coverage biological soil crust （FC） in Mu Us desert. The mean height and coverage of plants increased with sand stabilization, while species diversity and richness increased initially and then reduced significantly. Correlation analysis and CCA revealed that slope, soil organic carbon, and nutrient contents, proportion of fine soil particles, soil moisture, and thickness of biological soil crust were all highly correlated with vegetation characteristics. These environmental factors could explain 40.42 % of the vege- tation-environment relationships at the three habitats. The distribution of plant species was positively related to soil moisture in the SF dune. Soil moisture, soil nutrient, and fine-particle contents mainly affected plants distribution in the F dune. In the FC dune, distribution of plant species was positively and negatively correlated with the thickness of biological soil crust and soil moisture at a depth 0-20 cm, respectively. The dominance value of typical steppe species increased significantly following sand-dune stabilization and relations between species and samples in CCA ordination bi-plots showed that perennial grasses could invade the A. ordosica community on FC, indicating A. ordosica communities had a tendency to change into typical steppe vegetation with the further fixation. We conclude that the significant differentiation not only occurred in community characteristics, but also in the relationships between vegetation and environmental factors among the three stages of dune fixation. So, restoration of degraded dune ecosystems should be based on habitat conditions and ecological needs.

Geochemical weathering of aeolian sand and its palaeoclimatic implications in the Mu Us Desert,northern China,since the Late Holocene

In the semi-arid and arid regions of northern China,geochemical behavior of the aeolian deposit is closely related to climatic and environmental changes,which was used to reconstruct the past history of environmental evolution and possibly forcing mechanisms.However,the related result was still scarce due to the lack of detailed geochemical analysis results in the desert sediments.In the present study,we systematically analyzed the geochemical components and parameters of the paleo-aeolian sand dune and modern mobile sand deposits in the Mu Us Desert and discuss the climatic variation inferred from the paleo-aeolian sand dune during the past 4.2 ka BP.The results indicated that （1） geochemical composition of the sandy deposits were dominated by SiO_2,Al_2O_3 and Na_2O and the deposits probably originated from the widespread upper continental crust （UCC） and were formed by long-term weathering,transport and re-deposition;（2） these sandy deposits were subjected to weaker weathering or uneven weathering under cold and dry conditions,and had highly similar material sources and degrees of weathering and leaching in general;and （3） the direct OSL （Optically Stimulated Luminescence） dating ages and geochemical parameters from the palaeosol-aeolian sand dune indicated that the regional climate change experienced several typically cold and warm intervals.These intervals are 4.2,2.8 ka BP and Little Ice Age and Medieval Warm Period,which probably attributed to periodic variations of the Asian summer monsoonal strength and cold events of the northern Atlantic Ocean in low and high latitudes of the Northern Hemisphere.Our results suggest that the development of the sand dune in the Mu Us Desert provided a suitable archive for understanding the past local climatic change,which is linked to the global climatic change.

Holocene climatic change reconstructed from trace elements of an aeolian deposit in the southeastern Mu Us Desert, northern China

In semi-arid and arid desert regions of northern China, aeolian deposits document the framework variation of an Asian monsoon during the late Quaternary. However, there is still a lack of detailed data pertaining to Holocene Asian monsoonal variation especial in the modern Asian summer monsoonal boundary belt. In this study, we reconstructed Holocene millennial-scale climatic changes in the Mu Us Desert, northern China, through systematic analysis of the variation of trace elements(324 samples) in different lithological units of the palaeosol-aeolian sand deposit, in combination with14 C and OSL chronology. Statistical results, correlation and clustering analysis indicate that the high content of 11 trace elements(V, Y, Cr, Nb, P, Mn, Cu, Zr, As, Ni and Rb, represented by P) and lower Sr content corresponding to periods of palaeosol development, marked increase of vegetation, weathering degree, and enhanced Asian summer monsoonal strength. In contrast, their opposed variation are coincident with accumulated aeolian sand layers, implying weaker summer monsoons and less geochemical weathering and degraded vegetation. These associations can be considered as signaling regional humid and dry changes of the Holocene environment. Accordingly, relatively arid conditions dominated the region before 7.2 ka, and there was an optimal humid climate in 7.2-4.6 ka. Afterwards, the climate became obviously dry, accompanied with several cycles of relatively wet and dry, such as relatively wet intervals around 4.1-3.7 ka, 3.5-3.3 ka and 2.5 ka. In addition, six millennial-scale dry events were recorded, and these events were consistent with weaker Asian summer monsoonal intervals in low latitudes, declined palaeosol development and precipitation in middle latitudes, as well as increased winter monsoon and periodic ice-rafting events in high latitudes of the Northern Hemisphere, within limits of accuracy of existing dating ages. This possibly suggests a noteworthy synchronism between millennial-scale climatic changes in this region and on a global scale.

Processes of the deposition and vicissitude of Mu Us Desert,China since 150 ka B.P.

Milanggouwan stratigraphical section" named lately takes down 27 cycles of alternately evolutionary histories of desert depositions in the Mu Us area with the fluviolacustrine facies and palaeosols since 150 ka B.P. Studies show that the sedimentary form was induced by the growth and decline and confrontation each other between the winter monsoon and the summer monsoon of East Asia in the past 150 ka.

Remote sensing based shrub above-ground biomass and carbon storage mapping in Mu Us desert,China

The estimation of above-ground biomass(AGB) and carbon storage is very important for arid and semi-arid ecosystems.HJ-1A/B satellite data combined with field measurement data was used for the estimation of shrub AGB and carbon storage in the Mu Us desert,China.The correlations of shrub AGB and spectral reflectance of four bands as well as their combined vegetation indexes were respectively analyzed and stepwise regression analysis was employed to establish AGB prediction equation.The prediction equation based on ratio vegetation index(RVI)was proved to be more suitable for shrub AGB estimation in the Mu Us desert than others.Shrub AGB and carbon storage were mapped using the RVI based prediction model in final.The statistics showed the western Mu Us desert has relatively high AGB and carbon storage,and that the gross shrub carton storage in Mu Us desert reaches 16 799 200 t,which has greatly contributed to the carbon fixation in northern China.

Distribution of sand dunes and sand shifts along the southern fringe of the Mu Us Desert since the Ming Dynasty

This article takes the two segments of the Ming Great Walls,Dabian and Erbian,and their associated barracks and forts as geographical references. Based on a detailed scrutiny of historical records of the Ming and Qing dynasties,and on field surveys,the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in the Ming and Qing dynasties are carefully reconstructed. A comparison of the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in Ming and Qing with the modern boundary revealed in remote sensing imagery clearly shows that the southern boundary of dunes and shifts in the Mu us Desert has expanded only in a few areas and on a small scale. In the area to the south of Changle Fort,along the direction of annually prevailing winds,sand drifts have pene-trated through the Jialu River valley into the loess region and have formed a sand strip of 32 km long and 3 km wide. To the east of Qingping Fort,sand drifts penetrated toward the eastern loess region through the Luhe River valley and have formed another sand strip of 8 km long and 2 km wide. Gener-ally speaking,though the intensity of human activity has been increasing in this area since the Ming Dynasty,the Mu Us Desert has not significantly expanded toward the southeast or southwest. The sand-loess boundary in the southern fringe of the Mu Us Desert has been almost unchanged since the Ming Dynasty.

THE FORMATION, EVOLUTION AND CAUSE OF THE Mu Us DESERT IN CHINA

Comprehensive correlation and analysis on the stratigraphic structure of the Quaternaryeolian sand in the Mu Us Desert comfirm that the Desert has been in existenceintermittently since the initial stage of the Quaternary at latest. The Desert is asteppe type sandy desert characterized by mosaic distribution of shifting, semi-shifting, semi-fixed and fixed dune and areas of loess grass land. It did not evolve toward uniform shift-ing sand, but underwent a series of normal and reverse development processes from the occur-rence of shifting sand to the spread, fixation and reduction of the sandy desert to grassland.Climatic fluctuation since the Quaternary is the primary factor for the formation and evolutionof the Desert, while neotectonics and human activities are the secondary factors.

Validating a dust production model by field experiment in Mu Us Desert, China

Field experiments of dust production have been seldom performed in Chinese deserts that are identified as one of main dust sources in the world, and such an experiment to validate a dust production model (DPM) has not been made in China until now. Saltation flux, dust emission flux, surface features and meteorological parameters (U*, Z0, Ri, etc.) were investigated in Mu Us Desert of China to verify the DPM model and accumulate dust emission data during the spring of 2002. It indicates that observed saltation fluxes from 0.07 to 8.00 g·m?1·s?1 are in good agreement with the ones predicted by the DPM model when the constant of the saltation flux equation is tuned to about 2.61, which corresponds to wind fric- tion velocities from 0.26 to 0.35 m·s?1. Unfortunately, during three local dust emission events, the observed dust fluxes are from 1 to 3 μg· m?2· s?1, lower than the modeled ones, implying that the model needs to be improved further under lower wind velocity. In comparison with data from a sandy soil with physical crust and a loam soil, saltation fluxes of the loose sandy soil in Mu Us Desert are obviously higher, which suggests that deserts and sandy land with desertification are major dust sources in northern China.

毛乌素沙地土壤解磷菌的分离筛选及其解磷机制

为探究毛乌素沙地土壤中可培养解磷细菌的种类、解磷能力和作用机制,该研究利用磷酸三钙为磷源的培养基,从黑沙蒿(Artemisia ordosica)林地土壤中分离出61株解磷细菌,其中变形菌门(Pseudomonadota)假单胞菌属(Pseudomonas)为优势类群。最终筛选出4株高效解磷菌(命名为R1、R4、NR1和NR3),磷增量分别为501.24、67.78、55.48和800.28 mg/L。基于形态特征、生理生化特性和系统发育分析,鉴定R4和NR1为假单胞菌属,R1和NR3分别为拟无枝酸菌属(Amycolatopsis)和泛菌属(Pantoea)。这些菌株的解磷能力与其分泌的草酸、乙酸、酒石酸量及pH值显著相关。结果表明,具有较强耐盐碱性的4株高效解磷菌,通过分泌有机酸和调节pH值显著提升了有效磷含量,显示出其作为微生物菌剂在干旱地区土壤改良和植被恢复中的潜在应用价值。

Vegetation monitoring using diferent scale of remote sensing data

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Precipitation Pulses and Soil CO_2 Emission in Desert Shrubland of Artemisia ordosica on the Ordos Plateau of Inner Mongolia,China

Precipitation is the major driver of ecosystem functions and processes in semiarid and arid regions. In such water- limited ecosystems, pulsed water inputs directly control the belowground processes through a series of soil drying and rewetting cycles. To investigate the effects of sporadic addition of water on soil CO 2 efflux, an artificial precipitation event (3 mm) was applied to a desert shrub ecosystem in the Mu Us Sand Land of the Ordos Plateau in China. Soil respiration rate increased 2.8-4.1 times immediately after adding water in the field, and then it returned to background level within 48 h. During the experiment, soil CO 2 production was between 2 047.0 and 7 383.0 mg m -2 . In the shrubland, soil respiration responses showed spatial variations, having stronger pulse effects beneath the shrubs than in the interplant spaces. The spatial variation of the soil respiration responses was closely related with the heterogeneity of soil substrate availability. Apart from precipitation, soil organic carbon and total nitrogen pool were also identified as determinants of soil CO2 loss in desert ecosystems.

毛乌素沙地植被物候变化及其对气候的响应

【目的】探讨毛乌素沙地植被物候长期趋势特征和年际波动及其与气象因素的关系。【方法】本研究利用2001-2020年的MODIS MOD13Q1归一化植被指数(NDVI),在TIMESAT3.3软件中利用动态阈值法提取毛乌素沙地植被物候指标,包括生长季开始日期(SOS)、生长季结束日期(EOS)和生长季长度(LOS),分析SOS与EOS的长期趋势与年际波动的时间特征和空间分布特征,并利用偏相关性分析法探究其与气温和降水量的关系。【结果】(1)物候指标的多年均值表现出显著的空间变异:SOS平均在第(140±15)天(儒略日),从西到东以及从北向南逐渐提前;EOS平均在第(291±6)天,从北向南逐渐推迟;LOS平均在(151±18)d,从西到东以及从北向南长度逐渐延长。(2)物候指标在研究期内整体趋势:SOS呈现提前趋势(0.58 d/a);EOS呈现推迟趋势(-0.25 d/a);LOS呈现显著延长趋势(0.83 d/a)。物候长期趋势也表现出显著的空间变异,总体上由西向东逐渐变慢。(3)毛乌素沙地植被物候(SOS、EOS)的长期趋势与年际波动都受同样的气象因子影响。毛乌素沙地SOS的长期趋势与年际波动都与季前第一个月的温度与降水呈负相关,EOS的长期趋势与年际波动都与季前第一个月的温度与季前累计降水呈正相关。【结论】随经度和纬度的增加,毛乌素沙地SOS与LOS分别呈现提前和延长的趋势。SOS的提前和EOS的推迟导致LOS呈现延长的趋势,且西部区域LOS延长的速率高于东部区域;SOS与EOS的长期趋势与年际波动在降水较多的中东部地区主要受温度影响而分别提前和推迟,而在降水偏少的西部地区,SOS和EOS的长期趋势与年际波动主要受降水影响而分别提前和推迟。

晚全新世毛乌素沙地东南缘沉积物粒度特征及其指示的环境变化

地处我国东亚季风边缘区的毛乌素沙地,因其对气候变化响应敏感而成为研究古气候环境变迁的理想场所。利用毛乌素沙地东南缘厚273 cm的沉积地层,通过分析沉积物粒度端元特征和环境指示意义,并结合光释光(OSL)测年结果和磁化率指标,重建了研究区2.6 ka B.P.以来的环境变化过程。结果表明:①剖面沉积物的粒度组成以粗粉砂、极细砂和细砂为主,其中细砂最多,平均体积分数为57.29%;粉砂层细砂体积分数明显低于砂层,粗粉砂和极细砂显著增多;沉积物粒度频率分布曲线多呈现典型的风成沉积物特点,峰高且窄,分选性较好。②剖面沉积物粒度可分离为3个端元组分,端元EM1是最细的粒度端元组分,指示了短时间的强尘暴活动,端元EM2和EM3是在不同风动力条件下跃移搬运的亚组分,端元EM3指示了当地风沙活动的强弱。③研究区晚全新世环境变化过程可分为3个阶段。2.6 ka B.P.之前,冬季风较强,气候冷干;2.6 ka B.P.之后到近百年,冬季风减弱,气候趋于暖湿;近百年以来,风沙活动增强,人类活动影响较大。

玉米和马铃薯轮作的复配土的有机碳矿化特征

以玉米和马铃薯轮作下的复配土为研究对象,设计砒砂岩与风沙土体积比为0∶1(CK)、1∶5(C1)、1∶2(C2)和1∶1(C3)的4种复配农田(复配土),采用碱液吸收法对复配土有机碳的矿化过程进行研究。结果表明:相同复配比的土壤有机碳含量差异无统计学意义,当季种植玉米和马铃薯的复配土有机碳含量较CK的分别提高了27.27%~46.59%、42.47%~70.57%,除种植玉米的C1外,差异均有统计学意义(P<0.05);培养过程中,复配土有机碳矿化速率呈现急剧下降、缓慢下降、平稳的3个阶段,在培养结束时,均以C3的降幅最大;复配土有机碳累积矿化量随培养时间的延长呈指数形式上升,当季作物和复配比及互作效应均对有机碳累积矿化量影响显著,种植玉米的C1的有机碳累积矿化量较大,种植马铃薯的则C3的较大;复配土有机碳累积矿化率在2种作物间的差异较大,种植玉米的C2和种植马铃薯的C1的有机碳累积矿化率较低;复配土有机碳矿化速率常数与半周转期变化趋势相反,种植玉米的C2和种植马铃薯的C1的有机碳矿化半周转期较大。可见,当季作物和复配比均对复配土有机碳矿化产生了影响,玉米和马铃薯轮作以砒砂岩与风沙土体积比1∶2较适,可作为一种生产实践助推毛乌素沙地的生态化发展。

毛乌素沙地与植被有关的地下水环境研究(英文)

[Objective] The research aimed to study the groundwater environment related to vegetation in Mu Us Desert.[Method] Choosing the hinterland of Mu Us Desert,the relationship between vegetation and groundwater in the desert was studied.The indicator system for the relationship between vegetation and groundwater in the sandy area was established,including vegetation population,vegetation cover,groundwater depth,vadose zone moisture content,groundwater mineralization and vadose zone salinity,as well as the corresponding field work methods.[Result] The result showed that the nine primary vegetation populations were distributed in the study area,and Artemisia,Salix and Cares were the dominant vegetation species.The groundwater mineralization in the sand dunes was 100-300mg/L,and 800mg/L in the beach,vadose zone moisture content remained at 8%-16%.The dunes salinity was less than 0.2%,and beaches were higher than 0.3%.[Conclusion] These results provided a basis for study on the relationship between vegetation and groundwater in Mu Us Desert.

毛乌素沙漠东南缘全新世剖面光释光年代及古气候意义

在毛乌素沙漠东南缘锦界地区发现的具有3层深棕色至黑色古土壤的全新世剖面,记录了至少3次大型沙地固定与活化的交替演化。在锦界剖面厚约5m的全新世地层中采集了10个光释光样品,利用石英光释光测年单片再生法(SAR),建立了锦界剖面全新世(>7.5～0.2ka)年代格架。结合粒度、磁化率气候变化代用指标和光释光年龄序列,得到毛乌素沙漠全新世时期沙漠演化和气候变化记录:7.5ka之前,地表植被稀疏,为气候干旱时期;7.5～3.9ka时段毛乌素经历了一个湿润成壤期,地表植被发育厚层黑色古土壤;约3.9～2.9ka为沙丘活跃期;2.9～1.7ka时段为较弱成壤期,发育深棕色古土壤;1.7ka以来,气候波动频繁,气候环境整体较之前干旱,1.0～0.5ka经历短暂温暖期,200年左右气候再次趋于干旱,但近1.0ka气候记录可能受到了人类活动干扰。随着冬夏季风的相互对峙、占主导时期不同,毛乌素沙漠响应气候的变化也随之扩张收缩变迁。同时,锦界剖面记录的毛乌素沙漠气候变化与全球变化的干旱、寒冷事件以及温暖事件可以对应。

毛乌素沙地植被与地下水关系

以植被的种群和盖度、地下水埋深、包气带含水率、地下水矿化度和包气带含盐量等指标,研究毛乌素沙漠腹地地区植被与地下水的关系,确立了研究区优势植被沙蒿(Artemisia)、沙柳(Salix psammophila)和苔草(Carex)的适生地下水埋深、包气带含水率、地下水矿化度和包气带含盐量。研究表明:地下水埋深、包气带含水量对植被种群影响非常敏感,而地下水矿化度和包气带含盐量则为不敏感指标。另外,地下水埋深对以地下水为水分来源的植被盖度较为敏感,而总盖度为不敏感指标。