Vegetation fractional coverage change in a typical oasis region in Tarim River Watershed based on remote sensing

Vegetation fractional coverage （VFC） is an important index to describe and evaluate the ecological system. The vegetation index is widely used to monitor vegetation coverage in the field of remote sensing （RS）. In this paper, the author conducted a case study of the delta oasis of Weigan and Kuqa rivers, which is a typical saline area in the Tarim River Watershed. The current study was based on the TM/ETM＋ images of 1989, 2001, and 2006, and supported by Geographic Information System （GIS） spatial analysis, vegetation index, and dimidiate pixel model. In addition, VBSl （vegetation, bare soil and shadow indices） suitable for TM/ETM＋ irrlages, constructed with FCD （forest canopy density） model principle and put forward by ITTO （International Tropical Timber Organization）, was used, and it was applied to estimate the VFC. The estimation accuracy was later prow^n to be up to 83.52%. Further, the study analyzed and appraised the changes in vegetation patterns and revealed a pattern of spatial change in the vegetation coverage of the study area by producing the map of VFC levels in the delta oasis. Forest, grassland, and farmland were the three main land-use types with high and extremely-high coverage, and they played an important role in maintaining the vegetation. The forest area determined the changes of the coverage area, whereas the other two land types affected the directions of change. Therefore, planting trees, protecting grasslands, reclaiming farmlands, and controlling unused lands should be included in a long-term program because of their importance in keeping regional vegetation coverage. Finally, the dynamic variation of VFC in the study area was evaluated according to the quantity and spatial distribution rendered by plant cover diigital images to deeply analyze the reason behind the variation.

Evaluation of oasis stability in the lower reaches of the Tarim River

Oasis stability in the lower reaches of the Tarim River was assessed at the landscape scale（including changes in landscape pattern and land use in the oasis） and at the regional scale（including the cold-island effect and NDVI of the oasis） based on the methods of landscape ecology,GIS and Remote Sensing（RS）.Thematic Mapping（TM） remote sensing images from 1990,2000 and 2009 were employed along with the related meteorological and hydrological data pertaining to the reclamation area of the oasis in the lower reaches of the Tarim River.The results indicated that landscape heterogeneity and oasis complexity increased between 1990 and 2000.The comprehensive index of the degree of land use,the average index of the cold-island effect,NDVI value and oasis stability all decreased.However,the change trends in the indices referred to above were opposite between 2000 and 2009,and oasis stability was enhanced to some extent.

The Effects of the Chemical Components of Soil Salinity on Electrical Conductivity in the Region of the Delta Oasis of Weigan and Kuqa Rivers,China

In order to assess the effects of chemical properties of soil salinity on electrical conductivity of 1：5 soil/water extract （EC1：5）, the study focused on revealing the main chemical factors contributing to EC of soil extracts and their relative importance. The relationship between EC1：5 and the chemical properties of soil salinity in the delta oasis of Weigan and Kuqa rivers, China, were studied using path coefficient analysis, a path analysis method. We studied each key element affecting EC1：5 either directly or indirectly. The results obtained show that the salt content, total dissolved solids （TDS）, and the sum of the sodium ion concentration and the kalium ion concentration are the most influential factors on 1：5 soil/ water extract （EC1：5） in the 0-10 cm and the 30-50 cm soil layer. The results show that the sequence of direct path coefficients in the 0-10 cm and the 30-50 cm soil layers on soil conductivity is TDS→Na^＋ ＋ K^＋→Salt content→Ca^2＋→Cl-→the sodium dianion ratio （SDR）→pH→ SO4^2-→HCO3^-→Mg^2＋→the soluble sodium percentage （SSP） sodium absorption ratio （SAR） and TDS→Salt content→Na^＋ ＋ K^＋→Ca^2＋→SDR→Mg^2＋→HCO3^-→SSP→pH→SO4^2-→SAR→Cl^-. The salt content, chlorine ion, and SAR are the main factors affecting 1：5 soil/water extract （EC1：5） in the 10-30 centimeter soil layer. The order of direct path coefficients result is as follows： Salt content→Cl^-→SAR→SSP→TDS→Ca^2＋→Mg^2＋= SO4^2-→HCO3^-→pH→SDR→Na^- ＋ K^＋. Moreover, the effects of HCO3^-, pH were very weak. Though the direct path coefficients between EC1：5 and SAR, SO4^2- and Ca^2＋ were not high, influence of other chemical factors caused the coefficients to increase, making the summation of their direct and indirect path coefficients relatively high. The models of the different soil layers were structured separately. Evidences showed that multiple regression relations between EC1：5 and most of the primary factors had sound reliability and very good accuracy. The research results can serve as a reference to the scientific management amelioration and utilization of saline in the Delta Oasis of Weigan and Kuqa rivers.

Evolution Stages of Oasis Economy and Its Dependence on Natural Resources in Tarim River Basin

This paper examines spatio-temporal characteristics of an oasis economy and its relationship with water and mineral resources in the Tarim River Basin from 1965 to 2005. A spatial autocorrelation model, the center of gravity model, and index system of the regional central city are used to probe the evolution laws of spatial structure of oasis economy. The study finds that: 1) The economic centre of gravity, whose variation track during this period follows linear rate law, was moving from headstream to middle reaches of the Tarim River. 2) Positive spatial autocorrelation which showed a waving and ascending trend of regional economy was significant and the neighbor effect of regional economic growth was strengthened continuously. 3) The regional economic centre was located in Hotan City before 1980, moved to Aksu City during the 1980s and to Korla City after 1990. We conclude that above all, during the recent four decades the evolution of the oasis economy in this region has gone through three stages: a traditional agriculture stage (before 1980), oasis agriculture and agricultural product processing stage (1980–1990) and oasis energy industry stage (after 1990). Furthermore, the dependence degree of the oasis economy on natural resources in different stages are studied by using dominance index, regression model, and grey relation method, which shows that an oasis econ- omy highly depends on water resources in the oasis agriculture and agricultural product processing stage while it de- pends more on mineral resources such as oil and natural gas during the oasis energy industry stage.

Oasis System and Its Reasonable Development in Sangong River Watershed in North of the Tianshan Mountains,Xinjiang,China

Under the guide of system theory, taking the oasis in the Sangong River watershed as a case study, this paper analyzes the oasis structure and function from 4 aspects including oasis spatial structure, water resources structure, vegetation structure, economic structure and their corresponding functions. The results indicate that as a typical small-scale watershed, Sangong River watershed has the relatively complete mountain-basin structure, and ecological and productive function. Because of human drastic activity the utilization rate of water resources was as high as 98.7%, and the utilization of groundwater was not reasonable, which resulted in an average annual decline of 0.353m in the water table of alluvial-diluvial-fan oasis, and an average annual increase of 0.047m in the alluvial-plain. The layout of crop and shelter forest benefits to the utilization of water and land resources. The development of oasis economy is at low level, and its eco-economic function is weak.

AREAL DIFFERENTIATION AND CONSTRUCTION OF OASIS AGRICULTURAL ECOSYSTEM IN THE SHIYANG RIVER BASIN

On the basis of the study on areal differentiation of the natural environment of oasis agriculture ecosystems in the Shiyang River Basin, this paper comparatively analyzes the natural productivities, water economic benefits, production efficiency, ecological stabilities and developmental conditions of the Wuwei Oasis agricultural ecosystem in the middle reaches of the river basin and the Minqin Oasis agricultural ecosystem in the lower reaches. Under a same management level and investment of . material and energy, primary productiveness and economic benefits of the former are higher than those of the latter. Construction directions of Wuwei and Minqin oases should be different in order to alleviate the water- use contradiction between the middle and lower reaches. The construction objective of Wuwei Oasis should be efficient irrigated farming production system and Minqin Oasis should become a mixed forestry-pastoral-farming ecosystem taking ecological protection as its major function.

Hydrochemical characteristics and evolution of groundwater in the dried-up river oasis of the Tarim Basin,Central Asia

Intense human activities in arid areas have great impacts on groundwater hydrochemical cycling by causing groundwater salinization.The spatiotemporal distributions of groundwater hydrochemistry are crucial for studying groundwater salt migration,and also vital to understand hydrological and hydrogeochemical processes of groundwater in arid inland oasis areas.However,due to constraints posed by the paucity of observation data and intense human activities,these processes are not well known in the dried-up river oases of arid areas.Here,we examined spatiotemporal variations and evolution of groundwater hydrochemistry using data from 199 water samples collected in the Wei-Ku Oasis,a typical arid inland oasis in Tarim Basin of Central Asia.As findings,groundwater hydrochemistry showed a spatiotemporal dynamic,while its spatial distribution was complex.TDS and δ18O of river water in the upstream increased from west to east,whereas ion concentrations of shallow groundwater increased from northwest to southeast.Higher TDS was detected in spring for shallow groundwater and in summer for middle groundwater.Pronounced spatiotemporal heterogeneity demonstrated the impacts of geogenic,climatic,and anthropogenic conditions.For that,hydrochemical evolution of phreatic groundwater was primarily controlled by rock dominance and evaporation-crystallization process.Agricultural irrigation and drainage,land cover change,and groundwater extraction reshaped the spatiotemporal patterns of groundwater hydrochemistry.Groundwater overexploitation altered the leaking direction between the aquifers,causing the interaction between saltwater and freshwater and the deterioration of groundwater environment.These findings could provide an insight into groundwater salt migration under human activities,and hence be significant in groundwater quality management in arid inland oasis areas.

Vulnerability and adaptation of an oasis social–ecological system affected by glacier change in an arid region of northwestern China

The Hexi Inland River Basin in an arid region of northwestern China was chosen as the study area for this research. The authors define the vulnerability of an oasis social-ecological system to glacier change; select 16 indicators from natural and socioeconomic systems according to exposure, sensitivity, and adaptive capacity; and construct a vulnerability-assessment indicator system aimed at an inland river basin in the arid region of Northwestern China. Vulnerability of the oasis socialecological system affected by glacier change in the study area is evaluated by Spatial Principal Component Analysis(SPCA) under the circumstance of glacier change. The key factors affecting the vulnerability are analyzed. The vulnerability of the oasis social-ecological system in the Hexi Inland River Basin affected by glacier change is of more than medium grade, accounting for about 48.0% of the total number of counties in the study area. In terms of the spatial pattern of the vulnerability, the oasis economic belt is the most vulnerable. With the rapid development of the area's society and economy, the exposure of the system to glacial changes is significantly increased; and an increase in glacial meltwater is not enough to overcome the impact of increased exposure, which is the main reason for the high vulnerability. Based on the result of the vulnerability analysis and combined with the present industrial structure in the Hexi Inland River Basin, near-,medium-, and long-term adaptation initiatives are put forward in the article.

考虑生态耗水的干旱区绿洲灌溉用水效率评价指标与方法

针对现行干旱区绿洲尺度灌溉用水效率评价对生态服务效益考虑不足的问题,提出了在绿洲尺度上考虑生态耗水的灌溉用水效率评价指标和方法,并应用于宁夏引黄灌溉绿洲。结果表明:宁夏引黄灌溉绿洲农田蒸散消耗水量中的灌溉水量平均占比达74.7%,生态系统蒸散消耗水量中的灌溉水量平均占比达39.8%,灌溉水对生态系统的支撑作用显著;考虑生态耗水前后的灌溉用水效率差为0.052~0.074,占未考虑生态耗水灌溉用水效率的13.9%~16.1%,灌溉水的生态服务效益明显;提出的评价指标与方法合理可行,能客观反映干旱区灌溉用水的综合效益。

干旱区绿洲农田土壤重金属含量高光谱反演

对新疆渭库绿洲土壤样本的As、Hg、Pb、Cr、Zn和Cu共6种重金属含量与高光谱关系进行分析,基于逐步回归方法筛选出特征波段,采用地理加权回归(GWR)和普通最小二乘法回归(OLS)构建土壤重金属的高光谱反演模型.结果显示:1)研究区的6种重金属元素含量存在一定的差异,土壤中的平均重金属含量依次为Zn>Pb>Cr>Cu>As>Hg,均未超过国家土壤背景值.研究区的Pb平均含量高于当地(新疆)土壤背景值,即研究区表土层中的Pb元素明显富集;2)不同的光谱变换使土壤重金属的光谱特征均得到了增强,但强度有所差异,经过二阶微分变换(SD)和一阶立方根微分变换(CRFD)的土壤光谱相对于原始光谱增强最显著;3)从模型验证来看,在反演6个土壤重金属元素含量时,GWR的R^(2)高于OLS,其中Zn的R^(2)接近0.8,Cu的R^(2)接近0.6,表明模型有一定预测能力,而As、Hg、Pb和Cr的R^(2)均依然低于0.5,模型预测能力并不理想;4)两种模型预测的6种土壤重金属含量的空间分布表现出一定的空间差异性.其中,As元素空间分布差异在这两种预测模型中最大,而其余5种重金属元素Hg、Pb、Cr、Zn和Cu的分布则较为均匀.通过高光谱反射率估算土壤重金属元素含量,实现了干旱区绿洲农田土壤重金属元素含量的高效快速反演,为干旱区绿洲农田土壤重金属元素含量动态监测提供了可靠的技术支撑.

塔里木河流域水储量变化及绿洲生态安全评估

绿洲是干旱、半干旱地区最具生态敏感性和独特性的景观类型,是维系人类生存和社会经济发展的重要区域。然而,在气候变化与人类活动双重影响下,干旱区水资源及其绿洲生境正发生剧烈变化。基于2000—2020年MODIS、GRACE卫星数据、土地利用数据和气象观测资料,通过计算植被覆盖度,估算植被初级生产力(NPP)和遥感生态指数(RSEI),系统分析了过去20 a塔里木河(简称塔河)流域陆地水储量和绿洲的动态变化并完成了绿洲区生态安全评估。结果表明:(1)2002—2020年塔河流域陆地水储量以0.27 mm·月-1的速率减少,空间上塔河流域陆地水储量在北部和西部区域显著减少,而在南部区域显著增加。(2)2000—2020年塔河流域绿洲面积显著增加,面积增加6.49%(0.42×10^(4)km^(2))。塔河流域整体生态环境呈转好趋势,生态等级由较差级别转为中等级别,生态改善区占总流域面积的69%,而生态退化区面积不足5%。塔河流域归一化植被指数(NDVI)由2000年的0.13增至2020年的0.16,近20 a植被覆盖度增加36.79%,NPP增加31.55%。(3)气温升高和降水增多的同时伴随下游河川径流增加,这进一步加剧了塔河流域陆地水资源储量的时空差异性,但人类活动仍是绿洲显著扩张最根本的原因。

宁夏沿黄绿洲参考作物蒸散演变特征及其归因

参考作物蒸散(Reference crop evapotranspiration,ET_(0))是生态水文过程中的关键因子,研究ET_(0)在干旱绿洲区的演变,不仅有助于理解气候变化背景下的绿洲水文过程响应,亦对绿洲水土资源高效配置和生态系统稳定性维持有指导意义。以宁夏沿黄绿洲为例,基于1960—2019年的气象资料和Penman-Monteith模型计算ET_(0),利用Mann-kendall突变检验、相对敏感系数和Morlet小波分析等方法,对宁夏沿黄绿洲近60 a的ET_(0)演变特征及其归因进行研究。结果表明:(1)宁夏沿黄绿洲ET_(0)年内呈单峰形态,ET_(0)在5—7月间较高,累积ET_(0)占年总ET_(0)的43.6%;近60 a的ET_(0)年均值为1226.38 mm,并以1.66 mm/a(P<0.01)幅度上升,但年际波动特征明显,其中在1988年突变之前,ET_(0)无显著变化趋势,而突变之后则以每10 a左右的周期显著增加或降低。(2)年ET_(0)主要以20—40 a和50—60 a周期振荡,且有多重时间尺度的复杂嵌套现象,不同季节的周期振荡差异较大,夏、秋季振荡幅度较强,其周期接近于年ET_(0)规律,而冬、春季振荡幅度较弱。(3)虽然ET_(0)与6种气象因子均存在显著相关性,但ET_(0)对不同气象因子的敏感性存在差异,其中对最高温度和相对湿度的敏感性较高,敏感系数分别为11.58%和8.40%。(4)宁夏沿黄绿洲ET_(0)与区域气候变化特征有较强的耦合性,区域气候的持续升温和相对湿度持续降低、以及由此引发的饱和水汽压亏缺持续增强是推动ET_(0)上升的重要原因,而气候由湿润向干旱的突变和平均风速的异常波动是诱发ET_(0)突变的原因。

基于遥感影像的新疆渭干河—库车河三角洲土壤水盐与植被覆盖度的关系

基于土壤样本实测数据及遥感影像数据,以典型干旱区新疆渭干河—库车河三角洲绿洲为研究区,采用像元二分模型估算植被覆盖度(Fractional vegetation cover,FVC),利用反距离权重插值及相关、中介效应等统计学分析方法,研究0~50 cm不同深度土壤水盐含量与FVC的关系,可为干旱区优化资源配置和制定生态恢复措施提供理论依据。结果表明:(1)FVC在空间上呈现由西向东逐渐减少的趋势,且随着土壤含水量的减少和含盐量的增加而减少。(2)各土层含水量均呈自上而下逐渐增加的趋势,各土层含盐量均呈自上而下逐渐减少的趋势,且不同深度水盐含量呈中等及以上变异性。(3)仅10~20 cm土壤含水量、FVC和0~10 cm土壤含水量间有中介效应的存在。深层10~20 cm、10~30 cm和30~50 cm土壤含盐量、FVC和0~10 cm表层土壤含盐量间有中介效应,即深层土壤含盐量通过影响表层土壤含盐量而对FVC产生影响。(4)0~10 cm表层土壤含盐量对FVC的影响最大,47.90%以上的FVC空间变异会受到该层土壤含盐量的影响,且不同深度土壤含盐量对FVC的影响效果均大于土壤含水量的影响效果。

LAND DESERTIFICATION(DEGRADATION) AND ITS CONTROL IN LOWER REACH REGION OF HEIHE RIVER

The lower reach of Heihe River, also known as Ejina River, was called Ruoshui Riverin ancient times. This area, although fallen into extremely arid temperate desert in the EjinaBanner, Inner Mongolia, has been a main line of communication since then and formed thefertile Ejina Oasis relying on the water source flowing from the Qilian mountains. However,in the recent years the land desertification (degradation) in this area has developed rapidly,

Shiyang River ecosystem problems and countermeasures

With the increase of population and the development of social economy, contradiction between water supply and demand of Shiyang River Basin become more outstanding. Unreasonable exploitation and utilization of water resources cause the serious deterioration of ecological environment. According to the present ecoligical situation, by analyzing some actual problems of the ecosystem of Shiyang River Basin, a series of feasible control countermeasures are proposed. The article provide theoretical basis for the treatment and recovery of the degradation of ecological environment of Shiyang Rive Basin.

基于机器学习算法的干旱区绿洲地上生物量估算

植被地上生物量是反映陆地生态系统固碳能力的重要指标,利用遥感技术开展干旱区植被地上生物量估算与空间反演,可为荒漠绿洲生态系统的健康评价与碳储量估算提供重要依据。以野外调查和实地采样数据为基础,利用Landsat 8 OLI多光谱影像提取的7个植被指数和13个波段变量构成4种建模变量组合,采用支持向量机(Support Vector Machine,SVM)、反向传播神经网络(Back Propagation Neural Network,BPNN)、极端梯度提升(e Xtreme Gradient Boosting,XGBoost)和随机森林(Random Forest,RF)这4种机器学习算法对新疆渭干河-库车河三角洲绿洲地上生物量进行遥感估算和空间反演。结果表明,(1)由波段变量和随机蛙跳算法优选变量构建的植被地上生物量反演模型,其估测精度明显优于全变量和指数变量,预测能力更为稳定。与SVM和BPNN算法相比,XGBoost和RF算法构建的模型具有更好的估测效果,能更准确地估算研究区植被地上生物量。(2)在构建的估测模型中,波段变量结合RF算法模型的精度最高,稳定性最强,其建模集和验证集的决定系数分别为0.898和0.742,平均绝对误差分别为82.1 g·m^(-2)和79.2 g·m^(-2),均方根误差为110.8 g·m^(-2)和132.1g·m^(-2),相对分析误差均大于1.8,模型拟合效果最佳。(3)研究区植被地上生物量的空间分异较为明显,整体呈现出绿洲区高,荒漠区低,由绿洲内部向绿洲外围逐渐降低的变化趋势。与其他3种机器学习算法相比,随机森林算法构建的估测模型具有良好的估测能力和稳定性,可准确估算干旱区绿洲地上生物量。同时,基于最优变量组合的机器学习算法模型为地上生物量反演提供了科学依据。

基于GEE平台渭库绿洲棉花水分生产率遥感估算

作物水分生产率的准确和定量化评价是提高干旱区作物产量的基础,对缓解水资源短缺和农业可持续发展具有重要意义。以塔里木盆地北岸的渭干河-库车河绿洲(渭库绿洲)为典型区域,基于Google Earth Engine(GEE)云平台,通过建立2009—2020年流域SEBAL遥感蒸散发模型、棉花分布识别模型及估产模型,对流域棉花水分生产率进行评价。结果表明:(1)渭库绿洲棉花产量从2009年的1610.10 kg·hm-2增长到2020年的1855.05 kg·hm-2,增长率为13.20%,棉花种植面积逐年向绿洲边缘延伸,棉花产量重心整体自西向东移动2485 m。(2)棉花生长期2009年蒸散发均值为686.80 mm,2020年为738.66 mm,整体呈上升趋势,其增长率为7.02%,棉花生长期蒸散发最大值为花铃期和吐絮期,蒸散发较高值主要分布在绿洲内部与塔里木河北岸边缘。(3)2009年水分生产率均值为0.21 kg·m^(-3),2020年均值为0.25 kg·m^(-3),12 a间水分生产率均值增长率为16%。在空间上,渭库绿洲水分生产率重心在红旗镇自东北向西南移动1832 m,年均移动速度为152.67m·a^(-1)。绿洲棉花水分生产率呈现东西方向大于南北方向扩张趋势,空间分布方向趋势增强,空间格局趋向集聚化。(4)12 a间产量的增长速度超过了蒸散发的上升速度,促使水分生产率提高。其次,水分生产率与棉花种植面积和合理的水量灌溉技术密切相关,水分生产率高值主要分布于沙雅县新垦农场和新和县桑塔木农场,由于农场规模化种植和集约化管理,促进了棉花增产、农业水资源的稳定分配和高效利用。

干旱区绿洲-城镇-荒漠景观演变及生态环境效应

绿洲、城镇和荒漠是干旱区内陆河流域重要的景观类型,随着流域社会经济发展,干旱区生态环境问题日益凸显。本研究选取我国西北干旱区第二大内陆河——黑河流域内绿洲-城镇-荒漠的景观组合作为研究对象,利用景观转型核密度与景观结构指数分析2000—2020年期间黑河流域绿洲-城镇-荒漠的时空格局与转型特征,借助多元回归树(MRT)模型探究三类景观转型之间的权衡-协同关系,基于遥感生态指数(RSEI)与景观转型生态贡献率揭示绿洲-城镇-荒漠景观转型的生态环境效应。结果显示:(1)黑河流域荒漠广布,绿洲仅在中下游河道沿岸集中分布,城镇面积占比最小,其空间分布和规模结构与绿洲有紧密关联;(2)黑河流域绿洲-城镇-荒漠景观转型可概括为:农业活动主导期(2000—2005年)、产业快速发展期(2005—2015年)和发展转型协调期(2015—2020年);(3)气温、GDP、海拔、降水量是影响绿洲-城镇-荒漠景观转型之间权衡-协同关系的主要因素;(4)2000—2020年期间流域景观转型以正的生态环境效应为主,耕地扩张是正效应的主导因素;耕地退化、水域减少与草地退化则是带来负效应的主要因素。研究结果可为干旱区内陆河流域实施生态保护与高质量发展提供理论指导。

GIS支持下绿洲生态敏感性研究——以伊犁河谷为例

为探索绿洲生态环境保护方法,解决绿洲生态环境与社会经济发展的矛盾,本文选取7项生态敏感性评价因子,结合层次分析法和均方差决策法确定各因子权重,对伊犁河谷生态敏感性进行评价分析;选取4项社会经济指标,利用莫兰指数进行空间自相关性分析,研究伊犁河谷生态敏感性与社会经济的相关性。结果表明:①海拔因子和植被因子对伊犁河谷生态敏感性影响最强烈。②伊犁河谷生态敏感性总体适中,主要受垂直地带性影响,敏感性与海拔、坡度呈正相关关系;受自然环境影响,敏感性与水体和植被呈负相关关系。③伊犁河谷生态敏感性与社会经济呈负空间相关性。研究生态敏感性与社会经济的相关性,为未来伊犁河谷生态保护、国土空间规划、社会经济发展等提供了一定的理论指导和参考。