Current Location:home > Browse

Institution

Your conditions: Geosciences(1,456)

1. chinaXiv:202201.00020 [pdf]

Estimation of rock Fe content based on hyperspectral indices

WANG Jinlin; WANG Wei; CHENG Yinyi; ZHANG Zhixin; WANG Shanshan; ZHOU Kefa; LI Pingheng
Subjects: Geosciences >> Geography

Information on the Fe content of bare rocks is needed for implementing geochemical processes and identifying mines. However, the influence of Fe content on the spectra of bare rocks has not been thoroughly analyzed in previous studies. The Saur Mountain region within the Hoboksar of the Russell Hill depression was selected as the study area. Specifically, we analyzed six hyperspectral indices related to rock Fe content based on laboratory measurements (Dataset I) and field measurements (Dataset II). In situ field measurements were acquired to verify the laboratory measurements. Fe content of the rock samples collected from different fresh and weathered rock surfaces were divided into six levels to reveal the spatial distributions of Fe content of these samples. In addition, we clearly displayed wavelengths with obvious characteristics by analyzing the spectra of these samples. The results of this work indicated that Fe content estimation models based on the fresh rock surface measurements in the laboratory can be applied to in situ field or satellite-based measurements of Fe content of the weathered rock surfaces. It is not the best way to use only the single wavelengths reflectance at all absorption wavelengths or the depth of these absorption features to estimate Fe content. Based on sample data analysis, the comparison with other indices revealed that the performance of the modified normalized difference index is the best indicator for estimating rock Fe content, with R2 values of 0.45 and 0.40 corresponding to datasets I and II, respectively. Hence, the modified normalized difference index (the wavelengths of 2220, 2290, and 2370 nm) identified in this study could contribute considerably to improve the identification accuracy of rock Fe content in the bare rock areas. The method proposed in this study can obviously provide an efficient solution for large-scale rock Fe content measurements in the field.

submitted time 2021-12-30 From cooperative journals:《Journal of Arid Land》 Hits4204Downloads62 Comment 0

2. chinaXiv:202201.00021 [pdf]

Land use/land cover change responses to ecological water conveyance in the lower reaches of Tarim River, China

WANG Shanshan; ZHOU Kefa; ZUO Qiting; WANG Jinlin; WANG Wei
Subjects: Geosciences >> Geography

The Tarim River is the longest inland river in China and is considered as an important river to protect the oasis economy and environment of the Tarim Basin. However, excessive exploitation and over-utilization of natural resources, particularly water resources, have triggered a series of ecological and environmental problems, such as the reduction in the volume of water in the main river, deterioration of water quality, drying up of downstream rivers, degradation of vegetation, and land desertification. In this study, the land use/land cover change (LUCC) responses to ecological water conveyance in the lower reaches of the Tarim River were investigated using ENVI (Environment for Visualizing Images) and GIS (Geographic Information System) data analysis software for the period of 1990–2018. Multi-temporal remote sensing images and ecological water conveyance data from 1990 to 2018 were used. The results indicate that LUCC covered an area of 2644.34 km2 during this period, accounting for 15.79% of the total study area. From 1990 to 2018, wetland, farmland, forestland, and artificial surfaces increased by 533.42 km2 (216.77%), 446.68 km2 (123.66%), 284.55 km2 (5.67%), and 57.51 km2 (217.96%), respectively, whereas areas covered by grassland and other land use/land cover types, such as Gobi, bare soil, and deserts, decreased by 103.34 km2 (14.31%) and 1218.83 km2 (11.75%), respectively. Vegetation area decreased first and then increased, with the order of 2010<2000<1990<2018. LUCC in the overflow and stagnant areas in the lower reaches of the Tarim River was mainly characterized by fragmentation, irregularity, and complexity. By analyzing the LUCC responses to 19 rounds of ecological water conveyance in the lower reaches of the Tarim River from 2000 to the end of 2018, we proposed guidelines for the rational development and utilization of water and soil resources and formulation of strategies for the sustainable development of the lower reaches of the Tarim River. This study provides scientific guidance for optimal scheduling of water resources in the region.

submitted time 2021-12-30 From cooperative journals:《Journal of Arid Land》 Hits4205Downloads64 Comment 0

3. chinaXiv:202201.00022 [pdf]

Mass balance of saline lakes considering inflow loads of rivers and groundwater: the case of Lake Issyk- Kul, Central Asia

Kei SAITOH; Rysbek SATYLKANOV; Kenji OKUBO
Subjects: Geosciences >> Geography

This study aimed to elucidate the influence of inflow water on the salinity concentration process of a saline lake and the mass balance of Lake Issyk-Kul, a tectonic saltwater lake in Kyrgyzstan. Based on the survey results and meteorological data from 2012 to 2015, we analyzed the dissolved chemical composition loads due to water inflow. Then, we discussed the relationship between the increase in salinity and water inflow into the lake. Through the water quality analysis data, we used the tank model to estimate the river inflow and analyze the loads by the L-Q curve. The groundwater loads were then estimated from the average annual increase in salinity of the lake over a period of 30 a. The results suggest that Lake Issyk-Kul was temporarily freshened between about AD 1500 and 1800 when an outflowing river existed, and thereafter, it became a closed lake in AD 1800 and continued to remain a saline lake until present. The chemical components that cause salinization are supplied from the rivers and groundwater in the catchment area, and when they flow into the lake, Ca2+, HCO3? and Mg2+ precipitate as CaCO3 and MgCO3. These compounds were confirmed to have been left on the lakeshore as evaporite. The model analysis showed that 1.67 mg/L of Ca2+ and Mg2+ supplied from rivers and groundwater are precipitated as evaporite and in other forms per year. On the other hand, salinity continues to remain in the lake water at a rate of 27.5 mg/L per year. These are the main causes of increased salinity in Lake Issyk-Kul. Since Na+ and Cl– are considered to be derived from geothermal water, they will continue to flow in regardless of the effects of human activities. Therefore, as long as these components are accumulated in Lake Issyk-Kul as a closed lake, the salinity will continue to increase in the future.

submitted time 2021-12-30 From cooperative journals:《Journal of Arid Land》 Hits4425Downloads88 Comment 0

4. chinaXiv:202201.00023 [pdf]

Drought and flood characteristics in the farming- pastoral ecotone of northern China based on the Standardized Precipitation Index

CAO Huicong; YAN Dandan; JU Yuelin
Subjects: Geosciences >> Geography

The farming-pastoral ecotone of northern China (FPENC) provides an important ecological barrier which restrains the invasion of desert into Northwest China. Studying drought and flood characteristics in the FPENC can provide scientific support and practical basis for the protection of the FPENC. Based on monthly precipitation data from 115 meteorological stations, we determined the changes in climate and the temporal and spatial variations of drought and flood occurrence in the FPENC during 1960–2020 using the Standardized Precipitation Index (SPI), Morlet wavelet transform, and inverse distance weighted interpolation method. Annual precipitation in the FPENC showed a slightly increasing trend from 1960 to 2020, with an increasing rate of about 1.15 mm/a. The interannual SPI exhibited obvious fluctuations, showing an overall non-significant upward trend (increasing rate of 0.02/a). Therefore, the study area showed a wetting trend in recent years. Drought and flood disasters mainly occurred on an interannual change cycle of 2–6 and 9–17 a, respectively. In the future, a tendency towards drought can be expected in the FPENC. The temporal and spatial distribution of drought and flood differed in the northwestern, northern, and northeastern segments of the FPENC, and most of the drought and flood disasters occurred in local areas. Severe and extreme drought disasters were concentrated in the northwestern and northeastern segments, and severe and extreme flood disasters were mainly in the northeastern segment. Drought was most frequent in the northwestern segment, the central part of the northeastern segment, and the northern part of the northern segment. Flood was most frequent in the western part of the northwestern segment, the eastern part of the northeastern segment, and the eastern and western parts of the northern segment. The accurate evaluation of the degrees of drought and flood disasters in the FPENC will provide scientific basis for the regional climate study and critical information on which to base decisions regarding environmental protection and socio-economic development in this region.

submitted time 2021-12-30 From cooperative journals:《Journal of Arid Land》 Hits4008Downloads61 Comment 0

5. chinaXiv:202201.00024 [pdf]

Characterizing the spatiotemporal variations of evapotranspiration and aridity index in mid-western China from 2001 to 2016

MU Le; LU Yixiao; LIU Minguo; YANG Huimin; FENG Qisheng
Subjects: Geosciences >> Geography

Mid-western China is one of the most sensitive and fragile areas on the Earth. Evapotranspiration (ET) is a key part of hydrological cycle in these areas and is affected by both global climate change and human activities. The dynamic changes in ET and potential evapotranspiration (PET), which can reflect water consumption and demand, are still unclear, and there is a lack of predictive capacity on drought severity. In this study, we used global MODIS (moderate-resolution imaging spectroradiometer) terrestrial ET (MOD16) products, Morlet wavelet analysis, and simple linear regression to investigate the spatiotemporal variations of ET, PET, reference ET (ET0), and aridity index (AI) in mid-western pastoral regions of China (including Gansu Province, Qinghai Province, Ningxia Hui Autonomous Region, and part of Inner Mongolia Autonomous Region) from 2001 to 2016. The results showed that the overall ET gradually increased from east to southwest in the study area. Actual ET showed an increasing trend, whereas PET tended to decrease from 2001 to 2016. The change in ET was affected by vegetation types. During the study period, the average annual ET0 and AI tended to decrease. At the monthly scale within a year, AI value decreased from January to July and then increased. The interannual variations of ET0 and AI showed periodicity with a main period of 14 a, and two other periodicities of 11 and 5 a. This study showed that in recent years, drought in these pastoral regions of mid-western China has been alleviated. Therefore, it is foreseeable that the demand for irrigation water for agricultural production in these regions will decrease.

submitted time 2021-12-30 From cooperative journals:《Journal of Arid Land》 Hits4478Downloads49 Comment 0

6. chinaXiv:202201.00025 [pdf]

Contribution of underlying terrain to sand dunes: evidence from the Qaidam Basin, Northwest China

LI Jiyan; QU Xin; DONG Zhibao; CAI Yingying; LIU Min; REN Xiaozong; CUI Xujia
Subjects: Geosciences >> Geography

Underlying terrain strongly influences dune formation. However, the impacts of underlying terrain on the dune formation are poorly studied. In the present research, we focused on dunes that formed in the alluvial fans and dry salt flats in the Qaidam Basin, Northwest China. We quantified the dunes' sediment characteristics on different types of underlying terrain and the terrain' effects on the surface quartz grains by analyzing grain-size distribution, soluble salt contents and grain surface micro-textures. Results showed that barchan dunes were dominated by medium sands with a unimodal frequency distribution, whose peak corresponded to the saltation load. Linear dunes were mainly composed of fine sands with a bimodal frequency distribution, whose main peak represented the saltation load, and whose secondary peak represented the modified saltation or suspension load. Sand was transported from source area by running water (inland rivers) over short distances and by wind over relatively longer distances. Thus, quartz grains had poor roundness and were dominated by sub-angular and angular shapes. Surface micro-textures indicated that dune sands were successively transported by exogenic agents (glaciation, fluviation and wind). Soluble salt contents were low in dunes that developed in the alluvial fans, which represented a low-energy chemical environment, so the grain surface micro-textures mainly resulted from mechanical erosion, with weak micro-textures formed by SiO2 solution and precipitation. However, soluble salt contents were much higher in dunes that developed in the dry salt flats, which indicated a high-energy chemical environment. Therefore, in addition to micro-structures caused by mechanical erosion, micro-textures formed by SiO2 solution and precipitation also well developed. Our results improve understanding of the sediment characteristics of dune sands and the effects of underlying terrain on dune development in the Qaidam Basin, China.

submitted time 2021-12-30 From cooperative journals:《Journal of Arid Land》 Hits2225Downloads56 Comment 0

7. chinaXiv:202201.00026 [pdf]

Effects of restoration modes on the spatial distribu?tion of soil physical properties after land consolida?tion: a multifractal analysis

KE Zengming; LIU Xiaoli; MA Lihui; TU Wen; FENG Zhe; JIAO Feng; WANG Zhanli
Subjects: Geosciences >> Geography

soil physical properties (SPP) are considered to be important indices that reflect soil structure, hydrological conditions and soil quality. It is of substantial interest to study the spatial distribution of SPP owing to the high spatial variability caused by land consolidation under various land restoration modes in excavated farmland in the loess hilly area of China. In our study, three land restoration modes were selected including natural restoration land (NR), alfalfa land (AL) and maize land (ML). Soil texture composition, including the contents of clay, silt and sand, field capacity (FC), saturated conductivity (Ks) and bulk density (BD) were determined using a multifractal analysis. SPP were found to possess variable characteristics, although land consolidation destroyed the soil structure and decreased the spatial autocorrelation. Furthermore, SPP varied with land restoration and could be illustrated by the multifractal parameters of D1, ?D, ?α and ?f in different modes of land restoration. Owing to multiple compaction from large machinery in the surface soil, soil particles were fine-grained and increased the spatial variability in soil texture composition under all the land restoration modes. Plough numbers and vegetative root characteristics had the most significant impacts on the improvement in SPP, which resulted in the best spatial distribution characteristics of SPP found in ML compared with those in AL and NR. In addition, compared with ML, ?α values of NR and AL were 4.9- and 3.0-fold that of FC, respectively, and ?α values of NR and AL were 2.3- and 1.5-fold higher than those of Ks, respectively. These results indicate that SPP can be rapidly improved by increasing plough numbers and planting vegetation types after land consolidation. Thus, we conclude that ML is an optimal land restoration mode that results in favorable conditions to rapidly improve SPP.

submitted time 2021-12-30 From cooperative journals:《Journal of Arid Land》 Hits2227Downloads49 Comment 0

8. chinaXiv:202112.00052 [pdf]

生态移民区“三生”用地变化对生态系统服务的影响 ——以宁夏红寺堡区为例

安斯文
Subjects: Geosciences >> Geography

土地系统运行以土地可持续利用与人类福祉为准绳。以全国最大的生态移民区红寺堡区 为例,基于不同计量方法和 GIS 空间分析法,对红寺堡区 2000—2018 年的“三生”用地转型及生态 服务变化进行定量研究。结果表明:(1)红寺堡区基本形成以中部灌区生活生产、生产生态空间为 主,周边为生态空间的“三生”格局,国土开发格局逐渐优化。(2)生产生态用地减少 3.42×104 hm2, 生态用地增加 1.24×104 hm2,生态生产用地增加 0.16×104 hm2,生活生产用地增加 2.02×104 hm2。(3) 生态系统服务价值共增加 11.18×108 元。植被恢复是生态系统服务价值增加的主因,而建设用地对 其他用地的侵占则是导致生态系统服务价值降低的主因。(4)协同推进山水林田湖草治理,做好已有生态用地的质量提升和绿地生态网络建设,通过优化生态系统服务结构提升区域生态系统的服务功能,从而实现生产空间的集约化发展、生态空间的提质增效及生活空间的优美宜居

submitted time 2021-12-14 From cooperative journals:《干旱区地理》 Hits2474Downloads121 Comment 0

9. chinaXiv:202112.00053 [pdf]

新疆县市“三生”功能时空变化及耦合协调性分析

牛雅萱
Subjects: Geosciences >> Geography

基于“生产-生活-生态”功能视角构建评价体系并引入耦合协调模型,探究新疆县市土地 功能及功能间相互作用程度的时空演变规律,遴选影响区域发展的关键因子,为区域发展提供建议。研究结果表明:(1)新疆县市单元生产功能,生活功能,生态功能及“三生”功能综合评价的时空格局分布差异性显著,均呈现“北高南低”的空间分布特征,以天山北坡城市群为核心高值区。(2)新疆县市“三生”功能耦合协调性总体呈现“北高南低”空间分布态势,县市功能间的耦合协调 关系逐步向好,为区域后续的发展奠定了良好基础。(3)主导产业的选择对于新疆县市功能发展至关重要,同时宏观政策调控有助于功能间的耦合协调性提升,推动县市功能协调有序发展。

submitted time 2021-12-14 From cooperative journals:《干旱区地理》 Hits2966Downloads662 Comment 0

10. chinaXiv:202112.00056 [pdf]

乌兹别克斯坦灌溉农业发展及其对生态环境和经济发展的影响

李琦
Subjects: Geosciences >> Geography

乌兹别克斯坦作为中亚干旱区重要的农业大国,由于其独有的气候条件,灌溉是决定其农 业生产的主要控制因素,因此,研究其灌溉农业发展历程对于保障农业生产与自然环境安全具有 重要意义。通过查阅乌兹别克斯坦灌溉农业发展领域的相关文献,结合联合国粮食及农业组织、 联合国数据检索系统等官方网站提供的资料数据,总结灌溉农田面积、人口、主要作物产量及农业 产值等数据的变化规律,阐述了乌兹别克斯坦灌溉农业的发展历程,分析讨论由农业灌溉引起的一系列环境问题及其对社会经济的影响。结果表明:(1)由于气候干旱少雨,乌兹别克斯坦灌溉用水主要来自阿姆河及锡尔河,下游河道径流量及咸海蓄水量持续下降,暴露河床内大量松散沉积 物并导致频繁的沙尘天气。(2)乌兹别克斯坦整体农业灌溉技术较为落后,过度引水使得部分地表径流汇聚在灌区低洼地带,抬升地下水位,最终引发严重的区域土壤盐渍化,故全面推广先进灌排 技术,是该国未来灌溉农业与生态环境健康发展的主要方向。(3)农业生产是乌兹别克斯坦重要的经济来源,对国内生产总值有显著的正向影响。此研究可为干旱区农业发展及水资源管理提供借鉴。

submitted time 2021-12-14 From cooperative journals:《干旱区地理》 Hits2525Downloads137 Comment 0

12345678910  Last  Go  [146 Pages/ 1456 Totals]