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1. chinaXiv:201909.00020 [pdf]

玛纳斯河流域绿洲时空演变及其景观格局变化

黄犁
Subjects: Geosciences >> Geochemistry

基于1976、1989、1998、2006、2016年5期Landsat MSS/TM/OLI遥感影像,提取玛纳斯河流域近40 a的绿洲分布情况,利用数理统计模型及景观指数等方法分析了绿洲时空演变过程及其景观格局变化。结果表明:1976—2016年玛纳斯河流域中下游绿洲变迁呈退缩—扩张—急剧扩张的变化趋势,除1976—1989年绿洲处于退缩状态外,绿洲规模自1989年以来一直处于扩张状态,其中,以2006—2016年绿洲扩张速度最快,其面积增长量和净变化速度高达3 266 km2和4.43%,绿洲变化趋势表现出非平衡—极端不平衡的变化。1989—2006年草地对绿洲退缩的贡献率最大,2006年以后水域面积减少是绿洲退缩的主要贡献者,1989年以后耕地对绿洲扩张的贡献率最大;绿洲重心总体向西北方向迁移,各时期的绿洲重心迁移方向为东北—西南—西北—西南。绿洲景观几何形状趋于简单化,绿洲内部破碎化程度增加,这与草地景观破碎化程度不断增大有关,绿洲总体趋向于集中,绿洲聚集度有所增加,这与耕地景观聚集程度不断增大密切相关。

submitted time 2019-09-05 From cooperative journals:《干旱区研究》 Hits18Downloads8 Comment 0

2. chinaXiv:201909.00021 [pdf]

天山北坡植被NDVI时空变化及其与气候因子的关系

尼加提·伊米尔
Subjects: Geosciences >> Geochemistry

利用MODIS NDVI 数据产品并结合相应的气候数据,运用一元回归趋势分析法,相关分析法,探讨2000—2015年天山北坡年平均、月平均NDVI时空变化与气候因子的相关关系。结果表明:① 近16 a来,天山北坡年平均NDVI值在 0.27~0.31之间波动上升,总体上呈明显增加的趋势;月平均NDVI值每年4月开始植被覆盖迅速增加,到7月达到最大值,然后8月开始降低,月平均 NDVI值的变化呈现出单峰趋势。天山北坡不同季节植被指数都呈现上升的趋势。空间上天山北坡植被覆盖呈现出西部高东部低,南部高北部低的分布特征。生长季植被NDVI值和年平均植被 NDVI值的变化存在明显的空间差异,表现为中部植被覆盖增加,东北部,西部,南部的植被覆盖减少。② 天山北坡年平均气温和平均降水量逐步上升,变化趋势表现为上升—下降—上升的趋势。空间上天山北坡南部山地地区气温低,降水量多;北部平原区气温高,但降水量少。③ 植被NDVI值对气温和降水量存在一定的相关关系。气温与降水量对植被的生长均有影响,其中春季的植被NDVI值与气温的关系密切,夏季的植被NDVI值与降水量有密切的关系,综合分析,降水量对植被覆盖的影响大于气温对植被覆盖的影响。④ 生长季(5—9月)植被NDVI值与气温和降水量存在一定的滞后性。

submitted time 2019-09-05 From cooperative journals:《干旱区研究》 Hits18Downloads8 Comment 0

3. chinaXiv:201909.00022 [pdf]

2000—2015年乌兰察布市生长季NDVI时空变化及其影响因素

李建飞
Subjects: Geosciences >> Geochemistry

以2000—2015年MODIS中国500M NDVI月合成产品数据为基础,结合乌兰察布市同期降水和气温数据,采用趋势线分析法、差值法、复直线回归分析法和残差法等,对乌兰察布市近16 a来生长季归一化植被指数(NDVI)进行像元尺度的时空变化及影响因素分析。结果表明:① 2000—2015年乌兰察布市NDVI介于0.354~0.555,整体呈波动上升趋势,空间分布差异明显,且呈东南高西北低的特点;② 2000—2004年、2005—2009年、2010—2015年乌兰察布市植被覆盖变化类型呈改善→退化→改善。植被覆盖改善较退化的速度慢,且植被退化后恢复缓慢;③ 乌兰察布市植物生长受降水、气温的双重影响。NDVI与年均降水量呈显著正相关(R=0.730,P=0.001),并通过了0.01显著性水平检验,与气温呈负相关(R=-0.351,P=0.182),二者相关关系不显著,相较气温而言,降水是影响植物生长的主要气候因子。在排除人类活动的影响下,降水和气温对乌兰察布市NDVI的贡献自西北向东南由0.213逐渐增加至0.805;④ 人类活动对植被指数起消减作用的区域占研究区总面积的55.92%,对植被指数起积极作用的区域占研究区面积的44.08%。

submitted time 2019-09-05 From cooperative journals:《干旱区研究》 Hits21Downloads9 Comment 0

4. chinaXiv:201904.00084 [pdf]

A simulation study of GNSS-R polarimetric scattering from the bare soil surface based on the AIEM model

吴学睿
Subjects: Geosciences >> Geochemistry

In the past two decades, Global Navigation Satellite System-Reflectometry (GNSS-R) has emerged as a new remote sensing technique for soil moisture monitoring. Some experiments showed that the antenna of V polarization is more favorable to receive the reflected signals, and the interference pattern technique (IPT) was used for soil moisture and other geophysical parameters retrieval. Meanwhile, the lower satellite elevation angles are most impacted by the multipath. However, electromagnetic theoretical properties are not clear for GNSS-R soil moisture retrieval. In this paper, the Advanced Integral Equation Model (AIEM) is employed using the wave synthesis technique to simulate different polarimetric scattering at the specular directions. Results show when the incidence angles are larger than 70º, scattering at RR polarization (The transmitted signal is Right Hand Circular Polarization (RHCP), while the received one is also RHCP) is larger than that one at LR polarization (The transmitted signal is RHCP, while the received one is Left Hand Circular Polarization (LHCP)), while scattering at LR polarization is larger than that at RR polarization for the other incident angles(1º~70º). There is an apparent dip for VV and VR scattering due to the Brewster angle, which will result in the notch in the final receiving power and this phenomenon can be used for soil moisture retrieval or vegetation corrections. The volumetric soil moisture (vms) effects on their scattering are also presented. The larger soil moisture will result in lower scattering at RR polarization, and this is very different from the scattering of the other polarizations. It is interesting to note that the surface correlation function only affects the amplitudes of the scattering coefficients at much less level, but it has no effects on the angular trends of RR and LR polarizations.

submitted time 2019-04-10 Hits5202Downloads307 Comment 0

5. chinaXiv:201903.00238 [pdf]

Fluvial sediments in the Alagxa Plateau as a dust source: iron mineralogical and geochemical evidence

WANG Youjun; JIA Jia
Subjects: Geosciences >> Geochemistry

The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a source of eolian silty. The northeastern margin of the Tibetan Plateau is one of the most actively-growing mountain belt on earth, and has large amounts of debris, with masses of fine grained material, which were continuously mobilized and deposited in the Alagxa Plateau by rivers, forming broad alluvial fans. It is possible that the role of fluvial sediments as a source of silty dust in the Alagxa Plateau has been underestimated. In this study, we test this hypothesis by investigating the iron mineralogical and geochemical characteristics of the fluvial sediments and the surface material of the sandy desert in the Alagxa Plateau, and comparing them with paleo-eolian dust deposits (loess) in the adjacent Chinese Loess Plateau (CLP) to investigate the possible linkages among the fluvial sediments, sandy desert and the last glacial loess of the CLP. The results show that sandy desert typically have high contents of goethite, and high ratios of goethite to hematite, similar to the fluvial sediments in the Alagxa Plateau. Based on the major element characteristics, field investigations and the results of previous studies, we found a genetic link between the silt component of the fluvial sediments and the sandy desert in the Alagxa Plateau with high value of Gt (goethite) and similarity of the Gt/(Hm (hematite)+Gt) ratio. But the silt component of the sandy desert main come from the adjacent fluvial sediments. The iron mineralogical characteristics (magnetic susceptibility, ARM (anhysteretic susceptibility), SIRM (saturation isothermal remanent magnetization) and SIRMAF100mT (SIRM demagnetized at 100 mT)) of the CLP samples overlap with those of the fluvial sediments in the Alagxa Plateau, but there is a mismatch with the sandy desert samples. This suggests that the fluvial sediments are the source of a large amount of silty material which could be transported to the CLP. Therefore, we conclude that the fluvial sediment in the Alagxa Plateau is an important source of eolian silt, which is deposited in downwind region, and that this source has been previously underestimated.

submitted time 2019-03-28 From cooperative journals:《Journal of Arid Land》 Hits2992Downloads259 Comment 0

6. chinaXiv:201811.00067 [pdf]

腾格里沙漠昂格尔图湖记录的988 AD以来的古气候变化

曹志宏; 安成邦; 尹丽颖
Subjects: Geosciences >> Geochemistry

文章通过对腾格里沙漠东南部昂格尔图湖岩芯AGE15A的粒度、碳酸盐的百分含量和主要化学元素等多项沉积学气候代用指标及精确定年的综合分析,重建了该区域988 AD以来的古气候变化序列。研究结果表明,988 AD.以来的研究区的气候环境的演化过程与我国西北西风区古气候变化基本一致,呈现“冷湿-暖干”交替变化的特征,但在时间上存在一定的延迟。具体表现为:988~1383 AD,昂格尔图湖由洼地发育成小型湖泊,化学风化作用弱,湖区气候环境整体偏冷湿,期间出现几次暖波动;1383~1560 AD.,研究区处在中世纪暖期,为温暖、干旱的气候特征,此时湖泊扩张,湖中水生植物生长茂盛,呼吸作用增强,致使大量碳酸盐沉淀,最高值达到8.16%;1560~1700 AD.,研究区气候在昂格尔图湖形成之后出现最寒冷的时期,降水增加,气候湿冷,此时段与小冰期最盛期相对应;1700 AD.之后,温度开始上升,气候回暖,在1900 AD.左右达到最甚,此时沉积物中碳酸盐的百分含量也达到最大值,为10.15%,此期间湖泊继续扩张,出现几次气候冷波动。基于我国古代文献重建的历史时期气候变化基本不包括沙漠地区,所以本文利用湖相沉积记录来反演腾格里沙漠昂格尔图湖历史时期的气候环境演变,对中国沙漠研究有着重要参考价值,同时也为中国西北历史时期的气候重建提供科学依据。

submitted time 2018-11-13 From cooperative journals:《干旱区地理》 Hits1109Downloads228 Comment 0

7. chinaXiv:201807.00030 [pdf]

Toxic metal enrichment characteristics and sources of arid urban surface soil in Yinchuan City, China

ZHANG, Mingxin; LU, Xinwei; SHI, Dongqi; PAN, Huiyun
Subjects: Geosciences >> Geochemistry

To investigate the environmental quality of the urban surface soil in Yinchuan City, the capital of Ningxia Hui Autonomous Region (Ningxia), China, we sampled surface soil and measured the concentrations of 8 toxic metals (Pb, Cr, Cu, Zn, Co, Bi, Ni and V) using X-ray fluorescence spectrometry. The enrichment characteristics and sources of these toxic metals in the soil were analyzed by the enrichment factor (EF) and multivariate statistical analysis. The results showed that the mean concentrations of these toxic metals in the soil samples were 25.0, 109.1, 16.8, 26.0, 37.2, 2.7, 25.3 and 59.9 mg/kg for Pb, Cr, Cu, Zn, Co, Bi, Ni and V, respectively, which were 1.2, 1.8, 0.8, 0.4, 3.2, 8.7, 0.7 and 0.8 times of the corresponding background values of Ningxia soil, respectively. The variations of Pb, Zn, Co, Bi and Ni concentrations in the surface soil of Yinchuan were larger than those of the other metals. Our results also showed that the toxic metals investigated in the soil had different enrichment levels. Both Co and Bi were significantly enriched, whereas Cr was only moderately enriched in the soil. There was a deficiency or minimal enrichment of the other toxic metals in the soil. Source analysis results based on the concentration, enrichment characteristics and multivariate statistical analysis indicated that Cr, V and Ni originated from a combination of fossil fuel combustion, traffic pollution and natural occurrence. Pb, Cu and Zn were predominantly derived from natural and traffic sources, while Co and Bi primarily originated from construction sources.

submitted time 2018-07-05 From cooperative journals:《Journal of Arid Land》 Hits4179Downloads417 Comment 0

8. chinaXiv:201807.00031 [pdf]

Potato absorption and phytoavailability of Cd, Ni, Cu, Zn and Pb in sierozem soils amended with municipal sludge compost

LIU, Zheng; NAN, Zhongren; ZHAO, Chuanyan; YANG, Yang
Subjects: Geosciences >> Geochemistry

Effects of sludge utilization on the mobility and phytoavailability of heavy metals in soil-plant systems have attracted broad attention in recent years. In this study, we analyzed the effects of municipal sludge compost (MSC) on the solubility and plant uptake of Cd, Ni, Cu, Zn and Pb in a soil-potato system to explore the mobility, potato plant uptake and enrichment of these five heavy metals in sierozem soils amended with MSC through a potato cultivation trial in Lanzhou University of China in 2014. Ridge regression analysis was conducted to investigate the phytoavailability of heavy metals in amended soils. Furthermore, CaCl2, CH3COONH4, CH3COOH, diethylene triamine pentacetic acid (DTPA) and ethylene diamine tetraacetic acid (EDTA) were used to extract the labile fraction of heavy metals from the amended soils. The results show that the MSC could not only improve the fertility but also increase the dissolved organic carbon (DOC) content of sierozem soils. The total concentrations and labile fraction proportions of heavy metals increase with increasing MSC percentage in sierozem soils. In amended soils, Cd has the highest solubility and mobility while Ni has the lowest solubility and mobility among the five heavy metals. The MSC increases the concentrations of heavy metals in the root, stem, peel and tuber of the potato plant, with the concentrations being much higher in the stem and root than in the peel and tuber. Among the five heavy metals, the bioconcentration factor value of Cd is the highest, while that of Ni is the lowest. The complexing agent (DTPA and EDTA) extractable fractions of heavy metals are the highest in terms of phytoavailability. Soil properties (including organic matter, pH and DOC) have important impacts on the phytoavailability of heavy metals. Our results suggest that in soil-potato systems, although the MSC may improve soil fertility, it can also increase the risk of soils exposed to heavy metals.

submitted time 2018-07-05 From cooperative journals:《Journal of Arid Land》 Hits4233Downloads457 Comment 0

9. chinaXiv:201710.00017 [pdf]

Low-T Thermo: a new program for arbitrarily combining low-T thermochronological data to model thermal history

丁汝鑫
Subjects: Geosciences >> Geology
Subjects: Geosciences >> Geochemistry

A robust code, called Low-T Thermo, has been developed to combine low-T thermochronological data arbitrarily to model thermal history. After apatite fission-track age and confined length are decoupled into two completely independent data to inverse thermal history and thermal history inversion using mica Ar-Ar age or bedrock quartz optically stimulated luminescence age are developed, there are eight kinds of low-T thermochronological data used to inverse thermal history including apatite fission-track age, apatite fission-track confined length, zircon fission-track age, apatite (U–Th)/He age, zircon (U–Th)/He age, mica Ar-Ar, bedrock quartz optically stimulated luminescence age and vitrinite reflectance. A total of 247 kinds of combination modes can be used to jointly inverse thermal history in theory (except the eight single methods modelling). These arbitrary combinations are helpful to model thermal history with the “incomplete” low-T thermochronological data set regarded to be unuseful for thermal history modelling and reduce experimental cost. For arbitrary combination of different low-T thermochronological data, each low-T thermochronological method is independent incompletely and the equivalent p-value is used to be the identical evaluation indicator in the inverse process. The usefulness of the code is demonstrated by modelling thermal history of existing low-T thermochronological data in the areas of Dabie Mountain, Ahimanawa Range and Southern Alps.

submitted time 2017-10-26 Hits5933Downloads985 Comment 0

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