The Limiting Factor to the Outbreak of Lake Black Bloom: Roles of Ferrous Iron and Sulfide Ions          下载免费PDF全文

Qiushi Shen  Chengxin Fan  Cheng Liu  Chao Chen 《洁净——土壤、空气、水》2018,46(9)

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A new standardized Palmer drought index for hydro‐meteorological use          下载免费PDF全文

Mingwei Ma  Liliang Ren  Fei Yuan  Shanhu Jiang  Yi Liu  Hao Kong  Luyan Gong 《水文研究》2014,28(23):5645-5661

Accepting the concept of standardization introduced by the standardized precipitation index, similar methodologies have been developed to construct some other standardized drought indices such as the standardized precipitation evapotranspiration index (SPEI). In this study, the authors provided deep insight into the SPEI and recognized potential deficiencies/limitations in relating to the climatic water balance it used. By coupling another well‐known Palmer drought severity index (PDSI), we proposed a new standardized Palmer drought index (SPDI) through a moisture departure probabilistic approach, which allows multi‐scalar calculation for accurate temporal and spatial comparison of the hydro‐meteorological conditions of different locations. Using datasets of monthly precipitation, temperature and soil available water capacity, the moisture deficit/surplus was calculated at multiple temporal scales, and a couple of techniques were adopted to adjust corresponding time series to a generalized extreme value distribution out of several candidates. Results of the historical records (1900–2012) for diverse climates by multiple indices showed that the SPDI was highly consistent and correlated with the SPEI and self‐calibrated PDSI at most analysed time scales. Furthermore, a simple experiment of hypothetical temperature and/or precipitation change scenarios also verified the effectiveness of this newly derived SPDI in response to climate change impacts. Being more robust and preferable in spatial consistency and comparability as well as combining the simplicity of calculation with sufficient accounting of the physical nature of water supply and demand relating to droughts, the SPDI is promising to serve as a competent reference and an alternative for drought assessment and monitoring. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Using chlorofluorocarbons (CFCs) and tritium (3H) to estimate groundwater age and flow velocity in Hohhot Basin,China          下载免费PDF全文

Jun Liu  Zongyu Chen  Wen Wei  Yilong Zhang  Zhenghong Li  Fuliang Liu  Hualiang Guo 《水文研究》2014,28(3):1372-1382

The concentrations of chlorofluorocarbons (CFC‐11, CFC‐12 and CFC‐113) and tritium (³H) content in groundwater were used to date groundwater age, delineate groundwater flow systems and estimate flow velocity in the Hohhot basin. The estimated young groundwater age is fallen in the bracket of 21 ~ 50 a and indicates the presence of two different age profiles and flow systems in the shallow groundwater system. Older age waters occur under the topographically low areas, where the aquifer is double‐layer aquifer system consisting of shallow unconfined‐semi‐confined aquifer and deep confined aquifer. This reflects long flow paths associated with regional flow. Groundwater (range from 21 to 34 years) in the north piedmont and east hilly areas, where the aquifer is a single‐layer aquifer consisting of alluvial fans, are typically younger than those in the low areas. The combination of CFCs dating with hydrogeological information indicates that both local and regional flow systems are present at the basin. The regional groundwater flow mainly flows from the north and east to the southwest, the local groundwater flow system occurs nearby the Hohhot city. The mean regional groundwater flow velocity of the shallow groundwater is estimated about 0.73 km/a. These findings can aid in refining hydrogeological conceptual model of the study area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Zircon U–Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications     

Q. Liu  Y.‐B. Wu  H. Wang  S. Gao  Z.‐W. Qin  X.‐C. Liu  S.‐H. Yang  H.‐J. Gong 《Journal of Metamorphic Geology》2014,32(2):177-193

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra‐high‐P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.  相似文献   

Influence of a coarse interlayer on seawater intrusion and contaminant migration in coastal aquifers          下载免费PDF全文

Yi Liu  Xiaomin Mao  Jian Chen  D. A. Barry 《水文研究》2014,28(20):5162-5175

Vertical 2D slice laboratory experiments were carried out in homogenous and layered sand tanks to elucidate the effects of a highly permeable (coarse‐grained sand) interlayer on seawater intrusion and transport of contaminants to a coastal sea. Tidal fluctuations produced oscillations in the seawater–freshwater transition zone, fluctuations of the contaminant infiltration rate and a zigzag contaminant plume outline. The seawater wedge became discontinuous at the (vertical) edges of the interlayer because of increased lateral movement of the seawater–freshwater interface within the interlayer. The contaminant plume formed a tail within the interlayer depending on the tidal stage, and similar to the wedge, its movement was accentuated. A simple analytical model that neglected vertical flow reliably predicted steady‐state seawater intrusion into the coastal aquifer. Numerical modeling was used to gain insight into the groundwater hydrodynamics and contaminant migration. The numerical results confirmed the experimental findings, i.e. that a highly permeable interlayer can provide a rapid transit path for contaminants to reach the seaward boundary and that the interlayer amplifies the effects of tidal fluctuations, resulting in wider transition zones for the seawater wedge and contaminant plume. Numerical simulations further showed that, with increasing interlayer hydraulic conductivity, the maximum seawater intrusion distance inside the interlayer increases approximately linearly. For the fixed‐head contaminant injection condition used, the model showed that contaminant infiltration increases approximately logarithmically with increasing interlayer hydraulic conductivity (other factors held fixed). Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

A nonstationary extreme value distribution for analysing the cessation of karst spring discharge          下载免费PDF全文

Yan Liu  Yonghong Hao  Yonghui Fan  Tongke Wang  Xueli Huo  Youcun Liu  Tian‐Chyi J. Yeh 《水文研究》2014,28(20):5251-5258

The effects of climate change and population growth in recent decades are leading us to consider their combined and potentially extreme consequences, particularly regarding hydrological processes, which can be modeled using a generalized extreme value (GEV) distribution. Most of the GEV models were based on a stationary assumption for hydrological processes, in contrast to the nonstationary reality due to climate change and human activities. In this paper, we present the nonstationary generalized extreme value (NSGEV) distribution and use it to investigate the risk of Niangziguan Springs discharge decreasing to zero. Rather than assuming the location, scale, and shape parameters to be constant as one might do for a stationary GEV distribution analysis, the NSGEV approach can reflect the dynamic processes by defining the GEV parameters as functions of time. Because most of the GEV model is designed to evaluate maxima (e.g. flooding, represented by positive numbers), and spring discharge cessation is a ?minima’, we deduced an NSGEV model for minima by applying opposite numbers, i.e. negative instead of positive numbers. The results of the model application to Niangziguan Springs showed that the probability of zero discharge at Niangziguan Springs will be 1/80 in 2025, and 1/10 in 2030. After 2025, the rate of decrease in spring discharge will accelerate, and the probability that Niangziguan Springs will cease flowing will dramatically increase. The NSGEV model is a robust method for analysing karst spring discharge. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

论中国古代地缘战略制定中的“权衡”——以《盐铁论》为例   总被引：3，自引：1，他引：2  

王丰龙  刘云刚 《地理科学》2019,39(9):1407-1415

《盐铁论》是记录汉朝时期关于盐铁酒榷均输及对匈奴关系的辩论的一部重要著作,能够较典型地反映中国古代地缘战略制定中的“权衡”过程。构建中国古代地缘战略制定中的“权衡”理论分析框架,继而基于该分析框架对《盐铁论》中的地缘战略辩论进行详细解读。《盐铁论》中辩论双方“权衡”的要点包含匈奴对汉朝产生的威胁程度、领土扩张所带来的收益大小和相应地缘战略的合法性3个方面。从思想、方法、目的等比较中西方地缘政治研究差异,指出“权衡”思想为西方主导的地缘政治理论提供新视角。  相似文献   

施肥对新垦绿洲风沙土肥力及碳积累的影响     

苏永中  杨荣  刘婷娜 《中国沙漠》2019,39(3):1-6

利用2005年安排在临泽边缘绿洲沙地农田的长期施肥定位试验，研究不同用量有机肥、化肥、有机肥和化肥配施对绿洲沙地土壤肥力及有机碳积累的影响。试验包括高量有机肥单施（M3），氮磷化肥单施（NP3），低、中、高量氮磷钾化肥单施（NPK1，NPK2，NPK3），及低、中、高量氮磷钾化肥配施高、中、低量有机肥9个处理（NPK1M3，NPK2M2，NPK3M1），测定分析10年后不同施肥处理耕层（0~20 cm）土壤物理化学性状特征及有机碳动态。结果表明：施有机肥及有机无机配施处理较单施化肥处理容重下降0.13 g·cm^-3，田间持水量提高6.7%，单施有机肥、有机无机配施较单施化肥，土壤有机碳（SOC）和全氮含量分别提高64.8%、36.3%和64.9%、49.5%。高量施用氮磷化肥和氮磷钾化肥处理全磷含量最高，有机肥及有机无机配施较单施化肥有效氮含量显著增加，有机无机配施及高量施用磷肥土壤有效磷积累明显，高量施用有机肥能显著提升有效钾含量。连续施肥处理10年后，SOC含量提高了1.68~2.84倍，土壤全氮、全磷、碱解氮及有效磷均有一定程度的提高，但单施化肥及有机肥与氮磷化肥配施有效钾含量下降。SOC的积累速率单施化肥、有机无机配施，单施有机肥处理分别为0.27、0.59，0.87 g·kg^-1·a^-1。增施有机肥、适量减少化肥投入、氮磷钾化肥的平衡施用是绿洲沙地农田土壤肥力持续提升的施肥管理对策。  相似文献   

Concurrent Determination of U‐Pb Age and REE Mass Fractions of Zircon by High Mass Resolution SIMS     

Yu Liu  Qiu‐Li Li  Guo‐Qiang Tang  Xian‐Hua Li 《Geostandards and Geoanalytical Research》2020,44(3):421-437

A combined geochronological and geochemical investigation for the same domain of zircon provides valuable information on timing and genesis, particularly in the case of multi‐growth metamorphic zircon. A high spatial resolution concurrent analytical method for zircon U‐Pb age and rare earth element content was successfully achieved in this study, using a multi‐collector secondary ion mass spectrometer (SIMS) at a ~ 8 μm diameter scale. Special instrument parameters were employed, including a high mass resolution of approximately 15000 applied to replace the previous energy filter method, and a dynamic multi‐collector mode used to reduce the measurement time to 18 min per analysis. Six zircon reference materials yielded precise and accurate ²⁰⁶Pb/²³⁸U ages, which are comparable to those obtained by the ordinary mono‐collector method, but with 2–3 times higher spatial resolution. All zircon grains measured in this study showed enriched heavy‐REE (HREE) contents consistent with previously reported values determined by LA and solution ICP‐MS methods. The light‐REE (LREE) mass fractions measured using both SIMS and LA‐ICP‐MS methods in this study, although with quite different volume, show consistent results within uncertainties.  相似文献   

A sequential sparse polynomial chaos expansion using Bayesian regression for geotechnical reliability estimations     

Qiujing Pan  Xingru Qu  Leilei Liu  Daniel Dias 《国际地质力学数值与分析法杂志》2020,44(6):874-889

Polynomial chaos expansions (PCEs) have been widely employed to estimate failure probabilities in geotechnical engineering. However, PCEs suffer from two deficiencies: (a) PCE coefficients are solved by the least-square minimization method which easily causes overfitting issues; (b) building a high order PCE is often computationally expensive. In order to overcome the aforementioned drawbacks, the Bayesian regression technique is employed to evaluate PCE coefficients, which not only provides a sparse solution but also avoids overfitting. With the aid of the predictive means and variances given by Bayesian analysis, a learning function is proposed to sequentially select the most informative samples that are critical to build a PCE. This sequential learning scheme can highly enhance the computational efficiency of PCEs. Besides, importance sampling (IS) is incorporated into the sequential learning (SL)-PCEs to deal with geotechnical problems with small failure probabilities. The proposed method of SL-PCE-IS is applied to three illustrative examples, which shows that the improved PCE method is more effective and efficient than the common PCEs method, leading to accurate estimations of small failure probabilities using fewer training samples.  相似文献