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631.
Xiqiang Wang Rensheng Chen Guohua Liu Chuntan Han Yong Yang Yaoxuan Song Junfeng Liu Zhangwen Liu Xiaojiao Liu Shuhai Guo Lei Wang Qin Zheng 《水文研究》2019,33(1):66-75
The increase in low flows (winter discharge and minimum monthly discharge), caused primarily by permafrost degradation, is common in high‐latitude permafrost regions, whereas the dynamics of low flows in high‐altitude permafrost regions remain largely unknown. Long‐term discharge data from 28 unregulated catchments in western China were analysed, and the findings showed that winter discharge/minimum monthly discharge significantly increased (p ≤ 0.1) in 82/82%, 55/64%, and 0/0% of the catchments in the higher‐latitude mountain permafrost regions (Tienshan Mountains), mid‐latitude mountain permafrost regions (Qilian Mountains), and mid‐ to low‐latitude plateau permafrost regions (the source regions of the Yangtze and Yellow rivers), respectively. The differences in permafrost type and the distribution of permafrost and alpine cold desert (which is similar to tundra) were found to be the main causes for the different responses in the low flows. The rate of change of low flows (winter discharge and minimum monthly discharge) was negatively and linearly correlated with permafrost coverage when coverage was less than 40% of the catchment area, whereas the low flows changed only slightly when the permafrost coverage exceeded 40%. A significant thickening of the active layer increased the low flows in the lower permafrost‐covered catchments, which are dominated by warm permafrost. However, in the higher permafrost‐covered catchments with cold permafrost and a cold climate, only an increase in permafrost temperature (without a notable thickening of the active layer) occurred, resulting in non‐significant changes in low flows. 相似文献
632.
经研究确认,内蒙古查干哈达庙铜矿床属于块状硫化物型富铜矿床。该矿床类型的首次确认,为华北陆块北缘寻找古生代块状硫化物型富铜矿床提供了例证。查干哈达庙铜矿床位于华北陆块北缘,赋矿地层(即含矿岩系)为石炭系上统本巴图组流纹质凝灰岩、凝灰质板岩,其上为条带状结晶灰岩、生物碎屑结晶灰岩。含矿岩系中存在硅质岩、含铁硅质岩、碧玉岩及萤石重晶石矿层。硫化物矿体呈层状、似层状,产于流纹质凝灰岩、凝灰质板岩岩层中,产状与岩层产状一致。矿床含矿岩系具有"火山碎屑岩、硫化物矿体、碧玉岩"的"三位一体"特征。矿石具有条带状、层纹状构造。矿石中主成矿元素为Cu,伴生有益元素为Au,S,Pb,Zn,铜矿石品位较高,属富铜矿。矿床地质特征表明其属块状硫化物型铜矿床。该类型矿床的找矿标志是,在海相酸性火山岩及碳酸盐岩之间,地表存在与硅质岩共存的黄钾铁矾、铁帽型硫化物氧化带;具有以铜为主的铜、锌组合的化探异常;具有低阻高极化的物探异常。 相似文献
633.
近30a来若尔盖盆地沙漠化时空演变过程及成因分析 总被引:5,自引:0,他引:5
在遥感(RS)和地理信息系统(GIS)技术的支持下,采用1975年的MSS影像和2005年的TM影像对若尔盖盆地土地沙漠化的时空演变进行了监测。研究发现,从1975年到2005年的30年间,若尔盖盆地的沙漠化土地以年均70.18 km2的速度发展,共增加了2105.36 km2,其中主要以中、轻度沙漠化土地的增加为主,增加面积分别为957.13和1146.75 km2;重度沙漠化土地变化很小,仅增加了1.48 km2。在1965—2007年,若尔盖盆地年平均气温升高了1.41℃,年平均降水减少了34 mm,人类活动对环境的破坏作用加强,严重过度放牧,因此该地区沙漠化发展是自然环境变化和人类活动共同作用的结果。 相似文献
634.
The use of electrical resistivity surveys to locate karst conduits has shown mixed success. However, time‐lapse electrical resistivity imaging combined with salt injection improves conduit detection and can yield valuable insight into solute transport behaviour. We present a proof of concept above a known karst conduit in the Kentucky Horse Park (Lexington, Kentucky). A salt tracer solution was injected into a karst window over a 45‐min interval, and repeat resistivity surveys were collected every 20 min along a 125‐m transect near a monitoring well approximately 750 m downgradient from the injection site. In situ fluid conductivity measurements in the well peaked at approximately 25% of the initial value about 3 h after salt injection. Time‐lapse electrical resistivity inversions show two broad zones at the approximate conduit depth where resistivity decreased and then recovered in general agreement with in situ measurements. Combined salt injection and electrical resistivity imaging are a promising tool for locating karst conduits. The method is also useful for gaining insight into conduit geometry and could be expanded to include multiple electrical resistivity transects. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
635.
636.
Based on the moderate resolution imaging spectro-adiometer (MODIS)-acquired snow-covered days data (MSCD), validation of MSCD is performed by using 529 in situ observations of snow-covered days (SCD) from 2001 to 2006 in China. For the different characteristics of snow cover in four major snow-covered regions including the Tibetan Plateau, Xinjiang, and north-eastern and inner Mongolia, the validation process is divided into five parts for all of China. Our results indicate that except in the south-eastern part of the Tibetan Plateau, the MSCD is usually lower than the in situ SCD measurement. It is found that the MSCD have good polynomial regression agreement with the in situ measurements in Xinjiang and north-eastern and inner Mongolia with an R 2 values that reach 0.89, 0.78, and 0.87, respectively. Because the MSCD is smaller but with a good regression relationship with the in situ SCD, calibration of the MSCD images could significantly improve its precision in those regions. To be considered a stable snow-covered area, there must be greater than 60?days per year in which the pixels are covered by snow. Unstable snow-covered areas are ones in which fewer than 60?days but at least 1?day is covered by snow. The calibrated MSCD outcome indicates that the unstable snow-covered area can reach 555.2?×?104?km2, and the stable snow-covered area is approximately 273.1?×?104?km2. The area in the three major stable snow-covered regions of the Tibetan Plateau, Xinjiang, and north-eastern and inner Mongolia is approximately 100.4?×?104, 54.4?×?104, and 114.7?×?104?km2, respectively. 相似文献
637.
SIROCKO Frank 《中国地球化学学报》2011,30(4):479-489
A 475-cm long sediment core (QH-2005) from Lake Qinghai was used to carry out multi-proxy analysis of δ18O and body length of ostracod valves and redness and grain size of sediments, in order to reconstruct environ-mental changes during the past 13500 cal. a BP. The age model was based on 6 14C dates for bulk orgnic carbon (BOC) and 2 14C dates for lignin. The lignin 14C dates are apparently younger than the corresponding layers’ BOC 14C dates, indicating that the reservoir age varied from 728 to 1222 a since the Late Glacial and from 2390 to 2490 a immediately before the pre-bomb era. Hence, the 14C age model for Core QH-2005 was corrected by the changing reservoir age. Ostracod δ18O values were primarily related to dilution and evaporative enrichment of the lake water. The reconstructed salinity based on ostracod body length coincides well with ostracod δ18O values. High redness and mean grain size (MZ) values indicate increased riverine supply to Lake Qinghai associated with increasing monsoon rainfall. Multi-proxy results show that climate during 13500-10900 cal. a BP was relatively cold and dry with fre-quent short-term fluctuations; a warm and wet climate began at about 10900 cal. a BP and culminated around 6500 cal. a BP as a result of monsoon strengthening; the climate became cold and dry afterwards and has remained rela-tively stable since 3400 cal. a BP. Our data also reveal short-term (millennial/centennial timescales) climatic fluctua-tions including: Younger Dryas events, ice-rafting events 8 and 1 (by ~11000 cal. a BP and ~1600 cal. a BP respec-tively), 8200 cal. a BP cold event, Little Ice Age and the Medieval Warm Period. 相似文献
638.
639.
640.
Speciation and phytoavailability of heavy metals in sediments in Nanjing section of Changjiang River 总被引:3,自引:1,他引:2
Heavy metal pollution and their fractionations in the sediments of Changjiang River in Nanjing Reach was monitored for cadmium
(Cd), lead (Pb), zinc (Zn), chromium (Cr), and copper (Cu). Moreover, the biological enrichment of metals by riverine plants
was studied. The results demonstrated there were highly significant variations among different sampling stations for the concentrations
of tested metals. The highest range was for Cu (38.8–120.4 mg kg−1), followed by Cr (74.4–120.0 mg kg−1), Zn (80.9–121.1 mg kg−1), Ni (26.0–55.5 mg kg−1), Pb (15.8–46.7 mg kg−1) and Cd (0.28–0.48 mg kg−1). Cd was the element with highest biological enrichment factor (BEF). The highest BEF of Cd in Erigeron bonariensis reached 3.0, indicating a significant Cd enrichment in this aquatic plant. In addition, 60% of Cd was found in reducible
fraction and exchangeable and acid-soluble fraction, which was consistent with its high mobility. The consistency of Cd fraction
in sediment and suspended particle indicated they came from the same source. Accumulated Cd concentration calculated according
to the release curve showed significant relativity with the total Cd concentration in the sediment. 相似文献