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961.
Fossil oyster reefs are indicators of past sea levels, and their formation is usually dated by means of radiocarbon. However, radiocarbon dating of the shells from coastal areas may be complicated by the varying sources of carbon. Here we applied optical dating methods to date the samples from above and below a fossil oyster bed in a section on the coast of Bohai Bay, China. The optical ages of the sediments were used to constrain the oyster bed. Single-aliquot regenerative-dose procedures using the OSL signal from fine grain quartz, the IRSL and post-IR OSL signals from polymineral fine grains were employed to determine equivalent dose (De). The behaviors of the different luminescence signals from quartz and polymineral grains during De measurements were examined. The results showed that the quartz OSL signal is more reliable than the polymineral IRSL and post-IR OSL signals with respect to dating for these coastal samples. The optical ages indicated that the oyster reef formed between ca. 6.2 and 5.0 ka. 相似文献
962.
山东胶东半岛地区断裂最新活动性研究 总被引:5,自引:2,他引:5
山东胶东半岛地区发育有北北东-北东向和北西西向两组断裂,前者分属蓬莱-栖霞断裂系和即墨-牟平断裂带,为半岛的主体断裂构造;后者分布在半岛北缘及其北侧海域,由多条断裂组成。实地调查表明,断层在第四纪期间是活动的,控制着附近山地和盆地的构造演化与地貌发育,最新活动主要发生在第四纪早期,垂直活动幅度可达百米以上;第四纪晚期,断裂活动性迅速减弱,甚至停止,但依然发现北北东-北东向断裂的多个局部段落还在活动,明显地错断了晚更新世地层,垂直断距最大为10m左右。 相似文献
963.
基于小波包变换的面波分离技术研究 总被引:1,自引:0,他引:1
依据面波视速度的分布范围,提出一种新的叠前面波分离技术,即把地震波场分成不受面波影响的波场和受面波影响的波场,然后利用小波包变换对受面波影响的波场进行时频分析,通过分解与重构,从中提取有效波,再将其与不受面波影响的波场合并,就可得到面波分离后的地震波场。该方法在成功分离面波的同时,可使有效波的能量(尤其是其低频能量)不受损失,既有效地保持信号的频宽不变,又提高了记录的信噪比。实际资料的处理结果表明:此方法在叠前面波分离方面具有有良好的效果。 相似文献
964.
Evaluation of groundwater quality in coastal areas: implications for sustainable agriculture 总被引:4,自引:1,他引:4
Seawater intrusion is a problem in the coastal areas of Korea. Most productive agricultural fields are in the western and
southern coastal areas of the country where irrigation predominantly relies on groundwater. Seawater intrusion has affected
agricultural productivity. To evaluate progressive encroachment of saline water, the Korean government established a seawater
intrusion monitoring well network, especially in the western and southern part of the peninsula. Automatic water levels and
EC monitoring and periodic chemical analysis of groundwater help track salinization. Salinization of fresh groundwater is
highly associated with groundwater withdrawal. A large proportion of the groundwaters are classified as Na–Cl and Ca–Cl types.
The Na–Cl types represent effects of seawater intrusion. The highest EC level was over 1.6 km inland and high Cl values were
observed up to 1.2 km inland. Lower ratios of Na/Cl and SO4/Cl than seawater values indicate the seawater encroachment. A linear relation between Na and Cl represents simple mixing
of the fresh groundwater with the seawater. The saline Na–Cl typed groundwaters showed Br/Cl ratios similar to or less than
seawater values. The Ca–HCO3 type groundwaters had the highest Br/Cl ratios. Substantial proportions of the groundwaters showed potential for salinity
and should be better managed for sustainable agriculture. 相似文献
965.
覆膜态Fe(OH)3在厌氧条件下生物降解苯和甲苯的初探 总被引:2,自引:0,他引:2
天然条件下氯代烃的污染经常会与石油烃的污染共存,对于这种混合污染羽的治理,第一步采用粒状铁还原氯代烃,后续利用微生物和第一步产生的副产物生物降解石油烃。苯系物是石油烃中毒性较大、存留时间较长的污染物,本文利用批实验的方法研究了厌氧条件下用Fe(OH)3覆膜于石英砂表面的Fe(Ⅲ)作为电子受体降解苯和甲苯。结果表明,Fe(Ⅲ)作为电子受体时苯和甲苯能够发生厌氧生物降解,经过驯化后苯和甲苯的降解速度明显加快。降解实验表明甲苯的降解速度比苯的降解速度快,苯降解的半衰期是4.02d,甲苯降解的半衰期是3.81d。 相似文献
966.
The development and utilization of water and land resources in the Shiyang River basin are the highest among the inland rivers
in northwestern China. Using GIS and the landscape structure analysis program FRAGSTATS, landscape metrics of a study area
in the lake-district in Minqin Oasis in the lower reaches of Shiyang River basin were calculated and analyzed based on TM
images from 1987 to 2001 at class level and landscape level, respectively. Transformation matrix of the landscape mosaics
was also examined. The driving forces of landscape changes were analyzed, including the dynamics of runoff and groundwater
resources and their exploitation, and influences of policies and market economy. The results showed that: (1) Patch number
of farmland and desert decreased, but their mean patch area increased, indicating that reclamation and desertification was
very serious in the study area. Contagion index for oasis increased and edge density and landscape diversity were reduced.
(2) Farmland and desert areas have enlarged by 1,520.46 and 4,941.27 hm2, respectively. This increase was at the cost of woodland and grassland, which shrank by 1,520.46 and 4,941.27 hm2, respectively. (3) The net utilization of surface water decreased by 50% in the last 10 years, and dropped to 22.3 × 106 m3 in the later 1990s. Exploitation of groundwater increased remarkably, up to 80 × 106 m3 per year in the last 5 years. (4) The capability of the economic structure to withstand pressures of the market economy has
depressed distinctly because of the simplified planting pattern, which is dominated by salinity-enduring cash crops, such
as cotton. Based on the above analysis, strategies of ecological reconstruction in the lake-district were suggested. 相似文献
967.
内蒙古夏季干旱的水汽输送特征分析 总被引:6,自引:0,他引:6
对于大气中水汽的定性、定量测量是提高内蒙古干旱研究与预测的有效手段。利用NCEP再分析资料和内蒙古地区实测降水资料(1961-2000年),定性、定量地分析东亚水汽分布、水汽输送与内蒙古夏季干旱的关系。得出内蒙古地区上空低层大气的含水量偏少是内蒙古夏季干旱的一个重要因素。由于青藏高原大地形作用,孟加拉湾和南海的水汽北上受阻,不能达到内蒙古高原是形成内蒙古干旱的又一原因。受大气环流影响,内蒙古高原水汽辐合偏弱是内蒙古夏季干旱的重要原因。青藏高原的水汽通量与内蒙古东西部降水都存在明显负相关;孟加拉湾至内蒙古西部是内蒙古西部地区降水的水汽通道,南海至中国东北地区为内蒙古东部降水的水汽通道。 相似文献
968.
969.
970.
A. V. Suresh Babu V. Venkateshwar Rao I. V. Muralikrishna 《Journal of the Indian Society of Remote Sensing》2007,35(1):81-91
Water Utilisation Index (WUI) defined as area irrigated per unit volume is a measure of water delivery performance and constitutes
one of the important spatial performance indicators of an irrigation system. WUI also forms basis for evaluating the adequacy
of seasonal irrigation supplies in an irrigation system (inverse of WUI is delta, i.e. depth of water supplied to a given
irrigation unit). In the present study WUI and adequacy indicators were used in benchmarking the performance of Nagarjunasagar
Left Canal Command (NSLC) in Andhra Pradesh. Optimised temporal satellite data of rabi season during the years 1990–91 and
1998–99 was used in deriving irrigated crop areas adopting hierarchical classification approach. Paddy is the predominant
crop grown and cotton, chillies, sugarcane etc. are the other crops grown in the study area. Equivalent wet area (paddy crop
area) was estimated using the operationally used project specific conversion factors. WUI was estimated at disaggregated level
viz., distributary, irrigation block, irrigation zone level using the canal discharge data. At project level, WUI estimated
to be 65 ha/MCM and 92 ha/MCM during rabi season of 1990–91 and 1998–99 years respectively. A comparison of total irrigated
area and discharges corresponding to both the years indicate that irrigation service is extensive and sub optimal during 1998–99
and it is intensive and optimal in 1990–91. It was also observed that WUI is lesser in blocks of with higher Culturable Command
Area (CCA) compared to the blocks of lower CCA. All the disaggregated units were ranked into various groups of different levels
of water distribution performance. The study demonstrates the utility of WUI as spatial performance indicator and thus useful
for benchmarking studies of irrigation command areas. The WUI together with satellite data derived spatial irrigation intensity,
crop productivity constitutes important benchmarking indices in irrigation command areas. 相似文献