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981.
982.
Giles F S Wiggs Sarah L O'hara† Johannah Wegerdt‡ Joost Van Der Meer§ Ian Small‡ Richard Hubbard¶ 《The Geographical journal》2003,169(2):142-157
The drying up of the Aral Sea has been described as one of the most staggering environmental disasters of the twentieth century. Over the last 40 years over 36 000 km2 of the former seabed have been exposed, creating a potentially significant aeolian dust source. It is widely believed, but little researched, that increased dust storm activity in the region has had a major impact on human health. In this paper we report the findings of a study into the link between dust exposure and respiratory health amongst children in the Autonomous Republic of Karakalpakstan, Uzbekistan located on the southern shore of the Aral Sea. The findings indicate that dust deposition rates across the region are high, with sites located near the former shore of the sea being the worst affected. For these northerly regions the former bed of the Aral Sea is the most likely source of dust. The situation for the rest of the country appears to be far more complex. In these regions it appears that local sources and more distant sources to the south and south-west represent significant sediment providers, particularly in the early summer. Provisional analysis of the respiratory health data suggests that children living in the north of the country, where aeolian dust deposition rates are greater, show a lower frequency of respiratory problems. This inverse relationship requires further investigation, but highlights the complexities of environmental and human health inter-relationships. 相似文献
983.
泥盆纪是秦岭构造与古地理格局发生重大变革的时期。秦岭的泥盆系主要分布在南秦岭。资料表明,南秦岭泥盆系不是在统一的盆地中形成的,而是被古陆分隔的几个裂陷盆地的沉积产物。柞水石瓮子地处镇安盆地北缘,该处滑塌块体和斜坡砾岩广泛发育,物源为沿山阳-凤镇断裂向南作大规模逆冲推覆而被掩盖消失的小磨岭古陆,其形成受早古生代南秦岭区域抬升、全球海平面下降以及区内山阳-凤镇断裂和镇安-板岩镇断裂强烈活动的控制。区域性同造山陆块隆升与全球海平面下降造成了南秦岭晚古生代与早古生代地层之间区域性的不整合,一南秦岭在继续向北俯冲的同时,又沿南缘的勉略-巴山断裂带发生扩张,其内部也因拉张作用形成裂陷与块断隆起相间的古地理格局。南秦岭区域性隆起和裂陷可能与加里东运动和勉略有限洋盆的打开相关联。 相似文献
984.
Electric energy production and most heavy industry in Estonia are concentrated in the north-eastern part of the country. Thermoelectric power plants (total maximal capacity over 3 GW), cement and chemical industries are fueled by Kukersite oil shale, mined nearby. The mineral part of oil shale is rich in trace metals that can accumulate in the local ecosystem. Samples of epigeic mosses Pleurozium schreberi and Hylocomium splendens were taken in 1992, 1997 and 2002 from sites 1 km to 30 km from the main air pollution sources and analysed for Cd, Cr, Cu, Fe, Ni, Pb, V and Zn. For background data collection, analogous measurements within the national monitoring programme were used. Raster maps of concentrations were generated from the measurements, using the Kriging algorithm. These maps were compared with the model-estimated (AEROPOL model) maps of fly ash and cement dust deposit from the past. The concentration of trace metals in mosses is highly (Cr, Fe, Ni, V) or moderately (Cd, Cu, Pb, Zn) affected by the airborne emissions of the oil shale industry. During the past decade the uptake of the first group of elements in the industrial zone has decreased 3–4 times in proportion to emissions. 相似文献
985.
Fourteen samples of fresh falling snow were collected at Antarctic coastal base Dumont d'Urville in 1984. The samples have been analysed for major ions (including MSA) by ion chromatography and acid titration. The results are relevant to the chemical composition of background precipitation in polar marine conditions. The seasalt aerosol contribution is dominant. All samples are found to be acidic in the range 3–16 eq/l. The calculated non-seasalt sulfate (nssSO4
2-) concentration is significantly negative for 3 of the 14 samples. NssSO4
2- is found to be relatively high in summer and fall. MSA also exhibits the same pattern probably linked to local marine biogenic activity and/or atmospheric photochemical processes. The MSA to nssSO4
2- ratio is in good agreement with values reported for coastal Antarctic ice cores and subantarctic acrosol. The background mean value for nitrate concentration is 1.1 eq/l but two very strong spikes (up to 16 eq/l) are observed. The first seems to be linked with long range transport of continental air masses while the second (in winter) is clearly due to a sudden input of nitric acid, possibly from the stratosphere.This paper represents a preliminary approach to a larger air and snow monitoring to be developped at this site. 相似文献
986.
Donald F. Charles Michael W. Binford Edward T. Furlong Ronald A. Hites Myron J. Mitchell Stephen A. Norton Frank Oldfield Michael J. Paterson John P. Smol Allen J. Uutala Jeffrey R. White Donald R. Whitehead Robert J. Wise 《Journal of Paleolimnology》1990,3(3):195-241
Paleoecological analysis of the sediment record of 12 Adirondack lakes reveals that the 8 clearwater lakes with current pH < 5.5 and alkalinity < 10 eq l-1 have acidified recently. The onset of this acidification occurred between 1920 and 1970. Loss of alkalinity, based on quanitative analysis of diatom assemblages, ranged from 2 to 35 eq l-1. The acidification trends are substantiated by several lines of evidence including stratigraphies of diatom, chrysophyte, chironomid, and cladoceran remains, Ca:Ti and Mn:Ti ratios, sequentially extracted forms of Al, and historical fish data. Acidification trends appear to be continuing in some lakes, despite reductions in atmospheric sulfur loading that began in the early 1970s. The primary cause of the acidification trend is clearly increased atmospheric deposition of strong acids derived from the combustion of fossil fuels. Natural processes and watershed disturbances cannot account for the changes in water chemistry that have occurred, but they may play a role. Sediment core profiles of Pb, Cu, V, Zn, S, polycyclic aromatic hydrocarbons, magnetic particles, and coal and oil soot provide a clear record of increased atmospheric input of materials associated with the combustion of fossil fuels beginning in the late 1800s and early 1900s. The primary evidence for acidification occurs after that period, and the pattern of water chemistry response to increased acid inputs is consistent with current understanding of lake-watershed acidification processes.This is the second of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D.F. Charles and D.R. Whitehead are guest editors for this series. 相似文献
987.
988.
989.
Morphodynamics of ebb-tidal deltas: a model approach 总被引:1,自引:0,他引:1
S. M. van Leeuwen M. van der Vegt H. E. de Swart 《Estuarine, Coastal and Shelf Science》2003,57(5-6):899-907
The results of 2DH numerical models of the Frisian Inlet (located in the Dutch Wadden Sea) are discussed to gain further knowledge about the physical mechanisms causing the presence of both ebb-tidal deltas and of channels and shoals in tide-dominated inlet systems. A hydrodynamic model, extended with sediment transport formulations, was used to verify earlier conceptual models that deal with ebb-tidal delta characteristics. The model does not confirm their hypothesis concerning the observed spatial asymmetry of ebb-tidal deltas and suggests that long-term morphological simulations are needed to understand this aspect. Furthermore, the model indicates that the initial formation of the ebb-tidal delta is mainly due to convergence of the tidally averaged sediment flux related to residual currents, whilst the net sediment transport in the basin is mainly caused by tidal asymmetry. A second model (accounting for feedbacks between tidal motion and the erodible bottom) was used to simulate the long-term bathymetric evolution of the Frisian Inlet under fair weather conditions. This model reproduces the gross characteristics of the observed morphology: the presence of a double-inlet system with two distinct ebb-tidal deltas having different sizes and the presence of channels and shoals. The role of the ‘Engelsmanplaat’, a consolidated shoal in the middle of the Frisian Inlet, was not found to be crucial for the morphodynamic stability of this inlet system. 相似文献
990.
泥质潮坪磁组构特征及其意义研究 总被引:3,自引:4,他引:3
在1988年-1993年期间,对河北歧口及上海南汇海岸带泥质潮坪现行滩面积浦西曹杨新村近代亚潮坪沉积剖面进行了沉积动力环境与沉积动力环境与沉积磁组构特征测量分析。现行开敞海岸同物源潮坪沉积磁且构参量量值特征显示出,其K值高滩为高值,低潮滩次之,中潮滩为低。亚近开敞海岸泥质潮坪沉积剖面磁组构测量结果;K值是区分潮坪沉积动力活动带的高分辨率标志;P、L、F、q是分析潮坪沉积结构的分辨率标志;q是分析潮 相似文献