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991.
1 INTRODUCTION δ13C in organic matters from lacustrine sedi- ments varies with several factors including aquatic plants, vegetation type in the catchment, atmos- pheric CO2 concentration, climate (temperature and precipitation), and properties of water, … 相似文献
992.
Microcystis bloom, one of the most objectionable characteristics of eutrophication in tropical and subtropical waters, occurred in Donghu Lake (East lake) of Wuhan every summer from the 1970s up to 1984, but from 1985 up to now failed to occur there. The cause of its disappearance rema-ined in obscurity until recently. In situ enclosure experiments in the lake for three years showed that the stocking of the filter-feeding silver carp ( Hypophthalmichthys molitrix ) and big-head carp (Aristichthys nobilis ) played a decisive role in eliminating Microcystis bloom from the lake; but that recurrence of the bloom is possible under certain conditions. This paper presents the details and the results of enclosure ex-periments. The authors‘ analysis of fish biomass data obtained by echo-sounding and the fishery produc-tion of the lake over the years, revealed that the recurrence of Microcystis bloom can be prevented so long as the combined biomnss of silver carp and big-head carp remains at or exceeds 50 g per cubic meter of lakewater, as was the case in the lake‘s 1985 fish yield of 1015 t. 相似文献
993.
Jiaqi Chen 《中国地理科学(英文版)》1994,4(2):129-133
In Taihu Lake basin during June–July in 1991, there happened a catastrophic flood, the precipitation reached that of 1954
and the water level was the highest in the history in Taihu Lake. This heavy flood, happening in the relatively humid period
and being well accord with flood-drought change tendency, was early precautioned. The occurrence of the flood illustrated
that using records of historical climate to predict flood-drough tendency is practically significant for hazard-reduction
project. 相似文献
994.
We present evidence of a large lake (Glacial Lake Victoria) that existed in Victoria Valley in the dry valleys region of Antarctica between at least 20 000 and 8600 14C yr BP. At its highstands, Glacial Lake Victoria covered 100 km2 and was ca. 200 m deep. The chronology for lake‐level changes comes from 87 AMS radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present‐day lakes on the valley floor. The existence of Glacial Lake Victoria, as well as other large lakes in the dry valleys, indicates a climate regime significantly different from that of today at the last glacial maximum and in the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
995.
中国大陆及华北地区地震资料的小波分析 总被引:15,自引:8,他引:7
基于地震活动为多尺度多活动这一观点,运用小波变换方法,以不同的小波尺度分析了中国大陆1900~2001年和华北地区1500~2001年M≥5地震的本尼奥夫应变资料,得到了各种层次地震活跃期和平静期,分析结果可信而又符合实际。对历史地震研究和地震危险性预测具有一定的参考价值。 相似文献
996.
J. Huang N. Hotta K. Kasahara I. Ohta S. Ozawa T. Saito M. Shibata X. W. Xu T. Yuda 《Astroparticle Physics》2003,18(6):637-648
We have done extensive Monte Carlo simulations using the new simulation codes of CORSIKA and COSMOS to compare with the gamma-family data obtained at Mts. Fuji (3750 m above sea level) and Kanbala (5500 m above sea level). Then, we estimated the primary proton and helium spectra around the knee energy region using a multiple-layered feed-forward neural network as a classifier of primary particle kind. The selection efficiency of proton-induced family events is estimated to be 82%. The flux value of protons at 2×1015 eV is (5.5±1.5)×10−14 (m−2 s−1 sr−1 GeV−1). The result suggests heavy-enriched primary composition around the knee region. 相似文献
997.
Integrated Indicators-based Gradation of Cultivated Land Quality in Mountainous Region of Southwestern China 总被引:1,自引:0,他引:1
SHAO Jing'an WEI Chaofu XIE Deti ZHOU Yan 《山地科学学报》2006,3(3):259-270
1 Introduction The gradation of cultivated land is to assess the suitability of cultivated land for agricultural production in terms of natural and economic prop-erties of land (Feng et al. 2004). It can be used to evaluate sustainability of land use and … 相似文献
998.
QIAO Jia-jun LI Xiao-jian KONG Yun-feng 《中国地理科学(英文版)》2006,16(1):9-17
1INTRODUCTION Thequantitativestudyofregionalman-earthrelationship system can be traced back to a long time ago. Paul Vidal de la Blache, a human geographer from France, put for- ward the idea of man-earth relativity, which was further developed by his student named Jean Brunhen (BRUN- HEN, 1935). In the early 1980s, WU Chuan-jun, an aca- demician from Chinese Academy of Sciences, expanded the view of the man-earth areal system (WU, 1981), and he believed that onlythese qualitative … 相似文献
999.
Ruchi Mishra 《Planetary and Space Science》2006,54(2):188-199
Dispersion relation, resonant energy transferred, growth rate and marginal instability criteria for the electrostatic ion-cyclotron wave with general loss-cone distribution in low-β anisotropic, homogeneous plasma in the auroral acceleration region are discussed by investigating the trajectories of the charged particles. Effects of the parallel electric field, ion beam velocity, steepness of the loss-cone distribution and temperature anisotropy on resonant energy transferred and growth rate of the instability are discussed. It is found that the effect of the parallel electric field is to stabilize the wave and enhance the transverse acceleration of ions whereas the effect of steepness of loss-cone, ion beam velocity and the temperature anisotropy is to enhance the growth rate and decrease the transverse acceleration of ions. The steepness of the loss-cone also introduces a peak in the growth rate which shifts towards the lower side of the perpendicular wave number with the increasing steepness of the loss-cone. 相似文献
1000.
Late glacial and Holocene environmental change in the Lake Baikal region documented by oxygen isotopes from diatom silica 总被引:4,自引:0,他引:4
David W. Morley Melanie J. Leng Anson W. Mackay Hilary J. Sloane 《Global and Planetary Change》2005,46(1-4):221
We investigate late glacial and Holocene climate change recorded in Lake Baikal using the oxygen isotope composition of diatom silica (δ18ODIAT). Evaporation from the lake is minor, and the temperature fractionations of δ18O are unable to explain variations in the δ18ODIAT record alone. Isotopically, low meltwater input from glaciers may have some influence on δ18ODIAT, but the assumed periods of climatic warming and wastage do not coincide with large shifts in δ18ODIAT. There is a gradual oxygen isotope lowering from 27.0‰ to 20.6‰ over the late glacial, while, during the Holocene, δ18ODIAT values return to relatively high values. Previous studies of the modern oxygen and hydrogen isotope composition of Lake Baikal's inputs reveal that fluvial input to the lake's North Basin are isotopically lower than fluvial input from South Basin rivers. This north–south gradient of river δ18O and δD is mainly due to the greater input from isotopically low winter precipitation in the north and isotopically higher summer precipitation in the south. As a result, the δ18ODIAT record from Lake Baikal can at least in part be explained by varying input from these sources related to seasonal changes in precipitation. Changes in atmospheric conditions may have a role in altering seasonality and the distribution of precipitation over Lake Baikal's catchment. A feedback mechanism is well known linking higher Eurasian spring snow cover extent (ESSC) to the development of anticyclonic conditions and low precipitation the following summer in the areas south of Lake Baikal. A simultaneous increase in the importance of depleted water (snowmelt) input from the north and decreased enriched summer precipitation in the south is needed to explain depletions in δ18O of lake water and subsequently δ18ODIAT during colder periods. The opposite of this situation is required to enrich lake water during warmer periods. The analysis of δ18O from diatom silica is a useful proxy for environmental change, especially in lakes, like Lake Baikal, where carbonates are absent or diluted. However, analysis must be based on near pure diatom samples as even trace amounts of silt can have a dominating effect on δ18ODIAT values. 相似文献