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1.
Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China's Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42–7.23 m; medium, 7.23–8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth (SD), and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Water level regime mainly influenced interspecific relationships by changing the TN and COD concentration. The water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability. The biodiversity evaluation framework would provide a deeper insight into the hydrological process management for restoration of aquatic macrophyte communities in shallow lakes. 相似文献
2.
REGIONAL DEMOGRAPHIC STRUCTURE OF THE UNITED STATES 总被引:1,自引:0,他引:1
Richard L. Morrill 《The Professional geographer》1990,42(1):38-53
This paper analyzes the surprisingly great variation in demographic character across the states, utilizing data on fertility, mortality, age, sex, mobility, household character, abortion, race and ethnicity. A fairly simple regional pattern is revealed that is less related to levels of economic development than to long-standing historical cultural differences. 相似文献
3.
DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHEHEXIREGION,CHINA肖洪浪,高前兆,李福兴DEVELOPMENTSTRATEGIESOFWATERANDLANDRESOURCESINTHE... 相似文献
4.
《中国地理科学(英文版)》2004,14(4):296-303
1INTRODUCTIONUrbanrelationshipaswellasurbansystemhas beenthemostimportantandlastingdirectioninthestudyofur-bangeographysinceCHRISTALLER(1933)putfor-wardthecentralplacetheory.Alongwiththepaceofglobalizationinthe1980s,somepioneer researchessen-sitivelyexpoundedaworldcitysystem,includingworldcity,internationalcity,nationalcity,regionalcityandlocalcity(FRIEDMAN,1986).Lotsofresearchesfo-cusedonthedevelopingmechanismofthebigcitiesandurbansystemnetwork(GU,2000;ZHOU,1997;CUI,1992;HUeta… 相似文献
5.
6.
N. H. S. OLIVER I. CARTWRIGHT V. J. WALL S. D. GOLDING 《Journal of Metamorphic Geology》1993,11(5):705-720
Abstract Large calcite veins and pods in the Proterozoic Corella Formation of the Mount Isa Inlier provide evidence for kilometre-scale fluid transport during amphibolite facies metamorphism. These 10- to 100-m-scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 × 10-km Mary Kathleen Fold Belt, despite the isotopic heterogeneity of the surrounding wallrocks. The fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks. The pods have δ13Ccalcite values of –2 to –7% and δ18Ocalcite values of 10.5 to 12.5%. Away from the pods, metadolerite wallrocks have δ18Owhole-rock values of 3.5 to 7%. and unaltered banded calc-silicate and marble wallrocks have δ13Ccalcite of –1.6 to –0.6%, and δ18Ocalcite of 18 to 21%. In the alteration zones adjacent to the pods, the δ18O values of both metadolerite and calc-silicate rocks approach those of the pods. Large calcite pods hosted entirely in calc-silicates show little difference in isotopic composition from pods hosted entirely in metadolerite. Thus, 100- to 500-m-scale isotopic exchange with the surrounding metadolerites and calc-silicates does not explain the observation that the δ18O values of the pods are intermediate between these two rock types. Pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc-silicates. These data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the Corella Formation at the presently exposed crustal level, although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc-silicates, or thermal fluctuations attending deformation and metamorphism. The overall L-shaped trend of the data on plots of δ13C vs. δ18O is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc-silicate rocks. Localization of the vein systems in dilatant sites around metadolerite/calc-silicate boundaries indicates a strong structural control on fluid flow, and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km. The ultimate source for the external fluid is uncertain, but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle. Intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism. 相似文献
7.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts
such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes
the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities
between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links. 相似文献
8.
Zhu Ge-yan 《中国海洋湖沼学报》1996,14(4):308-315
The composition and distribution of benthic, periphytic and planktonic rotifers in different habitats in Krottensee were investigated.
Sixty-five rotifer taxa were identified, their relative abundance estimated.
Classification of the data set by cluster analysis allowed the recognition of distinct habitat groups confined to acid bog
ponds, macrophytes, sediments and open water. Five groups of rotifer taxa were identified on the basis of their habitat preferences
and the occurrence of the taxa. Highest diversities were found on macrophytes and in acid bog ponds. 相似文献
9.
1:25万区域地质调查修测的核心任务是挖掘、利用前人资料和对前人资料的二次开发。在1:25万玉林市幅数字地质填图试点的过程中.总结出一套基于数字填图系统的前人地质资料利用与数据采集的工作方法。其工作流程和工作步骤可分为6个阶段:①前期准备阶段;②室内地质资料录八阶段;③野外数字地质调查阶段;④室内资料整理阶段;⑤图件编制阶段;⑥成果提交阶段。该工作方法与传统的地质调查方法相比,提高了地质调查的工作效率和质量,已基本上达到了在1:252万区调修测区推广应用的“实战性”要求。 相似文献
10.
在对中国西部的区域划分进行界定并阐述中国西部区域特征的基础上,对中国西部的开发进行了历史回顾,并对中国西部开发的历史背景和现实基础、中国西部开发的优势和制约条件进行分析,最后提出了中国西部开发的发展战略和政策措施. 相似文献