首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
The Ordovician Changtu Fauna is recently discovered in the Xia' ertai and Hulan Groups in northernLiaoning-central Jilin. The fauna, containing 10 genera and 14 species (including 3 new genera, 9 new speciesand an unidentified species), is closely related in evolution with the Early Cambrian Qinghezhen Fauna. Thediscovery of this fauna is significant to the study on the age of the strata, Ordovician biostratigraphy and geo-logical evolution of the tectonostratigraphical terrane on the northern margin of the Sino-Korean plate.  相似文献   

2.
Arsenic is the 20th most abundant element in the Earth crust. Humans are exposed to naturally occurring and anthropogenic sources of arsenic compounds in the environment. A wide variety of adverse health effects have been attributed to chronic exposure to high levels of arsenic. More than two-dozen arsenic compounds （species） are present in the environment and in biological systems. The various arsenic species have dramatically different behavior and toxicity. This presentation briefly describes arsenic speciation analysis, human exposure to and metabolism of arsenic species. Environmental issues on arsenic in Canada are briefly discussed. These include （1） the arsenic waste left from previous gold mining and smelting activities; （2） the domestic use of wood treated with chromated copper arsenate; and （3） use of well water as the source of drinking water by approximately one third of the Canadian population.  相似文献   

3.
Members Ⅰ-Ⅳ of the Wumishan Formation of the Jixian System are exposed respectively in Mt. Cuihua and Mt. Hushan in the Ming Tombs, Beijing. Black banded cherts which are extensively developed in this formation contain an abundance ofmicrofossils that are well preserved and variable in form. A study of thin sections shows that the microfossils include 10 genera, 12 species, 3 of. species, 2 indeterminate species and 1 unnamed form, of which 1 genus and 7 species are newly erected. The present assemblage is morphologically comparable to those from the Wumishan Formation in the Western Hills of Beijing, Jixian County of Tianjin and Kuancheng of Hebei Province.  相似文献   

4.
During the last century, several lead mines and a metal smelter were in production in the Upper Ribeira Valley, southeastern Brazil. After fifty years of activity, the refinery was shut down in November 1995 and, thereafter the last mines in production were closed. Since 1998, a multidisciplinary research group has carried out an ambitious investigation among the population of five municipalities in the Ribeira Valley （sampled population of 472 children and 523 adults） to assess the human exposure to lead. The highest blood lead levels were found among the population of two villages in the vicinity of the smelter where soil and indoor-dust are highly contaminated. During the present study, the lead contents of several food species that are part of local population diet were investigated. Greens, vegetables, corn, chicken eggs and cow milk, were sampled in two occasions, July 2004 and February 2005. The analytical procedures included burning of organic matter, pre-concentration of lead and, finally, determination by AAS using background correction. The quantification limit was 0.05 μg/g Pb. Soil samples were also collected and analyzed by X-ray fluorescence spectroscopy with a quantification limit of 2 μg/g Pb. The results are very impressing since 100% of greens, vegetables and eggs yielded lead concentrations exceeding the upper limits established by Brazilian regulations whereas milk and maize samples presented lead contents below the regulated limit of 0.05 μg/g Pb. Lead concentrations in soil varied between 156 and 1292 μg/g Pb, resembling the results of previous studies and far exceeding the threshold of 200 μg/g Pb indicated as the intervention value. Lead contents in some species vary consistently with lead concentrations in soils, however, other factors may account for the bioavailability of lead and its intake by plants, like the soil pH, its cationic exchange capacity, clay and organic matter contents, characteristics of the plant species itself, climate, among others.  相似文献   

5.
The species of Cu, Pb, Zn, Cd and Cr in sediments of the Taihu Lake, China, have been analyzed using the sequential chemical extraction method. Variations in the chemical fractions of these metals and their geographic distributions have also been studied. For all five metals, the residual fraction is highest but the exchangeable fraction is lowest among all the fractions. Compared to other metals, Cd has the highest percentage in the exchangeable fraction, and Cr is associated mainly with the residual fraction. Cu in the organic fraction and Pb in the Fe-Mn fraction are the important species, whereas the lowest percentages are found for Cd in the organic fraction, Cu in the Fe-Mn oxide fraction and Pb in the carbonate fraction. With respect to spatial differences, the total contents in the non-residual fractions of the metals in bay sediments are found to be higher than those in other sediments. The fractions of Cd, Cu and Cr showed significant variations in different regions. The fractions of Pb and Zn, however, did not show significant variations in spatial distribution, suggesting different amounts and different paths of anthropogenic input for the metals. Comparisons of the metal speciation indicated that Cd might be the most bioavailable metal, followed by Pb.  相似文献   

6.
In 2003, we initiated the first systematic investigation of the occurrence of high-fluoride groundwaters in the Ninh Hoa district, China. The study involved the measurement of F- and other ionic species （by FISE and HPIC techniques） in well and bore samples throughout the district. The results helped ascertain the precise extent of fluorosis risk within the local population. Treatment of the data within a GIS enables recognition of particular hot-spots of fluoride concentration, and provides a valuable tool for the minimizing of local health risks and identification of possible source, or sources, of fluoride.  相似文献   

7.
A field survey of soils and herbaceous species growing in the Lanping Pb/Zn mining area in Yunnan Province, China, was conducted. Two major mining areas, Jiayashan and Beichang, were selected to investigate soil properties, herbaceous distribution and hea…  相似文献   

8.
This paper reports for the first time on the microfossils discovered in the black cherts of the basal part of the Lower Cambrian Shuijingtuo Formation at Miaohe village, Zigui County, Hubei Province, all of which were observed in thin sections. Nine genera, 9 species and 3 indeterminate species (including a new species) are described. According to these microfossils, the conclusion is made that the microfossil zone may be equivalent to the small shelly fossil assemblage zones 2—3 of the Meishucun stage. They have provided another important line of evidence for the correlation of the Sinian-Cambrian boundary strata with those of the adjacent areas.  相似文献   

9.
Along with the rapid development of science and technology, natural matter and energy are further exploited and used. The pollution imposed on nature has also sharply increased. Only do we know the pollution history, can we make a correct appraisal of local environment, get the hold of the main cause of environmental pollution, and then take the effective measures to control the environment？ The evolution of heavy metal concentrations with time in the soil environment in the southern suburbs of Beijing were studied by using annual growth rings of trees. The absorption of 12 elements by different tree species in the same soil type was studied according to their absorption coefficients. The study indicated the differences in adsorption of elements by different species of trees. The adsorption coefficients of the elements Zn, Cd and P are higher. The correlations of nine elements （Na, K, Cu, Zn, As, Sr, Cd, Ba and Pb） in growth rings of poplar trees and those in soils near their roots show that the element contents in growth rings have a positive correlation with the contents in soils near the roots. Based on the logarithmic linear correlation model, the evolution of the contents of the elements Cu, Zn, As, Cd, Ba and Pb in soils from 1982 to 2004 was deduced. The trees have the characters of confirming year precisely, long life and widespread distribution. They are the ideal objects of study on environmental pollution changes. At present, research in China in this aspect is less, and the field of research is expected to further expand. This method can be used to provide richer and more scientific information on the history of environmental pollution and changes during modem urbanization in the past few decades and predicting the evolutionary trend of pollution change.  相似文献   

10.
Mercury is an important pollutant in lakes. Methylmercury （MeHg）, the most toxic mercury species, which can be formed from inorganic mercury in lakes, can be bioaccumulated into high concentration in food chain and result in a potential threat to human beings. Sediments play an important role for the Hg biogeochemistry in the aquatic systems： Mercury methylation has been shown to be fastest in the surfacial sediments, where the microbial activity is highest. The formation of MeHg in lakes suggests that sediments and/or near-shore wetlands can be the sources of MeHg in aquatic environments. The Baihua Reservoir, located in the suburb of Guiyang, was impounded in 1966. From the 1970s to the 1990s, Guizhou Organic Chemical Plant which used inorganic mercury as catalyst to produce acetic acid, was responsible for the discharge of waste water with high mercury content.  相似文献   

11.
Biogeochemical investigation of Tamarix aphylla,a plant species, of the Las-bela area has been made.This area mainly consists of ophiolites associated with sed-imentary rocks of Jurassic and Cretaceous age .Quantitative estimations of important biogenic trace elements such as Fe,Mn,Pb,Zn,Cu,Cr,Ni, and Co have been carried out .Anomalous concentrations of these elements in plant species of certain regions can be used to locate possible occurrences of ore deposits in the area.The comparative strdy also reveals appreciable variations in the composition of trace elements in plants.The possible causes of variation in the constitrents of Tamarix aphylla from different localities have been discussed in the light of bed rock nature, mo-bility of element and average abundance in the plant.  相似文献   

12.
Changjiang County is located to the northwest of the tailing range of the Wuzhi Mountains on Hainan Island,facing the sea and being against he Mountains.From southeast to northwest,it gradually descends in relief from mountain,hill,tableland,terrace to coastal plain.Its sandy coastal line is measued at 44.85km in length and its rocky coastal line at 7.15km along the county.The desertified coastal land covers and area of about 61.15km^2,extending from hundreds of meters to 3 km in width,of which the active sand land accounts for 5.333km^2 and the semi-active sand land,7.333km^2.The dunes are developed at the rate of 10-30m per year from the seashore toward the hinterland. The Forest Departments of Hainan Province and Changjiang County done a series of sand-control experiments.The chief technological measures are as follows:(1)to stabilize the drift sand first to create an adequate condition for afforestation;(2)to plant the big and strong saplings of Casuarin equisetifolia with nutrient bags in deep pits;and(3) to apply new techniques in “dry-season planting”to guarantee the quality of afforestation.The above experiments were successful.However,there still exist some problems such as quite seriously wilting shoot,lower survival rate of Pandanus tectorius in the vertical lines to the usual wind direction,monotonous the species in afforestation and subsequent poor management.Thus some suggestions are offered in this paper for future extension;(1)to apply REE fertilizers in the process of afforestation to increase the resistance of the plants;(2)to increase the vertical lines of Pandanus tectorius to the usual wind direcion to raise their survival rate in the network of sand stabilization;(3)to enlarge he area of liana planting to enhance the stability of sand;(4) to try to introduce new tree species from oter regions,which are of good performance in sand stabilization;(5) to interplant th adaptable economic crops;and (6)to make more investments and better management and conduct more extensive environmental education o ensure the early accomplishment of the protection forest belt around the island.  相似文献   

13.
There have been divergent opinions on whether Conophyllia develops synapticulae and dissepiments since its erection in 1849, with different views existing on the morphology of columella in Conophyllia.This paper presents a comprehensive review of Conophyllia, and revises the diagnosis according to new material from the Renacuo area of Gêrzê, Tibet.The revised diagnosis emphasises the following features: solitary coral; abundant radial elements subequal in thickness, lateral faces with granules and synapticulae; parietal, papillar or incompact columella, a few species lacking in columella; developed dissepiments.Individuals of Conophyllia have laminar septa of Triadophyllum type in earlier ontogenetic stages, while their septa in later ontogenetic stages are more fenestrate.The geological and geographical distribution of this genus is discussed, with five species of Conophylliafrom the Renacuo area of Gêrzê, Tibet being described and illustrated, including one new species and two in open nomenclatue.  相似文献   

14.
Selenium （Se） is an essential micronutrient to biota, but can become a potent toxicant at elevated concentrations. The natural sources and chemical properties of Se species make the boundary between deficiency and toxicity narrow for some biota, with both phenomena common around the globe. Large areas of farmland in the Colorado River Basin （CRB） generate salinized drainage water with Se concentrations much higher than 5 μg/L, the U.S. Environmental Protection Agency chronic water-quality criterion for the protection of aquatic life. We have carried out detailed field and laboratory studies to investigate Se geochemistry and remediation in two of these areas： the Middle Green River Basin, Utah and the Salton Sea Basin, California, located respectively in the Upper and Lower CRB. Results from these and other studies show that approximately 90% of the dissolved Se in the Colorado River and its tributaries originally is derived from the Upper Cretaceous Mancos Shale and equivalent pyritic marine units that outcrop in the Upper CRB. Selenium is mobilized commonly by biogeochemical oxidation of this pyritic shale and is concentrated mainly as selenate （SeO4^2-） in soils and agricultural drainage water of dry climates by evaporation. Minor （0%-5%） amounts of Se are present as the selenite species （HSeO3^-） and （SEO3^2-）, but these species and the more reduced species, elemental Se （SeO） and selenide （Se^2-）, have much lower solubility and/or have high sorptive affinity towards organic matter, clay minerals and iron oxyhydroxides. The concentration of dissolved Se （-2.5 μg/L） and salinity in the Lower Colorado River water are among the highest of the world major rivers. Because of low precipitation （7 cm/a） and extreme evapotranspiration （-1.8 m/a） rates in the Salton Sea Basin, California, Se values in irrigation water imported from the Colorado River increase to 〉300 μg/L in drainage wastewater. Removal of Se from contaminated wastewater by nanofiltration membranes was demonstrated in laboratory and pilot-scale field experiments.  相似文献   

15.
Although numerous papers have been published on nutrients in Great Lakes, estuaries, continental shelf areas and marines in the aspects of determination, sediment-water-interface exchange, fluxes and budget estimation, eutrophication and microbial processes as well as modeling study, the knowledge of river condition （especially urban river） is uncertain and simply considered as a contributor to eutrophication of estuary. After a series of determinations of nitrogen species corresponding to ammonia-N （AN）, Kjeldahl-N （K-N）, and total nitrogen （TN） by means of National Standards for China, the nitrate ＆ nitrite （Nitr-N） and org-N were obtained by the difference of TN with K-N, and K-N with AN, respectively. Therefore, the behaviors of vertical distributions in overlying waters and porewaters in the Fu and Nan Rivers located in Chengdu City were achieved.  相似文献   

16.
New data from abundant vegetative shoots and cuticular analysis are provided for the Cretaceous cheirolepidiaceous conifer Pseudofrenelopsis gansuensis Deng, Yang et Lu. The material was found from a new locality of the Lower Cretaceous strata in the Luozigou Basin, Wangqing, Jilin Province, northeastern China. Pseudofrenelopsis is a common plant in the Dalazi Formation of the Yanji Basin about 150 km from Wangqing, but there exists different species, Pseudofrenelopsis dalatzensis only. Both P. dalatzensis and P. gansuensis have been recorded from the Lower Cretaceous of Jiuquan, Gansu Province, but they are in different stratigraphic horizons. The Lower Cretaceous plant-bearing strata in Luozigou have used to correlate with the Dalazi Formation of the Yanji Basin. The discovery of P. gansuensis, which is lower in horizon than P. dalatzensis in Jiuquan, may indicate that they are also different in horizon in Jilin. Cheirolepidiaceous conifers are among the few fossils of red beds of the Early Cretaceous in China. The present discovery of Pseudofrenelopsis gansuensis provides important evidence for classification, correlation and determination of geological ages of the Early Cretaceous non-marine red deposits of the two separate basins in remote areas of North China.  相似文献   

17.
The Distrbution of Various Mercury Species in Soil   总被引：2，自引：0，他引：2  
According to the mercury species with different solubilities,the analytical procedure involving sequential chemical extraction has been applied to partitioning the mercury species in soils into seven fractions.Soil samples collected from five localities in different areas (the high-mercury ares.the man-made mercury-polluted area and the reference area)were an alyzed for the seven mercury species.It is found that high mercury contents of soils can be attributed to both man-made pollution and geological processes,but the two kinds of solis show obvious differences in the distribution of their mercury species.  相似文献   

18.
<正>It is estimated that the world has discovered more than1000 species and 800 genera of dinosaurs.Chinese scientists have named more than 170 species of dinosaurs,with 17 genera and 44 species of dinosaur egg fossils,35genera and 39 species of dinosaur footprints,since their first discovery in China in 1902.China has dinosaur occurrences from the Upper Triassic to the Upper  相似文献   

19.
In the middle and lower reaches of the Salawusu River. the Salawusu Formation regarded traditionallyas fluvio-lacustrine deposits actually includes a series of strata which mainly consist of eolian sandy depositsnamed as "Chengchuan Formation" by the authors. The eolian sand of the Chengchuan Formation and theMalan loess distributed in the upper reaches of the Salawusu River are deposits of sand and loess faciesformed by wind action during the same period. The relationship of the Chengchuan Formation and theMalan Loess with the Salawusu Formation which is really of fluvio-lacustrine deposits is that the formertwo superpose the latter. This can be demonstrated by the difference of the extinct species proportion of thefaunas in different strata. In this area. the Salawusu formed during the early period of Late Pleistocene.while the Malan Loess and the Chengchuan Formation deposited during the late period of the LatePleistocene.  相似文献   

20.
To date our knowledge is limited with regard to the responses of ethylene and methane consumption by forest soils to tree species and soil types, and to the effect of presence of ethylene on atmospheric methane consumption. The soils at depths from tropical and temperate forests in China were used to study the responses of ethylene and methane consumption to tree species and soil types. The ethylene and methane consumption by soils beneath each forest floor was measured under the same oxic conditions, along with main properties of forest soils. The accumulation of ethylene was studied in the soil slurry （soil/water, 1/2.5）. In temperate soils under spruce and birch forests, maximal consumption rates of ethylene and methane were observed in the 2.5-5.0 cm and 5.0-7.5 cm soil layers, respectively （P〈0.05）. However, a maximal consumption of both occurred in the 0-2.5 cm soil layer under temperate Korean pine forest （P〈0.05）. Contrary to temperate forest soils, there was a significant lower consumption of ethylene and methane in tropical forest soils at less than 20 cm depths under a seasonal rainforest and secondary rubber forest （P〈0.05）. Hence, the potential of ethylene and methane consumption in the 0-20 cm soil profile was variable with tree species and soil types. According to ethylene formation in the soil slurry, there was greater accumulation of ethylene in the 0-2.5 cm soil under temperate forests than under tropical forests, and its accumulation under spruce and birch forests was more than under Korean pine forest （P〈0.05）. The presence of extrinsic ethylene can significantly inhibit the consumption of atmospheric methane by forest soils.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号