湘江中下游农田土壤和蔬菜的重金属污染

A total of 219 agricultural soil and 48 vegetable samples were collected from the midstream and downstream of the Xiangjiang River（the Hengyang-Changsha section）in Hunan Province.The accumulation characteristics,spatial distribution and potential risk of heavy metals in the agricultural soils and vegetables were depicted.There are higher accumulations of heavy metals such as As,Cd,Cu,Ni,Pb and Zn in agricultural soils,and the contents of Cd（2.44 mg kg^-1 ）,Pb（65.00 mg kg^-1 ）and Zn（144.13 mg kg^-1 ）are 7.97,3.69 and 1.63 times the corresponding background contents in soils of Hunan Province,respectively. 13.2%of As,68.5%of Cd,2.7%of Cu,2.7%of Ni,8.7%of Pb and 15.1%of Zn in soil samples from the investigated sites exceeded the maximum allowable heavy metal contents in the China Environmental Quality Standard for Soils（GB15618-1995,Grade Ⅱ）.The pollution characteristics of multi-metals in soils are mainly due to Cd.The contents of As,Cd,Cu,Pb and Zn in vegetable soils are significantly higher than the contents in paddy soils.95.8%, 68.8%,10.4%and 95.8%of vegetable samples exceeded the Maximum Levels of Contaminants in Foods（GB2762-2005）for As,Cd,Ni and Pb concentrations,respectively.There are significantly positive correlations between the concentrations of Cd,Pb and Zn in vegetables and the concentrations in the corresponding vegetable soils（p〈0.01）.It is very necessary to focus on the potential risk of heavy metals for food safety and human health in agricultural soils and vegetables in the midstream and downstream of the Xiangjiang River,Hunan Province of China.     

Periodic Hartree-Fock study of minerals: Tetracoordinated silica polymorphs

Periodic Hartree-Fock STO-3G calculations have been performed on several tetracoordinated silica polymorphs: low and high quartz, low and idealized high cristobalite and prototype tridymite. The optimized structural parameters are in overall good agreement with experimental data. In the particular case of -quartz, the SiO₄ tetrahedra are found to be irregular. The optimized values of the two different SiO bond lengths are respectively 1.608 Å and 1.613 Å. The potential energy versus tilt angle curves suggest a picture of the high temperature phases in terms of delocalized oxygen atoms which is consistent with a disordered structure. Finally, the bonding in silica polymorphs is discussed from electron density maps and Mulliken population analysis.     

Holocene environmental changes in the Whitefish Dunes Area, Door Peninsula, Northern Lake Michigan Basin, USA

A two meter sediment core taken from an inter-dune pond in Whitefish Dunes State Park, Door Peninsula, Wisconsin, provides a record of paleoenvironmental changes in the area from approximately 3600 RCYBP to 5100 RCYBP. The hydrology of the Whitefish Dunes pond is now apparently dependent on ground water recharge from local precipitation that infiltrates into the dunes and from Clark Lane, making it very sensitive to low magnitude, short term climate fluctuations.Changes in lithology, molluscan species diversity, oxygen isotopes from gastropod shells, and sediment organic content permit division of the core into several intervals representing different environmental regimes. The basal sediments are older than 5130 RCYBP and resemble those of the Liberty Grove Member of the Pleistocene Horicon Formation. The oldest Holocene sediments recorded in the core are an organic rich layer dated at 5130 RCYBP, which accumulated in a depression on the surface of a sand bar. Continued rise in the local water table during the Nipissing Transgression produced paludal conditions in the area, which were followed by the onset of lacustrine conditions. During this interval, the area supported a diverse molluscan fauna. Minor, short term climate fluctuations are reflected in sediment and oxygen isotope changes which are absent from the record in deep water cores from Lake Michigan. This phase in the history of the area ended with the eutrophication of the pond and the development of dunes. Information from Whitefish Dunes pond and other onshore sites within the Lake Michigan basin are an important source of data for reconstructing the history of water levels and climate changes for this area of the Great Lakes drainage.     

Climatic and environmental characteristics of Moscow megalopolis according to the data of the Moscow State University Meteorological Observatory over 60 years

Analyzed are the results of meteorological and environmental measurements performed over the 60-year period (1954–2013) at the Meteorological Observatory of Lomonosov Moscow State University. The significant positive temperature trend (0.04°C/year for 1954–2013) was obtained; it increased up to 0.07°C/year in 1976–2012. Considered are the features of seasonal variations of different atmospheric characteristics. Discussed are the type and causes of low-frequency changes in meteorological parameters, radiation balance components, radiation in different spectral ranges, and chemical composition of precipitation. Demonstrated are possible mechanisms of the more significant increase observed in air temperature in Moscow as compared with that in Central Federal District and their connection with the greenhouse effect in the urban atmosphere.     

Experimental investigation of atmospheric dispersion over the Swiss Plain — Experiment “SIESTA”

Between November 15 and 30, 1985, an international mesoscale transport experiment was performed on the Swiss Plain. Seven meteorological groups from Denmark, Germany, Italy and Switzerland measured diffusion properties of near neutral planetary boundary layers during six completely overcast days: four Bise (north-east wind) situations, one transitional situation and one west-wind situation. Diffusion was measured using SF₆ as tracer, which was released at the meteotower of the Gösgen nuclear power plant at 6 m above ground level. One hundred automatic samplers plus a mobile gas chromatograph were used to measure the concentration fields at distances up to 90 km downwind. Meteorological parameters were observed using radar-tracked constant-level balloons, tethered balloon soundings, sonic anemometers, an acoustic sounder and several meteorological ground stations, including a 110 m mast. All data were collected on a magnetic tape with free access to interested persons.The aim of the experiments was to obtain knowledge about the general nature of the turbulence, advection and atmospheric dispersion during neutral weak-wind situations over complex terrain. The collected data set will be useful for testing mesoscale transport and diffusion models. The results clearly show the channelling effect of the Jura mountains and the hilly prealpine region. An interesting result is that the SF₆ plumes showed intensive horizontal spread but only limited diffusion in the vertical direction.     

Native aluminium (spherules and particles) in the Central Indian Basin sediments: Implications on the occurrence of hydrothermal events

We have sampled particles of native aluminium (Al°) in two sediment cores from the Central Indian Basin (CIB). The cores are geographically separated but are located at the base of two seamounts. The native Al° particles occurring as grains and spherules, have an average Al content of  95% and are associated with volcanogenic–hydrothermal material. Morphologically and compositionally, the specimens are similar to those reported from the East Pacific Rise. After ruling out several processes for the presence of the native Al°, we hypothesize that during progressive melting of magma, a basaltic magma is produced which has high contents of reductants such as methane and hydrogen, and a low oxygen fugacity. During the upward migration of such magma, reduction to metallic aluminium and the formation of native Al° particles takes place.     

Model estimates for the mean gas exchange between the ocean and the atmosphere under the conditions of the present-day climate and its changes expected in the 21st century

Annual mean fluxes of CO₂ and oxygen across the sea surface are estimated with the use of numerical modeling for several regions located in the Gulf Stream and Kuroshio zones. The present-day climatic conditions and the climatic conditions expected in the middle and at the end of the 21st century are considered. Specific features of gas exchange under a strong wind that are associated with gas exchange by bubbles and with changes in the air-water difference of the gas concentrations were taken into account in the calculations. The estimates obtained differ substantially from the results based on the traditional approach, which disregards the above features. A considerable increase in the absorption of CO₂ by the ocean, which is mainly caused by the continuing increase in the CO₂ concentration in the air during its small changes in the ocean, is expected in the 21st century. At the same time, no trends are revealed in the annual mean fluxes of oxygen across the ocean surface. The conclusion is made that, in calculations of CO₂ absorption by the world ocean, it is necessary to take into account both specific features of gas transfer under a strong wind and an increase in the atmospheric concentration of CO₂.     

Basement structure and sedimentary cover seismostratigraphy in the northern part of the Japan Basin in the region of the Tarasov Rise (Sea of Japan)

The results of continuous seismic profiling thermodynamics performed in the northern part of the Japan Basin in the region of the Tarasov Rise and the data of a micropaleontological examination of the diatom remains encountered in the sediment samples from the rise and continental slope are presented. In the area studied, the topography of the acoustic basement features a vast rise (plateau) buried under the sedimentary cover outlined by the depth contour 5.8 s. The plateau has a relatively smooth top surface crossed by a series of rises of the acoustic basement. The two largest rises are represented by the ridges of the Tarasov Rise. The plateau is separated from the continental slope by a depression in the acoustic basement with a depth up to 6.8 s. From the end of the Middle Miocene up to the beginning of the Paleocene, the region of the plateau represented an area of active volcanism; it coincided in time with the stage of subsidence of the floor of the acoustic basement depression. At the end of the Late Miocene, the ridges of the Tarasov Rise started to sink. In the Pliocene, this process accelerated, and, at the beginning of the Pleistocene, it stopped. In the Middle Miocene-Early Pleistocene time, the portion of the continental slope adjacent to the plateau remained stable and suffered no significant vertical movements.     

Constraining the origin and evolution of confined turbidite systems: southern Cretan margin,Eastern Mediterranean Sea (34°30–36°N)

Bathymetric, 9.5-kHz long-range sidescan sonar (OKEAN), seismic reflection and sediment-core data are used in the analysis of two tectonic troughs south of Crete, Eastern Mediterranean Sea. Here, up to 1.2 s two-way travel time (TWTT) of strata have accumulated since the Middle Miocene in association with extension in the South Aegean region. The study area comprises >100-km- long by >25-km-wide basins filled by sediments subdivided into two seismic units: (1) an upper Unit 1 deposited in sub-basins which follow the present-day configuration of the southern Cretan margin; (2) a basal Unit 2, more than 500 ms (TWTT) thick, accumulated in deeper half-graben/grabens distinct from the present-day depocentres. Both units overlap a locally stratified Unit 3 comprising the pre-Neogene core complex of Crete and Gavdos. In this work, the interpreted seismic units are correlated with the onshore stratigraphy, demonstrating that denudation processes occurring on Crete and Gavdos in response to major tectonic events have been responsible for high sedimentation rates along the proximal southern Cretan margin. Consequently, topographically confined sedimentary units have been deposited south of Crete in the last 12 Ma, including turbidites and other mass-flow deposits fed by evolving transverse and axial channel systems. Surface processes controlling facies distribution include the direct inflow of sediment from alluvial-fan systems and incising mountain rivers onto the Cretan slope, where significant sediment instability processes occur at present. In this setting, seismic profiles reveal eight different types of stratigraphic contacts on basin-margin highs, and basinal areas show evidence of halokinesis and/or fluid escape. The acquired data also show that significant changes to the margin’s configuration occurred in association with the post-Alpine tectonic and eustatic episodes affecting the Eastern Mediterranean.