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排序方式: 共有401条查询结果,搜索用时 15 毫秒
21.
Sokrat Amataj Todor Anovski Ralf Benischke Romeo Eftimi Laurence L. Gourcy Liliana Kola Ioannis Leontiadis Eftim Micevski Alqiviadis Stamos Jovan Zoto 《Environmental Geology》2007,51(5):749-753
Prespa Lake and Ohrid Lake constitute a hydraulic system shared between Albania, FYR of Macedonia and Greece. Karst rocks
separate both lakes. The elevation of Prespa Lake is about 150 m higher than that of Ohrid Lake. Considering these facts,
Cvijić formulated in 1906 the hypothesis that Prespa Lake recharges the St. Naum and Tushemisht springs at Ohrid lakeside.
Environmental isotopes demonstrated that Prespa Lake recharges about 37–42 and 52–54% of water emerging in St. Naum, and Tushemisht
springs, respectively. An artificial tracer experiment carried out in 2002 physically demonstrated the underground connection
between both lakes. This experiment confirmed the supposed underground connection and brought important information about
the groundwater velocity, transit time, and karst water conduits development. 相似文献
22.
The freshwater snail fauna in 51 lakes on the Åland Islands was investigated. By means of cluster analysis it appears that lakes may be divided into four groups on the basis of snail species composition. The lakes of the four groups show a spatial distribution which is related to topographical differences, terrestrial vegetation and land use. Snails may be divided on the basis of water hardness into hard water species and calcium indifferent species or into demanding and modest/indifferent species when clustering is based on presence/absence. 相似文献
23.
Hans Güsten Günther Heinrich Ralf W. H. Schmidt Ulrich Schurath 《Journal of Atmospheric Chemistry》1992,14(1-4):73-84
A small, lightweight (1.5 kg) and fast-response ozone sensor for direct eddy flux measurements has been built. The basis for detection is the chemiluminescence of an organic dye adsorbed on dry silica gel in the reaction with ozone. The chemiluminescence is monitored with a cheap and small blue-sensitive photomultiplier. At a flow rate of 100 l min-1 the ozone sensor has a 90% response time of significantly better than 0.1 s with a detection limit lower than 50 ppt at S/N=3. There are no interferences from other atmospheric trace gases like NOx, H2O2 and PAN. Water vapour and SO2 enhance the chemiluminescence efficiency of the ozone sensor. Since their response times are 22 seconds and 30 minutes, respectively, no correlation between rapid ozone fluctuations and those of these two trace gases is noticed by the ozone sensor when operating at a frequency of 10 Hz.The ozone sensor was tested for several weeks in continuous measurements of ozone fluxes and deposition velocities over different croplands using the eddy correlation technique. Good agreement was found between ozone dry deposition velocities derived from profile measurements and by eddy correlation. 相似文献
24.
25.
A. Greve 《Solar physics》1973,29(1):263-266
The image degradation due to residual surface inaccuracies of the main optical element of a telescope is compared with the image degradation due to atmospheric turbulence. 相似文献
26.
Nico-Alexander Urbanski Malte Vöge Ralf Seyfried Lars Rüpke Tanja Petersen Till Hanebuth Matthias Hort 《International Journal of Earth Sciences》2002,91(4):712-722
The intention of our study was to gain new insight into the complex interplay between different types of eruption of the Stromboli volcano by combining detailed field observation with different geophysical methods. We recorded more than 600 eruptions by use of continuous Doppler radar measurements. We detected the onset of the seismic precursor and the beginning of the visible eruption by use of seismic and infrared data. Two soil samples per day were used to monitor the effect of humidity on the eruptive style. We mapped the crater region as a reference base for the long-term morphological changes of the active region and for the exact positions of our measurement systems. Two distinct types of eruption were distinguished from each other on the basis of seismic and radar data - short, wide-angle Strombolian explosions and pulsating, sharp angle fountain-like eruptions. Data and visual observations imply that weather conditions significantly effect volcanic activity. We also interpret the intensification of eruptive activity during our field study as replenishment of the reservoir with a new batch of magma in late September 2000. 相似文献
27.
Chemical contamination of fish from the Salton Sea, a quasi-marine lake in Southern California, could adversely impact millions of birds using the Pacific Flyway and thousands of humans using the lake for recreation. Bairdiella icistia (bairdiella), Cynoscion xanthulus (orangemouth corvina), and Oreochromis spp. (tilapia) were sampled from two river mouths and two nearshore areas of the Salton Sea. Muscle tissues were analyzed for a complete suite of 14 trace metals and 53 pesticides. Fish muscle tissues had concentrations of selenium ranging between 1.89 and 2.73 microg/g wet weight. 4,4'-DDE accounted for 94% of the total DDT metabolites. Total DDTs ranged between 17.1 and 239.0 and total PCBs between 2.5 and 18.6 ng/g wet weight. PCB congeners 132, 138, 153, 168, and 180 comprised over 50% of the total PCBs. Given the potential implementation of a commercial fishing at the Salton Sea in the future, the presence of persistent organic pollutants and selenium warrants further research into the effects of these mixtures on fish populations, and on wildlife and humans consuming fish. 相似文献
28.
The coastal zones are facing the prospect of changing storm surge statistics due to anthropogenic climate change. In the present study, we examine these prospects for the North Sea based on numerical modelling. The main tool is the barotropic tide-surge model TRIMGEO (Tidal Residual and Intertidal Mudflat Model) to derive storm surge climate and extremes from atmospheric conditions. The analysis is carried out by using an ensemble of four 30-year atmospheric regional simulations under present-day and possible future-enhanced greenhouse gas conditions. The atmospheric regional simulations were prepared within the EU project PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects). The research strategy of PRUDENCE is to compare simulations of different regional models driven by the same global control and climate change simulations. These global conditions, representative for 1961–1990 and 2071–2100 were prepared by the Hadley Center based on the IPCC A2 SRES scenario. The results suggest that under future climatic conditions, storm surge extremes may increase along the North Sea coast towards the end of this century. Based on a comparison between the results of the different ensemble members as well as on the variability estimated from a high-resolution storm surge reconstruction of the recent decades it is found that this increase is significantly different from zero at the 95% confidence level for most of the North Sea coast. An exception represents the East coast of the UK which is not affected by this increase of storm surge extremes. 相似文献
29.
Quantification of carbon flow from stable isotope fractionation in rice field soils with different organic matter content 总被引:1,自引:0,他引:1
Rice fields are an important source for the greenhouse gas methane produced by acetoclastic and hydrogenotrophic methanogenesis. Fractionation of 13C/12C can in principle be used to quantify the relative contribution of these pathways, but our knowledge of isotopic fractionation during reduction of CO2 and turnover of acetate in different methanogenic environments is still scarce. We therefore measured δ13C signatures in two types of anoxic Italian rice field soils, one with high and one with low degradable organic matter (OM) content. Both soils were incubated in the presence and absence of methyl fluoride, a specific inhibitor of acetoclastic methanogenesis. Optimization of methyl fluoride concentration resulted in complete inhibition of acetoclastic methanogenesis. CH4 was then exclusively produced by hydrogenotrophic methanogenesis, allowing determination of the isotopic signatures and fractionation factors specific for this methanogenic pathway. Acetate, which was then no longer consumed, accumulated and was used for determination of the isotopic signature of the fermentatively produced acetate (both total acetate and methyl carbon of acetate). Hence, all isotopic signatures, including fractionation factors were determined for the methanogenic soil. These data, were then used for computation of the relative contribution of the two methanogenic pathways. In the high OM soil, the contribution of acetoclastic methanogenesis to total CH4 production increased simultaneously with decreasing acetate concentration. In the low OM soil, methanogenesis from H2/CO2 was clearly greater than theoretically expected. Furthermore, isotope fractionation of hydrogenotrophic methanogenesis indicated that the in situ energy status of methanogens strongly depended on the availability of organic carbon in the rice field soil system. Collectively, our data show that the study of isotopic fractionation in methanogenic environments allows a deeper insight into the ongoing processes, which may be quite different in the same ecosystem with different content of degradable OM. 相似文献
30.
Niranjan D. Chatterjee Ralf Krüger Gerd Haller Walter Olbricht 《Contributions to Mineralogy and Petrology》1998,133(1-2):149-168
An internally consistent thermodynamic dataset has been derived for 148 endmember phases (145 solids and 3 fluids) comprising
the elements Li, Na, K, Be, Mg, Ca, Ti, Cr, Mn, Fe, Zn, Al, Si, C, H, and O. This has been achieved by simultaneous treatment
of phase property (like standard enthalpy of formation, standard entropy, molar heat capacity, molar volume, thermal expansivity,
bulk modulus etc.) and reaction reversal data by the Bayesian method. The theory underlying the approach, and the computational
methods involved, are briefly outlined. (For the benefit of readers unfamiliar with inference statistics, the basic concepts
of the Bayes method are also presented in such a way that they can be grasped intuitively.) Although not yet addressed, this
method can be extended to refine the thermodynamic mixing properties of crystalline solutions. The sources of the input data,
culled from the literature, are summarized in the Appendix. The resulting database is succinctly documented in this paper.
It includes the enthalpies of formation and entropies, their uncertainties, and the correlation among them. The database allows
calculation of P-T, T-X
CO2, P-X
CO2, and T-f
O2 sections, with error propagation into the computed phase diagrams on a routine basis. A user-friendly computer program has
been written to generate such phase diagrams. It is public domain software. The software and the thermodynamic database (which
includes a complete documentation of the thermodynamic data above and beyond those listed (Table 2, here) may be downloaded from the web site
http://homepage.ruhr-uni-bochum.de/niranjan.chatterjee/Index.htm. Examples of computed phase diagrams are given to illustrate
the quality of the data and the capabilities of the software.
Received: 11 March 1998 / Accepted: 11 June 1998 相似文献