This paper presents the results from analyses of water samples from 15 Bulgarian reservoirs and lakes for detection of microcystins presence by high‐performance liquid chromatography (HPLC) coupled to a ultraviolet (UV) and photo diode array (PDA) detector. In 3 of the studied drinking water reservoirs cyanobacterial blooms were not detected. Cyanobacterial blooms were observed in 6 of 12 investigated water bodies used for fishing and water sports. Microcystis was the dominant cyanobacterial genus. The concentration of total microcystins in the biomasses ranged from 8 to 1070 μg g–1 (d.w.). Microcystin‐LR and microcystin‐RR were the predominant microcystins, followed by microcystin‐YR. Presence of dissolved microcystins was obtained in one water sample with concentration of total microcystins 1.64 μg L–1. Presence of microcystin‐LF and ‐LW or unknown peaks possessing characteristic microcystin‐like UV‐spectra were not detected. Those first results for occurrence of microcystins in some Bulgarian reservoirs and lakes are a contribution to the knowledge on their distribution. 相似文献
Hard inorganic substrates (rock clasts and rocky bottom) belonging to the Ka
k Member of the Korycany Formation (upper Cenomanian–?lower Turonian) and to the Bílá Hora Formation (lower Turonian) have offered a good opportunity for the study of encrusting faunas of the Cenomanian–Turonian boundary interval. Distributional features of cemented epibionts and the recorded period of phosphogenesis enabled the differentiation of two-phases in the Ka
k Member conglomerate formation. During the first phase, the rock substrates were occupied by a so-called A-association of encrusters (29 species, with dominance of oysters and bryozoans). This fauna partly changed during the subsequent phosphogenic period and not only survived the following period of reworking and the second phase of conglomerate formation, but also persisted until the onset of calmer sedimentation in the early Turonian. This changed community is named theAtreta-Bdelloidinacommunity (23 species). The opportunistic agglutinated foraminifersBdelloidina cribrosaand/orAcruliammina longalocally dominated the respective communities during several physico-chemically stressed episodes. On sloping substrates, the bivalvesAtretaandSpondylusattached themselves in a preferred orientation (so-called slope orientation). This feature indicates the original position in which some mobile substrates were colonized. Other questions, such as the taphonomy of encrusters and the character of their substrates are also briefly discussed. 相似文献
The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to 20,000 yr ago. Cosmogenic isotope ages > 30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald’s Beringian ice-sheet hypothesis. 相似文献
Complex I-Xe and mineralogical studies have been performed on four heavily-altered Allende fine-grained spinel-rich Ca, Al-rich inclusions (CAIs) and four Allende dark inclusions (DIs) showing various degrees of iron-alkali metasomatic alteration. The CAIs are largely composed of Fe-rich spinel, Al-diopside, and secondary nepheline and sodalite. The DIs consist of chondrules and Allende-like matrix composed of lath-shaped fayalitic olivine, nepheline, sodalite, and Ca, Fe-rich pyroxene ± andradite ± FeNi-sulfide nodules. Chondrule phenocrysts are extensively or completely replaced by fayalitic olivine, nepheline, and sodalite; metal nodules are replaced by FeNi-sulfides, andradite and Ca, Fe-rich pyroxenes. The chondrules and matrices are crosscut by Ca, Fe-rich pyroxene ± FeNi-sulfide ± fayalitic olivine veins. DIs are surrounded by continuous Ca-rich rims composed of andradite, wollastonite, kirschsteinite, and Ca, Fe-rich pyroxenes, whereas the outer portions of the inclusions are depleted in Ca.Three CAIs yield well-defined I-Xe isochrons with ages 3.1 ± 0.2, 3.0 ± 0.2 and 3.7 ± 0.2 Ma younger than the Shallowater internal standard (4566 ± 2 Ma). Similar release profiles suggest the same iodine carrier (most probably sodalite) for all four CAIs. The Allende DIs yield I-Xe ages from 0.8 ± 0.3 to 1.9 ± 0.2 Ma older than Shallowater. Based on the petrographic observations, we infer that the DIs experienced at least two-stage alteration. During an early stage of the alteration, which took place in an asteroidal setting, but not in the current location of the DIs, chondrule silicates were replaced by secondary fayalitic olivine, nepheline, and sodalite. Calcium lost from the chondrules was redeposited as Ca, Fe-rich pyroxene veins and Ca, Fe-rich pyroxene ± andradite nodules in the matrix. The second stage of alteration resulted in mobilization of Ca from the DIs and its re-deposition as Ca-rich rims composed of Ca, Fe-rich pyroxenes, andradite, and wollastonite, around the DIs. We interpret I-Xe ages of the DIs as time of their alteration prior incorporation into Allende. The younger I-Xe ages of the fine-grained spinel-rich CAIs may reflect hydrothermal alteration of the Allende host, which could have occurred contemporaneously with the second stage of alteration of the Allende DIs. The lack of evidence for the disturbance of I-Xe system in the Allende DIs may suggest that fluid responsible for the alteration of the Allende CAIs was in equilibrium with the I- and Xe-bearing phases of the DIs. 相似文献
Nisyros island, a Quaternary volcanic center located at the SE of the Aegean Volcanic Arc, has been in the past characterized by periods of intense seismic activity accompanied sometimes by hydrothermal explosions, the last one being in 1887. The recent long lasting episode of unrest (1995–1998) in the area is the first instrumentally documented providing information on the behavior of the volcano. Evidence from seismicity and SAR interferometry suggests that the presently active part of the Kos–Nisyros volcano-tectonic complex is located at the NW coast of Nisyros island defining an area much smaller than the whole volcano-tectonic area. Seismicity patterns vary both temporally and spatially consistently with different rates of vertical ground deformation inferred from SAR interferometry. These observations help us to discuss the different elements controlling the behavior of the volcanic system such as: the existence, location and timing of magma chamber inflation, the occurrence of tensile failure at the boundaries of the chamber and the possibility of magmatic fluids being expelled to form a shallow magmatic intrusion, the seismic failure and migration of hypocenters indicating shallow magma transport. 相似文献
Based on data on the composition of ore-bearing hydrothermal solutions and parameters of ore-forming processes at various antimony and antimony-bearing deposits, which were obtained in studies of fluid inclusions in ore minerals, we investigated the behavior of Sb(III) in the system Sb–Cl–H2S–H2O describing the formation of these deposits.
We also performed thermodynamic modeling of native-antimony and stibnite dissolution in sulfide (mHS− = 0.0001−0.1) and chloride (mCl− = 0.1−5) solutions and the joint dissolution of Sb(s)0 and Sb2S3(s) in sulfide-chloride solution (mHS− = 0.01; mCl− = 1) depending on Eh, pH, and temperature. All thermodynamic calculations were carried out using the Chiller computer program. Under the above conditions, stibnite precipitates in acid, weakly acid to neutral, and medium redox solutions, whereas native antimony precipitates before stibnite under more reducing conditions in neutral to alkaline solutions.
The metal-bearing capacity of hydrothermal solutions (200–250 °C) of different compositions and origins has been predicted. We have established that the highest capacity is specific for acid (pH = 2–3) high-chloride solutions poor in sulfide sulfur and alkaline (pH = 7–8) low-chloride low-sulfide solutions. 相似文献
Reference samples of soils from the Institute of Applied Physics, Irkutsk (RIAP), the Institute of Geochemistry, Irkutsk (IGI) and the United States Geological Survey, Reston (USGS) were analysed with the aim of determining Ag, B, Ge, Mo, Sn, Tl and W abundances by an atomic emission method with air-stabilised D.C. arc excitation. Two series of reference samples of soils and bottom sediments, GSS-1-8 and GSD-1-12 (IGGE), were used to ensure the traceability link for the analytical results. Traceability was also demonstrated through the comparison of measured results by AES and ICP-MS methods. It is shown that the reference samples GSS-1-8 and GSD-1-12 satisfied the "fitness-for-purpose" criterion (uncertainty U of the certified value should be one-third to one-tenth the magnitude of routine laboratory data uncertainty S (S/U > 3-10)) and can be applied for calibrating AES techniques. 相似文献