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Experiments were conducted to investigate (i) the rate of O-isotope exchange between SO4 and water molecules at low pH and surface temperatures typical for conditions of acid mine drainage (AMD) and (ii) the O- and S-isotope composition of sulfates produced by pyrite oxidation under closed and open conditions (limited and free access of atmospheric O2) to identify the O source/s in sulfide oxidation (water or atmospheric molecular O2) and to better understand the pyrite oxidation pathway. An O-isotope exchange between SO4 and water was observed over a pH range of 0–2 only at 50 °C, whereas no exchange occurred at lower temperatures over a period of 8 a. The calculated half-time of the exchange rate for 50 °C (pH = 0 and 1) is in good agreement with former experimental data for higher and lower temperatures and excludes the possibility of isotope exchange for typical AMD conditions (T 25 °C, pH 3) for decades.Pyrite oxidation experiments revealed two dependencies of the O-isotope composition of dissolved sulfates: O-isotope values decreased with longer duration of experiments and increasing grain size of pyrite. Both changes are interpreted as evidence for chemisorption of molecular O2 to pyrite surface sites. The sorption of molecular O2 is important at initial oxidation stages and more abundant in finer grained pyrite fractions and leads to its incorporation in the produced SO4. The calculated bulk contribution of atmospheric O2 in the dissolved SO4 reached up to 50% during initial oxidation stages (first 5 days, pH 2, fine-grained pyrite fraction) and decreased to less than 20% after about 100 days. Based on the direct incorporation of molecular O2 in the early-formed sulfates, chemisorption and electron transfer of molecular O2 on S sites of the pyrite surface are proposed, in addition to chemisorption on Fe sites. After about 10 days, the O of all newly-formed sulfates originates only from water, indicating direct interaction of hydroxyls from water with S at the anodic S pyrite surface site. Then, the role of molecular O2 is as proposed in previous studies: acting as electron acceptor only at the cathodic Fe pyrite surface site for oxidation of Fe(II) to Fe(III). 相似文献
74.
Geomorphological mapping plays a key role in landscape representation: it is the starting point for many applications and for the realization of thematic maps, such as hazard and risk maps, geoheritage and geotourism maps. Traditional geomorphological maps are useful for scientific purposes but they need to be simplified for different aims as management and education. In tourism valorization, mapping of geomorphological resources (i.e., geosites, and geomorphosites), and of geomorphic evidences of past hazardous geomorphological events, is important for increasing knowledge about landscape evolution and active processes, potentially involving geomorphosites and hiking trails. Active geomorphosites, as those widespread in mountain regions, testify the high dynamicity of geomorphic processes and their link with climatic conditions. In the present paper, we propose a method to produce and to update cartographic supports (Geomorphological Boxes) realized starting from a traditional geomorphological survey and mapping. The Geomorphological Boxes are geomorphological representation of single, composed or complex landforms drawn on satellite images, using the official Italian geomorphological legend (ISPRA symbols). Such cartographic representation is also addressed to the analysis (identification, evaluation and selection) of Potential Geomorphosites and Geotrails. The method has been tested in the upper portion of the Loana Valley (Western Italian Alps), located within the borders of the Sesia Val Grande Geopark, recognized by UNESCO in 2013. The area has a good potential for geotourism and for educational purposes. We identified 15 Potential Geomorphosites located along 2 Geotrails; they were ranked according to specific attributes also in relation with a Reference Geomorphosite located in the Loana hydrographic basin and inserted in official national and regional databases of geosites (ISPRA; Regione Piemonte). Finally, the ranking of Potential Geomorphosites allowed to select the most valuable ones for valorization or geoconservation purposes. In this framework, examples of Geomorphological Boxes are proposed as supports to geo-risk education practices. 相似文献
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76.
Manuela Krügel Daniela Thaller Volker Tesmer Markus Rothacher Detlef Angermann Ralf Schmid 《Journal of Geodesy》2007,81(6-8):515-527
The combination of tropospheric parameters derived from different space-geodetic techniques has not been of large interest
in geodesy so far. However, due to the high correlation between station coordinates and tropospheric parameters, the latter
should not be neglected in combinations. This paper deals with the comparison and combination of tropospheric parameters derived
from global positioning system (GPS) and very long baseline interferometry (VLBI) observations stemming from a 15-day campaign
of continuous VLBI observations in 2002 (CONT02). The observation data of both techniques were processed homogeneously to
avoid systematic differences between the solutions. We compared the tropospheric estimates of GPS and VLBI at eight co-location
sites and found a very good agreement in the temporal behavior of the tropospheric zenith path delays (ZPD), reflected by
correlation factors up to 0.98. Following this, a combination of the tropospheric parameters was performed. We demonstrate
that the combination of tropospheric parameters leads to a stabilization of combined station networks. This becomes visible
in the improvement of the repeatabilities of the station height components. Furthermore, the potential use of independent
data from water vapor radiometers (WVRs) to validate space-technique-derived tropospheric parameters was investigated. Correlation
coefficients of 0.95 or better were estimated between the tropospheric parameters of WVR and GPS or VLBI. Additionally, the
utility of the tropospheric parameters for validation of local tie vectors was investigated. Both tropospheric zenith delays
and tropospheric gradients were found to be very suitable to validate the height component and the horizontal components of
the local tie, respectively. 相似文献
77.
Integrated modelling for water quality management in a eutrophic reservoir in south-eastern Portugal
David Brito Tiago B. Ramos Maria C. Gonçalves Manuela Morais Ramiro Neves 《Environmental Earth Sciences》2018,77(2):40
The Enxoé Reservoir was built in 1998. Since 2000, it has exhibited frequent high chlorophyll-a concentrations, reaching a geometric mean three times higher than the national limit for eutrophication, presenting the reservoir with the highest eutrophic state in Portugal. Toxic algal blooms have also often been observed, which pose serious challenges to water managers, as the reservoir is used for potable water production (25,000 inhabitants). The objective of this study was to implement a reservoir model (CE-QUAL-W2), with inputs from a watershed model (SWAT), in order to represent the actual reservoir state and to test management measures to reduce its trophic level and algal bloom concentration peaks. The integrated model was used to depict the origin of its trophic status. Simulations were also compared to measured data at the reservoir surface (water level, nitrate, orthophosphate, suspended solids, and oxygen) and in water profiles (temperature, oxygen). The model was able to represent stratification and thermocline depths, as well as the actual chlorophyll-a and dissolved oxygen concentrations. The model results showed that internal phosphorus load from deposited sediments was an important factor in fuelling the algal blooms. This process occurs predominantly in summer, when stratification takes place and aeration is reduced, promoting anoxic conditions in the bottom waters. Since the reservoir is relatively shallow (average 5 m), released phosphorus is then easily able to reach the photic zone in most parts of the reservoir, where it is consumed. Different management scenarios were tested, suggesting that a mesotrophic level could barely be reached and maintained simply by reducing the nutrient loads (both external and internal). It is suggested that only an increase in the reservoir dam height could produce a mesotrophic level, averting anoxia by blocking the release of phosphorus from sediments to the photic zone. Future work should focus on a cost–benefit analysis to test the feasibility of each of the proposed scenarios, taking advantage of the integration strategy to assess where in the watershed load reductions would be most effective. 相似文献
78.
Mormone Angela Ghiara Maria Rosaria Balassone Giuseppina Piochi Monica Lonis Roberto Rossi Manuela 《Mineralogy and Petrology》2018,112(6):767-788
Mineralogy and Petrology - The island of Sardinia (Italy) presents some of the most interesting zeolite ores in Europe, most of which are associated with old pyroclastic deposits. In particular,... 相似文献
79.
Elena Zanella Lucia Gurioli Roberto Lanza Roberto Sulpizio Manuela Bontempi 《Bulletin of Volcanology》2008,70(10):1237-1248
The deposition temperature of the pyroclastic density current (PDC) deposits emplaced during the AD 472 Pollena eruption (Somma-Vesuvius,
Italy) has been investigated using the thermal analysis of the magnetic remanence carried by lithic clasts embedded within
the deposits. A total of 310 lithic clasts were collected from all the PDC units in the Pollena stratigraphic succession,
at different distances from the inferred vent and at different stratigraphic levels. The temperature reached by each individual
clast during residence in the PDC was estimated through stepwise thermal demagnetization, with the values from all clasts
collected at each site being used to infer the deposition temperature (T
dep). Although the sedimentological features of these PDC deposits show some variation, the deposition temperature typically
falls in the range 300 to 320°C, with a maximum range of 260 to 360°C. The fairly uniform temperature observed in both the
dune bedded and massive deposits points to homogeneity in attainment of T
dep for the different deposits and suggests similarity in the depositional regime of the different PDCs and/or in heat transfer
to lithic fragments. Similarity in depositional regime was also favoured by the limited control exerted by topography on the
distribution of these PDCs, with the northern wall of the Somma caldera that did not act as a morphological barrier. As a
result the currents were capable of moving away from the vent, without topographic disturbances and, thus, significant variations
in the cooling regime. Because the Pollena eruption is considered similar to the maximum expected event at Somma-Vesuvius,
the characteristics of its deposits best simulate the likely maximum hazard for the Vesuvius region. In this regard, Pollena
produced hot, dilute PDCs which were able to travel up to 12 km from the vent maintaining high temperatures across this distance. 相似文献
80.
Roberto Paolucci Antonio Rovelli Ezio Faccioli Carlo Cauzzi Daniela Finazzi Manuela Vanini Carola Di Alessandro Giovanna Calderoni 《地震工程与结构动力学》2008,37(5):697-710
Using records from co‐located broadband and digital strong motion (SM) instruments, it is first shown that the displacement waveforms obtained by double integration of the accelerogram need not be free of unrealistic baseline drift to yield reliable spectral ordinates up to at least 10 s. Secondly, to provide objective criteria for selecting reliable digital SM records for ground motion predictions at long periods, a set of synthetic accelerograms contaminated by random long‐period noise has been used, and the difference between the original accelerograms and the spurious ones in terms of response spectra has been quantified, by introducing a noise index that can be easily calculated based on the velocity waveform of the record. The results of this study suggest that high‐pass filtering the digital acceleration record from a cutoff period selected to suppress baseline drifts on the displacement waveform appears to be in most cases too conservative and unduly depletes reliable information on long‐period spectral ordinates. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献