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21.
The irreversible water–rock mass exchanges leading to the production of the Fiume Grande valley (Calabria, Italy) stream waters
and groundwaters, starting from local rainwaters, were simulated through reaction path modeling in reaction progress (stoichiometric)
mode. The simulations assumed bulk dissolution of a phyllitic rock and calcite and precipitation of gibbsite, kaolinite, amorphous
silica, illite, a smectite solid mixture, a hydroxide solid mixture, and a trigonal carbonate solid mixture. The analytical
contents of major and trace elements in stream waters and groundwaters were satisfactorily reproduced. However, further investigations
are necessary to clarify the fate of As in this natural systems.
相似文献
| Rosanna De RosaEmail: |
22.
Previous work has demonstrated that suspended clay accumulating on filter paper can act as a membrane and affect chemical concentrations in the filtered water. For this reason, we looked at the possibility of membrane effects altering water chemistry during filtering for Missouri Rivers. Membrane effects during filtering could cause an initial decrease in sample concentrations as the filter cake began acting as a membrane, with a corresponding increase of concentration as the concentration polarization layer was formed behind the filter cake. Samples from five Missouri rivers were tested: the Mississippi River at St. Louis, the Missouri River at Kansas City, the Gasconade River at Jerome, the Osage River at the junction of Highway 63 and 50, and the Meramec River one mile downstream from springs. Three 1-l samples were filtered from each river using a 0.45 m filter. An unfiltered sample from each river underwent dialysis to determine the actual ion concentrations of the overall sample. None of the filtered samples demonstrated a statistically significant alteration of water chemistry using current filtering techniques in this preliminary study, suggesting that membrane effects due to accumulation of clay particles on filter paper may not be a common problem in Missouri and similar regions. 相似文献
23.
Marguerite S. Koch Demetris C. Kletou Rosanna Tursi 《Estuarine, Coastal and Shelf Science》2009,83(4):403-413
Few phosphorus-depleted coastal ecosystems have been examined for their ability to hydrolyze phosphomonoesters. We examined seasonal (August 2006–April 2007) alkaline phosphatase activity in Florida Bay, a phosphorus-limited shallow estuary, using fluorescent substrate at low concentrations (≤2.0 μM). In situ dissolved inorganic and organic phosphorus levels and phosphomonoester concentrations were also determined. Water column alkaline phosphatase activity was partitioned into two particulate size fractions (>1.2 and 0.2–1.2 μm) and freely dissolved enzymes (<0.2 μm). Water column alkaline phosphatase activity was also compared to leaf and epiphyte activity of the dominant tropical seagrass Thalassia testudinum. Our results indicate: (1) potential alkaline phosphatase activity in Florida Bay is high compared to other marine ecosystems, resulting in rapid phosphomonoester turnover times (2 h). (2) Water column alkaline phosphatase activity dominates, and is split equally between particulate and dissolved fractions. (3) Alkaline phosphatase activity was highest during cyanobacterial blooms, but not when normalized to chl a. These results suggest that dissolved, heterotrophic and autotrophic alkaline phosphatase activity is stimulated by phytoplankton blooms. (4) The dissolved alkaline phosphatase activity is relatively constant, while the particulate activity is seasonally and spatially dynamic, typically associated with phytoplankton blooms. (5) Phosphomonoester concentrations throughout the bay are low, even though potential hydrolysis rates are high. We propose that bioavailable dissolved organic P is hydrolyzed by dissolved and microbial alkaline phosphatase enzymes in Florida Bay. High alkaline phosphatase activity in the bay is also promoted by long hydraulic residence times. This background activity is primarily driven by carbon and phosphorus limitation of microorganisms, and regeneration of enzymes associated with cell lysis. Pulses of inorganic phosphorus and labile organic phosphorus and nitrogen may stimulate autotrophs, particularly cyanobacteria, which in turn promote biological activity that increase alkaline phosphatase activity of both autotrophs and heterotrophs in the bay. 相似文献
24.
The massive unit of a lava flow from Porri volcano (Salina, Aeolian Islands) displays many unusual structures related to
the physical interaction between two different magmas. The magma A represents approximately 80% of the exposed lava surface;
it has a crystal content of 51 vol.% and a dacitic glass composition (SiO2=63–64 wt.%). The magma B has a basaltic-andesite glass composition (SiO2=54–55 wt.%) and a crystal content of approximately 18 vol.%. It occurs as pillow-like enclaves, banding, boudin-like and
rolling structures which are hosted in magma A. Structural analysis suggests that banding and boudin-like structures are the
result of the deformation of enclaves at different shear strain. The linear correlation between strain and stratigraphic height
of the measured elements indicates a single mode of deformation. We deduce that the component B deformed according to a simple
shear model. Glass analyses of the A–B boundary indicate that A and B liquids mix together at high shear strain, whereas only
mingling occurs at low shear strain. This suggests that the amount of deformation (i.e. forced convection) plays an important
role in the formation of hybrid magmas. High shear strain may induce stretching, shearing and rolling of fluids which promote
both forced convection and dynamical diffusion processes. These processes allow mixing of magmas with large differences in
their physical properties.
Received: 15 July 1995 / Accepted: 30 May 1996 相似文献
25.
Numerical modeling of debris avalanche propagation from collapse of volcanic edifices 总被引：5，自引：3，他引：2
Debris avalanches produced from the collapse of volcanic edifices are destructive events that involve volumes up to two orders of magnitude larger (cubic kilometer) than most non-volcanic rock and debris avalanches. We replicate the motion and spreading of several volcanic collapses by means of a depth-averaged quasi-3D numerical code. The model assumes a frictional internal rheology and a variable basal rheology (i.e frictional, Voellmy and plastic). We back analyzed seven case-studies against observations reported in the literature to provide a set of calibrated cases. The ASTER and SRTM satellite-derived digital elevation models were used as topographic data. The numerical model captures the main features of the propagation process, including travel distance, lateral spreading and run up. At varying triggering factors and material characteristics the best fitting parameters span in a narrow interval and differ from those typical of non-volcanic rock and debris avalanches. The bulk basal friction angles (the sole parameter required in the frictional rheology) range within 3° and 7.5° whereas typical values for non-volcanic debris avalanches vary from 11° to 31°. The consistency of the back analyzed parameters is encouraging for a possible use of the model in the perspective of hazard mapping. The reconstruction of the pre-event topography is critical, and it is associated to large uncertainty. The quality of the terrain data, more than the resolution of the DEMs used, is relevant for the modeling. Resampling the original square grid to larger cell sizes determines a low increase in the back analyzed rheological parameters, as a result of the lower roughness of the terrain. 相似文献
26.
Hyperfiltration of Nacl Solutions Using a Simulated Clay/Sand Mixture at Low Compaction Pressures 总被引：1，自引：0，他引：1
It is widely recognized that clays and shales can demonstrate membrane properties. When a hydraulic head differential exists
across a membrane-functioning clay-rich barrier, some of the solute is rejected by the membrane. This process is known as
hyperfiltration. Some shallow geologic environments, including aquitards bounding shallow perched aquifers and unconfined
aquifers, some river and stream beds, and some lake bottoms contain clay–soil mixes. Many engineering structures such as landfill
liners, mixed soil augered barriers, and retention pond liners also consist of soil–clay mixes. No previous testing has been
performed to investigate the likelihood that hyperfiltration may occur in such mixed soils. Therefore, we performed five experiments
using different mixes of Na-bentonite and glass beads (100, 50, 25, 12 and 0% clay) to determine if any of these mixes exhibited
membrane properties and to investigate what effect clay content had upon the membrane properties of the soil. Each mixture
was compacted to 345 kPa and the sample mixtures were 0.58–0.97 mm thick. All the experiments used an approximately 35 ppm
Cl− solution under an average 103 kPa hydraulic head. Experimental results show that all the simulated clay–sand mixtures do
exhibit measurable membrane properties under these conditions. Values of the calculated reflection coefficient ranged from
a low of 0.03 for 12% bentonite to 0.19 for 100% bentonite. Solute rejection ranged from 5.2% for 12% clay to a high of over
30% for the 100% clay. The 100% glass bead sample exhibited no membrane properties. 相似文献
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28.
Ilaria Guagliardi Natalia Rovella Carmine Apollaro Andrea Bloise Rosanna De Rosa Fabio Scarciglia Gabriele Buttafuoco 《Journal of Earth System Science》2016,125(8):1569-1578
The activity of natural radionuclides in soil has become an environmental concern for local public and national authorities because of the harmful effects of radiation exposure on human health. In this context, modelling and mapping the activity of natural radionuclides in soil is an important research topic. The study was aimed to model, in a spatial sense, the soil radioactivity in an urban and peri-urban soils area in southern Italy to analyse the seasonal influence on soil radioactivity. Measures of gamma radiation naturally emitted through the decay of radioactive isotopes (potassium, uranium and thorium) were analysed using a geostatistical approach to map the spatial distribution of soil radioactivity. The activity of three radionuclides was measured at 181 locations using a high-resolution ?-ray spectrometry. To take into account the influence of season, the measurements were carried out in summer and in winter. Activity data were analysed by using a geostatistical approach and zones of relatively high or low radioactivity were delineated. Among the main processes which influence natural radioactivity such as geology, geochemical, pedological, and ecological processes, results of this study showed a prominent control of radio-emission measurements by seasonal changes. Low natural radioactivity levels were measured in December associated with winter weather and moist soil conditions (due to high rainfall and low temperature), and higher activity values in July, when the soil was dry and no precipitations occurred. 相似文献
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30.
Christopher L. Kirkland R. Hugh Smithies Ailsa J. Woodhouse Heather M. Howard Michael T.D. Wingate Elena A. Belousova John B. Cliff Rosanna C. Murphy Catherine V. Spaggiari 《Gondwana Research》2013,23(2):759-781
The Hf and Nd isotopic evolution of the Musgrave Province, central Australia, is used to constrain the timing of crust formation and lithospheric organisation of Proterozoic Australia. The dataset from this region challenges two widely held tenets of Hf and Nd isotope systematics, namely; that crust formation events can only be identified as periods when crystallisation ages correspond to model ages, and that linear Hf evolution arrays away from depleted mantle (along crustal Lu/Hf or Sm/Nd slopes) reflect reworking of the same source.Hf isotopes in Musgrave Province zircon crystals indicate two major crust formation events at c. 1900 Ma and at 1600–1550 Ma. Although no juvenile rocks or crystals are known from c. 1900 Ma, radiogenic addition into the crust at this time is required to account for consistent Nd and Hf evolution patterns, which show no indication of an initially heterogeneous source. Oxygen isotopes in zircon grains confirm that much of the c. 1900 Ma Hf isotopic signal is not compromised by mixtures. Furthermore, the correspondence between mantle extraction and the commencement of reworking of Archean material supports new crust generation at c. 1900 Ma and a coupling between lower and upper crustal processes. The c. 1900 Ma timing of juvenile addition is dissimilar to that in the Albany–Fraser and Arunta Orogens and may reflect continental arc development on the margin of a southern continent.The general Hf isotopic evolution trend of the Musgrave Province apparently reflects reworking from a dominant c. 1900 Ma source with some additional unradiogenic and radiogenic input through time. However, in the 1220–1050 Ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle-derived material. Intracontinental rifts and other regions with sustained very-high temperature crustal recycling processes generate magmatic provinces with extreme HFSE-enrichment. This can have a profound influence on isotopic evolution trends, suppressing typical juvenile addition patterns. Isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within HFSE enriched magmas without diverging isotopic signatures from apparent reworking trends. In the Musgrave Province, the crust had become so HFSE enriched during the prolonged Musgrave Orogeny (1220–1150 Ma) that it was insensitive to mantle input, which is estimated to have been as much as 85% during this event. 相似文献