Analysis of an illustrative interaction between structural features and earthworm populations in Brazilian ferralsols     

Michel Brossard  Gustavo Adolfo de Freitas Fregonezi  Maria de Fátima Guimarães  Cristiane de Conti Medina  Amarildo Pasini  Lourival Vilela  Miguel Angel Ayarza 《Comptes Rendus Geoscience》2012,344(1):41-49

Ferralsols are characterized by poorly-defined horizons, weak macrostructure and strong development of a fine granular structure comprising subangular micro-aggregates. In this study, the morphological and physical modifications caused by earthworm activity in a clayey ferralsol were analysed. After describing soil structures, undisturbed samples were taken for evaluating aggregates and determining clod bulk density and particle density. Soil water retention properties were measured and an inventory of soil invertebrate macrofauna was created. The structural and porous transformations were due to aggregates created by earthworm activity. Changes in bulk density can be associated with pore modifications caused by a change in the proportions of aggregate types, and a notable reduction of total porosity was measured, tending to increase soil volume with dense aggregates. Structural modifications affected the topsoil down to 0.5 m and water retention between −1 and −33 kPa, the principal water compartment of these soils.  相似文献   

Normative issues in the organization of modern retailers in Israel     

Maria Marinov  Daniel Czamanski 《GeoJournal》2012,77(3):383-398

This paper raises questions regarding the desirable sizes of retail facilities within an existing urban system. We address questions of efficiency by reference to a social welfare function and by reference to profit maximization by developers. To this end we utilize a gravity-type simulation model and apply it in the case of Haifa, Israel based on a unique data base. Based on simulations of a single developer who owns all the retail facilities the optimal locations yield large retail facilities away from residential areas and smaller ones in the locations closer to the buying power. In the case that each facility is owned separately, stepwise optimization yields optimal order of development, first at locations in close proximity to the buying power. In the early stages of the development of a retail system the revenues are expected to be high and the sizes of retailers moderate. The total amount of retail space supplied by the modern retailers in reality is significantly higher than the amount suggested by the optimization tests.  相似文献   

Major and trace metal mobility during weathering of mine tailings: Implications for floodplain soils     

David Kossoff  Karen A. Hudson-Edwards  William E. Dubbin  Maria Alfredsson 《Applied Geochemistry》2012

Mine tailings discharged to river systems have the potential to release significant quantities of major and trace metals to waters and soils when weathered. To provide data on the mechanisms and magnitudes of short- and long-term tailings weathering and its influence on floodplain environments, three calendar year-long column leaching experiments that incorporated tailings from Potosí, Bolivia, and soil from unaffected downstream floodplains, were carried out. These experiments were designed to model 20 cycles of wet and dry season conditions. Two duplicate columns modeled sub-aerial tailings weathering alone, a third modeled the effects of long-term floodplain tailings contamination and a fourth modeled that of a tailings dam spill on a previously contaminated floodplain. As far as was practical local climatic conditions were modeled. Chemical analysis of the leachate and column solids, optical mineralogy, XRD, SEM, EPMA, BCR and water-soluble chemical extractions and speciation modeling were carried out to determine the processes responsible for the leaching of Al, Ca, Cu, K, Na, Mg, Mn, Sn, Sr and Ti. Over the 20 cycles, the pH declined to a floor of ca. 2 in all columns. Calcium, Cu, Mg, Mn and Na showed significant cumulative losses of up to 100%, 60%, 30%, 95% and 40%, respectively, compared to those of Al, K, Sr, Sn and Ti, which were up to 3%, 1.5%, 5%, 1% and 0.05%, respectively. The high losses are attributed to the dissolution of relatively soluble minerals such as biotite, and oxidation of chalcopyrite and Cu-sulfosalts, while low losses are attributed to the presence of sparingly soluble minerals such as svanbergite, cassiterite and rutile. These results strongly suggest that the release of tailings to floodplains should be limited or prohibited, and that all tailings should be removed from floodplains following dam spills.  相似文献   

Simultaneous oxidation of arsenic and antimony at low and circumneutral pH,with and without microbial catalysis     

Maria P. Asta  D. Kirk Nordstrom  R. Blaine McCleskey 《Applied Geochemistry》2012

Arsenic and Sb are common mine-water pollutants and their toxicity and fate are strongly influenced by redox processes. In this study, simultaneous Fe(II), As(III) and Sb(III) oxidation experiments were conducted to obtain rates under laboratory conditions similar to those found in the field for mine waters of both low and circumneutral pH. Additional experiments were performed under abiotic sterile conditions to determine the biotic and abiotic contributions to the oxidation processes. The results showed that under abiotic conditions in aerated Fe(III)–H₂SO₄ solutions, Sb(III) oxidizes slightly faster than As(III). The oxidation rates of both elements were accelerated by increasing As(III), Sb(III), Fe(III), and Cl⁻ concentrations in the presence of light. For unfiltered circumneutral water from the Giant Mine (Yellowknife, NWT, Canada), As(III) oxidized at 15–78 μmol/L/h whereas Sb(III) oxidized at 0.03–0.05 μmol/L/h during microbial exponential growth. In contrast, As(III) and Sb(III) oxidation rates of 0.01–0.03 and 0.01–0.02 μmol/L/h, respectively, were obtained in experiments performed with acid unfiltered mine waters from the Iberian Pyritic Belt (SW Spain). These results suggest that the Fe(III) formed from microbial oxidation abiotically oxidized As(III) and Sb(III). After sterile filtration of both mine water samples, neither As(III), Sb(III), nor Fe(II) oxidation was observed. Hence, under the experimental conditions, bacteria were catalyzing As and Sb oxidation in the Giant Mine waters and Fe oxidation in the acid waters of the Iberian Pyrite Belt.  相似文献   

Algal blooms: a perspective from the coasts of India     

Maria Shamina D’Silva  Arga Chandrashekar Anil  Ravidas Krishna Naik  Priya Mallika D’Costa 《Natural Hazards》2012,63(2):1225-1253

Algal blooms have been documented along the west and east coasts of India. A review of bloom occurrences in Indian waters from 1908 to 2009 points out that a total of 101 cases have been reported. A comparison of the bloom cases reported before and after the 1950s reveals that there is an increase in the number of bloom occurrences. The reports of algal blooms indicate their predominance along the west coast of India especially the southern part. Majority of the blooms reported along the west coast of India are caused by dinoflagellates, whereas diatom blooms prevail along the east coast. There have been 39 causative species responsible for blooms, of which Noctiluca scintillans and Trichodesmium erythraeum are the most common. Reporting of massive fish mortality in Indian waters has been associated with the blooming of Cochlodinium polykrikoides, Karenia brevis, Karenia mikimotoi, N. scintillans, T. erythraeum, Trichodesmium thiebautii and Chattonella marina. Most of the blooms occurred during withdrawal of the south-west monsoon and pre-monsoon period. In Indian waters, this process is mainly influenced by seasonal upwelling and monsoonal forcing that causes high riverine discharge resulting in nutrient-enriched waters that provides a competitive edge for blooming of phytoplankton species.  相似文献   

Assessment of the sensitivity of the southern coast of the Gulf of Corinth (Peloponnese, Greece) to sea-level rise   总被引：1，自引：0，他引：1  

Efthimios Karymbalis  Christos Chalkias  George Chalkias  Eleni Grigoropoulou  George Manthos  Maria Ferentinou 《Central European Journal of Geosciences》2012,4(4):561-577

The eustatic sea-level rise due to global warming is predicted to reach approximately 18?C59 cm by the year 2100, which necessitates the identification and protection of sensitive sections of coastline. In this study, the classification of the southern coast of the Gulf of Corinth according to the sensitivity to the anticipated future sealevel rise is attempted by applying the Coastal Sensitivity Index (CSI), with variable ranges specifically modified for the coastal environment of Greece, utilizing GIS technology. The studied coastline has a length of 148 km and is oriented along the WNW-ESE direction. CSI calculation involves the relation of the following physical variables, associated with the sensitivity to long-term sea-level rise, in a quantifiable manner: geomorphology, coastal slope, relative sea-level rise rate, shoreline erosion or accretion rate, mean tidal range and mean wave height. For each variable, a relative risk value is assigned according to the potential magnitude of its contribution to physical changes on the coast as the sea-level rises. Every section of the coastline is assigned a risk ranking based on each variable, and the CSI is calculated as the square root of the product of the ranked variables divided by the total number of variables. Subsequently, a CSI map is produced for the studied coastline. This map showed that an extensive length of the coast (57.0 km, corresponding to 38.7% of the entire coastline) is characterized as highly and very highly sensitive primarily due to the low topography, the presence of erosionsusceptible geological formations and landforms and fast relative sea-level rise rates. Areas of high and very high CSI values host socio-economically important land uses and activities.  相似文献   

Spectral characteristics of rocks: Effects of composition and texture and implications for the interpretation of planet surface compositions     

Cristian Carli  Maria Sgavetti 《Icarus》2011,211(2):1034-1048

In spectroscopic remote sensing for the exploration of the surface compositions of Earth and terrestrial planets, reflectance spectra with very low spectral contrast and even devoid of diagnostic absorption bands can be observed, which make the interpretation of the component minerals ambiguous. Using selected examples of terrestrial rock samples from intrusive and effusive geologic systems, we discuss compositional and textural properties related to these particular spectral shapes. We show that: (1) this spectral behaviour is common for coarse grains of multimineral rocks, where the optical coupling is expected to occur between welded mineral particles; (2) it is emphasised by the presence of opaque minerals with various compositions, such as ulvospinel, magnetite and chromite in effusive rock groundmass and in intrusive rocks; (3) it is controlled by the number of silicate phases within which the FeO is distributed, irrespective of the total iron content in the rock: a rock composition with a high number of iron-bearing minerals producing this kind of low contrast, almost featureless spectra is indicated here as “critical mode”; (4) it is also strongly intensified by aqueous alteration of silicates.These observations suggest unpredictable combinations of several different petrographic variables affecting the spectra of some compact rocks, and stimulate both targeted studies to quantitatively relate spectral and petrographic parameters, and the development of appropriate methods of spectral decomposition. Our ongoing work is at present focused on the spectroscopic effects of the FeO concentration in transparent neutral plagioclase, the different compositions of the opaque neutral minerals, and the iron bearing amorphous phases.We also discuss the analogy between the rocks used in the analysis reported here and the crustal rock compositions observed on Mars and inferred for Mercury as well as the compatibility of the factors responsible for the low spectral contrast of terrestrial rock samples with the factors expected for the two planets. We observe that a coarse-grained surface and a composition approaching a critical mode could explain the featureless Acidalia spectra on Mars, and suggest that the still open questions about Mercury’s surface regolith characteristics and composition do not exclude a priori the contribution of some of the factors examined in this paper to the peculiar surface properties of this planet.  相似文献   

Mercury crater statistics from MESSENGER flybys: Implications for stratigraphy and resurfacing history     

Robert G. Strom  Maria E. Banks  Clark R. Chapman  Caleb I. Fassett  Jeffrey A. Forde  James W. Head III  William J. Merline  Louise M. Prockter  Sean C. Solomon 《Planetary and Space Science》2011,59(15):1960-1967

The primary crater population on Mercury has been modified by volcanism and secondary craters. Two phases of volcanism are recognized. One volcanic episode that produced widespread intercrater plains occurred during the period of the Late Heavy Bombardment and markedly altered the surface in many areas. The second episode is typified by the smooth plains interior and exterior to the Caloris basin, both of which have a different crater size-frequency distribution than the intercrater plains, consistent with a cratering record dominated by a younger population of impactors. These two phases may have overlapped as parts of a continuous period of volcanism during which the volcanic flux tended to decrease with time. The youngest age of smooth plains volcanism cannot yet be determined, but at least small expanses of plains are substantially younger than the plains associated with the Caloris basin. The spatial and temporal variations of volcanic resurfacing events can be used to reconstruct Mercury's geologic history from images and compositional and topographic data to be acquired during the orbital phase of the MESSENGER mission.  相似文献   

Radius and limb topography of Mercury obtained from images acquired during the MESSENGER flybys     

Jürgen Oberst  Stephan Elgner  F. Scott Turner  Mark E. Perry  Robert W. Gaskell  Maria T. Zuber  Mark S. Robinson  Sean C. Solomon 《Planetary and Space Science》2011,59(15):1918-1924

Analysis of images obtained by the MESSENGER spacecraft during its three flybys of Mercury yields a new estimate for the planet's mean radius of 2439.25±0.69 km, in agreement with results from Mariner 10 and Earth-based observations, as well as with MESSENGER altimeter and occultation data. The mean equatorial radius and polar radius are identical to within error, suggesting that rotational oblateness is negligible when compared with other sources of topography. This result is consistent with the small gravitational oblateness of the planet. Minor differences in radius obtained at different locations reflect regional variations in topography. Residual topography along three limb profiles has a dynamic range of 7.4 km and a root-mean-square roughness of 0.8 km over hemispherical scales. Following MESSENGER's entry into orbit about Mercury in March 2011, we expect considerable additional improvements to our knowledge of Mercury's size and shape.  相似文献   

Seismic effects of the Caloris basin impact, Mercury     

Jiangning Lü  Youshun Sun  M. Nafi Toksöz  Yingcai Zheng  Maria T. Zuber 《Planetary and Space Science》2011,59(15):1981-1991

Striking geological features on Mercury's surface have been linked to tectonic disruption associated with the Caloris impact and have the potential to provide information on the interior structure of Mercury. The unusual disrupted terrain located directly at the antipode of the 1500-km-diameter Caloris basin could have plausibly formed as a consequence of focused seismic waves generated by the massive impact event. In this paper, we revisit the antipodal seismic focusing effects of the Caloris impact by developing physically consistent structure models for Mercury and parameterized seismic source models for the Caloris impact. If the focused seismic body waves caused the disrupted terrain, then the amplitudes of the waves and the areal extent of surface disruptions could be used for estimating the seismic energy imparted by the impact.In this study, we show that effects of direct body waves are small relative to those of focused guided waves. Two types of guided waves are produced by the Caloris impact. One is the conventional Rayleigh wave generated by the impact. The second is the mantle guided waves trapped between the core and the free surface. Mantle guided waves, not recognized in previous studies, may have played an important role in the creation of the disrupted terrain. We find that the early core state has only moderate effects on the antipodal response to the Caloris impact. The fact that the zone of predicted disruption for both fluid and solid core cases is smaller than the observed region of chaotic terrain suggests either that the antipodal response to the Caloris impact was modulated by the shallow structure of Mercury, or that the energy imparted by the impact was larger than those used in this study.  相似文献