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Physics and Chemistry of the Earth, Parts A/B/C

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ISSN (Print) 1474-7065
Published by Elsevier

[2564 journals]

Contamination in water
- Abstract: Publication date: Available online 14 May 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Hossain Md Anawar
  
  PubDate: 2013-05-15T08:08:33Z
Improving the Mediterranean seismicity picture thanks to international collaborations
- Abstract: Publication date: Available online 9 May 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): S. Godey , R. Bossu
  The seismicity of the Mediterranean, compiled by the Euro-Mediterranean Seismological Centre (EMSC), is presented for the period 1998 to 2010. The data set contains earthquakes recorded by more than 3,000 stations operated by 78 networks. The Euro-Med Bulletin (EMB) provides parametric information for 273,000 tectonic events. The location resolution is characterized by a constant improvement over the years made possible by gathering steadily increasing data contribution. Dedicated collaboration with the network operators through regular discussion and interaction allow proper review of input and output information. In addition to natural events, seismic networks report data related to non tectonic activity. Discrimination is a crucial step in the production of seismicity catalogues to provide accurate information used for seismic hazard assessment. Over 13 years, 62,000 artificial events are characterized, mostly located in the vicinity of the largest mine and quarry areas of the region. While a large amount of man-related seismic activity is properly described, we show that through statistical analysis, discrimination in the EMB can still be improved. This is especially useful to scan past data, when routine discrimination was usually not performed by local networks. Seismicity catalogues are also useful for integrated access data portal to diverse and distributed seismological products as multi-disciplinary approaches of seismology is necessary. It leads us to the propose and develop an e-Bulletin where the scientists could access all type of seismological and engineering products (from strong motion or broad band waveforms to macroseismic analysis) by simply connecting to a single event dedicated web page.
  
  PubDate: 2013-05-11T08:10:00Z
Characteristics and role of groundwater dissolved organic matter on arsenic mobilization and poisoning in Bangladesh
- Abstract: Publication date: Available online 9 May 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Shafi M. Tareq , Masahiro Maruo , Keiichi Oht
  The fluorescence and molecular weight characteristics of dissolved organic matter (DOM) in groundwater of Bangladesh were investigated to evaluate its multiple roles on arsenic (As) mobilization and poisoning. Fluorescence properties of DOM were measured in groundwater samples collected from two As contaminated areas of Bangladesh (Faridpur at the Ganges floodplain and Sonargaon at the Meghna floodplain) from different locations and depths. The three dimensional excitation-emission matrix (3DEEM) fluorescence spectra of groundwater samples showed two characteristic peaks around Ex/Em = 335-365nm/435-480nm for fulvic-like peaks and peak at around Ex/Em = 275-290 nm/310-335 nm for the protein-like materials. The similarity of fluorescence spectra of groundwater and surface water of both the study areas with high intensity of fluorescence and its strong correlation with DOC reflect the in situ generation of fluorescent DOM from sedimentary organic matter (SOM) and recent recharge of terrestrial labile organic carbon into shallow aquifer. High performance size-exclusion chromatography (HPSEC) analysis of DOM shows positive correlations between fluorescence intensities (FI) of small molecular fractions (0.65 KDa) and As concentrations, with the signatures of protein-like peaks of DOM in groundwater. This result provides new evidence that small molecular weight fraction of DOM in groundwater of Bangladesh can play an important role on As mobilization and toxicity. In addition, high concentration of fluorescence materials in DOM of As contaminated groundwater of Bangladesh may pose a threat to public health.
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  PubDate: 2013-05-11T08:10:00Z
Scaling Earthquake Ground Motions in Western Anatolia, Turkey
- Abstract: Publication date: Available online 9 May 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): A. Akinci , S. D’Amico , L. Malagnini , A. Mercuri
  In this study, we provide a complete description of the ground-motion characteristics of the western Anatolia region of Turkey. The attenuation of ground motions with distance and the variability in excitation with magnitude are parameterized using three-component 0.25-10.0 Hz earthquake ground motions at distances of 15 - 250 km. The data set is comprised of more than 11,600 three-component seismograms from 902 regional earthquakes of local magnitude (ML) 2.5 to 5.8, recorded during the Western Anatolia Seismic Recording Experiment (WASRE) between November 2002 and October 2003. We used regression analysis to relate the logarithm of measured ground motion to the excitation, site, and propagation effects. Instead of trying to reproduce the details of the high-frequency ground motion in the time domain, we use a source model and a regional scaling law to predict the spectral shape and amplitudes of ground motion at various source-receiver distances. We fit a regression to the peak values of narrow bandpass filtered ground velocity time histories, and root mean square and RMS-average Fourier spectral amplitudes for a range of frequencies to define regional attenuation functions characterized by piece-wise linear geometric spreading (in log-log space) and a frequency-dependent crustal Q(f). An excitation function is also determined, which contains the competing effects of an effective stress parameter Δσ and a high-frequency attenuation term exp(-πκf). The anelastic attenuation coefficient for the entire region is given by Q(f) = 180f 0.55. The duration of motion for each record is defined as the value that yields the observed relationship between time-domain and spectral-domain amplitudes, according to random process theory. Anatolian excitation spectra are calibrated for our empirical results by using a Brune model with a stress drop of 10 MPa for the largest event in our data set (Mw 5.8) and a near-surface attenuation parameter of ψ=0.045 s. These quantities, together with the effective duration of ground motion in the region, are used to estimate the peak ground motion (PGA, PGV). Using stochastic ground motion simulations, we predict the absolute level of ground shaking and compare them with strong-motion data in the region. The attenuation of simulated ground motion is compared with recent global and regional ground motion prediction equations (GMPEs). The performance of the stochastic model is also tested against small and intermediate-sized earthquakes (the M3.9 11 November 2007, M5.9 17 October 2005 and M5.7 20 October 2005 Izmir-Urla earthquakes) recorded by strong motion stations in the National Strong Ground Motion Network (operated by the Earthquake Department of the Disaster and Emergency Management Presidency, AFAD).
  
  PubDate: 2013-05-11T08:10:00Z
Hydro-climatic trends in the Abay / Upper Blue Nile basin, Ethiopia
- Abstract: Publication date: Available online 7 May 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): S. Tekleab , Y. Mohamed , S. Uhlenbrook
  Trends of the three hydro-meteorological variables precipitation, temperature and stream flow, represented by 13, 12, and 9 gauging stations, respectively, within the Abay /Upper Blue Nile basin have been studied to support water management in the region. The Trends were evaluated over different time periods depending on data availability at the stations. The statistical Mann-Kendall and Pettitt tests have been used to assess trends and change points respectively. The tests have been applied to mean annual, monthly, seasonal, 1- and 7-days annual minimum and maximum values for streamflow, while mean annual, monthly and seasonal timescales were applied to meteorological variables. The results are heterogeneous and depict statistically significant increasing/decreasing trends. Besides, it showed significant abrupt change of point upward/downward shift for streamflow and temperature time series. However, precipitation time series did not show any statistically significant trends in mean annual and seasonal scales across the examined stations. Increasing trends in temperature at different weather stations for the mean annual, rainy, dry and small rainy seasons are apparent. The mean temperature at Bahir Dar– typical station in the Lake Tana sub basin, has been increasing at the rate of about 0.50C/decade, 0.30C/decade in rainy season (June to September), 0.60C/decade in small rainy season (March to May), and 0.6 0C/decade in dry season (October to February). Other stations in the Abay / Upper Blue Nile show comparable results. Overall it is found that trends and change point times varied considerably across the stations and catchment to catchment. Identified significant trends can help to make better planning decisions for water management. However, the cause attributes to the observed changes in hydro-meteorological variables need further research. In particular the combined effects of land use / land cover change and climate variability on streamflow of Abay / Blue Nile basin and its tributaries needs to be understood better.
  
  PubDate: 2013-05-07T08:10:42Z
Directional site effects in a non-volcanic gas-emission area (Mefite d’Ansanto, southern Italy): evidence of a local transfer fault transversal to large NW-SE extensional faults?
- Abstract: Publication date: Available online 4 May 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Marta Pischiutta , Mario Anselmi , Paola Cianfarra , Antonio Rovelli , Francesco Salvini
  The wavefield polarisation technique is applied to ambient vibrations recorded in the Mefite d’Ansanto area, which is a site of natural non-volcanic emissions of low-temperature CO2-enriched gases. Twenty-five measurements were taken in the study area: eleven near the emission site and the remaining fourteen at different locations within 5 km. Polarisations are assessed in both the frequency and time domains through individual-station horizontal-to-vertical spectral ratios and a covariance matrix analysis, respectively. We find that ground motions in the emission area tend to be polarised in the horizontal plane, with a predominantly N115° trend. This polarisation disappears with increasing distance from the site. Studies in other areas have shown that such a directional effect is likely caused by fault-induced fractures and tends to be orthogonal to the fracture strike; however, the predominant NW-SE regional faulting does not agree with the N115° polarisation direction observed here. To explain these observations, we propose an interpretation in terms of a NE-SW-oriented local transfer fault, inferred from lineament analysis. The intersection of the damage zone of this fault with the regional NW-SE normal-fault system could easily be responsible for the gas emissions, as it favours a localised crustal weakness.
  
  PubDate: 2013-05-07T08:10:42Z
Relationship of arsenic concentration with ammonium-nitrogen concentration, oxidation reduction potential and pH of groundwater in arsenic-contaminated areas in Asia
- Abstract: Publication date: Available online 30 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Kiyoshi Kurosawa , Kazuhiko Egashira , Masakazu Tani
  This study examines how arsenic (As) concentration is related to ammonium-nitrogen (NH4-N) concentration, oxidation reduction potential (ORP) and pH in groundwater to determine if they have common characteristics in groundwater with high As concentrations in the As-contaminated areas of Bangladesh, Nepal, Cambodia and Vietnam. For the groundwater samples having the three highest As concentrations (top three groundwaters) selected as representatives at each location, As and NH4-N concentrations varied, but ORP and pH did not vary by locations. The ORP value of 30-110 mV, indicating the reducing condition, and the neutral to slightly alkaline pH (pH 7.0-7.6) were presumed to be the key conditions for high As concentrations in groundwater of the study areas. According to the ORP (Eh)–pH diagram, the dominant As species in the top three groundwaters from each location was hydrogen arsenate (HAsO4 2-). Out of the correlations between the four elements for the top three groundwaters in the areas, only the correlation between As and NH4-N concentrations was positive and significant. Thus, it was identified that NH4-N had an effect on increasing As concentration in groundwater.
  
  PubDate: 2013-05-03T08:08:58Z
Mineralogical approach in elucidation of contamination mechanism for toxic trace elements in the environment: special reference to arsenic contamination in groundwater
- Abstract: Publication date: Available online 29 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Junji Akai , Hossain Md Anawar
  Mineralogy and mineral-microbe interactions play a significant role in the environmental contamination of toxic trace elements in groundwater and wetland ecosystems. This review has described the importance of use of TEM that is an essential tool to study the environmental mineralogy and mineral-microbe interactions. Biomineralization process that can advance the succession and evolution of biosphere on the earth has also been summarized briefly. This study explained the role of minerals to control the mechanism of adsorption, desorption, mobility and transport of toxic trace elements, especially arsenic (As) in the groundwater. Finally, this review has explored the evolution of As contamination in groundwater of the Quaternary age deposits including the Holocene and Pleistocene with special reference to groundwater of Bangladesh, West Bengal (India), Vietnam and Inner Mongolia (China).
  
  PubDate: 2013-05-03T08:08:58Z
Status of groundwater arsenic pollution in Holocene aquifers from parts of the Ghaghara Basin, India: Its relation to geomorphology and hydrogeological setting
- Abstract: Publication date: Available online 30 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Babar Ali Shah
  A groundwater arsenic (As) survey was carried out for the first time in Faizabad, Gonda, and Basti districts of UP and 38%, 61%, and 42% of tubewells in these districts, respectively have As > 10 μg/l (WHO guideline). Moreover, 15%, 45%, and 26% of tubewells in Faizabad, Gonda, and Basti districts, respectively have As above 50 μg/l, the Indian standards for As in drinking water. About 86%, 69%, and 35% of tubewells in Faizabad, Gonda, and Basti districts, respectively are from shallow depth (21 to 45 m), and it is worth noticing that 47% As-contaminated (As > 10 μg/l) tubewells in these three districts are located within the depth of 10 to 35 m in Holocene Newer Alluvium aquifers. The high content of As (7.11 mg/kg) is recorded in suspended river sediments of the Ghaghara River as well. Most of the As-contaminated tubewells in Faizabad, Gonda, and Basti districts are located close to abandoned or present meander channels and floodplains of the Ghaghara River. In contrast, tubewells in Faizabad, Ayodhya, and Nawabganj towns are As-safe because of their positions on the Pleistocene Older Alluvium upland surfaces. Deeper tubewells (>50 m) in Pleistocene Older Alluvium aquifers are suggested as option for As-safe groundwater.
  
  PubDate: 2013-05-03T08:08:58Z
Is organic matter a source or redox driver or both for arsenic release in groundwater?
- Abstract: Publication date: Available online 27 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Hossain Md Anawar , Shafi M. Tareq , Golam Ahmed
  Arsenic (As) contamination in groundwater is a global public health issue, because groundwater is the main source of drinking water worldwide. Arsenic contamination in groundwater is directly or indirectly associated with organic matter (OM). Therefore, this study investigated the role of OM in mobilization of As in the subterranean aquifers. The reduced concentrations of terminal electron acceptors (dissolved O2, NO3 -, and SO4 2-), enhanced concentrations of dissolved organic carbon (DOC), HCO3 - and NH4 + ions, and strong correlations between NH4 + and DOC indicate the reducing geochemical environment of aquifer in Bangladesh, where DOC might have originated from microbial oxidation of sedimentary OM, humic substances, surface derived terrestrial OM and petroleum. Groundwater samples exhibit variations in the concentrations of DOC (0.20 to 5.09 mg/l), fluorescence intensity and As depending on the depth and locations of the sampling site suggesting that the aquifers have different characteristics and different sources of DOC. The DOC concentrations in the upper aquifer (up to 41 m) are higher than those in the middle and lower aquifers (> 55 m) suggesting that the recent inflow of surface derived terrestrial OM with recharge water and petroleum in the shallow parts of the aquifer promoted the peak of high dissolved As, where older water mixes with recent recharge water containing organic carbon. Hydrogeochemical data and sediment geochemistry indicates that As mobilization from the sediment occurs through the microbial-mediated reductive dissolution of iron oxyhydroxide, where OM is the main redox driver facilitating As release into groundwater. Organic matter can strongly influence the solubility and mobility of As mainly through redox reactions, competitive adsorption, desorption and complexation reactions. Furthermore, based on the results of sediment and groundwater geochemistry, and As speciation in plant tissue, it can be concluded that OM is not only a redox driver, but also one of the sources of As in groundwater.
  
  PubDate: 2013-04-29T08:11:34Z
Mineralogical and geomicrobial examination of soil contamination by radioactive Cs due to 2011 Fukushima Daiichi Nuclear Power Plant accident
- Abstract: Publication date: Available online 25 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Junji Akai , Nao Nomura , Shin Matsushita , Hisaaki Kudo , Haruo Fukuhara , Shiro Matsuoka , Jinko Matsumoto
  Soil contamination by radioactive Cs from Fukushima Daiichi Nuclear Power plant accident was investigated. Absorption and desorption experiments of Cs were conducted for several phyllosillicates (kaolinite, sericite, montmorillonite, vermiculite, chrysotile and biotite), zeolite and solid organic matter (dead and green leaves). The results confirmed the characteristic sorption and desorption of Cs by these materials. The 2:1 type phyllosilicate, especially, vermiculite and montmorillonite absorbed Cs well. Heated vermiculite for agricultural use and weathered montmorillonite also adsorbed Cs. Leaves also absorbed Cs considerably but easily desorbed it. In summary, the relative capacity and strength of different materials for sorption of Cs followed the order: zeolite (clinoptilolite) > 2:1 type clay mineral > 1:1 type clay mineral > dead and green leaves. Culture experiments using bacteria of both naturally living on dead leaves in Iitate village, Fukushima Pref. and bacterial strains of Bacillus subtillis, Rhodococus erythropolis, Streptomyces aomiensisand Actinomycetospora chlora were carried out. Non-radioactive 1% Cs solution (CsCl) was added to the culture media. Two types of strong or considerable bacterial uptakes of Cs were found in bacterial cells. One is that Cs was contained mainly as globules inside bacteria and the other is that Cs was absorbed in the whole bacterial cells. The globules consisted mainly of Cs and P. Based on all these results, future diffusion and re-circulation behavior of Cs in the surface environment was discussed.
  
  PubDate: 2013-04-25T08:11:17Z
Ocean manganese nodules as stromatolite with a fractal like-signature
- Abstract: Publication date: Available online 18 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Junji Akai , Shigeki Akiyama , Akira Tsuchiyama , Kurumi Akai
  Deep-sea manganese (Mn) nodules are problematic in terms of factors such as their characteristic form and genesis. There are many reports of bacterial species from manganese nodules. However, the genesis of these nodules has not been fully confirmed. Samples, mainly from the Clarion Clipperton Fracture zone in the Pacific Ocean, were examined by mineralogical methods and X-ray CT. Thin sections of these samples showed columnar stromatolite structures with rhythmic bands. Mineralized bacteria were observed by SEM and TEM. Surface morphology could be described as having a fractal-like nature. The fractal characteristics of spherical to dome-like forms were fundamentally composed of at least four ranks. The 4th order form corresponds to the stromatolite dome top shapes. Similar granular domain units and porous characteristics in manganese nodules were clearly observed by X-ray CT sections. Mathematical simulation based on fractal models reproduced similar morphological characteristics to the natural samples. So, we arrived at the concluding hypothesis that manganese nodules are aggregated stromatolite with fractal-like characteristics. Furthermore, we discussed the possibility that the nature of the layer manganese oxide minerals as the major component of the nodule and associated Fe-oxyhydroxide minerals may become an absorber/scavenger of strategic heavy metals and also toxic metals in the environments.
  
  PubDate: 2013-04-21T08:08:33Z
Patterns and estimates of post-Rupelian burial and erosion in the Campine area, north-eastern Belgium
- Abstract: Publication date: Available online 18 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): K. Beerten , M. De Craen , L. Wouters
  We have compiled a dataset containing information on patterns of burial and erosion that occurred during the last ca. 30 Ma in the Campine area, north-eastern Belgium. This area coincides with the occurrence of the Rupelian Boom Clay which is considered as one of the potential host formations for radwaste disposal. Patterns and estimates of erosion and sedimentation, based on geological and geomorphological data, from several locations within the Boom Clay outcrop and subcrop zone, show increasing burial in northern and north-eastern direction over the last 30 Ma. More southern areas have experienced erosion and denudation during some geological stages, usually in the order of several 10 meters, up to 100 m at most at two discrete locations. During the Quaternary, erosion is a widespread phenomenon in the Campine area, except in the Roer Valley Graben. The obtained estimates of erosion and burial are compared and discussed in the context of the overall geodynamic evolution of north-western Europe.
  
  PubDate: 2013-04-21T08:08:33Z
Structural Geomorphology, Active Faulting and Slope Deformations in the Epicentre Area of the MW 7.0, 1857, Southern Italy Earthquake
- Abstract: Publication date: Available online 18 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Francesco Bucci , Mauro Cardinali , Fausto Guzzetti
  In tectonically active domains, fault propagation processes are revealed by landforms. A characteristic morphological feature of exposed active faults is the occurrence of triangular facets. Triangle-shaped landforms morphologically similar to fault-related triangular facets result from erosion of moderately-to-steeply dipping strata or layered successions along fold limbs and are known as flatirons. Triangular facets and flatirons may commonly coexist in mountain chains resulting from the superposition of recent extensional faulting on inherited fold-and-thrust architecture. In these settings analysis of flatirons and triangular facets is not trivial and may result in geomorphologic misinterpretations, hence undermine the interpretations of the geological structure and related deformation history. Here we show that active fault lineaments can be discriminate by inherited morpho-structure. We present the combined results of photo-geological and field survey carried out along well-exposed triangular shaped landforms located in the seismically active Upper Agri River Valley of the Southern Apennine. We found that triangular shaped landforms develop along a major fold back-limb, the Mt. Lama western slope, making it possible to unequivocally interpret these as flatirons. Downslope, Mt. Lama back limb is affected by a large deep-sited landslide whose scarp bound the Flatirons and mimics a Holocene fault scarp. This inference appears significant, since the investigated landforms were interpreted by many authors as triangular facets related to an active normal fault, located at its foot, responsible for large historical earthquakes (i.e., the 1857 earthquake). We provide new criteria to discriminate morphologic convergence in tectonically active domains, with consequences for the regional geological interpretation, and for the assessment of geological hazards.
  
  PubDate: 2013-04-21T08:08:33Z
Monitoring of groundwater chemistry in terms of physical and chemical parameters of Gajraula, a semi-urbanized town of North India
- Abstract: Publication date: Available online 18 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Bineet Singh , Vikas Jain , Anuraag Mohan
  Groundwater happens to be a major source of drinking water for urban and rural India. With rapid growth in industrial sector, the shallow groundwater regime has become more vulnerable to industrial contamination and human activity. In this study, the drinking water quality of Gajraula and its suburbs, a semi-urbanized town of northern India, was assessed. The water samples from pre-identified 14 wells with different depths were analyzed for two years i.e. 2008 and 2009. The samples were taken thrice a year in May (summers), August (monsoon) and December (winters). The compiled results were compared with recommended values of World Health Organization (WHO) and Bureau of Indian Standards (BIS) for drinking water. The analysis showed that concentration levels of TDS, BOD, NO3- and Ca2+ exceeded the desirable limits of WHO and BIS in certain wells. The levels of trace metals Fe and Pb exceeded the limits in almost all the wells, while pH, Cl-, SO4 2-, Mg2+, Zn, Cr and Ni were well within the limits. The contamination levels in most cases were higher during summers as compared to monsoon and winters, which may be due to high build–up of dissolved solids. The quality of water from shallow hand pumps in vicinity to industries were unsuitable for human consumption as compared to public deep bore wells. Agro-chemicals, irrigation by effluent discharge and wastewater from commercial-residential area were the main sources of groundwater pollution. A study based on long-term surveillance of water systems, incorporating individual exposure assessment of users of private wells, should be considered for a lasting solution.
  
  PubDate: 2013-04-21T08:08:33Z
Impact of climate change on acid mine drainage generation and contaminant transport in water ecosystems of semi-arid and arid mining areas
- Abstract: Publication date: Available online 18 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Hossain Md Anawar
  Disposal of untreated and treated mining wastes and tailings exerts a significant threat and hazard for environmental contamination including groundwater, surface water, wetlands, land, foodchain and animals. In order to facilitate remediation techniques, it is important to understand the oxidation of sulphidic minerals, and the hydrolysis of the oxidation products that result in production of acid mine drainage (AMD), toxic metals, low pH, SO4 2- and Fe. This review has summarized the impacts of climate change on geochemical reactions, AMD generation, and water quality in semi-arid/arid mining environments. Besides this, the study included the effects of hydrological, seasonal and climate change on composition of AMD, contaminant transport in watersheds and restoration of mining sites. Different models have different types of limitations and benefits that control their adaptability and suitability of application in various mining enviroments. This review has made a comparative discussion of a few most potential and widely used reactive transport models that can be applied to simulate the effect of climate change on sulphide oxidation and AMD production from mining waste, and contaminant transport in surface and groundwater systems.
  
  PubDate: 2013-04-21T08:08:33Z
Evaluation of building dynamic properties through in-situ experimental techniques and 1D modelling: the example of Catania, Italy
- Abstract: Publication date: Available online 19 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): F. Panzera , G. Lombardo , I. Muzzetta
  Ambient noise records, processed through spectral ratio techniques were used to assess the dynamic properties of a sample survey of both reinforced concrete and masonry buildings. Soil-structure interactions were also investigated using simple 1D modelling to evaluate site amplifications, comparing the results with target spectra postulated by Eurocode8 requirements. The experimental periods obtained are always lower than those proposed by the building regulations. Therefore one has to pay attention in estimating seismic actions, particularly in those sites of the urban area where there are outcrops of either volcanic products or soft coarse materials.
  
  PubDate: 2013-04-21T08:08:33Z
Geomicrobiological Properties of Tertiary Sedimentary Rocks from the Deep Terrestrial Subsurface
- Abstract: Publication date: Available online 19 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): Takeshi Suko , Mariko Kouduka , Akari Fukuda , Kenji Nanba , Manabu Takahashi , Kazumasa Ito , Yohey Suzuki
  Microbial metabolic activity within the deep subsurface can potentially impact radionuclide migration during geological disposal of nuclear waste. To evaluate the geomicrobiological properties of Tertiary sedimentary rocks, which are widely distributed in the repository environment in Japan, aseptic and deoxygenated drilling was conducted with the installation of a multi-packer system to collect cores and groundwater. Integrated results from measurements on potential rates of denitrification and pore-size distributions in drill core samples indicated that in situ microbial activity is constrained by the availability of pore spaces larger than 0.1 μm in radius. Comparison of geochemical profiles of porewater extracted from the core samples and groundwater collected within multi-packer intervals revealed that terminal electron acceptors such as nitrite and sulfate were depleted in groundwater. Microbial community structures based on 16S rRNA gene sequences were represented by phylotypes related to Fe-, Mn-, elemental sulfur- and sulfate-reducing bacteria in groundwater. In addition, a phylotype closely related to denitrifying Acidovorax sp. of the β-Proteobacteria was dominant in the lower borehole interval. From our results, it is likely that groundwater microorganisms mediate redox reactions that influence the mobility of radionuclides in the deep subsurface.
  
  PubDate: 2013-04-21T08:08:33Z
Temporal variation of arsenic and nitrate content in groundwater of the Duero River Basin (Spain)
- Abstract: Publication date: Available online 19 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  Author(s): P. Mayorga , A. Moyano , Hossain M. Anawar , A. García-Sánchez
  High concentrations of arsenic (As) in groundwater of the Duero River Basin have created a public health concern in some provinces of Spain. However, the mechanism of As mobilization and influence of surface water-groundwater interaction, nutrients and different geochemical reactions on As removal have not yet been clearly reported. Therefore, this study investigated the possible mechanisms of As release, and temporal variations of As with respect to nitrate content in groundwater. Hydrogeochemical characteristics of groundwater sampled along three years in a region of central Spain showed high As contents exceeding EU guideline value of 10 μg/l. Significant positive correlations were found between As and bicarbonate concentrations in water samples. These results suggest a possible mechanism of As mobilization from sediments to groundwater as follows: bicarbonate ions can displace HAsO4 2- adsorbed on surface of aquifer Fe oxyhydroxide, other minerals and sediments. In addition, the high pH values of the groundwater might also favour the As desorption processes. The results showed that As concentrations in water samples decreased along with the increase in nitrate concentrations across the whole period of study (2001, 2003 and 2007). The negative and significant correlations between As and nitrate contents in water reflect the temporal variation of As concentration due to the effect of surface water-groundwater interaction and nutrient input into groundwater. The increased use of nitrogen fertilizers and pig manure in agriculture practices increased the nitrate content in groundwater during the period of this study, which could have favoured the precipitation of Fe oxyhydroxides and As adsorption.
  
  PubDate: 2013-04-21T08:08:33Z
Comparison of Sediment Transport Computations Using Hydrodynamic versus Hydrologic Models in the Simiyu River in Tanzania
- Abstract: Publication date: Available online 10 April 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  This paper presents the results of a study that compares the sediment routing of the Simiyu River using the hydrologic model, Soil and Water Assessment Tool (SWAT) and the 1D hydrodynamic simulation software for Rivers and Estuaries (SOBEK-RE) model. Routing in SWAT is completed using the simplified Bagnold’s equation and in the SOBEK-RE model is undertaken using the Saint Venant equation. The upstream boundary conditions for the routing modules were derived from the subcatchments sediment yields that were estimated by SWAT using the Modified Universal Soil Loss Equation (MUSLE). The sediment loads extrapolated or interpolated from the sediment rating curve for the catchment outlet were used for calibration and validation purposes. The SWAT model predicted an erosion rate of 2.09 Mt/yr. The total sediment load transported to the main outlet of the catchment simulated by the SWAT and SOBEK-RE models was equal to 2.94 and 2.72 Mt/yr, respectively. Thus the models computed a net erosion in the channels of 0.84 Mt/yr (SWAT) and 0.63 Mt/yr (SOBEK-RE). When comparing the results of the models for the different reaches of the main channel and main tributaries, the models showed different results both in magnitude and in sign (erosion /deposition). However, in a situation where data is scarce(such as grain size, channel geometry), the more complex hydrodynamic model does not necessarily lead to more reliable results.
  
  PubDate: 2013-04-13T08:08:45Z
Characterizing soil salinity in irrigated agriculture using a remote sensing approach
- Abstract: 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 55–57
  
  Managing salinity in irrigated agriculture is crucial for minimising its negative environmental impacts and for ensuring the long-term sustainability of irrigated agriculture. It demands establishing rapid monitoring systems that help develop sustainable management plans. Remote sensing offers several advantages over the conventional proximal methods to map and predict areas at salinity risk. This paper presents an integrated approach to characterize soil salinity using remotely-sensed data in the District Faisalabad, Punjab, Pakistan. The IRS-1B LISS-II digital data was acquired and analysed in combination with field data and topographical maps. Remotely-sensed data based salinity indices or band combinations were developed to monitor the occurrence pattern of salt-affected soils. Using supervised maximum likelihood classification, the images were classified into eight land use classes with an overall accuracy of around 90%. The classified images showed that 22.2% of the total area was under salt-affected soils in 1992. The occurrence pattern of salt-affected soils varied with positive and negative trends during 1992–1995 to a minimum of 10.6%. The delineation analysis into levels of saline soils revealed three types based on USDA classification (USDA, 1954). The slightly saline, moderately saline and strongly saline soils during 1992 were in the order of 15%, 3%, and 1% respectively. The interactive behaviour of salinity and sodicity and their combinations showed that saline-sodic soils occurred predominantly ranging from 6.9% to 17.3% of the salt-affected soils. The shallow watertable was found to be of hazardous quality in 28% of the study area. The relationship between salt-affected soils, waterlogged soils and groundwater quality revealed that 60–70% of the salt-affected soils occurred in shallow watertable areas during 1992–1995. The reuse of poor quality groundwater for irrigation and the failure of tile drainage system in the area are likely to further increase the risk of salinisation in the Indus Basin of Pakistan.
  
  PubDate: 2013-04-05T14:12:56Z
Characteristics of trace elements in aerosols collected in Northern Tunisia
- Abstract: 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 55–57
  
  In order to investigate the chemical characteristics of atmospheric aerosols, the sources and variability of atmospheric inputs, aerosols samples were collected during April 2006 and June 2007 in the coastal area of Boumhel, Tunisia. The samples were analysed for thirteen elements including Ca, Fe, Al, Si, Ti, Mg, Mn, K, Na, Cl, S, Zn and Pb using a wavelength dispersive X-ray fluorescence spectrometry. All elements measured in the aerosols of Boumhel revealed differences between the two seasons: the concentrations of all elements were the highest in June and the lowest in April due to the importance of meteorological conditions. The cascade impactor provided mass distributions indicate that Al, Fe, Si, Ti, Na, Cl and S are concentrated in coarse particles. The enrichment factors (EFs) of all elements indicate that Al, Fe, Si, Ca and Ti are mainly derived from soil sources. Na, S and Cl are mostly due to sea salts.
  
  PubDate: 2013-04-05T14:12:56Z
Evapotranspiration in the Pampean Region using field measurements and satellite data
- Abstract: 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 55–57
  
  Evapotranspiration (LE) is an important factor for monitoring crops, water requirements, and water consumption at local and regional scale. In this paper, we applied the semi-empirical model to estimate the daily latent heat flux (LEd = Rnd + A − B(Ts − Ta)). LEd has been estimated using satellite images (Thematic Mapper sensor) and a local dataset (incoming and outgoing short- and long-wave radiation) measured during three years. We first estimated the daily net Radiation (Rnd ) from a linear equation derived from the instantaneous net Radiation (Rnd = CRni + D). Subsequently, coefficients A and B have been estimated for two different cover vegetations (pasture and soybean). For each vegetation cover, an error analysis combining Rnd , A, B, and surface and air temperatures has been calculated. Results showed that Rnd had good performance (nonbias and low RMSE). LEd errors for pasture and soybean were ±28Wm−2 and ±40Wm−2 respectively.
  
  PubDate: 2013-04-05T14:12:56Z
Variability of GPS derived water vapor and comparison with MODIS data over the Indo-Gangetic plains
- Abstract: 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 55–57
  
  The water vapor is one of the important constituents of the atmosphere that affects the thermodynamics of the atmosphere and has direct impact on the weather conditions. The total column atmospheric water vapor, obtained from Global Positioning System (GPS) and Moderate Resolution Imaging Spectroradiometer (MODIS), is found to be very dynamic over the Indo-Gangetic (IG) plains. In this paper, we present an analysis of GPS data recently deployed (as of May 2007) on the campus of Banaras Hindu University, Varanasi (latitude 25°15′N, longitude 82°59′E). Further, we have compared the variability of water vapor from Kanpur GPS, AERONET and MODIS water vapor data for the year 2007. The monthly variability of water vapor shows characteristic features and dynamics of water vapor between two closely spaced GPS stations, found to be controlled by monsoon dynamics and wind pattern.
  
  PubDate: 2013-04-05T14:12:56Z
On the observations of unique low latitude whistler-triggered VLF/ELF emissions
- Abstract: 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 55–57
  
  A detailed analysis of the VLF/ELF wave data obtained during a whistler campaign under All India Coordinated Program of Ionosphere Thermosphere Studies (AICPITS) at our low latitude Indian ground station Jammu (geomag. lat. = 22°26′ N, L =1.17) has yielded two types of unusual and unique whistler-triggered VLF/ELF emissions. These include (1) whistler-triggered hook emissions and (2) whistler-triggered long enduring discrete chorus riser emissions in VLF/ELF frequency range during night time. Such types of whistler-triggered emissions have not been reported earlier from any of the ground observations at low latitudes. In the present study, the observed characteristics of these emissions are described and interpreted. Dispersion analysis of these emissions show that the whistlers as well as emissions have propagated along a higher geomagnetic field line path with L-values lying ∼L =4, suggesting that these triggered emissions are to be regarded as mid-latitude emissions. These waves could have propagated along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal (PL) mode. The measured intensity of the triggered emissions is almost equal to that of the source waves and does not vary throughout the period of observation on that day. It is speculated that these emissions may have been generated through a process of resonant interaction of the whistler waves with energetic electrons. Parameters related to this interaction are computed for different values of L and wave amplitude. The proposed mechanism explains some aspects of the dynamic spectra.
  
  PubDate: 2013-04-05T14:12:56Z
Landsat TM image segmentation for delineating geological zone correlated vegetation stratification in the Kruger National Park, South Africa
- Abstract: 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 55–57
  
  Image classification approaches are widely used in mapping vegetation on remotely sensed images. Vegetation assemblages are equivalent to habitats. Whereas sub-pixel classification approaches potentially can produce more realistic, homogenous habitat maps, pixel-based hard classifier approaches often result in non-homogenous habitat zones. This salt-and-pepper habitat mapping is particularly a challenge on images of savannas, given the characteristic patchy texture of scattered trees and grass. Image segmentation techniques offer possibilities for homogenous habitat classification. This study aimed at establishing the extent to which established, field surveyed and geology-related vegetation types in South Africa’s Kruger National Park (KNP) can be reproduced using image segmentation. Rain season Landsat TM images were used, selected to coincide with the peak in vegetation productivity, which was deemed the time of year when discrimination between key habitats in KNP is most likely to be successful. The multiresolution segmentation mode in eCognition 5.0 was employed, object classification accomplished using the nearest neighbour (NN) classifier, using object texture and training area mean values in the NN feature space. Compared to delineations of the vegetation types of KNP on a digital map of the vegetation zones that was tested, image segmentation successfully mapped the zones (overall accuracy 85.3%, K^=82.7%) despite slight shifts in the location of vegetation zone boundaries. Maximum likelihood classification (MLC) of the same images was only 37% accurate (K^=24.2%). Whereas the vegetation zones resulting from MLC were non-homogenous, with considerable spectral confusion among the vegetation zones, image segmentation produced more homogenous vegetation zones, comparably more useful for conservation management, because realistic and meaningful habitat maps are important in biodiversity conservation as input data upon which to base management decisions. Image segmentation appears to be a useful approach in mapping savanna vegetation.
  
  PubDate: 2013-04-05T14:12:56Z
Knowledge, transparency, and refutability in groundwater models, an example from the Death Valley Regional Groundwater Flow System
- Abstract: Available online 3 April 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  This work demonstrates how available knowledge can be used to build more transparent and refutable computer models of groundwater systems. The Death Valley regional groundwater flow system, which surrounds a proposed site for a high level nuclear waste repository of the United States of America, and the Nevada National Security Site (NNSS), where nuclear weapons were tested, is used to explore model adequacy, identify parameters important to (and informed by) observations, and identify existing old and potential new observations important to predictions. Model development is pursued using a set of fundamental questions addressed with carefully designed metrics. Critical methods include using a hydrogeologic model, managing model nonlinearity by designing models that are robust while maintaining realism, using error-based weighting to combine disparate types of data, and identifying important and unimportant parameters and observations and optimizing parameter values with computationally frugal schemes. The frugal schemes employed in this study require relatively few (10s to 1,000s), parallelizable model runs. This is beneficial because models able to approximate the complex site geology defensibly tend to have high computational cost. The issue of model defensibility is particularly important given the contentious political issues involved.
  
  PubDate: 2013-04-05T14:12:56Z
Geochemical impact of a low-pH cement liner on the near field of a repository for spent fuel and high-level radioactive waste
- Abstract: Available online 3 April 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  In Switzerland the geological storage in the Opalinus Clay formation is the preferred option for the disposal of spent fuel (SF) and high-level radioactive waste (HLW). The waste will be encapsulated in steel canisters and emplaced into long tunnels that are backfilled with bentonite. Due to uncertainties in the depth of the repository and the associated stress state, a concrete liner might be used for support of emplacement tunnels. Numerical reactive transport calculations are presented that investigate the influence of a concrete liner on the adjacent barrier materials, namely bentonite and Opalinus Clay. The geochemical setup was tailored to the specific materials foreseen in the Swiss repository concept, namely MX-80 bentonite, low-pH concrete (ESDRED) and Opalinus Clay. The heart of the bentonite model is a new conceptual approach for representing thermodynamic properties of montmorillonite which is formulated as a multi –component solid solution comprised of several end-members. The presented calculations provide information on the extent of pH fronts, on the sequence and extent of mineral phase transformations, and on porosity changes on cement – clay interfaces. It was found that the thickness of the zone containing significant mineralogical alterations is at most a few tens of centimeters thick in both the bentonite and the Opalinus Clay adjacent to the liner. Near both interfaces, bentonite – concrete liner and concrete liner – Opalinus Clay, the precipitation of minerals causes a reduction in the porosity. The effect is more pronounced and faster at the concrete liner – Opalinus Clay interface. The simulations reveal that significant pH-changes (i.e. pH > 9) in bentonite and Opalinus Clay are limited to small zones, less than 10 cm thick at the end of the simulations. It is not to be expected that the zone of elevated pH will extend much further at longer times.
  
  PubDate: 2013-04-05T14:12:56Z
Analysis of Aftershock Sequences in South and Southeastern Spain
- Abstract: Available online 4 April 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  A probabilistic modeling is used to analyze the spatio-temporal behavior of eleven aftershock sequences occurred in South and Southeastern Spain. This study focuses on the analysis of two seismicity parameters: the b-value of the frequency-magnitude distribution, and the p-value, explaining the temporal decay rate of aftershocks. The estimated b values range between 0.77±0.05 and 1.18±0.10 close to the typical b-values of the aftershock frequency-magnitude relationship b ≈ 1.0. The estimated p-values range between 0.75±0.03 and 1.43±.010 showing broad regimes of the temporal decay of aftershocks. The modified Bath’s law used to analyze the energy partitioning, suggests that a large fraction of the accumulated energy is released in the mainshock and relatively small fraction of energy is released during aftershock sequence, for example 80% of the total energy is released during the Mula 1999 mainshock, 88% during Bullas 2002 mainshock and 87% during La Paca 2005 mainshock. The fractal dimension D 2 is estimated using the correlation integral, and then used to derive the slip ratio, as the ratio of the slip occurred on primary fault segment to the total slip. For example, we obtained a slip ratio equal to 71% for the Mula 1999 aftershock sequence, 61% for the Bullas 2002 event, 58% for the La Paca 2005 aftershock, 50% for the Lorca 2011 sequence and 63% for the sequence triggered by the Gador 2002 mainshock. Finally, the correlations between the fractal dimension, the b-value and the p-value is analyzed, and the Aki’s relation D = 3b/c is discussed as well.
  
  PubDate: 2013-04-05T14:12:56Z
Identification of Potential Driving Mechanisms for HM Coupled Time-Dependent Deformation of Argillaceous Rocks
- Abstract: Available online 30 March 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  With respect to radioactive waste confinement indurated clays are potential host rocks as well as barrier rock formations. Regarding the tight coupling between fluid flow processes and time-dependent deformation in argillaceous rock mass this paper presents recent experimental findings obtained in the Mont Terri URL which are interpreted in terms of potential driving mechanisms for the time-dependent deformation behaviour of the rock. Within the interpretation process, numerical modelling work, reflecting the actual properties of the rock in situ, is performed and the simulation results are compared to the experimental results. The discussion also touches on the work which is in progress on validating the Finite Element Code for physical modelling and numerical simulation (CODE_BRIGHT).
  
  PubDate: 2013-04-01T08:09:27Z
Interaction of seismic sources in the Apennine belt
- Abstract: Available online 30 March 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  By analyzing the historical seismicity of the Apennines since AD 1000, we have identified 4 major seismic sequence occurred from 1349 to 1353, 1456 to 1461, 1688 to 1706 and 1915 to 1920. Each of these crises is characterized by several strong earthquakes and by the fact that seismic activity progressively migrated from the Southern to Northern Apennines. In order to provide a plausible explanation for this phenomenology, we have elaborated a detailed seismotectonic model of the Apennines, compatible with the implications of plate tectonics in the central Mediterranean region. In our model, the seismic motion of a tectonic block, induced by tectonic forces, stresses the surrounding blocks eventually causing further earthquake activity. The temporal delay between the triggering shock and subsequent strong earthquakes depends on the rheological properties of the crust-mantle system, that control post-seismic strain and stress perturbations. We argue that the spatio-temporal distribution of major earthquakes which have occurred in the Apennine belt during the most intense seismic crises since AD 1300 is consistent with the short-term implications of the ongoing tectonic setting in the central Mediterranean area and with the expected effects of post-seismic relaxation, quantified by numerical experiments based on the stress diffusion model. The results obtained point out an agreement between earthquake occurrence and the arrival of the predicted maximum amplitude of post-seismic strain and strain rate perturbation in the relevant seismic zones. Moreover, in most cases the strain regime induced by post-seismic perturbation may be compatible with the geometry and kinematics of fault systems recognized in the zones considered. These results might delineate an important tool for recognizing the zones most prone to next strong earthquakes in the study area.
  
  PubDate: 2013-04-01T08:09:27Z
OSL chronology of Quaternary terraced deposits outcropping between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy)
- Abstract: Available online 26 March 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  In this paper we tested the applicability of the Optically Stimulated Luminescence (OSL) technique through Single-Aliquot Regenerative-dose (SAR) protocol, on single grain quartz grains extracted from alluvial-coastal sediments. Five samples were collected from deposits belonging to a flight of seven orders of coastal-alluvial terraces outcropping in the area between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy), at the front of the Sicilian fold and thrust system. After various performance tests, we obtained OSL ages ranging between 240±12 and 80±4 ka, consistent with the normal evolutionary model of a terraced sequence, moving from the highest to the lowest elevation. Obtained data allowed us to determine a mean uplift rate of 1.2 mm/yr during the last 330 ka, mostly related to regional uplift processes coupled with sea-level changes. Moreover, terraces belonging to the two highest orders are folded, forming a large anticline. According to our results, the frontal thrust of the Sicilian chain was active between 236 and 197 ka ago, even though seismological and geodetic data suggest current activity to the back.
  
  PubDate: 2013-03-28T09:11:06Z
Earthquake site effect modeling in the Granada basin using a 3-D indirect boundary element method
- Abstract: Available online 20 March 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  In this work, we develop the indirect boundary element method (IBEM) to simulate the seismic site response in a realistic, large-scale 3-D sedimentary basin. Most previous applications of boundary element method have used full-space Green’s functions for wave propagation between element points. We use half-space Green’s functions, which include the seismic wavefield interactions at the free surface and require only the boundary elements of the basin interface. In this way, the size of the matrix equation for solution in the IBEM can be reduced to approximately a quarter of that using full-space Green’s functions. The site response modeling of the Granada basin in southern Spain using the IBEM shows that the basin-induced scattering waves were identified as propagating back and forth inside the basin. The scattered waves also generate surface waves that are weakly propagated outside of the basin. The wave propagation inside and outside of the basin shows different patterns. We observe that the scattered wave is locally amplified, and its propagation direction deviates from that of the incident waves propagation direction. Therefore, the computed seismic response in the basin could provide us with good estimates of the seismic motion.
  
  PubDate: 2013-03-20T09:12:00Z
Coda-Q and its Lapse Time Dependence Analysis in the Interaction Zone of the Dinarides, the Alps and the Pannonian Basin
- Abstract: Available online 20 March 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  The single backscattering model was used to estimate total attenuation of coda waves (Qc ) of local earthquakes recorded on eight seismological stations in the complex area of the western continental Croatia. We estimated Q 0 and n, parameters of the frequency dependent coda-Q using the relation Qc = Q 0 fn . Lapse time dependence of these parameters was studied using a constant 30 s long time window that was slid along the coda of seismograms. Obtained Qc were distributed into classes according to their lapse time, tL . For tL = 20–50 s we estimated Q 0 = 45–184 and n = 0.49–0.94, and for tL = 60–100 s we obtained Q 0 = 119–316 and n = 0.37–0.82. There is a tendency of decrease of parameter n with increasing Q 0, and vice versa. The rates of change of both Q 0 and n seem to decrease for lapse times larger than 50–80 s, indicating an alteration in rock properties controlling coda attenuation at depths of about 100–160 km. A very good correlation was found between the frequency dependence parameter n and the Moho depths for lapse times of 50, 60 and 70 s.
  
  PubDate: 2013-03-20T09:12:00Z
Scenario-based water resources planning for utilities in the Lake Victoria region
- Abstract: Available online 16 March 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  Urban areas in the Lake Victoria (LV) region are experiencing the highest growth rates in Africa. As efforts to meet increasing demand accelerate, integrated water resources management (IWRM) tools provide opportunities for utilities and other stakeholders to develop a planning framework comprehensive enough to include short term (e.g. landuse change), as well as longer term (e.g. climate change) scenarios. This paper presents IWRM models built using the Water Evaluation And Planning (WEAP) decision support system, for three towns in the LV region - Bukoba (Tanzania), Masaka (Uganda), and Kisii (Kenya). Each model was calibrated under current system performance based on site visits, utility reporting and interviews. Projected water supply, demand, revenues and costs were then evaluated against a combination of climate, demographic and infrastructure scenarios upto 2050. Our results show that water supply in all three towns is currently infrastructure limited; achieving existing design capacity could meet most projected demand until 2020’s in Masaka beyond which new supply and conservation strategies would be needed. In Bukoba, reducing leakages would provide little performance improvement in the short-term, but doubling capacity would meet all demands until 2050. In Kisii, major infrastructure investment is urgently needed. In Masaka, streamflow simulations show that wetland sources could satisfy all demand until 2050, but at the cost of almost no water downstream of the intake. These models demonstrate the value of IWRM tools for developing water management plans that integrate hydroclimatology-driven supply to demand projections on a single platform.
  
  PubDate: 2013-03-20T09:12:00Z
Source Parameters of Small and Moderate Earthquakes in the Area of the 2009 L’aquila Earthquake Sequence (Central Italy)
- Abstract: Available online 14 March 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  The main goal of this study is to provide moment tensor solutions for small and moderate earthquakes of the 2009 L’Aquila seismic sequence (central Italy). The analysis was performed by using data coming from the permanent Italian seismic network run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the “Cut And Paste” (CAP) method based on broadband waveform inversion. Focal mechanisms, source depths and moment magnitudes are determined through a grid search technique. By allowing time shifts between synthetics and observed data the CAP method reduces dependence of the solution on the assumed velocity model and on earthquake location. We computed seismic moment tensors for 312 earthquakes having local magnitude in the range between 2.7 and 5.9. The CAP method has made possible to considerably expand the database of focal mechanisms from waveform analysis in the lowest magnitude range (i.e. in the neighbourhood of magnitude 3) without overlooking the reliability of results. The obtained focal mechanisms generally show NW-SE striking focal planes in agreement with mapped faults in the region. Comparisons with the already published solutions and with seismological and geological information available allowed us to proper interpret the moment tensor solutions in the frame of the seismic sequence evolution and also to furnish additional information about less energetic seismic phases. Focal data were inverted to obtain the seismogenic stress in the study area. Results are compatible with the major tectonic domain. We also obtained a relation between moment and local magnitude suitable for the area and for the available magnitude range.
  
  PubDate: 2013-03-16T09:09:55Z
Level-2 Susceptibility Zoning on Seismic-induced landslides: an application to Sannio and Irpinia areas, Southern Italy
- Abstract: Available online 16 February 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  In this paper we recall a method for medium scale (level-2) zoning of seismic-induced landslide susceptibility and present its application to the Sannio-Irpinia area, Southern Italy. Previous small scale studies of the entire Campania Region identified this area as one of the most susceptible to earthquake-induced landslides in the region. The area’s intense seismic and landslide activity and the characteristics of the deposits involved in landslides make this analysis an interesting case study for land planning, management and protection of an area characterized by high seismic and hydrogeological hazard. The result of the zoning shows good agreement between the distribution of the historical earthquake-triggered landslides and the areas defined by the method as the most susceptible ones. They also highlight the method’s effectiveness in the presence of complex clayey deposits.
  Highlights ► Application of a level-2 zoning method for seismic-induced landslide susceptibility. ► Application of the method to the Sannio and Irpinia areas, Southern Italy. ► Effectiveness of the method in presence of complex clayey deposits.
  
  PubDate: 2013-02-20T03:12:00Z
Modeling the influence of MgSO4 invariant points on multiphase reactive transport process during saline soil evaporation
- Abstract: Available online 16 February 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  In the present work, we modeled a laboratory experiment where a sand column saturated with a MgSO4 solution is subject to evaporation. We used a compositional formulation capable of representing the effect of geochemistry on flow and transport for concentrated solutions under extreme dry conditions. The model accounts for the water sink/sources terms due to hydrated mineral dissolution/precipitation and the occurrence of invariant points, which prescribe the water activity. Results show that the occurrence of the invariant points at the top of the domain could affect the vapor flux at the column top and salt precipitation along the column. In fact, the invariant points occurrence could explain the spatial fluctuation on the salt precipitates formation. Results also suggest that the complex hydrochemical interactions occurring during soil salinization, including osmotic effects, are crucial not only to understand the salt precipitation, but also the evaporation rate.
  Highlights ► Modeling evaporation of sand column with MgSO4 solution. ► Model involves oven dry conditions, high salinity, hydrated mineral precipitation. ► Coupling effects: geochemical reactions on water content and therefore on flow. ► Modeling invariant points: mineral paragenesis prescribes water activity. ► Invariant points affects evaporation, vapor flux, salt distribution.
  
  PubDate: 2013-02-20T03:12:00Z
The evolution of clay rock/cement interfaces in a cementitious repository for low- and intermediate level radioactive waste
- Abstract: Available online 1 February 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  In Switzerland, deep geological storage in clay rich host rocks is the preferred option for low- and intermediate-level radioactive waste. For these waste types cementitious materials are used for tunnel support and backfill, waste containers and waste matrixes. The different geochemical characteristics of clay and cementitious materials may induce mineralogical and pore water changes which might affect the barrier functionality of host rocks and concretes. We present numerical reactive transport calculations that systematically compare the geochemical evolution at cement/clay interfaces for the proposed host rocks in Switzerland for different transport scenarios. We developed a consistent set of thermodynamic data, simultaneously valid for cementitious (concrete) and clay materials. With our setup we successfully reproduced mineralogies, water contents and pore water compositions of the proposed host rocks and of a reference concrete. Our calculations show that the effects of geochemical gradients between concrete and clay materials are very similar for all investigated host rocks. The mineralogical changes at material interfaces are restricted to narrow zones for all host rocks. The extent of strong pH increase in the host rocks is limited, although a slight increase of pH over greater distances seems possible in advective transport scenarios. Our diffusive and partially also the advective calculations show massive porosity changes due to precipitation/dissolution of mineral phases near the interface, in line with many other reported transport calculations on cement/clay interactions. For all investigated transport scenarios the degradation of concrete materials in emplacement caverns due to diffusive and advective transport of clay pore water into the caverns is limited to narrow zones. A specific effort has been made to improve the geochemical setup and the extensive use of solid solution phases demonstrated the successful application of a thermodynamically consistent union of very different materials like hydrated cement and clay phases. A reactive system utilizing a novel solid-solution approach is used, where cation exchange is an intrinsic property of the mineral phase definition. Although such features were not the primary aim of the study, they offer a large potential for studies where ion exchange and changing sorption properties are of interest.
  Highlights ► We compared geochemical evolution at host rock / concrete interfaces. ► We developed a set of thermodynamic data, valid for different materials. ► The thermodynamic model contains intrinsically varying cation exchange properties. ► The mineralogical changes at material interfaces are restricted to narrow zones. ► The calculations show massive porosity changes near the interface.
  
  PubDate: 2013-02-08T03:16:02Z
Thermal Coupling May Control Mechanical Stability of Geothermal Reservoirs During Cold Water Injection
- Abstract: Available online 17 January 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  Hydraulic stimulation and geothermal reservoir operation may compromise the rock mechanical stability and trigger micro seismic events. The mechanisms leading to this induced seismicity are still not completely understood. It is clear that injection causes an overpressure that reduces the effective stress, bringing the system closer to failure conditions. However, rock instability may not result only from hydraulic effects, but also from thermal effects. In fact, hydro-mechanical (i.e., isothermal) models often fail to reproduce field observations because the injection of cold water into a hot reservoir induces thermal stresses due to rock contraction. Thus, rock instability is likely to result from the superposition of hydraulic and thermal effects. Here, we perform coupled thermo-hydro-mechanical and hydro-mechanical simulations to investigate the effects of cold water injection in a fracture zone-intact rock system. Results show that thermal effects induce a significant perturbation on the stress in the intact rock affected by the temperature drop. This perturbation is likely to trigger induced seismicity in the surroundings of critically oriented fractures near the injection well. Hydro-mechanical simulations show that the behavior depends on the orientation of the faults and on the initial stress tensor. In the direction of the fractures, where the strains are more constrained, total stress increases with increasing pressure; thus, deviatoric stress increases or decreases depending on the initial stress state. The comparison between hydraulic and thermal effects shows that, when the largest confining stress acts perpendicular to the fractures, thermoelastic effects dominate and could trigger induced seismicity.
  Highlights ► We investigate the effects of cold water injection in a fracture zone-intact rock system. ► Coupled thermo-hydro-mechanical and hydro-mechanical simulations are performed. ► THM coupling describes processes that can play a key role in the triggering of induced seismicity. ► The greatest thermal effects occur in the rock mass surrounding the fracture zone.
  
  PubDate: 2013-01-19T07:48:24Z
Reactive transport modeling of the clogging process at Maqarin natural analogue site
- Abstract: Available online 18 January 2013
  Publication year: 2013
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  The Maqarin site in Jordan has been investigated for three decades as a natural analogue for the long term changes of materials in contact with hyper-alkaline solutions. Similar processes are expected in radioactive waste disposal sites, where cement based materials are in contact with natural rocks or other e.g. clay based materials. In this context, a numerical reactive transport model was used to study local geochemical alterations and induced porosity changes for the Maqarin marl rock in contact with the hyper-alkaline solution. The geochemical setup for the rock mineralogy and the pore water was calibrated to match measurements from the Maqarin site. The setup includes several clay and zeolite minerals, considers cation exchange processes, and a state-of-the-art model for cement phases. Similar to earlier calculations by Steefel and Lichtner (1998) who used a much simpler geochemical model, the pore clogging occurred after several hundred years at a distance of 5 – 10 mm from the contact to the hyper-alkaline solution. In our calculations, this was caused by a massive precipitation of ettringite and C-S-H minerals. We performed a sensitivity study by varying the intrinsic diffusion coefficient, the Archie’s law exponential factor, and the mineral surface area available for dissolution and precipitation. We found that the dissolution of clay minerals controls the availability of Al, which is needed for ettringite and C-S-H phase precipitation. Thus, the amount and kinetically controlled dissolution of clay minerals controls the spatial and temporal evolution of porosity changes. The simulations reveal that neither cation exchange processes nor the formation of zeolite minerals strongly influence the geochemical evolution of the system.
  Highlights ► Geochemical clogging process in Maqarin marl rock formation was simulated. ► State-of-the-art model for cement phases considered. ► Rock clay content was to control available Al, thus affect clogging. ► Neither cation exchange nor zeolite formations strongly influence the clogging.
  
  PubDate: 2013-01-19T07:48:24Z
Prediction of water temperature in stratified reservoir and effects on downstream irrigation area: A case study of Xiahushan reservoir
- Abstract: 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 53–54
  
  With increasing concern in environmental and ecological protection, more studies have focused on solving the problems caused by dam. Large reservoirs often release low-temperature water in spring and summer, which have adverse effects on downstream ecosystem. The 3-D Environmental Fluid Dynamics Code (EFDC) and 1-D longitudinal stream temperature model were used in this paper, to predict the water temperature in reservoir and canal and analyze the effects on irrigation area. The results indicate that the affected area is within a 55km distance mainly in the period between April and June. Some management and engineering measures should be adopted to reduce the impact.
  Highlights ► Simulated the water temperature of a stratified reservoir and river channel. ► Illustrated the rice growth will be affected by cool water during April and June. ► Predicted the influence range on the irrigation area.
  
  PubDate: 2012-12-18T09:23:58Z
Methane and nitrous oxide emissions from paddy field as affected by water-saving irrigation
- Abstract: 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 53–54
  
  Water-saving practices for rice production has become one of the major agricultural policies in China due to the severe water scarcity. However, greenhouse gases emissions from paddy field may be changed with water-saving practices. In the two-year field experiment at Thaihu Lake Basin of China, CH4 and N2O fluxes from paddy field under controlled irrigation and continuous flooding irrigation were monitored using closed chambers. Total CH4 emission from paddy field under controlled irrigation during the rice-growing period were 2.47 and 1.88gm−2 in 2006 and 2007, respectively, reduced by 79.1% on average compared with continuous flooding irrigation. The CH4 emission from paddy field was further concentrated in the initial and middle tillering stages of rice growth under controlled irrigation for 2years. The N2O emission from paddy field under controlled irrigation was mostly larger than those from flooding irrigation during the rice-growing period. Total N2O emission from paddy field under controlled irrigation during the rice-growing period was 106mgm−2, increased by 10.6% compared with those from flooding irrigation. Carbon dioxide equivalents of CH4 and N2O emissions from paddy field during the rice-growing period under controlled irrigation were 788kg CO2 ha−1, reduced by 61.4% compared with those from flooding irrigation. It can be concluded that controlled irrigation is an effective technique for mitigating the carbon dioxide equivalents of CH4 and N2O emissions from paddy field.
  Highlights ► We examine N2O emission from paddy field under non-flooding controlled irrigation. ► Controlled irrigation effectively decreases CH4 emission from paddy field. ► Wet-dry cycle is the reason for the changes of CH4 and N2O emission from paddy field. ► Controlled irrigation mitigates carbon dioxide equivalents from paddy field.
  
  PubDate: 2012-12-18T09:23:58Z
Modeling and assessing hydrologic processes for historical and potential land-cover change in the Duoyingping watershed, southwest China
- Abstract: 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 53–54
  
  Land-cover change significantly influences hydrologic processes at the watershed level. The mountainous Duoyingping watershed in upstream Yangtze River, China, has undergone dramatic land-cover change in the past three decades. It is likely to maintain this trend in the future, inevitably altering hydrologic processes in the region to a certain degree. Therefore, the effects of land-cover change on runoff, evapotranspiration (ET), and soil moisture in the watershed were assessed using a large-scale Variable Infiltration Capacity (VIC) hydrologic model. To minimize the effect of climate change on simulation results, we used detrended climate data over the period 1980–2005 in forcing the VIC model. The dynamics in the spatial distribution of land-cover types in the Duoyingping watershed from 1980 to 2000 were first examined, revealing that reforestation and deforestation were the major change patterns. On the basis of various land-use policies, potential land-cover scenarios for 2030 were established using an integrated land-use change model (CLUE-S). The scenarios were developed using 2000 land-use data as bases. Finally, the calibrated VIC model was applied in the scenarios to assess land-cover effects on hydrology. Hydrologic simulations showed that the effects of historical land-cover change on hydrology were discernible in the sub-watersheds of Nanba, Yingjing, and Yuxi. The annual ET was projected to decrease by 0.8–22.3% because of deforestation, and increase by 2.3–27.4% because of shrubland–forest conversion. Different potential land-cover scenarios play various roles in the effect on hydrology because of various land-use policies. In the scenario concerning forest protection policy, annual ET increased by more than 15%, while annual runoff decreased by 6%. However, a negligible effect on hydrology was found under the scenario involving cropland expansion. On the basis of the results, it is concluded that ET is more sensitive to land-cover change than are other hydrologic components. Hydrologic alteration caused by reforestation and deforestation during the dry season was more significant than that during wet season. Generally, the proposed approach in the study can be a useful means of assessing hydrologic responses to land-cover change.
  Highlights ► We simulate the effects of historical and potential land-cover change on hydrology. ► Reforestation and deforestation are the major land-cover change patterns. ► Increasing forest will increase ET and decrease runoff and soil moisture. ► ET is most sensitive to land-cover change. ► Hydrologic changes in the dry season are more obvious than those in the wet season.
  
  PubDate: 2012-12-18T09:23:58Z
Numerical modeling groundwater recharge and its implication in water cycles of two interdunal valleys in the Sand Hills of Nebraska
- Abstract: 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 53–54
  
  The topography and geomorphology of the sand dunes and interdunal valleys in the Nebraska Sand Hills play important roles in regional water cycle by influencing groundwater recharge and evapotranspiration (ET). In this study, groundwater recharge, associated with precipitation and ET as well as soil hydraulics, and its spatial variations owing to the topography of dunes and valleys are examined. A method is developed to describe the recharge as a function of the storage capacity of dunes of various heights. After the method is tested using observations from a network of wells in the Sand Hills, it is used in the MODFLOW model to simulate and describe recharge effects on groundwater table depth at two different dune-valley sites. Analysis of modeled groundwater budget shows that the groundwater table depth in the interdunal valleys is critically influenced by vertical groundwater flows from surrounding dunes. At the site of higher dunes there are steadier and larger vertical groundwater flows in the dunes from their previous storage of precipitation. These vertical flows change to be horizontal converging groundwater flows and create upwelling in the interdunal valleys, where larger ET loss at the surface further enhances groundwater upwelling. Such interdunal valley is the major concentration area of the surface water and groundwater flow in the Sand Hills. At the site of shallow dunes and a broad interdunal valley the supply of groundwater from the dunes is trivial and inadequate to support upwelling of groundwater in the valley. The groundwater flows downward in the valley, and the valley surface is dry. Weak ET loss at the surface has a smaller effect on the groundwater storage than the precipitation recharge, making such area a source for groundwater.
  Highlights ► The monthly recharge is estimated by a function of the depth to groundwater table. ► Water cycle at interdunal valleys was investigated by numerical groundwater model. ► The vertical flows at higher dunes create upwelling in the interdunal valleys.
  
  PubDate: 2012-12-18T09:23:58Z
Investigation into the impacts of land-use change on sediment yield characteristics in the upper Huaihe River basin, China
- Abstract: 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 53–54
  
  The processes of sediment generation in the upper Huaihe River basin have been altered by the intensified human activities over the past decades, particularly land-use change. To investigate the impacts of land-use change on the sediment yield characteristics in the upper Huaihe River, the catchment above the Xixian hydrological controlling station was selected as the case study site. The Soil and Water Assessment Tool (SWAT) model was used to simulate land-use change effects on sediment yield by the use of three-phase (1980s, 1990s and 2000s) land-use maps, soil type map (1:200,000) and 1987–2008 daily time series of rainfall from the upper Huaihe River basin. On the basis of the simulated time series of daily sediment concentration, land-use change effects on spatio-temporal change patterns of soil erosion modulus, rainfall–sediment yield relationship, and the sensitivity of rainfall–sediment yield relationship to rainfall for different types of land use were explored. The results revealed that under the same condition of soil texture and terrain slope the advantage for sediment yield and the sensitivity of rainfall–sediment yield relationship to rainfall descended by woodland, paddy field and farmland. The outputs of the paper could provide references for soil and water conservation and river health protection in the upper stream of Huaihe River.
  Highlights ► SWAT model was applied to study the effects of LUCC on sediment yield characteristics. ► Effects of LUCC on spatio-temporal change pattern of soil erosion modulus was studied. ► Rainfall–sediment yield relationship for different types of land use were studied. ► Sensitivity of R–S relationship to rainfall for different land use was studied. ► *LUCC means land use/cover change, * R–S means rainfall–sediment yield relationship.
  
  PubDate: 2012-12-18T09:23:58Z
Evaluating watershed service availability under future management and climate change scenarios in the Pangani Basin
- Abstract: Available online 3 September 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  Watershed services are the benefits people obtain from the flow of water through a watershed. While demand for such services is increasing in most parts of the world, supply is getting more insecure due to human impacts on ecosystems such as climate or land use change. Population and water management authorities therefore require information on the potential availability of watershed services in the future and the trade-offs involved. In this study, the Soil and Water Assessment Tool (SWAT) is used to model watershed service availability for future management and climate change scenarios in the East African Pangani Basin. In order to quantify actual “benefits”, SWAT2005 was slightly modified, calibrated and configured at the required spatial and temporal resolution so that simulated water resources and processes could be characterized based on their valuation by stakeholders and their accessibility. The calibrated model was then used to evaluate three management and three climate scenarios. The results show that by the year 2025, not primarily the physical availability of water, but access to water resources and efficiency of use represent the greatest challenges. Water to cover basic human needs is available at least 95% of time but must be made accessible to the population through investments in distribution infrastructure. Concerning the trade-off between agricultural use and hydropower production, there is virtually no potential for an increase in hydropower even if it is given priority. Agriculture will necessarily expand spatially as a result of population growth, and can even benefit from higher irrigation water availability per area unit, given improved irrigation efficiency and enforced regulation to ensure equitable distribution of available water. The decline in services from natural terrestrial ecosystems (e.g. charcoal, food), due to the expansion of agriculture, increases the vulnerability of residents who depend on such services mostly in times of drought. The expected impacts of climate change may contribute to an increase or decrease in watershed service availability, but are only marginal and much lower than management impacts up to the year 2025.
  Highlights ► Future management and climate scenarios for Pangani Basin were simulated using SWAT. ► Watershed service availability indicators were derived from model outputs. ► Investments in infrastructure can improve water provision even with increased demand. ► The decline of natural vegetation increases vulnerability of subsistence farmers.
  
  PubDate: 2012-12-18T09:23:58Z
Crack healing in rocksalt via diffusion in adsorbed aqueous films: Microphysical modelling versus experiments
- Abstract: Available online 12 October 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  Microcracks within the excavation damaged or disturbed zone (EDZ) in a salt-based radioactive waste repository (or an energy storage facility) can heal/seal by mechanical closure driven by compaction creep, by surface-energy-driven processes like diffusive mass transfer, and by recrystallization. It follows that permeability evolution in the excavation damaged zone around a backfilled or plugged cavity will in the short term be dominated by mechanical closure of the cracks, while in the longer term diffusive mass transfer effects are expected to become more important. This paper describes a contribution to assessing the integrity of radioactive waste repositories sited in rocksalt formations by developing a microphysical model for single crack healing in rocksalt. More specifically, single crack healing models for cracks containing a thin adsorbed water film are developed. These microphysical models are compared with single crack healing experiments, which conclusively demonstrate diffusion controlled healing. Calibration of unknown model parameters, related to crack surface diffusivity, against the experimental data enable crack healing rates under repository conditions to be estimated. The results show that after the stress re-equilibration that follows repository sealing, crack disconnection can be expected on a timescale of a few years at laboratory humidity levels. However, much longer times are needed under very dry conditions where adsorbed aqueous films are very thin.
  Highlights ► Crack healing/sealing of excavation damaged zones in salt based waste repositories. ► Single crack healing models for cracks containing a thin adsorbed water film. ► Microphysical models are compared with single crack healing experiments. ► Crack disconnection (i.e. bottleneck-closure) is expected within a few years at laboratory humidity levels. ► However, longer times are needed under very dry conditions.
  
  PubDate: 2012-12-18T09:23:58Z
Radionuclide transport during glacial cycles: Comparison of two approaches for representing flow transients
- Abstract: Available online 24 October 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  The effect of future, transient ice sheet movement and permafrost development on transport of radionuclides from a proposed repository site is investigated using numerical groundwater flow and radionuclide transport modelling. Two different transport approaches are compared, both utilizing groundwater flow simulations of future climate conditions. The first transport approach uses steady-state particle trajectories representing temperate climate conditions, but modifies the transport velocity along the trajectories according to the changing climate. The second approach is pseudo-transient by performing particle tracking in each individual flow field representing a given time epoch. Two different climate sequences are analyzed. First, a simplified sequence is assessed in order to understand if the two different transport approaches yield significantly different breakthrough characteristics. Second, a sequence representing conditions relevant for real safety assessment applications is considered. Results indicate that the transport approach using fixed trajectories tends to significantly over predict breakthrough during permafrost conditions relative to the pseudo-transient approach. The major difference between the two approaches is related to discharge locations. The fixed trajectory approach yields discharge locations constant in time whereas the pseudo-transient approach is characterized by discharge centres moving in time according to the different climate conditions.
  Highlights ► We model the effect of ice sheet movement and permafrost on geosphere radionuclide transport. ► A novel Monte Carlo time-domain particle tracking scheme is used for the transport simulations. ► We compare transport in steady-state flow with transport in pseudo-transient flow. ► The steady-state method with varying velocity magnitude captures main breakthrough features. ► The pseudo-transient method is needed to capture discharge locations during a glacial cycle.
  
  PubDate: 2012-12-18T09:23:58Z
Long-term cement corrosion in chloride-rich solutions relevant to radioactive waste disposal in rock salt - leaching experiments and thermodynamic simulations
- Abstract: Available online 1 December 2012
  Publication year: 2012
  Source:Physics and Chemistry of the Earth, Parts A/B/C
  
  Low- and intermediate-level radioactive wastes are frequently solidified in a cement matrix. In a potential repository for nuclear wastes, the cementitious matrix is altered upon contact with solution and the resulting secondary phases may provide for significant retention of the radionuclides incorporated in the wastes. In order to assess the secondary phases formed upon corrosion in chloride-rich solutions, which are relevant for nuclear waste disposal in rock salt, leaching experiments were performed. Conventional laboratory batch experiments using powdered hardened cement paste in MgCl2-rich solutions were left to equilibrate for up to three years and full-scale cemented waste products were exposed to NaCl-rich and MgCl2-rich solutions for more than twenty years, respectively. Solid phase analyses revealed that corrosion of hardened cement in MgCl2-rich solutions advanced faster than in NaCl-rich solutions due to the extensive exchange of Mg from solution against Ca from the cementitious solid. Thermodynamic equilibrium simulations compared well to results at the final stages of the respective experiments indicating that close to equilibrium conditions were reached. At high cement product to brine ratios (>0.65gmL-1), the solution composition in the laboratory-scale experiments was close to that of the full-scale experiments (cement to brine ratio of 2.5gmL-1) in the MgCl2 systems. The present study demonstrates the applicability of thermodynamic methods used in this approach to adequately describe full-scale long-term experiments with cemented waste simulates.
  
  PubDate: 2012-12-18T09:23:58Z