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  Subjects -> PHYSICS (Total: 754 journals)
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PHYSICS (546 journals)            First | 1 2 3 4 5 6 | Last

Particuology     Hybrid Journal  
Pattern Recognition in Physics     Open Access   (Followers: 1)
Pergamon Materials Series     Full-text available via subscription  
Phase Transitions and Critical Phenomena     Full-text available via subscription   (Followers: 1)
Philosophical Magazine     Hybrid Journal   (Followers: 2)
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences     Full-text available via subscription   (Followers: 5)
Philosophy and Foundations of Physics     Full-text available via subscription  
Physica B: Condensed Matter     Hybrid Journal   (Followers: 5)
physica status solidi (a)     Hybrid Journal   (Followers: 1)
physica status solidi (b)     Hybrid Journal   (Followers: 1)
physica status solidi (c)     Hybrid Journal   (Followers: 1)
Physica Status Solidi - Rapid Research Letters     Hybrid Journal   (Followers: 1)
Physical Communication     Hybrid Journal  
Physical Review C     Full-text available via subscription   (Followers: 17)
Physical Review Special Topics - Physics Education Research     Open Access   (Followers: 6)
Physical Review X     Open Access   (Followers: 4)
Physical Sciences Data     Full-text available via subscription   (Followers: 1)
Physics - spotlighting exceptional research     Full-text available via subscription   (Followers: 1)
Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B     Full-text available via subscription   (Followers: 2)
Physics and Chemistry of Liquids: An International Journal     Hybrid Journal  
Physics and Chemistry of the Earth, Parts A/B/C     Hybrid Journal   (Followers: 3)
Physics and Materials Chemistry     Open Access  
Physics Essays     Full-text available via subscription  
Physics in Medicine & Biology     Full-text available via subscription   (Followers: 8)
Physics in Perspective     Hybrid Journal   (Followers: 1)
Physics International     Open Access   (Followers: 2)
Physics Letters A     Hybrid Journal   (Followers: 10)
Physics Letters B     Open Access   (Followers: 3)
Physics of Fluids     Hybrid Journal   (Followers: 24)
Physics of Life Reviews     Hybrid Journal   (Followers: 1)
Physics of Plasmas     Hybrid Journal   (Followers: 6)
Physics of the Dark Universe     Open Access  
Physics of the Solid State     Hybrid Journal   (Followers: 3)
Physics of Wave Phenomena     Hybrid Journal   (Followers: 1)
Physics Procedia     Partially Free   (Followers: 1)
Physics Reports     Full-text available via subscription   (Followers: 2)
Physics Research International     Open Access   (Followers: 1)
Physics Today     Hybrid Journal   (Followers: 19)
Physics World     Full-text available via subscription   (Followers: 3)
Physics-Uspekhi     Full-text available via subscription  
Physik in unserer Zeit     Hybrid Journal  
Physik Journal     Hybrid Journal  
Plasma Physics and Controlled Fusion     Hybrid Journal   (Followers: 2)
Plasma Physics Reports     Hybrid Journal   (Followers: 2)
Pramana     Open Access   (Followers: 9)
Preview     Hybrid Journal  
Proceedings of the National Academy of Sciences     Full-text available via subscription   (Followers: 458)
Proceedings of the National Academy of Sciences, India Section A     Hybrid Journal   (Followers: 3)
Progress in Materials Science     Hybrid Journal   (Followers: 18)
Progress in Planning     Hybrid Journal   (Followers: 1)
Progress of Theoretical and Experimental Physics     Open Access  
Quantum Electronics     Full-text available via subscription   (Followers: 2)
Quantum Measurements and Quantum Metrology     Open Access  
Quarterly Journal of Mechanics and Applied Mathematics     Hybrid Journal   (Followers: 3)
Radiation Effects and Defects in Solids     Hybrid Journal   (Followers: 1)
Radiation Measurements     Hybrid Journal   (Followers: 2)
Radiation Physics and Chemistry     Hybrid Journal   (Followers: 1)
Radiation Protection Dosimetry     Hybrid Journal   (Followers: 2)
Radiation Research     Full-text available via subscription   (Followers: 2)
Radio Science     Full-text available via subscription   (Followers: 3)
Radiological Physics and Technology     Hybrid Journal   (Followers: 1)
Reflets de la physique     Full-text available via subscription  
Reports on Mathematical Physics     Full-text available via subscription  
Reports on Progress in Physics     Full-text available via subscription   (Followers: 2)
Research & Reviews : Journal of Physics     Full-text available via subscription  
Research in Drama Education     Hybrid Journal   (Followers: 9)
Research Journal of Physics     Open Access  
Results in Physics     Open Access   (Followers: 1)
Reviews in Mathematical Physics     Hybrid Journal  
Reviews of Accelerator Science and Technology     Hybrid Journal  
Reviews of Geophysics     Full-text available via subscription   (Followers: 19)
Reviews of Modern Physics     Full-text available via subscription   (Followers: 17)
Revista Colombiana de Física     Open Access  
Revista Mexicana de Astronomía y Astrofísica     Open Access  
Revista Mexicana de Física     Open Access  
Revista mexicana de física E     Open Access  
Rheologica Acta     Hybrid Journal   (Followers: 3)
Russian Journal of Mathematical Physics     Hybrid Journal  
Russian Journal of Nondestructive Testing     Hybrid Journal   (Followers: 1)
Russian Physics Journal     Hybrid Journal  
Samuel Beckett Today/Aujourd'hui     Full-text available via subscription   (Followers: 2)
Science and Technology of Nuclear Installations     Open Access   (Followers: 1)
Science China : Physics, Mechanics & Astronomy     Full-text available via subscription   (Followers: 1)
Science Foundation in China     Full-text available via subscription   (Followers: 2)
Scientific Journal of Physical Science     Open Access  
Scientific Reports     Open Access   (Followers: 11)
Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of     Hybrid Journal   (Followers: 16)
Sensor Letters     Full-text available via subscription   (Followers: 1)
Sensors and Actuators A: Physical     Hybrid Journal   (Followers: 31)
Services Computing, IEEE Transactions on     Hybrid Journal   (Followers: 3)
Shock and Vibration     Hybrid Journal   (Followers: 7)
Shock Waves     Hybrid Journal   (Followers: 4)
Small     Hybrid Journal   (Followers: 8)
Software Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 20)
Solid State Physics     Full-text available via subscription  
Solid-State Circuits Magazine, IEEE     Hybrid Journal   (Followers: 1)
South African Journal for Research in Sport, Physical Education and Recreation     Full-text available via subscription   (Followers: 4)
Space Research Journal     Open Access   (Followers: 2)
Space Weather     Full-text available via subscription   (Followers: 3)
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy     Hybrid Journal   (Followers: 8)

  First | 1 2 3 4 5 6 | Last

Journal Cover Physics and Chemistry of the Earth, Parts A/B/C
   [5 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1474-7065
     Published by Elsevier Homepage  [2573 journals]   [SJR: 0.423]   [H-I: 36]
  • Sustainability of Donor-Funded Rural Water Supply and Sanitation Projects
           in Mbire District, Zimbabwe
    • Abstract: Publication date: Available online 31 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Johnson Kwangware , Aloyce Mayo , Zvikomborero Hoko
      The sustainability of donor-funded rural water supply and sanitation projects was assessed in Mbire district, Zimbabwe in terms of level of community participation, quality of implementation and reliability of the systems. The study was carried out through questionnaires, focus group discussions, interviews and field observations. The results show that the quality of implementation of the projects was deemed to be good and participation of the communities in project ideas initiation and choice of technology was found to be very low. Reliability of the systems was found to be very high with 97% of the boreholes in all the three wards studied being functional. Financial management mechanisms were very poor because water consumers were not willing to pay for operation and maintenance. The projects were classified as potentially sustainable with sustainability index between 5.00 and 6.67. Poor financial management mechanisms for effective borehole maintenance, poor quality of construction and lack of community participation in project planning were found to be potential threats to the sustainability of the projects. Future projects should establish the need for the service and should thus be demand driven to ensure effective participation of the water consumers and enhance project’s potential for sustainability.


      PubDate: 2014-11-21T04:51:15Z
       
  • An assessment of effectiveness of the Lunyangwa River catchment
           co-management model in Mzuzu City, Northern Malawi
    • Abstract: Publication date: Available online 31 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Elijah M.M. Wanda , Lewis C. Gulula , James Kushe
      An assessment of the effectiveness of Lunyangwa River catchment co-management model in Mzuzu City, Northern Malawi has been carried out. This study was aimed at assessing the effectiveness of the approach in boosting Northern Region Water Board’s (NRWB) water production capacities and simultaneously addressing water quality challenges facing NRWB. A questionnaire survey was carried out to elicit information pertaining to formation and implementation of the approach. The results of the survey were analysed to assess the strengths and weaknesses of management policies and programs, from the perspective of catchment co-management. Literature was reviewed to form a conceptual framework for the investigation of the effectiveness of catchment co-management. Direct observations were also done to collect data on the physical attributes of the catchment area. Water samples were collected from 54 sites using standard sampling procedures and analysed for pH, EC, TDS, turbidity and faecal coliform count using standard methods. The study revealed that there was a quest to empower and improve the capacity of grass-root level community members to participate effectively in co-management decision making. However, it was observed that regardless of season, the population-poverty-environment nexus is negatively affecting the implementation of the co-management approach. The nexus has led to degradation of trees for community livelihoods, which results in increased levels of silt loads that increases turbidity in Lunyangwa River catchment and Gulliver dam (turbidity range=130–225 NTU). The high turbidity levels led to increase in the amount of coagulant dose used to treat raw water. Raw water of turbidity levels higher than 200 NTU used a coagulant dose of about 7.5mg/ℓ, which is higher than a 0.5mg/ℓ coagulant dose that was being used before high turbidity problems. In addition, inadequate sanitary facilities for human settlements, particularly those established in upper Lunyangwa River catchment area also contributed to the deterioration of the microbial quality of water in Lunyangwa River catchment and dam (faecal coliform>1000counts/mℓ). The water from Lunyangwa River could be classified as freshwater (TDS<1000mg/ℓ) which registered a uniformly fair water quality rating (WQI range=33.12–35.03%). The water levels in Gulliver dam were also observed to have been going down. A collaborative and systems approach is suggested for sustainable management of freshwater resources in Lunyangwa River catchment area since co-management is a novel approach and might require more effort to be understood by grass-root level community and stakeholders.


      PubDate: 2014-11-21T04:51:15Z
       
  • Wastewater treatment for reuse in urban agriculture; the case of Moshi
           Municipality, Tanzania
    • Abstract: Publication date: Available online 1 November 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Jacob Kihila , Kelvin M. Mtei , Karoli N. Njau
      Urban agriculture is practiced by dwellers as an adaptive response to improve their food security, household income, create informal employment and diversify their livelihood through sales of surplus produce or savings. People in many cities, who practice urban agriculture, are in most cases unemployed and poor and are faced with water shortages to irrigate their crops. But treated wastewater can offer both water and nutrients needed for crop growth partly covering the water shortage already experienced. Therefore in this case, wastewater reuse becomes one of the important alternative ways to provide water for irrigation. The objective of this study was to monitor the effluent quality of the waste stabilization pond (WSP) and a combined WSP-constructed wetland (WSP-CW) treatment systems, assess its suitability for irrigation purposes and understand the public perception on the use of the treated effluent for agricultural production. This paper brings out the experience of the Moshi urban water authority in wastewater treatment and reuse for irrigation purposes. It looks on the quality of effluent from the two systems under their current operational regime and deduces the public health and socio economic implications. The results indicates the recorded TDS mean values of 587mg/L and 627mg/L, Nitrate–Nitrogen values of 9.19mg/L and 2.35mg/L, Fecal Coliform values of 1000 counts per 100mL and 4626 counts per 100mL, COD values of 159mgO2/L and 149mgO2/L for the WSP and WSP-CW effluents respectively. From the findings it has been shown that the treated effluent is suitable for restricted irrigation. It has also been shown that when improperly practiced, the use of the effluent is associated with public health risk to the workers who handle it, but despite this fact there is still some positive social economic implications. The community members who practice irrigated agriculture using the effluent as irrigation water have positive attitude on its use. The findings from this case study, is considered as an important learning in establishing an optimal wastewater treatment configuration to render suitable effluent for irrigation purposes.


      PubDate: 2014-11-21T04:51:15Z
       
  • An experiment on temperature variations in sandstone during biaxial
           loading
    • Abstract: Publication date: Available online 1 November 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Shunyun Chen , Peixun Liu , Yanshuang Guo , Liqiang Liu , Jin Ma
      The temperature response to stress–strain variations in rock is useful in developing an understanding of the thermodynamic property of crust. In this study, the temperature of sandstone during loading was investigated using laboratory biaxial testing. By changing the loading patterns, the deformation of a specimen was controlled to produce two distinct modes of strain: volume strain only and shear strain only. These strain modes were produced separately such that the temperature variation associated with the different deformation modes could be analysed. Experimental results indicate that temperature, as a scalar quantity, is notably sensitive to rock deformation. In the case of the volume strain, the temperature variation is positively correlated with the variation in the bulk stress. The temperature rises with the increase in hydrostatic pressure, and vice versa. In the case of the shear strain, experimental results repeatedly show two characteristics: firstly, there appears obvious increase in temperature in the area of pure shear strain, which is most likely related to local plastic deformation; secondly, the temperature drops in the area of tension during loading, whereas the temperature rises within the area of compression. This is to say, the state of crustal stress–strain should be obtained through the measurement of rock temperature.


      PubDate: 2014-11-21T04:51:15Z
       
  • Ionospheric activity and possible connection with seismicity: Contribution
           from the analysis of long time series of GNSS signals
    • Abstract: Publication date: Available online 1 November 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Francesco Mancini , Angelo Galeandro , Michaela De Giglio , Maurizio Barbarella
      The modifications of some atmospheric physical properties prior to a high magnitude earthquake were debated in the frame of the Lithosphere Atmosphere Ionosphere Coupling (LAIC) model. In this work, among the variety of involved phenomena, the ionisation of air at the ionospheric levels triggered by the leaking of gases from the Earth’s crust was investigated through the analysis of GNSS (Global Navigation Satellite System) signals. In particular, the authors analysed a 5year (2008–2012) long series of GNSS based ionospheric TEC to produce maps over an area surrounding the epicentre of the L’Aquila (Italy, M w =6.3) earthquake of April 6th, 2009. The series was used to detect and quantify amplitude and duration of episodes of ionospheric disturbances by a statistical approach and to discriminate local and global effects on the ionosphere comparing these series with TEC values provided by the analysis of GNSS data from international permanent trackers distributed over a wider region. The study found that during this time interval only three statistically meaningful episodes of ionospheric disturbances were observed. One of them, occurring during the night of 16th of March 2009, anticipated the main shock by 3weeks and could be connected with the strong earthquake of 6th of April. The other two significant episodes were detected within periods that were not close to the main seismic events and are more likely due to various and global reasons.


      PubDate: 2014-11-21T04:51:15Z
       
  • Accessing the Regional Spatio-Temporal Pattern of Water Stress: A Case
           Study in Zhangye City of China
    • Abstract: Publication date: Available online 6 November 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Qian Zhang , Bing Liu , Weige Zhang , Gui Jin , Zhaohua Li
      Water scarcity and stress have attracted increasing attention as water has become increasingly regarded as one of the most critical resources in the world’s sustainable development. The water poverty index (WPI), an interdisciplinary but straightforward measure that considers water availability from both a bio-geophysical perspective and the socio-economic perspective of people’s capacity to access water, has been successfully applied at national, regional, and local levels around the world. However, the general assessment of water stress at a macro level over only a snapshot limits the understanding of the geographic differences in and dynamics of water stress; this will, in turn, mislead decision-makers and may result in improper water strategies being implemented. In addition, to date, the typologies and trajectories of water stress have been underexplored. To fill in this knowledge gap, we examine the spatio-temporal patterns, trajectories, and typologies of water stress using adapted WPI for six counties in Zhangye City, which lies within an arid region of China, in order to provide policy priorities for each county. The results of our assessment indicate that water stress has become more severe over time (2005–2011) in most of the counties in Zhangye City. The results also show a distinct spatial variation in water scarcity and stress. Specifically, the results for Shandan County reflect its progressive policies on water access and management, and this county is regarded as engaging in good water governance. In contrast, Ganzhou District has faced more severe water pressure and is regarded as practicing poor water governance. Typology results show that each county faces its own particular challenges and opportunities in the context of water scarcity and stress. In addition, the trajectory map reveals that none of the counties has shown substantial improvement in both water access and management, a finding that should draw policy-makers’ close attention.


      PubDate: 2014-11-21T04:51:15Z
       
  • Discrimination of crop types with TerraSAR-X-derived information
    • Abstract: Publication date: Available online 13 November 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Rei Sonobe , Hiroshi Tani , Xiufeng Wang , Nobuyuki Kobayashi , Hideki Shimamura
      Although classification maps are required for management and for the estimation of agricultural disaster compensation, those techniques have yet to be established. This paper describes the comparison of three different classification algorithms for mapping crops in Hokkaido, Japan, using TerraSAR-X (including TanDEM-X) dual-polarimetric data. In the study area, beans, beets, grasslands, maize, potatoes and winter wheat were cultivated. In this study, classification using TerraSAR-X-derived information was performed. Coherence values, polarimetric parameters and gamma nought values were also obtained and evaluated regarding their usefulness in crop classification. Accurate classification may be possible with currently existing supervised learning models. A comparison between the classification and regression tree (CART), support vector machine (SVM) and random forests (RF) algorithms was performed. Even though J-M distances were lower than 1.0 on all TerraSAR-X acquisition days, good results were achieved (e.g., separability between winter wheat and grass) due to the characteristics of the machine learning algorithm. It was found that SVM performed best, achieving an overall accuracy of 95.0% based on the polarimetric parameters and gamma nought values for HH and VV polarizations. The misclassified fields were less than 100 a in area and 79.5-96.3% were less than 200 a with the exception of grassland. When some feature such as a road or windbreak forest is present in the TerraSAR-X data, the ratio of its extent to that of the field is relatively higher for the smaller fields, which leads to misclassifications.


      PubDate: 2014-11-21T04:51:15Z
       
  • Baseflow prediction in a data-scarce catchment with Inselberg topography,
           Central Mozambique
    • Abstract: Publication date: Available online 13 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): H. Weemstra , A.L. Oord , F.S. de Boer , P.W. Beekman
      This study aimed to improve the understanding of hydrological processes in a humid (sub)tropical area in Africa with Inselberg topography. Additionally, the study intended to develop an approach for selective discharge data acquisition to determine water availability for smallholder irrigation in similar data-scarce catchments. During the December 2012–August 2013 field campaign meteorological and river stage data were collected at the Messica catchment in Central Mozambique. The 220km2 catchment has an estimated 1000ha of irrigated land, developed by smallholder farmers. Baseflow in the perennial tributary streams on the slopes of a meta-sedimentary Inselberg is the source of irrigation water. The baseflow recession curve of one of these tributaries is analysed and the water balance of an average year was determined. Precipitation, potential evapotranspiration, actual evapotranspiration and discharge were estimated to be 1224, 1462, 949 and 266mm/year respectively. Differential gauging showed that the perennial tributaries gain water; the groundwater contribution increased with approximately 50% over two and a half month relative to the downstream discharge from March to May. In the downstream parts the groundwater contribution per metre stream length is between 30% and 100% higher compared to the upstream parts for two of the tributaries. Nevertheless, due to natural streambed infiltration and irrigation canals, discharge varies over the length of these tributaries. A rainfall–runoff model (HBV) was calibrated using the field data to examine the relation between precipitation characteristics and discharge at the start of the dry season. For precipitation scenarios with low and high intensity precipitation, discharges from June onwards were approximately similar in size according to the calibrated model. This suggest that discharge at the start of the dry season is mainly determined by total precipitation and the timing of precipitation (i.e. early or late in the wet season), not by individual rainfall events or rainfall intensity. It is concluded that the use of selective discharge measurements and low frequency precipitation measurements can effectively be used for water availability assessments in Inselberg catchments. Further research should be conducted to verify the validity of the used techniques in other humid sub-tropical Inselberg areas.


      PubDate: 2014-11-21T04:51:15Z
       
  • A fingerprinting method for the identification of uranium sources in
           alluvial aquifers: An example from the Khan and Swakop Rivers, Namibia
    • Abstract: Publication date: Available online 13 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): J.T. Hamutoko , B.S. Mapani , R. Ellmies , A. Bittner , C. Kuells
      A fingerprinting method for identifying sources of uranium in shallow groundwater alluvial aquifers of the Khan and Swakop Rivers was established using 234U/238U ratios and 235U/238U ratios in the areas that drain the Rossing Uranium mine and the Langer Heinrich Uranium mine, in Namibia. In most groundwater aquifers that drain basement granitoids enriched in uranium the contribution of the total uranium in the shallow alluvial aquifers may be significant. Another source of uranium in shallow alluvial aquifers maybe from anthropogenic sources associated with mining activities as is the case in our study area. The distribution of radionuclides in water depend on various factors that influence their solubility and mobility and control their concentration in water such as pH, Eh, O2 and availability of ligands. The study identified a methodology that can fingerprint the two sources i.e., a natural source where 234U/238U ratios are above unity and a second one where this ratio is below unity implying that the source is anthropogenic. In the study area, 234U/238U activity ratio is above unity (1.3–1.7) and 235U/238U is 0.045±0.015 that both identify a natural source for all elevated uranium and other radionuclides in groundwater of the study area. The uranium values in groundwater exceed the WHO guideline value of 15μg/l and it increases in the lowest part of Swakop River; but there is no gradual or systematic change in uranium concentration thus indicating that concentration is related to local factors such as the geology and lithology of the aquifer material, Eh and pH for each borehole. The 238U decay series exhibits disequilibrium due to different fractionation processes that include decaying of radioactive elements and alpha recoiling.


      PubDate: 2014-11-21T04:51:15Z
       
  • Application of rice hull ash for turbidity removal from water
    • Abstract: Publication date: Available online 13 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): F.V. Adams , A.F. Mulaba-Bafubiandi
      Rice hull ash containing amorphous silica was produced from locally available rice hulls (unparboiled and parboiled), using a muffle furnace at 800°C. The ashes obtained from the two rice hulls samples were washed with distilled water and characterised using scanning electron microscope with electron dispersive spectroscopy (SEM/EDS) and BET analysis. The laboratory filtration experiments were carried out in order to study the performance of the rice hull ash in removing turbidity from water. This was done using water with an initial turbidity, pH and total dissolved solids (TDS) of 88 NTU, 6.63 and 127ppm respectively. The parboiled rice hull ash (PRHA) sample showed higher surface area, but lower pore volume and pore sizes compared to the unparboiled rice hull ash (URHA) sample. Also, PRHA contained higher silica content and sum of the other elemental compositions than the URHA sample. All the ashes used showed controlled pH to the acceptable level (7.00–8.50). A good percentage of turbidity removal up to 96% with increasing TDS (816ppm) was reached.
      Graphical abstract image

      PubDate: 2014-11-21T04:51:15Z
       
  • A global and regional perspective of rainwater harvesting in sub-Saharan
           Africa’s rainfed farming systems
    • Abstract: Publication date: Available online 18 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Timothy Karpouzoglou , Jennie Barron
      In semi-arid and sub-humid sub-Saharan Africa highly variable rainfall, frequent droughts and low water productivity are consistently undermining food security. Rainwater harvesting technologies (RWHTs) help utilise water more productively whilst raising yield levels. In this article it is argued that realising the potential of RWHTs for resilience building and climate adaptation requires a better understanding of global and regional processes influencing RWHTs adoption combined with pre-existing analysis at the household scale. On the basis of a systematic literature review, processes of influence in the diffusion and uptake of RWHTs are identified. These relate to shifting ideology associated with food production systems; the scope of investments in agriculture science and technology; emergent actors shaping development assistance; and patterns of farmer mobility. Drawing insights from theory on transformations for sustainability and development, this article adds to the understanding of connectedness between farm-level adoption of RWHTs, and regional to global level actors, institutions and processes.
      Graphical abstract image

      PubDate: 2014-11-21T04:51:15Z
       
  • Removal mechanisms of nitrogen in waste stabilization ponds
    • Abstract: Publication date: Available online 23 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Aloyce W. Mayo , Muslim Abbas
      The aim of this research work was to determine the major nitrogen transformation and removal mechanisms in primary and maturation ponds. To accomplished this objective, nitrogen mass balance in waste stabilization pond system was determined using a dynamic mathematical model in order to elucidate the biological nitrogen transformation mechanisms that are effective for removal of nitrogen in this pond system. Results show that nitrogen removal efficiency in a primary facultative pond unit was 13.2%, which was largely due to net loss of organic nitrogen to sediments (9.76%) and denitrification (3.42%). On the other hand, maturation pond removed 15.2% of nitrogen received in the influent with denitrification (13.55%) being the major pathway for nitrogen removal. Ammonia volatilization was not a predominant mechanism for nitrogen removal in both primary facultative and maturation ponds. The major nitrogen transformation routes were mineralization and ammonia uptake in the primary facultative pond, but ammonia uptake by microorganisms was a predominant nitrogen transformation mechanism in maturation pond.


      PubDate: 2014-11-21T04:51:15Z
       
  • Nitrification–denitrification in a coupled high rate – Water
           hyacinth ponds
    • Abstract: Publication date: Available online 24 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): A.W. Mayo , E.E. Hanai , O. Kibazohi
      Nitrogen transformation was studied in a coupled high rate and water hyacinth (Eichhornia crassipes) ponds at the University of Dar es Salaam. Samples of wastewater were collected and examined for water quality parameters which were used as input parameters in a mathematical model. A conceptual model was then developed to model various processes in the system using STELLA 6.0.1 software. The studGupta and Sujathay demonstrated the dominant nitrogen transformation process in high rate pond (HRP) was nitrification, but denitrification dominated in water hyacinth pond (WHP). In a HRP denitrification and volatilization accounted for 69.1% and 23.8% of removed nitrogen, respectively. On the other hand, denitrification and net sedimentation were the major nitrogen removal mechanisms in WHP accounting for 81.9% and 13.1% of removed nitrogen, respectively. Model results indicated that 1.22gN/m2 day and 0.37gN/m2 day of nitrogen was removed in presence and absence of biofilm, respectively. The decrease in nitrogen removal in absence of biofilm, demonstrates the importance of biofilm attached onto plants. It was concluded that incorporation of HRP improved denitrification in WHP because it enhanced formation of more nitrates in HRP in order to promote denitrification in wetland unit due to anoxic conditions.


      PubDate: 2014-11-21T04:51:15Z
       
  • Identifying the potential for irrigation development in Mozambique:
           Capitalizing on the drivers behind farmer-led irrigation expansion
    • Abstract: Publication date: Available online 30 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): W. Beekman , G.J. Veldwisch , A. Bolding
      Smallholder irrigation in Central Mozambique predominantly takes place in an informal setting. This renders these smallholders and their activities invisible for policy purposes. Identification efforts of smallholder irrigation as well as the potential for new irrigation development are often the basis for policy setting. But the potential is often approached technocratically: the technical availability of water and land with the assumption that smallholder irrigation is not happening and should be developed. Although more and more effort is done to include social economical aspects into the identification as well, it remains a GIS exercise, based on incomplete data using large pixel sizes, analyzing countries or continents as a whole. This study describes and presents the methodology and the results of an irrigation potential identification exercise carried out in two studies in Central Mozambique. Apart from describing the identification methods used, this study highlights the extent of farmer-led irrigation development, its drivers and the potential for farmer-led smallholder irrigation development. This study demonstrates the prolific nature of smallholder irrigation, arguing for the recognition that smallholder farmers are already developing irrigation and that this should lead to changing the focus of identification efforts towards the drivers behind farmer-led irrigation development. Using these context-specific drivers to define the potential for new irrigation development should result in a better response in policy to both the technical and socio-economical potential of smallholder irrigation development.


      PubDate: 2014-11-21T04:51:15Z
       
  • Preparation of SPE hybrid mesoporous silica sorbents for the analysis and
           removal of organic pollutants in water
    • Abstract: Publication date: Available online 12 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): D.T. Maiga , T.A.M. Msagati , K.F. Kilulya , B.B. Mamba
      Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants that threaten the health of humans and the environment. PAHs are found naturally in the environment but they can also be man-made. PAHs are produced when products like coal, oil, gas, and garbage are burned in an incomplete burning process. PAH’s can be introduced into water bodies in several ways including industrial, domestic and commercial effluents, sewage, agricultural runoff and wastes. Monitoring of PAH’s in water is of great importance because of their mutagenic and carcinogenic properties. The aim of this study was to develop the hybrid mesoporous silica sorbents for the analysis and removal of organic pollutants (OPs) in water especially PAH’s. The determination of PAHs was performed using gas chromatography coupled to time of flight mass spectrometry (GCxGC-TOFMS). The hybrid materials were successfully synthesized using silica gel as a source of silica followed by modification with organic compounds. However the performance of the materials was evaluated using GCxGC-TOFMS for the determination of recovery PAH’s concentrations. At optimum conditions sorbent materials were able to remove 95.9±12.21% of the PAHs in spiked water samples at a laboratory scale.


      PubDate: 2014-10-13T00:40:06Z
       
  • Synthesis and application of reduced graphene oxide and molecularly
           imprinted polymers composite in a chemo-sensor for trichloroacetic acid
           detection in aqueous solution
    • Abstract: Publication date: Available online 8 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Rose W. Kibechu , Messai A. Mamo , Titus A.M. Msagati , S. Sampath , Bhekie B. Mamba
      This work presents the fabrication of a simple, cheap and fast thin film chemo sensor for detection of trichloroacetic acid (TCAA) in aqueous solutions. Reduced graphene oxide (RGO) based molecular imprinted polymers (MIP) chemo-sensor has been developed. The recognition of TCAA was achieved by imprinted polymers synthesized by copolymerization of 4-vinylpyridine (4-VP) and a crosslinking monomer ethylene glycol dimethacrylate (EDGMA) in acetonitrile using bulk polymerization method. Adsorption studies to determine the rebinding properties of the MIP with the template were conducted using ultra violet visible spectrophotometry (UV-Vis). The imprinted sensor exhibited high recognition ability and affinity for HAA in comparison with the non-imprinted one which was employed as a control, this indicated that the MIP could selectively rebind with TCAA. Reduced graphene oxide (RGO) was used to improve conductivity of the sensor; RGO was obtained from reduction of graphene oxide (GO) synthesized using modified Stauddmer and Hummers method. Polysulphone was used in solution blending of MIP and RGO to form a hybrid which was deposited between two gold plated electrodes by spin coating to form a thin film. The performance of the imprinted sensor was studied using a homemade circuit. The results demonstrate that the sensor based on TCAA-imprinted polymer is fast, cheap and sensitive screening method of TCAA in drinking water.


      PubDate: 2014-10-12T00:34:18Z
       
  • Analysis of Water Stable Isotopes fingerprinting to inform conservation
           management : Lake Urema Wetland System, Mozambique
    • Abstract: Publication date: Available online 2 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Franziska Steinbruch , Stephan M. Weise
      The present study focusses on the analysis of water stable isotopes to contribute to understanding the hydrology of the Lake Urema wetland system in central Mozambique towards conservation management. Lake Urema Wetland is located in the Gorongosa National Park at the southernmost extent of the East African Rift System and is situated entirely within the Urema catchment. Of particular concern to the park’s management is the understanding of hydrological processes as these may trigger transformations of ecosystems, habitat losses and wildlife migrations. Concerns over the Lake Urema wetland’s drying up and the trapping of sediments in the floodplain have been raised for some time by conservationists. Water samples were collected for stable water isotope analyses during the wet and the dry seasons for the period 2006 to 2010 from springs, boreholes, rivers, and Lake Urema. In addition monthly composite precipitation was collected at two rain gauges. The results show that Lake Urema is maintained throughout the dry season merely from water generated during the wet season. It receives water from wet season precipitation and the runoff generated from this precipitation. The water source areas of the lake are the Gorongosa Mountain and the Barue Basement geomorphological units. Consequently, the source of the sediments which have been trapped into the lake and the floodplain has to be identified in these two catchment areas and urgent action is required to rescue the lake. This water body constitutes a groundwater buffer system which supports a unique wetland landscape. The annual inundations’ processes leading to the recharge-drainage cycle in the floodplain are most sensitive to the deposition of sediments, changing hydraulic gradients, and reducing wet season inflows and increasing drainage rates.


      PubDate: 2014-10-02T23:57:57Z
       
  • The Viability Assessment of Microcystis aeruginosa cells after
           co-culturing with Bacillus mycoides B16 Using Flow Cytometry
    • Abstract: Publication date: Available online 2 October 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): JR Gumbo , TE Cloete , GJJ van Zyl , JEM Sommerville
      Microcystis aeruginosa is the dominate cyanobacteria in freshwater bodies causing proliferation of toxic harmful algal blooms (HABs), worldwide. Thus a biological control method based on predatory bacteria is an alternative environmental solution to the control of these HABs, A Flow cytometric technique was used to assess the viability of Microcystis spp cells after deliberate co-culturing with a predatory bacterium, Bacillus mycoides B16. Under static conditions, B. mycoides had a lytic effect on Microcystis cells that resulted in a significant (p = 0.0000) population decline of 97% in six days. In contrast under turbulent conditions, B. mycoides had a lytic effect on Microcystis spp cells resulting in a significant (df = 5; t = -7.21; p= 0.0003) population decrease of 85% in the same time period. The Levene test also showed a significant (p = 0.0003) decrease in Microcystis cell numbers, which also coincided with a significant (t = 11.31; p = 0.0001) increase in B. mycoides cell numbers. This suggested that B. mycoides, a heterotroph, was utilizing the Microcystis as a source of nutrition. The effect of agitation may have contributed to the delay in cell lysis as it disturbed the physical contact between the predator and prey. The control samples showed a significant (df = 5; t = + 6.86; p = 0.0010) increase in Microcystis spp cell numbers. B. mycoides was able to lyse Microcystis spp cells under these conditions and may thus be considered as a potential biological control agent for the management of Microcystis spp harmful algal blooms.


      PubDate: 2014-10-02T23:57:57Z
       
  • Streamflow variation due to glacier melting and climate change in upstream
           Heihe River Basin, Northwest China
    • Abstract: Publication date: Available online 18 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Feng Wu , Jinyan Zhan , Zhan Wang , Qian Zhang
      Streamflow simulation is often challenging in mountainous watersheds because of incomplete hydrological models, irregular topography, immeasurable snowpack or glacier, and low data resolution. In this study, a semi-distributed conceptual hydrological model (SWAT-Soil Water Assessment Tool) coupled with a glacier melting algorithm was applied to investigate the sensitivity of streamflow to climatic and glacial changes in the upstream Heihe River Basin. The glacier mass balance was calculated at daily time-step using a distributed temperature-index melting and accumulation algorithm embedded in the SWAT model. Specifically, the model was calibrated and validated using daily streamflow data measured at Yingluoxia Hydrological Station and decadal ice volume changes derived from survey maps and remote sensing images between 1960 and 2010. This study highlights the effects of glacier melting on streamflow and their future changes in the mountainous watersheds. We simulate the contribution of glacier melting to streamflow change under different scenarios of climate changes in terms of temperature and precipitation dynamics. The rising temperature positively contributed to streamflow due to the increase of snowmelt and glacier melting. The rising precipitation directly contributes to streamflow and it contributed more to streamflow than the rising temperature. The results show that glacial meltwater has contributed about 3.25 billion m3 to streamflow during 1960-2010. However, the depth of runoff within the watershed increased by about 2.3 mm due to the release of water from glacial storage to supply the intensified evapotranspiration and infiltration. The simulation results indicate that the glacier made about 8.9% contribution to streamflow in 2010. The research approach used in this study is feasible to estimate the glacial contribution to streamflow in other similar mountainous watersheds elsewhere.


      PubDate: 2014-09-21T23:07:48Z
       
  • Streamflow forecasting for operational water management in the Incomati
           River Basin, Southern Africa
    • Abstract: Publication date: Available online 18 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): R.K.M. Sunday , I. Masih , M. Werner , P. van der Zaag
      If the future availability of water is uncertain to water managers, dam operators and water users, then an effective allocation among competing uses can be difficult. The difficulties can partly be alleviated by including streamflow forecasting as a tool for informed decision making. The Incomati basin in Southern Africa frequently experiences water shortages, and here streamflow forecasting can contribute to an improved water management. This paper explores the skill of streamflow forecasting and its usefulness in decision making in the Incomati basin. The study applies correlation and regression methods to forecast streamflow, and standard verification scores to evaluate the skill of the forecasts. Suitable statistical forecasting techniques were analysed and tested. The data used for forecasting include Sea Surface Temperature (SST), El Niño Southern Oscillation (ENSO), rainfall and streamflow. Results show that there is some scope for streamflow forecasting that can support water management decision making in the basin. The rainfall and streamflow of the previous months and/or season can be used to predict the streamflow in the next month and/or season with reasonable to good results. Results obtained during low flow periods (May-September) were found to be better than those obtained for the high flow periods (October-April). However, inclusion of ENSO and/or SST as an explanatory variable enhanced forecast skill, particularly during high flow periods. Forecasts were conducted for streamflow being in the below normal, above normal or normal terciles, with the forecasts for the extremes found to have better skill than forecast for the sreamflow being in the normal tercile. Forecasts for low flows demonstrated the best skills, with these being of most use to the allocation of the scarce water resources.


      PubDate: 2014-09-21T23:07:48Z
       
  • Quality of Drinking Water and Cholera prevalence in Ndirande Township,
           City of Blantyre, Malawi
    • Abstract: Publication date: Available online 18 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): John F. Kamanula , Omega J. Zambasa , Wellington R.L. Masamba
      Scarcity of safe drinking water is a big problem in Ndirande Township, City of Blantyre. Consequently, residents use unsafe sources of drinking water other than the potable water provided by Blantyre Water Board (BWB). This study was conducted from November 2007 to April 2008 to assess the quality of drinking water and cholera prevalence in Makata, Chinseu, Golio, Safalao and Newlines, in Ndirande Township. A survey using semi-structured questionnaire was conducted to gather information on the sources of drinking water and prevalence of cholera in the Township. Data on cholera cases and number of deaths in Ndirande Township which occurred between November 2007 and April 2008 was sourced from Ndirande Health Centre in Blantyre City. Water samples were collected from unprotected shallow wells, boreholes and taps and analysed for Escherichia coli, metals and non-metals. Data was analysed for pH, turbidity, total dissolved solids, sulphate, phosphate, nitrate, hardness, chloride, chromium, lead, cadmium, iron, sodium and potassium. Results showed that 85% of 150 respondents drink water from shallow wells, rain water and boreholes in addition to treated water provided by BWB. Only 15% of the respondents get water from BWB without supplementation from the other sources. Forty percent of the respondents indicated that they did not treat their water before consumption. Cholera cases (176), were prevalent throughout the study period with highest number (85) recorded in December 2007. Two deaths were recorded in November 2007. Over 80% of water samples from shall wells and boreholes contained E. coli. Concentrations of total dissolved solids, sulphates, sodium, potassium, lead, cadmium and chromium in all water samples were within the acceptable limits by World Health Organisation (WHO) and Malawi Bureau of Standards (MBS). Based on the results of this study, water from boreholes and shallow wells was heavily polluted with faecal matter, and therefore, not suitable for human consumption. Use of water disinfectants to treat well and borehole waters in the study area should be intensified. Furthermore, research on use of solar radiation to disinfect untreated water and use of plant materials, for example, Moringa oleifera seed kernel to clarify water should be investigated.


      PubDate: 2014-09-21T23:07:48Z
       
  • Efficiency of a constructed wetland in removing microbial contaminants
           from pre-treated municipal wastewater
    • Abstract: Publication date: Available online 17 September 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): H.J. Kipasika , J. Buza , Beatus Lyimo , W.A. Miller , K.N. Njau
      In most capital towns, urban wastewater discharging into environment is highly enriched in a wide range of microbial contaminants, thus threatening people’s health and the quality of the receiving basin water and other water for reuse. This study focused on evaluating the efficiency of the removal of faecal coliform indicator bacteria and salmonella spp. by Moshi Municipal urban wastewater treatment system composed of a constructed wetland (CW) system and waste stabilization ponds (WSP) operating in parallel. The CW system is a sub-surface flow type designed in the year 2002 for treating effluent from the second maturation pond of the treatment system. The study considered faecal coliform data taken in 2009 and 2012 and both salmonella and faecal coliform data taken in 2013 and 2014. Data generated monthly in 2009 and 2012 showed high variations in faecal coliform removal with a mean efficiency of less than 60 percent. The levels of faecal coliform from both the CW and the last maturation pond were below the acceptable limit. However, a similar investigation done in 2013 and 2014 on the removal of specific pathogen – salmonella spp. showed that the CW is discharging significantly higher amount of salmonella spp. than the maturation system. The treated wastewater is currently used for paddy farming, in this way exposing people to health risks. The results highlight the necessity for improving the system monitoring and also the management taking into consideration the end users of effluent water.


      PubDate: 2014-09-17T22:53:21Z
       
  • Benchmarking land use change impacts on direct runoff in ungauged urban
           watersheds
    • Abstract: Publication date: Available online 14 August 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Hasan Ozdemir , Emre Elbaşı
      This paper describes the results of benchmark testing of land use change impact on direct runoff using Soil Conservation Service –Curve Number (SCS-CN) model in two ungauged neighbouring urban watersheds (Çınar and Kadıyakuplu) in Istanbul, Turkey. To examine this impact, the model was applied to daily rainfall data using three different dated (1982, 1996 and 2012) hydrological soil groups and land use of the two ungauged urban watersheds. Finally, the impact of land use change and model performance were evaluated with the rainfall-runoff regression, the coefficient of determination and the NSE test using benchmark runoff data based on 1982 land use conditions. The results of the analysis indicate that the changing of land use types from natural surfaces to impervious surfaces has a significant impact on surface runoff. Additionally, remarkable spatial variations of the land use changes and their impact on the runoff in 1996 and 2012 were more detected in the Çınar watershed compared with the Kadıyakuplu watershed. The planning decision on land use of the watersheds, has vital role in these differences. The results of this research also reveal that change to intensive land use in urban watersheds has a significantly larger impact on runoff generation than those rainfall.


      PubDate: 2014-08-16T20:15:43Z
       
  • Preconcentration and spectrophotometric determination of polyDADMAC in
           treated water by insitu co-precipitation with naphthalene
    • Abstract: Publication date: Available online 27 July 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Isaac W. Mwangi , J. Catherine Ngila , Patrick Ndungu , T. Msagati
      Polydiallyldimethylammonium chloride (polyDADMAC) is a water-soluble cationic polyelectrolyte used as a flocculant in water treatment works. Unreacted traces in water react with chlorine to produce a carcinogenic compound during the disinfectation process. This study reports on a preconcentration procedure and spectrophotometric determination of polyDADMAC at trace levels in treated water by insitu co-precipitation with naphthalene with a view to come up with an analytical tool that will be used by water works to routinely monitor the polycation in an effort to supply safe water to consumers. Preconcentration of polyDADMAC polyelectrolyte in water at trace levels was achieved by co-precipitating the polyelectrolyte with naphthalene. This resulted in the formation of a water insoluble adsorbent with a high affinity for azo dyes. The formation of this material was based on multilayer assembly of organic polyelectrolyte systems resulting to multilayers through a layer-by-layer self-assembly process. The co-precipitate was formed by mixing aqueous solutions containing varying concentrations of polyDADMAC with different volumes of solutions containing 0.75 g of naphthalene dissolved in acetone. The resulting respective precipitates were packed in different glass columns and a solution of the dye was eluted through each column. The contents of each column were then dissolved in 10 mL of dimethylformamide (DMF) and the absorbance readings of the resulting solutions recorded. The wavelength of maximum absorption was found to be 540 nm at pH 12.0. A linear calibration for polyDADMAC solutions was obtained with a correlation coefficient of 0.976. The detection limit was found to be 1.90 x 10-4 μg mL-1 and the method was applied to determine the concentration of polyDADMAC residue in treated water.


      PubDate: 2014-07-28T18:58:27Z
       
  • Mechanisms and modelling of waste-cement and cement-host rock interactions
    • Abstract: Publication date: 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 70–71
      Author(s): Diederik Jacques , Barbara Lothenbach , Erich Wieland



      PubDate: 2014-06-18T15:59:57Z
       
  • Implementing water science research to benefit all
    • Abstract: Publication date: 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volumes 67–69
      Author(s): Hodson Makurira , Benjamin Mapani , Dominic Mazvimavi , Marloes Mul , Barbara Tapela , Victor Wepener



      PubDate: 2014-06-18T15:59:57Z
       
  • Radial diffusion of radiocaesium and radioiodide through cementitious
           backfill
    • Abstract: Publication date: Available online 21 April 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M. Felipe-Sotelo , J. Hinchliff , D. Drury , N. Evans , S. Williams , D. Read
      The function of the backfill material in a geological disposal facility (GDF) is to chemically condition the environment of the near field and thereby chemically retard the transport of the radionuclides present in the waste. This function of the backfill material is usually referred to as chemical containment. Diffusion experiments are being carried out over periods up to four years to assess the diffusion of Cs, Ni, Eu, Th, U and I (as I-) through Nirex Reference Vault Backfill (NRVB). The method uses cylinders of NRVB (40 mm diameter, 40-45 mm height) which can be doped via a central well with the radionuclides of interest. Diffusion occurs radially into a surrounding solution already pre-equilibrated with the cement. This paper shows the results obtained during the first two years for experiments undertaken using 137Cs and 125I- tracers with and without carrier. Comparison is made to tritiated water under identical experimental conditions. Breakthrough of Cs and I- occurred within the first week of the experiments, reaching steady state in the surrounding solution after 20 to 50 days. The maximum concentrations expected from the original inventories based on a simple dilution calculation have not been reached, indicating that retention in the matrix has occurred; ranging from 10% to 40% for Cs, and up to 50% for I-. Corresponding experiments using a solution containing cellulose degradation products (CDP) showed an increased diffusion for both Cs and I. Migration profiles have been obtained and the relative retention of each radionuclide has been confirmed using digital autoradiography. The results indicate that, for both isotopes, migration occurs through the cement matrix rather than through microfissures. However, whereas Cs is homogeneously distributed within the blocks, there is evidence of zones of preferential I- accumulation even where concentrations in solution have reached steady state. Transport modelling using GoldSim has replicated experimental observations, producing comparable partition ratios (Rd) to those reported in the literature.


      PubDate: 2014-04-29T06:45:15Z
       
  • Constraints from sulfur isotopes on the origin of gypsum at
           concrete/claystone interfaces
    • Abstract: Publication date: Available online 4 February 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Catherine Lerouge , Francis Claret , Christophe Tournassat , Sylvain Grangeon , Stéphane Gaboreau , Bernard Boyer , Daniel Borschnek , Yannick Linard
      Two in situ concrete/claystone interfaces were sampled at the laboratory level in the Andra Meuse/Haute Marne (France) Underground Research Laboratory (URL) in order to study five years of interactions between Callovian–Oxfordian (COx) claystone and two cementitious materials (concrete bottom slab and shotcrete on the walls of the main gallery), with a specific focus on sulfur. Combined mineralogical, chemical and sulfur isotopic investigations were carried out to define the degree of the perturbation of the sulfur system in the claystone and in both the cementitious materials. At both interfaces, results show that the main perturbation on the claystone side is the formation of scarce μm-sized gypsum, the sulfur content of which is essentially derived from pyrite oxidation. The distribution of gypsum is highly correlated with the fissure network of the damaged zone due to excavation of the gallery. Its presence is also often associated with a loss of cohesion of the concrete/claystone interface. Due to the small amounts of gypsum and its μm-size, measurements were performed by ion microprobe. Adaptations were needed on account of the reactivity of gypsum and sulfates in general under the beam. The use of ion microprobe analysis provided evidence of high local isotopic heterogeneity that could be attributed to kinetic fractionation effects. Some analyses suggest a minor contribution of dissolved sulfates in pore water of claystone and possibly of concrete. The perturbation on the concrete side is marked by a significant increase in the bulk sulfur content within three millimeters of the interface with the claystone, showing a sulfur gradient from claystone to concrete. The main objective of this work was to define the extent of the chemical and mineralogical perturbations, taking into account in situ URL conditions, i.e. hydrodynamic conditions (shotcrete sprayed on the gallery walls and subjected to ventilation of the galleries), damaged zone of claystone induced by excavation and multi-scale heterogeneity. This identifies the relevant parameters to better constrain predictive reactive transport models of concrete/claystone interactions at a realistic scale.


      PubDate: 2014-04-29T06:45:15Z
       
  • Estimation of design floods in ungauged catchments using a regional index
           flood method. A case study of Lake Victoria Basin in Kenya
    • Abstract: Publication date: Available online 20 February 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Joel Nobert , Margaret Mugo , Hussein Gadain
      Reliable estimation of flood magnitudes corresponding to required return periods, vital for structural design purposes, is impacted by lack of hydrological data in the study area of Lake Victoria Basin in Kenya. Use of regional information, derived from data at gauged sites and regionalized for use at any location within a homogenous region, would improve the reliability of the design flood estimation. Therefore, the regional index flood method has been applied. Based on data from 14 gauged sites, a delineation of the basin into two homogenous regions was achieved using elevation variation (90-m DEM), spatial annual rainfall pattern and Principal Component Analysis of seasonal rainfall patterns (from 94 rainfall stations). At site annual maximum series were modelled using the Log normal (LN) (3P), Log Logistic Distribution (LLG), Generalized Extreme Value (GEV) and Log Pearson Type 3 (LP3) distributions. The parameters of the distributions were estimated using the method of probability weighted moments. Goodness of fit tests were applied and the GEV was identified as the most appropriate model for each site. Based on the GEV model, flood quantiles were estimated and regional frequency curves derived from the averaged at site growth curves. Using the least squares regression method, relationships were developed between the index flood, which is defined as the Mean Annual Flood (MAF) and catchment characteristics. The relationships indicated area, mean annual rainfall and altitude were the three significant variables that greatly influence the index flood. Thereafter, estimates of flood magnitudes in ungauged catchments within a homogenous region were estimated from the derived equations for index flood and quantiles from the regional curves. These estimates will improve flood risk estimation and to support water management and engineering decisions and actions.


      PubDate: 2014-04-29T06:45:15Z
       
  • Connectivity influences on nutrient and sediment migration in the Wartburg
           catchment, KwaZulu-Natal Province, South Africa
    • Abstract: Publication date: Available online 17 February 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Kipkemboi J. Kollongei , Simon A. Lorentz
      Non-point-source (NPS) pollution of surface and groundwater by sediment and nutrient loads emanating from agricultural catchments is a prominent environmental issue, with major consequences on water supply and aquatic ecosystem quality. The concept of connectivity has proved invaluable in understanding migration of NPS pollutants in catchments. Observations of sediments or suspended solids (SS), nitrate (NO3) and phosphorous (P) fluxes alongside stable water isotope sampling were made on a nested basis at field and catchment (41km2) scales for a series of events in the Wartburg catchment, South Africa. The nested catchment scale sampling was focused on control features in the stream network, including road crossings, farm dams and wetland zones. The analyzed stable water (δ18O and δ2H) isotopes results were used to interpret the connectivity of the contributing land forms and the stream network. The results reveal the dominant influences of farm dams and wetlands in limiting the downstream migration of sediment and nutrients for all but the most intense events. Certain events resulted in mixing in the dams and larger resultant outflow than inflow loads. These occurrences appear to be as a result of combinations of reservoir status, catchment antecedent conditions and rainfall depth and intensity. The nutrients loads between Bridge 1 and Bridge 2 stations reflect the bedrock control, where contributions from sugar cane hillslopes between these stations are not retained, even in the short wetland upstream of Bridge 2. Isotope analyses reveal that the headwaters, comprising 70% of the catchment area, contribute as little as 29% of the total catchment discharge, due to impoundments in this area. However, this contribution varies significantly for different events, reaching a maximum of 78% of the catchment discharge. It can therefore be concluded that nutrients and sediment migration in the Wartburg catchment is greatly influenced by connectivity. The δ18O and δ2H water isotopes can be used to assess the contributions of different sources of water which impact the transport of nutrients and sediments in catchments.


      PubDate: 2014-04-29T06:45:15Z
       
  • Characterization and radionuclide retention properties of heat-treated
           concrete
    • Abstract: Publication date: Available online 3 March 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): B. Kienzler , C. Borkel , N. Finck , S. Heck , S. Hilpp , M. Schlieker , V. Metz , M. Plaschke , E. Soballa , T. Cron , A. Miassoedov
      This study was performed to obtain insight into the characteristics of contaminated cementitious materials which may result from a light water reactor core melt down accident. Such material arose in a huge amount from the Fukushima disaster. We analyzed the elemental and mineralogical composition of similar, heat-treated material and investigated its radionuclide retention properties. We present the radionuclide retention properties of concrete samples which originally were part of an experiment using a thick-walled concrete recipient that had been heated by simulating a reactor melt down. Batch sorption experiments have been performed with the elements Cs(I), Co(II), and Eu(III) in seawater under aerobic conditions. Sorption coefficients were measured: Rs (Eu) ∼5800mlg−1 and Rs (Co) ∼110mlg−1. A tentative value for Cs was determined, adulterated by the relatively high release of Cs from the concrete itself.


      PubDate: 2014-04-29T06:45:15Z
       
  • A versatile pore-scale multicomponent reactive transport approach based on
           lattice Boltzmann method: Application to portlandite dissolution
    • Abstract: Publication date: Available online 13 April 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Ravi A. Patel , Janez Perko , Diederik Jacques , Geert De Schutter , Klaas Van Breugel , Guang Ye
      A versatile lattice Boltzmann (LB) based pore-scale multicomponent reactive transport approach is presented in this paper. This approach is intended to capture mineral phase and pore structure evolution resulting from geochemical interactions applicable, for example to model microstructural evolution of hardened cement paste during chemical degradation. In the proposed approach heterogeneous reactions are conceptualized as pseudo-homogenous (volumetric) reactions by introducing an additional source term in the fluid node located at the interface adjacent to a solid node, and not as flux boundaries as used in previously proposed approaches. This allows a complete decoupling of transport and reaction computations, thus different reaction systems can be introduced within the LB framework through coupling with external geochemical codes. A systematic framework for coupling an external geochemical code with the LB including pore geometry evolution is presented, with the generic geochemical code PHREEQC as an example. The developed approach is validated with a set of benchmarks. A first example demonstrates the ability of the developed approach to capture the influence of pH on average portlandite dissolution rate and surface evolution. This example is further extended to illustrate the influence of reactive surface area and spatial arrangement of mineral grains on average dissolution rate. It was demonstrated that both location of mineral grains and surface area play a crucial role in determining average dissolution rate and pore structure evolution.


      PubDate: 2014-04-29T06:45:15Z
       
  • Competition behaviour of metal uptake in cementitious systems: An XRD and
           EXAFS investigation of Nd- and Zn-loaded 11 Å tobermorite
    • Abstract: Publication date: Available online 23 January 2014
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M. Vespa , R. Dähn , E. Wieland
      Cement-based materials play an important role in multi-barrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. Cement is used to condition and stabilize the waste materials and to construct the engineered barrier systems (container, backfill and liner materials) of repositories for radioactive waste. In this study, bulk-X-ray absorption spectroscopy (XAS) was used to investigate the uptake mechanism of Nd on the crystalline C-S-H phase 11 Å tobermorite in the presence of Zn (co-absorbing metal), and vice versa, as potential competitor under strongly alkaline conditions (pH=12.5-13.3). The Zn and Nd concentration in all samples was 50 000 ppm, whereas the reaction times varied from one to six months. Extended X-ray absorption fine structure (EXAFS) data of the Nd LIII-edge indicate that the local structural environment of Nd consists of ∼7-8 O atoms at 2.42 Å, ∼7-8 Si at ∼3.67 Å and ∼5-6 Ca at ∼3.8 Å, and that this environment remains unchanged in the presence and absence of Zn. In contrary, Zn K-edge EXAFS data exhibit distinct differences in the presence and absence of Nd as co-absorbing element. Data analysis indicates that Zn is tetrahedrally coordinated (∼ 4 O at ∼1.96 Å) and the obtained structural data in the simultaneous presence of Nd and Zn are consistent with the formation of mixed Zn surface complexes and Zn bound in the interlayer remaining in these positions also with prolonged reaction times (up to 6 months). However, without the co-absorbing element Nd, strong structural changes in the uptake mechanisms of Zn are observable, e.g., after 3 month reaction time Zn-Zn backscattering pairs can be observed. These findings suggest that Nd has an influence on the incorporation of Zn in the tobermorite structure. In addition, the results of this study indicate that competitive uptake of metal cations with similar sorption behaviour by C-S-H phases can take place, deserving further attention in future assessments of the safe disposal of radioactive wastes in cement-based repositories.


      PubDate: 2014-01-24T10:11:25Z
       
  • Docking 90Sr Radionuclide in Cement: An Atomistic Modeling Study
    • Abstract: Publication date: Available online 16 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Mostafa Youssef , Roland J.-M. Pellenq , Bilge Yildiz
      Cementitious materials are considered to be a waste form for the ultimate disposal of radioactive materials in geological repositories. We investigated by means of atomistic simulations the encapsulation of strontium-90, an important radionuclide, in calcium-silicate-hydrate (C-S-H) and its crystalline analogue, the 9 Å-tobermorite. C-S-H is the major binding phase of cement. Strontium was shown to energetically favor substituting calcium in the interlayer sites in C-S-H and 9 Å-tobermorite with the trend more pronounced in the latter. The integrity of the silicate chains in both cementitious waste forms were not affected by strontium substitution within the time span of molecular dynamics simulation. Finally, we observed a limited degradation of the mechanical properties in the strontium-containing cementitious waste form with the increasing strontium concentration. These results suggest the cement hydrate as a good candidate for immobilizing radioactive strontium.
      Graphical abstract image Highlights

      PubDate: 2013-12-19T08:39:42Z
       
  • Conceptual Model Analysis of Interaction at a Concrete – Boom Clay
           Interface
    • Abstract: Publication date: Available online 13 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Sanheng Liu , Diederik Jacques , Joan Govaerts , Lian Wang
      In many concepts for deep disposal of high-level radioactive waste, cementitious materials are used in the engineered barriers. For example, in Belgium theengineered barrier system is based ona considerable amount of cementitious materials as buffer and backfill in the so-called supercontainer embedded in the hosting geological formation. A potential hosting formation is Boom Clay. Insight in the interaction between the high-pH pore water of the cementitious materials and neutral-pH Boom Clay pore water is required. Two problems are quite common for modeling of such a system. The first one is the computational cost due to the long timescale model assessments envisaged for the deep disposal system. Also a very fine grid (in sub-millimeter), especially at interfaces has to be used in order to accurately predict the evolution of the system. The second one is whether to use equilibrium or kinetic reaction models. The objectives of this paper are twofold. First, we develop an efficient coupled reactive transport code for this diffusion-dominated system by making full use of multi-processors/cores computers. Second, we investigate how sensitive the system is to chemical reaction models especially when pore clogging due to mineral precipitation is considered within the cementitious system. To do this, we selected two portlandite dissolution models, i.e., equilibrium (fastest) and diffusion-controlled model with precipitation of a calcite layer around portlandite particles (diffusion-controlled dissolution). The results show that with shrinking core model portlandite dissolution and calcite precipitation are much slower than with the equilibrium model. Also diffusion-controlled dissolution smooths out dissolution fronts compared to the equilibrium model. However, only a slight difference with respect to the clogging time can be found even though we use a very small diffusion coefficient (10-20 m2/s) in the precipitated calcite layer.


      PubDate: 2013-12-15T03:31:45Z
       
  • OpenGeoSys-Gem: A numerical tool for calculating geochemical and porosity
           changes in saturated and partially saturated media
    • Abstract: Publication date: Available online 8 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Georg Kosakowski , Norihiro Watanabe
      Reactive transport codes that use a Gibbs Energy Minimization (GEM) to solve chemical equilibria are uncommon. We present a new coupling of the Richards flow module of the Finite Element (FE) based OpenGeoSys code with the GEM based chemical solver GEMS3K. The coupled code is highly parallelized using an overlapping domain decomposition approach in combination with execution of multiple threads that solve chemical equilibria in parallel. FE reactive transport schemes are often affected by spurious concentration oscillations. We effectively suppress these oscillations with a linearized algebraic flux corrected transport (FCT) algorithm. An application example is presented which investigates the evolution of material interfaces in a deep geological repository for nuclear waste. The example uses all features of the new coupled code: flow and multi-component transport in variably saturated media, and a very complex chemical setup which makes extensive use of (non-linear) solid solution formulations for mineral phases.


      PubDate: 2013-12-11T07:49:59Z
       
  • Combining thermodynamic simulations, element and surface analytics to
           study U(VI) retention in corroded cement monoliths upon &gt; 20 years
           of leaching
    • Abstract: Publication date: Available online 9 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): C. Bube , V. Metz , D. Schild , J. Rothe , K. Dardenne , M. Lagos , M. Plaschke , B. Kienzler
      Retention or release of radionuclides in a deep geological repository for radioactive wastes strongly depends on the geochemical environment and on the interaction with near-field components, e.g. waste packages and backfill materials. Deep geological disposal in rock salt is one of the concepts considered for cemented low- and intermediate-level wastes. Long-term experiments were performed to observe the evolution of full-scale cemented waste simulates (doped with (NH4)2U2O7) upon reaction with relevant salt brines, e.g. MgCl2-rich and saturated NaCl solutions, and to examine the binding mechanisms of uranium. Throughout the experiments, concentrations of major solution components, uranium and pH values were monitored regularly and compared to thermodynamic equilibrium calculations, which indicate that close-to-equilibrium conditions have been achieved after 13-14 years duration of the leaching experiments. Two of the full-scale cemented waste simulates were recovered from the solutions after 17-18 years and studied by different analytical methods to characterize the solids, especially with respect to uranium incorporation. In drill core fragments of various lateral and horizontal positions of the corroded monoliths, U-rich aggregates were detected and analyzed by means of space-resolved techniques. Raman, μ-XANES and μ-XRD analyses of several aggregates demonstrate that they consist of an amorphous diuranate-type solid. Within error, calculated U solubilities controlled by Na-diuranate (Na2U2O7·H2O) are consistent with measured U concentrations in both, the NaCl and the MgCl2-system. Since uranophane occurs also in the corroded monoliths, it is proposed that a transition towards the thermodynamic equilibrium U(VI) phase is kinetically hindered.


      PubDate: 2013-12-11T07:49:59Z
       
  • Dissolution kinetics of C-S-H gel. Flow-through experiments
    • Abstract: Publication date: Available online 4 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Ana Trapote-Barreira , Jordi Cama , Josep M. Soler
      C-S-H gel dissolution kinetics was studied by means of flow-through experiments under CO2-free atmosphere at room temperature (23 ± 2 °C). The starting C-S-H gel was obtained by hydration of commercial C3S (3CaO·SiO2) and consisted of 67 wt% C-S-H with a Ca/Si ratio of 1.7 ± 0.1 and 33 wt% portlandite. Based on the changes in aqueous chemistry and in the C-S-H solid, it was observed that the C-S-H gel dissolves incongruently when the Ca/Si ratio is high and congruently as the Ca/Si ratio decreases to the tobermorite stoichiometric Ca/Si ratio of 0.83. First, a dissolution rate law for C-S-H gel with Ca/Si ratio equal to 0.83 is proposed based on the dissolution rates normalized to the final BET surface area. Additionally, reactive transport modeling of the changes in aqueous chemistry allowed the fitting of the rate constants for C-S-H with Ca/Si ratio ranging from 1.7 to 0.83. Solid examination by SEM-EDX and EPMA before and after the experiments showed some variability of the Ca/Si ratios of the analyzed particles, suggesting the existence of compositional domains with variable Ca/Si ratios. 29Si MAS NMR spectra showed an increase in polymerization of the reacted C-S-H, and also the formation of Si-rich domains in some cases, mainly under slow flow conditions. Inhibition of the rates in these cases will have to be further investigated.


      PubDate: 2013-12-07T06:23:02Z
       
  • Reactive Transport Modelling of Organic Complexing Agents in Cement
           Stabilized Low and Intermediate Level Waste
    • Abstract: Publication date: Available online 28 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Henrik von Schenck , Klas Källström
      The Swedish final repository for short-lived radioactive waste (SFR 1) is located at Forsmark in Sweden. It holds low and intermediate-level operational waste from the Swedish nuclear power plants, as well as industrial, research-related, and medical waste. A variety of low molecular weight organic compounds are present in the waste or in its matrix. Such compounds can also be formed by chemical degradation of organic macromolecules. These organics can ligate to metal atoms forming stable complexes and also adsorb to the surface of cement, thereby influencing the net release of radionuclides from the repository. This motivates the study of the concentration distribution of complexing agents in the repository as a function of time. The following paper reports the results of mass transport modelling, describing the transport of complexing agents through the cementitous matrix in the rock vault for intermediate-level waste in the SFR 1 repository. Nitrilotriacetate (NTA) and isosaccharinate (ISA) have been investigated, where the former is considered to be non-sorbing and non-reacting, while the latter is produced from cellulose degradation and adsorbs strongly to cement. The 3D model considers advection, diffusion, and sorption of solvated species in cement pore water over a time period of 20000 years. The model accounts for the spatial distribution of the flow field in the repository structure and also considers changing groundwater flow during the investigated time period. It is found that 99% of the NTA is removed after approximately 4000 years, while 90% of the ISA is retained in the rock vault after 20000 years. The maximum pore water concentration of ISA is found to be 8.6 mol/m3 after approximately 2300 years, based on the degradation of the deposited amounts of cellulose. Over the investigated time scale, the ligands retained in the repository can redistribute across several waste compartments where the organic compounds were not originally deposited. In the case of ISA this effect is dampened due the influence of sorption.


      PubDate: 2013-12-02T11:22:31Z
       
  • Application of polysulfone/cyclodextrin mixed-matrix Membranes in the
           removal of natural organic matter from water
    • Abstract: Publication date: Available online 1 December 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): F.V. Adams , E.N. Nxumalo , R.W.M. Krause , E.M.V. Hoek , B.B. Mamba
      The removal of natural organic matter (NOM) by polysulfone/β-cyclodextrin polyurethane (PSf/ β-CDPU) mixed matrix membranes (MMMs) was investigated in order to establish the effect of the addition of β-cyclodextrin polyurethane (β-CDPU) in polysulfone (PSf) membrane on the rejection of NOM (humic acid) and the fouling resistance of MMMs. It was found that the effective pore sizes and molecular-weight-cut-off (MWCO) of hand-cast PSf membranes were improved by β-CDPU addition due to its large pore size and its conical structure being capable of allowing easy passage of water molecules. An increase in pure water flux was achieved with increase in β-CDPU concentration in the PSf MMMs. Furthermore, the pure water flux of the hand-cast PSf membrane improved from 12 to 137 l/m2h when the applied pressure was increased from 0.62 to 2.41 MPa. The highest NOM removal efficiency achieved was 69% based on TOC measurements whereas a 76% NOM removal efficiency was attained as calculated from UV254 analysis. Fourier transform infrared (FT-IR) spectroscopy analyses confirmed the absence of -OH and -CH groups on all membranes after NOM rejection. This accounted for the increase in contact angle obtained after rejection tests. It is suggested that solution-diffusion mechanism is responsible for NOM filtration/rejection process. In addition, scanning electron microscopy (SEM) micrographs (after NOM rejection tests) revealed that the addition of β-CDPU in PSf resulted in improved antifouling properties based on the agglomeration of NOM on the membrane surfaces.
      Graphical abstract image

      PubDate: 2013-12-02T11:22:31Z
       
  • Experimental characterization of cement-bentonite interaction using core
           infiltration techniques and 4D computed tomography
    • Abstract: Publication date: Available online 27 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): F. Dolder , U. Mäder , A. Jenni , N. Schwendener
      Deep geological storage of radioactive waste foresees cementitious materials as reinforcement of tunnels and as backfill. Bentonite is proposed to enclose spent fuel drums, and as drift seals. The emplacement of cementitious material next to clay material generates an enormous chemical gradient in pore water composition that drives diffusive solute transport. Laboratory studies and reactive transport modeling predict significant mineral alteration at and near interfaces, mainly resulting in a decrease of porosity in bentonite. The goal of this project is to characterize and quantify the cement/bentonite skin effects spatially and temporally in laboratory experiments. A newly developed mobile X-ray transparent core infiltration device was used, which allows performing X-ray computed tomography (CT) periodically without interrupting a running experiment. A pre-saturated cylindrical MX-80 bentonite sample (1920 kg/m3 average wet density) is subjected to a confining pressure as a constant total pressure boundary condition. The infiltration of a hyperalkaline (pH 13.4), artificial OPC (ordinary Portland cement) pore water into the bentonite plug alters the mineral assemblage over time as an advancing reaction front. The related changes in X-ray attenuation values are related to changes in phase densities, porosity and local bulk density and are tracked over time periodically by non-destructive CT scans. Mineral precipitation is observed in the inflow filter. Mineral alteration in the first millimeters of the bentonite sample is clearly detected and the reaction front is presently progressing with an average linear velocity that is 8 times slower than that for anions. The reaction zone is characterized by a higher X-ray attenuation compared to the signal of the pre-existing mineralogy. Chemical analysis of the outflow fluid showed initially elevated anion and cation concentrations compared to the infiltration fluid due to anion exclusion effects related to compaction of the bentonite core that was adjusting to the experimental conditions. Subsequently, the OPC fluid is fully buffered, and a gradually decreasing ionic strength is observed as a result of progressive consumption of hydroxide at the mineral reaction front.


      PubDate: 2013-11-28T11:26:04Z
       
  • In-situ interaction between different concretes and Opalinus Clay
    • Abstract: Publication date: Available online 27 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): A. Jenni , U. Mäder , C. Lerouge , S. Gaboreau , B. Schwyn
      Interactions between cementitious materials and claystone are driven by chemical gradients in pore water and might lead to mineralogical modifications in both materials. In the context of a radioactive waste repository, this alteration might influence safety-relevant clay properties like swelling pressure, permeability, or specific retention. In this study, interfaces of Opalinus Clay, a potential host-rock in Switzerland, and three concrete formulations emplaced in the Cement-Clay Interaction (CI) Experiment at the Mont Terri Underground Laboratory (St. Ursanne, Switzerland) were analysed after 2.2 years of interaction. Sampling techniques with interface stabilisation followed by inclined intersection drilling were developed. Element distribution maps of the concrete-clay interfaces show complex zonations like sulphur enrichment, zones depleted in Ca but enriched in Mg, strong Mg enrichment adjacent to the interface, or carbonation. Consistently, the carbonated zone shows a reduced porosity. Properties of the complex zonation strongly depend on cement properties like water content and pH (ordinary Portland cement vs. low-pH cement). An increased Ca or Mg content in the first 100 μm next to the interface is observed in Opalinus Clay. The cation occupancy of clay exchanger phases next to the ordinary Portland cement interface is depleted in Mg, but enriched in Na, whereas porosity shows no changes at all. The current data suggests migration of CO2/HCO3 -, SO4 2-, and Mg species from clay into cement. pH decrease in the cement next to the interface leads to instability of ettringite, and the sulphate liberated diffuses towards higher pH regions (away from the interface), where additional ettringite can form.


      PubDate: 2013-11-28T11:26:04Z
       
  • Detection of Chloroform in water using an azo dye-Modified
           β-Cyclodextrin – Epichlorohydrin Copolymer as a Fluorescent
           Probe
    • Abstract: Publication date: Available online 9 November 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Phendukani Ncube , Rui W.M. Krause , Bhekie B. Mamba
      Chlorination disinfection by-products (DBPs) in water pose a health threat to humans and the aquatic environment. Their detection in water sources is therefore vital. Herein we present the detection of chloroform, a DBP, using a molecular fluorescent probe. The detection was based on the quenching of fluorescence of the probe by chloroform due to host-guest complex formation between β-cyclodextrin in the probe and the chloroform molecule. The stability constant for the host-guest complex was high at 3.825 x 104 M-1. Chloroform quenched the fluorescence of the copolymer the most compared to the other small chlorinated compounds studied, suggesting that the probe was more sensitive to chloroform, with a sensing factor of 0.35 compared to as low as 0.0073 for dichloromethane. There was no interference from other chloroalkanes on the quenching efficiency of chloroform. The probe was used to detect chloroform in dam water as well as in bottled water. Detection of chloroform in both water samples using the probe was possible without chemically treating the water samples which may introduce other pollutants.
      Graphical abstract image Highlights

      PubDate: 2013-11-13T10:30:52Z
       
  • X-ray micro-diffraction studies of heterogeneous interfaces between
           cementitious materials and geological formations
    • Abstract: Publication date: Available online 28 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): R. Dähn , D. Popov , Ph. Schaub , P. Pattison , D. Grolimund , U. Mäder , A. Jenni , E. Wieland
      In the present study the challenge of analyzing complex micro X-ray diffraction (microXRD) patterns from cement-clay interfaces has been addressed. In order to extract the maximum information concerning both the spatial distribution and the crystal structure type associated with each of the many diffracting grains in heterogeneous, polycrystalline samples, an approach has been developed in which microXRD was applied to thin sections which were rotated in the X-ray beam. The data analysis, performed on microXRD patterns collected from a filled vein of a cement-clay interface from the natural analogue in Maqarin (Jordan), and a sample from a two-year-old altered interface between cement and argillaceous rock, demonstrate the potential of this method.


      PubDate: 2013-11-01T10:30:21Z
       
  • Validation of Remotely Sensed Rainfall over Major Climatic Regions in
           Northeast Tanzania
    • Abstract: Publication date: Available online 19 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Fredrick Mashingia , Felix Mtalo , Michael Bruen
      Increase in population has resulted in pressure for more land and water use for food security in northeast Tanzania. This calls for proper understanding of spatial-temporal variations of quality and quantity of water to ensure sustainable management. The number of hydrometeorological stations such as rainfall stations and flow measuring stations has not increased and even the functioning of the existing ones is deteriorating. Satellite rainfall estimates (SRE) are being used widely in place of gauge observations or to supplement gauge observations. However, rigorous validation is necessary to have some level of confidence in using the satellite products for different applications. This paper discusses the results of application of SRE over a data scarce tropical complex region in northeast Tanzania. We selected river catchments found in two different climatological zones: the inland region mountains (ie. Kikuletwa and Ruvu basins) and the coastal region mountains (ie. Mkomazi, Luengera and Zigi basins), characterized by semi arid, sub humid to humid tropical climate. Thus, the validation sites were ideal for testing the different SRE products. In this study, we evaluated two gauge corrected high resolution SRE products which combine both infrared and passive-microwave estimates; the National Oceanographic and Atmospheric Administration Climate Prediction Center (NOAA-CPC) African Rainfall Estimation (RFE2) and the Tropical Rainfall Measuring Mission product 3B42 (TRMM-3B42) using station network. The accuracy of the products was evaluated through a comparison with available gauge data. The comparison was made on pair-wise (point to pixel) and sub-basin level with the reproduction of rainfall volume, rainfall intensity and consistency of rain and no-rain days. The SRE products performed reasonably well over both regions in detecting the occurrence of rainfall. The underestimation was mainly ascribed to topology and the coastal effect. Whereas, the overestimation was mainly ascribed to evaporation of rainfall in the dry atmosphere under the cloud base. Local calibration of satellite-derived rainfall estimates and merging of satellite estimates with locally available rain-gauge observations are some of the approaches that could be employed to alleviate these problems. Although, the products did not show strong correlation to the observed rainfall over the complex tropical mountainous catchments considered, they have high potential to augment gauge observations in data sparse basins.


      PubDate: 2013-10-20T09:31:27Z
       
  • Calibration, Performance, Parameter Indentifiability and Uncertainty
           Analysis of a 2 – Parameter Parsimonious Monthly Rainfall-Runoff
           Model in Two Catchments in Zimbabwe
    • Abstract: Publication date: Available online 10 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): D.T. Rwasoka , C.E. Madamombe , W. Gumindoga , A.T. Kabobah
      Hydrologic modelling lies at the core of hydrology and water resources management. Attempts at gaining a holistic grasp on model robustness, hydrologic theory and processes have inadvertently led to models that are not-well structured or too complex to apply in arid and semi-arid catchments and in Africa, in particular. In view of this, this paper reports on the application of a monthly parsimonious hydrologic model in two catchments in Zimbabwe, the Nyatsime and Upper Save river catchments. The two (2) parameter monthly parsimonious GR2M model was applied. The inputs were rainfall and potential evapotranspiration. Measured discharge was used for calibration and validation. Calibration and uncertainty analysis were done using the Differential Evolution Adaptive Metropolis (DREAM) algorithm. The performance of the GR2M model was evaluated using ten (10) model performance metrics. Parameter indentifiability was analysed on the basis of the shape of the posterior distribution of parameters. Parameter and total uncertainty were analysed in the context of the formal Bayesian DREAM approach. The 10 performance evaluation metrics showed that the model performed satisfactorily during calibration and validation in terms of the overall fit of observed and simulated data, low flows and the runoff volumes. The NSE was > 0.85, the Kling-Gupta Efficiency (KGE) was > 80% and Volume Efficiency was > 59% during calibration. Slight performance drops were noted during validation except for the NSE in Nyatsime catchment whilst the KGE remained relatively high. The validation NSE was > 0.65, the Kling-Gupta Efficiency (KGE) was > 71% and Volume Efficiency was > 55%. Calibrated parameters values showed good time-stability and were well identifiable with posterior parameter distributions having Gaussian shapes. Parameter uncertainty, in relation to total uncertainty was low. Parameter uncertainty constituted about 7% of the total uncertainty region. It was concluded that, although the model only had two parameters, the model performed quite satisfactorily in the simulation of monthly flows which makes it a good tool for operational hydrology and water resources modelling, planning and management in most data poor regions.


      PubDate: 2013-10-12T09:30:59Z
       
  • Impact of spatial input data resolution on hydrological and erosion
           modelling: recommendations from a global assessment
    • Abstract: Publication date: Available online 5 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): V. Chaplot
      The need to precisely describe the characteristics of a landscape is well-known in mathematical modeling from different environmental disciplines. Because spatial input data, such as climate, relief and soil maps are costly to obtain, especially when large areas are considered, several research studies have investigated the extent to which the resolution of these can be reduced. Yet, a consensus has not been reached on the question of models’ sensitivity to the whole range of spatial input data and for different environmental conditions. This issue was illustrated with the analysis of existing results from 41 watersheds from 30 research studies using the Soil and Water Assessment Tool (SWAT). Because these studies were not consistent in the type of spatial input data considered and the range of resolutions, an application of SWAT was performed in a flat 2,612 ha flat watershed of central Iowa (USA) where the sensitivity of runoff (R), NO3-N (N) and sediment (SED) yields was tested for changes in the resolution of all the required spatial input data (digital elevation model: DEM: 20-500m; n=12; number of rain gauge: NRAIN from 1 to 13; n=8; soil map: SOIL: 1/25,000-1/500,000; n=3) and in the number of watershed sub-divisions (NSW from 4 to 115; n=4). At the flat watershed, a Canonical Correlation Analysis with 67.4% of data variance explained by the two first variates, revealed that R and SED predictions were affected, mostly by NSW (r=0.95), followed by SOIL (r=0.18). N loads were the most sensitive to RAIN (r=0.76) and DEM (r=0.41), followed by SOIL (r=0.23) and NSW (r=-0.17). The Kolmogorov–Smirnov statistic (KS), that describes the significance of resolution changes for a considered spatial input data, showed that the model’s sensitivity was greater for SSW below 261ha, for 30<DEM<100m and across the whole range of NRAIN. Finally, the analysis of watersheds with different sizes and environmental conditions revealed that the minimum spatial input data resolution needed, to achieve accurate modeling results can be predicted from watersheds’ terrain declivity and mean annual precipitation. These results are expected to help modelers weight the level of investment to be made in generating spatial input data and in subdividing their watersheds as a function of both watersheds’ environmental conditions and desired level of accuracy in the output variables.


      PubDate: 2013-10-08T09:31:15Z
       
  • Impacts of Climate Change on Water Resources in Southern Africa: A Review
    • Abstract: Publication date: Available online 2 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Samuel Kusangaya , Michele Lynn Warburton , Emma Archer Van Garderen , Graham P.W. Jewitt
      The Intergovernmental Panel on Climate Change concluded that there is consensus that the increase of atmospheric greenhouse gases will result in climate change which will cause the sea level to rise, increased frequency of extreme climatic events including intense storms, heavy rainfall events and droughts. This will increase the frequency of climate-related hazards, causing loss of life, social disruption and economic hardships. There is less consensus on the magnitude of change of climatic variables, but several studies have shown that climate change will impact on the availability and demand for water resources. In southern Africa, climate change is likely to affect nearly every aspect of human well-being, from agricultural productivity and energy use to flood control, municipal and industrial water supply to wildlife management, since the region is characterised by highly spatial and temporally variable rainfall and, in some cases, scarce water resources. Vulnerability is exacerbated by the region’s low adaptive capacity, widespread poverty and low technology uptake. This paper reviews the potential impacts of climate change on water resources in southern Africa. The outcomes of this review include highlighting studies on detected climate changes particularly focusing on temperature and rainfall. Additionally, the impacts of climate change are highlighted, and respective studies on hydrological responses to climate change are examined. The review also discusses the challenges in climate change impact analysis, which inevitably represents existing research and knowledge gaps. Finally the paper concludes by outlining possible research areas in the realm of climate change impacts on water resources, particularly knowledge gaps in uncertainty analysis for both climate change and hydrological modelling.


      PubDate: 2013-10-04T09:30:56Z
       
  • A multiplier-based method of generating stochastic areal rainfall from
           point rainfalls
    • Abstract: Publication date: Available online 1 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): J.G. Ndiritu
      Catchment modelling for water resources assessment is still mainly based on rain gauge measurements as these are more easily available and cover longer periods than radar and satellite-based measurements. Rain gauges however measure the rain falling on an extremely small proportion of the catchment and the areal rainfall obtained from these point measurements are consequently substantially uncertain. These uncertainties in areal rainfall estimation are generally ignored and the need to assess their impact on catchment modelling and water resources assessment is therefore imperative. A method that stochastically generates daily areal rainfall from point rainfall using multiplicative perturbations as a means of dealing with these uncertainties is developed and tested on the Berg catchment in the Western Cape of South Africa. The differences in areal rainfall obtained by alternately omitting some of the rain gauges are used to obtain a population of plausible multiplicative perturbations. Upper bounds on the applicable perturbations are set to prevent the generation of unrealistically large rainfall and to obtain unbiased stochastic rainfall. The perturbations within the set bounds are then fitted into probability density functions to stochastically generate the perturbations to impose on areal rainfall. By using 100 randomly-initialized calibrations of the AWBM catchment model and Sequent Peak Analysis, the effects of incorporating areal rainfall uncertainties on storage-yield-reliability analysis are assessed. Incorporating rainfall uncertainty is found to reduce the required storage by up to 20%. Rainfall uncertainty also increases flow-duration variability considerably and reduces the median flow-duration values by an average of about 20%.


      PubDate: 2013-10-04T09:30:56Z
       
  • Hydration of a silica fume blended low-alkali shotcrete cement
    • Abstract: Publication date: Available online 24 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Barbara Lothenbach , Daniel Rentsch , Erich Wieland
      Ettringite and C-S-H are the main hydrates formed during the hydration of the low-alkali cement “ESDRED” consisting of 60% CEM I, 40% microsilica and 4.8% set accelerator. Small quantities of portlandite and hemicarbonate present as intermediate phases destabilise within a few weeks. The use of a set accelerator leads to massive ettringite precipitation, a moderate decalcification of C-S-H and reduction of pH due to presence of dissolved formate. The slow reaction of the silica fume during hydration decalcifies the C-S-H and decreases the alkali concentration to 30 mM and the pH value of the pore solution to 11.5 after 1 year and longer. The further reaction of the silica fume is expected to be slow and to result in a decrease of pH to 11. Further, the destabilisation of ettringite to thaumasite is expected. The long-term stability of C-S-H and the pH of approximately 11 make ESDRED a good candidate for usage in contact with the clay-based barriers of a repository for radioactive waste.


      PubDate: 2013-09-26T14:00:43Z
       
 
 
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