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Photonics Letters of Poland     Open Access  
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Physics of the Dark Universe     Open Access  

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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  [2556 journals]   [SJR: 0.423]   [H-I: 36]
  • 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
    • 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 > 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
    • 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
  • Analysing changes in water availability to assess environmental water
           requirements in the Rivirivi River basin, southern Malawi
    • Abstract: Publication date: Available online 30 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Mavuto Chimtengo , Cosmo Ngongondo , Michael Tumbare , Maurice Monjerezi
      The headwater catchments of the Rivirivi River basin in Malawi play a vital role in meeting downstream water requirements. In recent years, the Rivirivi River flow regime has experienced changes in its hydrological regime, including an increased number of zero-flow days. This study was aimed at investigating some of the causes of these changes. Water quantity indicators were assessed through flow duration analysis of the river flow regime behavior before and after the introduction of the traditional water allocation practices and dam construction. Further, a desktop reserve model was applied to estimate the environmental water requirements. Anthropogenic land use induced change patterns were investigated by time series analysis of satellite imagery and their potential effect on water resources were inferred. The results indicate that there was a considerable difference in average annual stream flow between two identified main periods (between 1963 to 1983 and 1984 to 2004) and zero flows increased from 5% to 12%. In addition, the area experienced a 65% reduction in forest cover from 1992 to 2008 which resulted in increased high flow index by 16%. Furthermore, the ecosystems need approximately the range of 35–40% of the MAR to be maintained at Class A and the range of 9–13% of MAR for class D. The results suggest that anthropogenic activities have negatively affected low flow environmental flows requirements by increasing zero flow days in Rivirivi River catchment. However, total water usage remains below the river’s MAR and the river can meet all water needs with proper management of the river flow regime.

      PubDate: 2013-11-01T10:30:21Z
  • 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
  • Putting science into practice
    • Abstract: Publication date: 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 66
      Author(s): Hodson Makurira , Benjamin Mapani , Dominic Mazvimavi , Marloes Mul , Victor Wepener

      PubDate: 2013-11-01T10:30:21Z
  • Determination of Volatile Fatty Acids in Wastewater by Solvent Extraction
           and Gas Chromatography
    • Abstract: Publication date: Available online 30 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Nontando T. Mkhize , Titus A.M. Msagati , Bhekie B. Mamba , Maggy Momba
      The purpose of this study was to develop a liquid-liquid extraction method for the analysis of volatile fatty acids collected at the elutriation units of Unit 3, 4 and 5 at Johannesburg Water-Northern Works Wastewater treatment plant. Liquid-Liquid extraction (LLE) method employing dichloromethane (DCM) and methyl-tert-butyl- ether (MTBE) as extracting solvents was used during the quantitative analysis of volatile fatty acids namely acetic, propionic, butyric, isobutyric, valeric, isovaleric and heptanoic acid. The detection of the extracts was by gas chromatography coupled to a mass spectrometer operating under electron ionization mode (GC-EI-MS). The results showed that MTBE was a better extraction solvent than DCM as it gave much higher recoveries (> 5 folds). On the other hand, the overall reactor performance for all the three units in the period when the samples were collected, which was measured by the ratio of propionic to acetic acid was good since the ratio o did not exceed 1.4 with the exception of the samples collected on the 3rd of October where the ratio exceeded 1.4 significantly. The concentration of acetic acid, another indicator for the reactor performance in all three units was way below 800 mg/L thus the digester balance was on par.

      PubDate: 2013-11-01T10:30:21Z
  • Spatial-Temporal Variability In Water Quality and Macro-Invertebrate
           Assemblages In The Upper Mara River Basin, Kenya
    • Abstract: Publication date: Available online 26 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Fidelis Kilonzo , Frank O. Masese , Ann Van Griensven , Willy Bauwens , Joy Obando , Piet N.L. Lens
      Tropical rivers display profound temporal and spatial heterogeneity in terms of environmental conditions. This aspect needs to be considered when designing a monitoring program for water quality in rivers. Therefore, the physico-chemical composition and the nutrient loading of the Upper Mara River and its two main tributaries, the Amala and Nyangores were monitored. Initial daily, and later a weekly monitoring schedule for four months spanning through the wet and dry seasons was adopted. Benthic macro-invertebrates were also collected during the initial sampling to be used as indicators of water quality. The aim of the current study was to investigate the physico-chemical status and biological integrity of the Upper Mara River basin. This was achieved by examining trends in nutrient concentrations and analysing the structure, diversity and abundance of benthic macro-invertebrates in relation to varying land use patterns. Sampling sites were selected based on catchment land use and the level of human disturbance, and using historical records of previous water quality studies. River water pH, dissolved oxygen, electrical conductivity (EC), temperature, and turbidity were determined in situ. All investigated parameters except iron and manganese had concentration values within allowable limits according to Kenyan and international standards for drinking water. The Amala tributary is more mineralized and also shows higher levels of pH and EC than water from the Nyangores tributary. The latter, however, has a higher variability in both the total phosphorus (TP) and total nitrogen (TN) concentrations. The variability in TP and TN concentrations increases downstream for both tributaries and is more pronounced for TN than for TP. Macro-invertebrate assemblages responded to the changes in land use and water quality in terms of community composition and diversity. The study recommends detailed continuous monitoring of the water quality at shorter time intervals and to identify key macro-invertebrate taxa that can be used to monitor changes of the water quality in rivers of the Mara basin as a result of anthropogenic changes.

      PubDate: 2013-10-28T13:12:43Z
  • Microwave-Induced Synthesis Of B-Cyclodextrin/N-Doped Carbon Nanotube
           Polyurethane Nanocomposites For Water Purification
    • Abstract: Publication date: Available online 25 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Sello P Masinga , Edward N Nxumalo , Bhekie B Mamba , Sabelo D Mhlanga
      The fabrication of polymer nanocomposites for the removal of organic species in aqueous media is achieved using conventional methods. However, these methods are expensive and deteriorating to the environment due to high energy demands and high organic solvent volume requirements. This work discusses the synthesis of nanocomposite polymers of β-cyclodextrin (β-CD) and nitrogen-doped carbon nanotubes (N-CNTs) under microwave irradiation for the first time. This novel method is efficient, greener and time saving. Typically, the reaction to prepare β-CD polymers takes about 24 h. Here we report a novel method to synthesize the polymers in 10 min. N-CNTs were synthesized via chemical vapour deposition method (CVD) using a 10 wt% Fe-Co/CaCO3 catalyst. The N-CNTs were found to contain ∼ 2 at% nitrogen by CN analysis. The N-CNTs were of high purity and were oxidized with acid functional groups (-COOH, -CO, -OH) using nitric acid under reflux. Zeta potential studies indicated that the quantity of acid functional groups increases with increase in acid treatment times. The functionalised N-CNTs (fN-CNTs) were then polymerized with β-CD using hexamethylene diisocyanate as the functional cross-linker in a microwave under an inert gas atmosphere. The polymers showed an efficient removal of p-nitrophenol from spiked water samples as confirmed by UV-Vis spectroscopy.
      Graphical abstract image Highlights

      PubDate: 2013-10-28T13:12:43Z
  • Characterisation of raw sewage and performance assessment of Primary
           Settling Tanks at Firle Sewage Treatment Works, Harare, Zimbabwe
    • Abstract: Publication date: Available online 25 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Simon Takawira Muserere , Zvikomborero Hoko , Innocent Nhapi
      The need for more stringent effluent discharge standards as prescribed by the Environmental Management Act 20:27 to protect the environment can be sustainably achieved with the aid of Activated Sludge Models. Thus, the researchers believe it is time to re-evaluate wastewater characteristics at Firle Sewage Treatment Works (STW) and make use of activated sludge simulators to address pollution challenges caused by the sewage plant. Therefore, this paper characterizes raw sewage and assesses settled and unsettled sewage in order to evaluate the performance of the primary treatment system and the suitability of the settled sewage for treatment by the subsequent Biological Nutrient Removal (BNR) system at Firle STW. Parameters studied included COD, BOD, TKN, TP, NH3, TSS, pH and Alkalinity. Composite samples were collected over a 9-day campaign period (27 June to 6 July 2012), hourly grab samples over 24 hrs and composite samples on 6 March 2012 which were then analysed in the lab in accordance with Standard Methods for the Examination of Water and Wastewater to support the City of Harare 2004 to 2012 lab historical records. Concentrations for unsettled sewage in mg/L were COD (527 ± 32), BOD (297 ± 83) TKN (19.0 ± 2.0), TP (18 ± 3), NH3 (24.0 ± 12.9), TSS (219 ± 57), while pH was 7.0 ± 0 and Alkalinity 266 ± 36 mg/L. For settled sewage the corresponding values in mg/L were COD (522 ± 15), BOD (324 ± 102), TKN (21.0 ± 3.0), TP (19.0 ± 2.0), NH3 (25.6 ± 11.2), TSS (250 ± 66), while pH was 7.0 ± 0 and Alkalinity 271 ± 17 mg/L. The plant design values for raw sewage are COD (650 mg/L), BOD (200mg/L), TKN (40 mg/L) and TP (11 mg/L). Thus COD and Nitrogen were within the plant design range while BOD and TP were higher. Treatability of sewage in BNR systems is often inferred from the levels of critical parameters and also the ratios of TKN/COD and COD/TP. The wastewater average settled COD/BOD, COD/TP and TKN/COD ratio were 1.7 ± 0.5, 27.1 ± 3.1 and 0.04 ± 0.01 respectively and corresponding unsettled ratios were 1.8 ± 0.5, 30.77 ± 6.8 and 0.04 ± 0 respectively. Thus, treatability by the 3-stage BNR system appears highly feasible for nitrogen and is likely to be complex for phosphorous. Fractionation of COD, TP and TN is recommended to appropriately advise further steps to optimise the plant operations.

      PubDate: 2013-10-28T13:12:43Z
  • The Seasonal influence on the spatial distribution of dissolved selected
           metals in Lake Naivasha, Kenya
    • Abstract: Publication date: Available online 23 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Joseph Nyingi Kamau , Anthony Gachanja , Catherine Ngila , Johnson Michael Kazungu , Mingzhe Zhai
      Lake Naivasha is the only freshwater Lake in Rift Valley, in Kenya. It lies in a fertile semi-arid basin. The Lake has no surface water outlet and is presumed to be under stress. Dissolved metals are directly taken up by bacteria, algae, plants, and planktonic and benthic organisms. Dissolved metals can also adsorb to particulate matter in water column and enter aquatic organisms through various routes. Cadmium, copper, lead and zinc may bioaccumulate within lower organisms, yet they do not biomagnify up the food chain as do mercury and selenium. This study reports on the levels and distribution of dissolved heavy metals and investigates the influence of physicochemical parameters on metal mobilization. The bioavailability of selected metals was investigated by relating the levels of dissolved metals to that in fish. Water abstraction for irrigation and domestic use, compounded with organic matter inflow will affect physicochemical parameters and hence influences the mobilization of heavy metals. Dissolved Zn correlated highly with sediment pH (r=0.67) indicating that dissolution increases with increase in pH. In addition, the fact that the pH also correlated positively with organic matter r=0.50, Eh r=0.63, temperature r=0.56 and dissolved oxygen r=56, would suggest that organic bound Zn contributed significantly to the concentration of dissolved Zn. In situ flux experiments indicated that the fringing papyrus reeds located along the shores of Lake Naivasha provided sites for metal immobilization due to their coprecipitation on redox sensitive

      PubDate: 2013-10-24T09:34:55Z
  • Assessing Indigenous Knowledge Systems and Climate Change Adaptation
           Strategies in Agriculture: A Case Study of Chagaka Village, Chikhwawa,
           Southern Malawi
    • Abstract: Publication date: Available online 16 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Emmanuel Charles Mkomwa , Miriam Kalanda Joshua , Cosmo Ngongondo , Maurice Monjerezi , Felistus Chipungu
      In Malawi, production from subsistence rain fed agriculture is highly vulnerable to climate change and variability. In response to the adverse effects of climate change and variability, a National Adaptation Programme of Action is used as framework for implementing adaptation programmes. However, this framework puts limited significance on indigenous knowledge systems (IKS). In many parts of the world, IKS have shown potential in the development of locally relevant and therefore sustainable adaptation strategies. This study was aimed at assessing the role of IKS in adaptation to climate change and variability in the agricultural sector in a rural district of Chikhwawa, southern Malawi. The study used both qualitative data from focus group and key informant interviews and quantitative data from household interviews and secondary data to address the research objectives. The study established that the local communities are able to recognize the changes in their climate and local environment. Commonly mentioned indicators of changing climatic patterns included delayed and unpredictable onset of rainfall, declining rainfall trends, warming temperatures and increased frequency of prolonged dry spells. An analysis of empirical data data corroborates the people’s perception. In addition, the community is able to use their IKS to adapt their agricultural systems to partially offset the effects of climate change. Like vulnerability to climate change, IKS varies over a short spatial scale, providing locally relevant adaptation to impacts of climate change. This paper therefore advocates for the integration of IKS in programmes addressing adaptation to climate change and vulnerability. This will serve to ensure sustainable and relevant adaptation strategies.

      PubDate: 2013-10-20T09:31:27Z
  • 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
  • Coping with droughts and floods: A Case study of Kanyemba, Mbire district,
    • Abstract: Publication date: Available online 19 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): G. Bola , C. Mabiza , J. Goldin , K. Kujinga , I. Nhapi , H. Makurira , D. Mashauri
      Most of Southern Africa is affected by extreme weather events, droughts and floods being the most common. The frequency of floods and droughts in Southern Africa in general, of which the Zambezi River Basin is part of, has been linked to climate change. Droughts and floods impact on the natural environment, and directly and indirectly impact on livelihoods. In the Middle Zambezi River Basin, which is located between Kariba and Cahora Bassa dams, extreme weather events are exacerbated by human activities, in particular the operation of both the Kariba and the Cahora Bassa reservoirs. To understand better, whether, and in what ways extreme weather events impact on livelihoods, this study used both quantitative and qualitative research methods to analyse rainfall variability and coping strategies used by households in the river basin. Data collection was done using semi-structured interviews, focus group discussions and structured questionnaires which were administered to 144 households. An analysis of rainfall variability and Cahora Bassa water level over 23 years was carried out. The study found that perceptions of households were that average rainfall has decreased over the years, and dry-spells have become more frequent. Furthermore, households perceived flood events to have increased over the last two decades. However, the analysis of rainfall variability revealed that the average rainfall received between 1988 and 2011 had not changed but the frequency of dry-spells and floods had increased. The occurrence of floods in the study area was found to be linked to heavy local rain and backflow from Cahora Bassa dam. The study found that households adopted a number of strategies to cope with droughts and floods, such as vegetable farming and crop production in the floodplain, taking on local jobs that brought in wages, planting late and livestock disposals. Some households also resorted to out-migration on a daily basis to Zambia or Mozambique. The study concluded that coping mechanisms were found to be inflexible and poorly suited to adapt to floods and droughts. The study recommends the implementation of adaptation measures such as the cultivation of drought-resistant crop varieties, irrigation and off-farm employment opportunities.

      PubDate: 2013-10-20T09:31:27Z
  • Clayey Materials In River Basin Enhancing Microbial Contamination Of River
    • Abstract: Publication date: Available online 19 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): E. Fosso-Kankeu , A.F. Mulaba-Bafubiandi , T.G. Barnard
      Mineral constituents of clay materials may promote interaction, adsorption and attachment of microorganisms, often resulting in biofilms’ formation. In this study investigation is made to determine how littoral clayey materials on the shores of a river promote accumulation of bacteria and increase contamination of river water. Clayey samples were collected at various points along the shore of a river around Mondeor in Johannesburg and the mineralogical composition was determined using XRD and XRF. Microorganisms in clay-biofilm and river water were identified by DNA sequencing and plate count. Results showed that total coliforms, Escherichia coli, Pseudomonas sp. and presumptive indigenous microorganisms attached to littoral clayey materials containing the mineral muscovite (characterising argillaceous soils). Bacteria number on clayey materials was significantly higher than on overlying water especially before rainy season. However a decrease of the number of bacteria in clayey materials concurrent with an increase in the number of suspended bacteria after rain events, was the result of the action of high and fast flows in the basin, eroding the biofilms. Attachment of microorganisms in clayey material as observed in this study could be ascribed to the glue-like aspect of soil (due to muscovite) that facilitates adhesion. It therefore demonstrates the potential of clayey materials to encourage biofilm formation and enhance microbial contamination of river water as shown here.

      PubDate: 2013-10-20T09:31:27Z
  • Implication of plants and microbial metalloproteins in the bioremediation
           of polluted waters: a review
    • Abstract: Publication date: Available online 10 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): E. Fosso-Kankeu , A.F. Mulaba-Bafubiandi
      Traditional approaches to municipal water monitoring barely includes procedures for toxic heavy metals testing. However, the presence of such contaminants in water sources is expected in South African surface and ground waters as a result of dispersion of effluents from acid mine drainage sites. Cheap and eco-friendly methods using microorganisms and plants are discussed in this review. Metal uptake mechanisms involving special proteins namely metalloproteins or metal-binding proteins and peptides, are elaborated and supported with some examples. The potential of phytochelatins and metallothioneins as metal chelating ligands in plants and microorganisms are reviewed and suggestion made to engineer these peptides in microbial sorbents for improved metal uptake. This review covers a number of approaches in the bioremediation of metal polluted effluents and systematically explains the mechanisms involved in the bio-uptake of metals, while highlighting the contribution of metal-binding proteins.

      PubDate: 2013-10-12T09:30:59Z
  • 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
  • Direct Spectrophotometric Detection of the Endpoint in Metachromatic
           Titration of Polydiallyldimethylammonium Chloride in Water
    • Abstract: Publication date: Available online 10 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): B. Gumbi , J.C. Ngila , P.G. Ndungu
      Polydiallyldimethylammonium chloride (poly-DADMAC) is a water soluble polymer that easily ionizes when dissolved in water. This cationic polyelectrolyte is mainly used as a flocculant within the water treatment industry, but little is known of its toxicological properties or its fate in the environment. It is often assumed that the polyelectrolyte sorbs onto solid surfaces in the water treatment stream and may be removed with the sludge or by a sand bed filter; which may not always be the case. In any event, reliable analytical techniques are needed for the determination of poly-DADMAC in matrices of environmental relevance. Metachromatic polyelectrolyte titration was used to quantify poly-DADMAC in model and tap water samples. We compared a routine visual titration method with a direct spectrophotometric technique that uses a dip probe, spectrometer, and computer. The direct spectrophotometric technique allowed for the determination of titration curves at 634 nm and 510 nm, whereby the later value has never been successfully utilised in the literature. The method simplifies the data analysis, and our recovery and matrix interference experiments demonstrate that the method is accurate, precise, and robust. The detection limit for this method was 0.1 mg L-1 in model water and 0.5 mg L-1 in tap water. The limit of quantification for both water matrices was 0.5 mg L-1.

      PubDate: 2013-10-12T09:30:59Z
  • Preparation of antifouling polyvinylpyrrolidone (PVP 40K) modified
           polyethersulfone (PES) ultrafiltration (UF) membrane for water
    • Abstract: Publication date: Available online 5 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Banele Vatsha , Jane Catherine Ngila , Richard M. Moutloali
      This study reports the fabrication of polyethersulfone (PES) membrane using the phase inversion method in the presence of polyvinylpyrrolidone (PVP, 40K) as pore-forming agent. The membranes were made from two PES concentration types i.e. 16 and 18 wt.%. The effect of high molecular weight PVP concentration (2 to 10%) was examined in order to obtain a membrane with good performance i.e. high water flux and reasonable Bovine Serum Albumin (BSA, protein model solution) rejection. The optimised membranes were characterised by ATR-FTIR, AFM, SEM, contact angle and dead-end membrane filtration tests. It was found that PVP moieties have positive influence in the prepared PES membranes. SEM surface and cross-sectional images were used to observed morphological changes as PVP content was varied. The pore sizes increased with PVP content for membranes prepared from 16 wt.% PES polymer, whereas at the higher PVP content in 18 wt.% PES membrane, pore sizes tend to decrease or completely disappear. The CA decreased gradually for the 16 wt.% PES with increasing PVP content whereas in the 18 wt.% PES the CA decreased initially before tapering off or increasing slightly. The rejection of BSA solution by both neat PES and PVP-containing PES membrane was above 85%. AFM surface topography exhibited increase in roughness value with PVP content. FTIR/ATR spectra corroborated the functional composition of neat PES and PVP molecule dispersed on PES membrane backbone. The results attained confirmed the potential industrial application of PVP molecule to minimise fouling tendencies.

      PubDate: 2013-10-08T09:31:15Z
  • Reactive-transport modeling of fly ash-water-brines interactions from
           laboratory-scale column studies
    • Abstract: Publication date: Available online 4 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): John M. Mbugua , J. Catherine Ngila , Andrew Kindness , Molla Demlie
      Dynamic leaching tests are important studies that provide more insights into time-dependent leaching mechanisms of any given solid waste. Hydrogeochemical modeling using PHREEQC was applied for column modeling of two ash recipes and brines generated from South African coal utility plants, Sasol and Eskom. The modeling results were part of a larger ash-brine study aimed at acquiring knowledge on (i) quantification and characterization of the products formed when ash is in contact with water-brines in different scenarios, (ii) the mineralogical changes associated with water-brine-ash interactions over time, (iii) species concentration, (iv) leaching and transport controlling factors. The column modeling was successfully identified and quantified as important reactive mineralogical phases controlling major, minor and trace elements’ release. The pH of the solution was found to be a very important controlling factor in leaching chemistry. The highest mineralogical transformation took place in the first 10 days of ash contact with either water or brines, and within 0.1 meter from the column inflow. Many of the major and trace elements (Ca, Mg, Na, K, Sr, S(VI), Fe, are leached easily into water systems and their concentration fronts were high at the beginning (within 0.1 meter from the column inflow and within the first 10 days) upon contact with the liquid phase. However, their concentration decreased with time until a steady state was reached. Modeling results also revealed that geochemical reactions taking place during ash-water-brine interactions does affect the porosity of the ash, whereas the leaching processes lead to increased porosity. Besides supporting experimental data, modeling results gave predictive insights on leaching of elements which may directly impact on the environment, particularly ground water. These predictions will help develop scenarios and offer potential guide for future sustainable waste management practices as a way of addressing the co-disposal of brines within inland ash dams and heaps.

      PubDate: 2013-10-08T09:31:15Z
  • Assessing the relationship between water quality parameters and changes in
           landuse patterns in the Upper Manyame River, Zimbabwe
    • Abstract: Publication date: Available online 7 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): J. Kibena , I. Nhapi , W. Gumindoga
      For the past 30 years, the increases in population pressure and external influences, such as economic growth, have accelerated the demand for land within the Upper Manyame River catchment in Zimbabwe which has caused substantial changes in landuse. The general objective of this research was to assess the impacts of landuse activities on the water quality of the Upper Manyame River which drains the rural and urbanized part of the catchment up to flow gauging station C21. Landcover data for the month of April in years of 1984, 1995, 2003 and 2011 were acquired from available Landsat TM and ETM images and were classified through the maximum likelihood digital image classification using the supervised classification approach. The status of water quality of the Upper Manyame River was also assessed through analyses of historical concentrations and pollution loads for TP, DO, BOD5, EC, PO4-P and TN at the Environmental Management Agency (EMA) gauging station CR21 sampling point for 1996, 2000/1 and 2008/9. Water quality of 15 monitoring sites comprising 25 water quality parameters were monitored monthly from January to June 2012. These locations were selected to reflect a wide array of landuse for both the dry and wet seasons. The results indicated that there was an increase in pollution load from 1995-2012; for TP from 130 kg/day to 376 kg/d, and for TN from 290 kg/day to 494 kg/d. This indicates high pollution levels which have severe impacts on downstream users. Significant deviations occurred in DO (0.1 - 6.8) mg/L, COD (11 - 569) mg/L, BOD5 (5 - 341) mg/L, PO4-P (0.01 - 4.45) mg/L, NH3-N (0.001 - 6.800) mg/L and EC (38 - 642) μS/cm. These values indicate sewage contamination. Hydrologic Response Unit and Buffer Analysis were used to determine the dominant landuse which contributes to a certain water quality. Results of digital image classification indicate that woodland/forest, grassland and bareland decreased between years 1984 to 2011 by 24.0 %, 22.6 % and 31.7 % respectively. This was mainly due to expansion or increase of agriculture and urban areas by 24.4% and 41.6 % respectively over the same time period. It was concluded that settlements and agricultural areas are the ones mainly affecting the water quality in Upper Manyame River with a Pearson’s correlation coefficient of r = 0.97 for COD and r = 0.78 for TSS respectively. It was also observed that the water quality status of the Upper Manyame River and its tributaries is very poor and the level of pollution generally increases from upstream to downstream. The results obtained provided baseline information which may be used in the development of appropriate water quality management systems in the catchment. Thus the study recommended a combined programme of point source control and landuse modification.

      PubDate: 2013-10-08T09:31:15Z
  • 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
  • Stability studies of commercial ZnO engineered nanoparticles in domestic
    • Abstract: Publication date: Available online 7 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): E.F.C. Chaúque , J.N. Zvimba , J.C. Ngila , N. Musee
      Most wastewater treatment plants (WWTPs) employ activated sludge processes to treat wastewater. The bacteria found in these systems degrade organic matter but are very sensitive to toxic compounds such as heavy metals, among others. The impact of emerging contaminants, such as engineered nanoparticles (ENPs) on the treatment efficiency of WWTPs is yet to be fully elucidated. The effects of physicochemical parameters; the pH and ionic strength on ZnO ENPs in domestic wastewater were investigated to establish their fate and behaviour in wastewater treatment systems, as well as potential release into the environment if they pass untreated. Our findings showed a decrease in zinc concentration in the filtrate as pH and ionic strength increased which indicated its possible removal through the abiotic, biosorption, and biosolid settling mechanisms. This phenomenon was further confirmed by transmission electron microscopy (TEM) images which showed agglomerates of ZnO ENPs in wastewater compared with de-ionized water. The dynamic light scattering (DLS) analysis of ZnO ENPs suspension in the wastewater showed their stability over a period of 2-h, with energy dispersive X-ray (EDS) analysis showing the presence of zinc on the sludge surface, while X-ray diffraction (XRD) analysis confirmed the presence of ZnO ENPs in the sludge over typical wastewater pH ranges. The results of this study will inform the integrated water management on the impact of nanotechnology based industries and the best approach in handling wastewater treatment products.

      PubDate: 2013-10-08T09:31:15Z
  • An analsis of factors contributing to household water security problems
           and threats in different settlement categories of ngamiland, botswana
    • Abstract: Publication date: Available online 7 October 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Krasposy Kujinga , Cornelis Vanderpost , Gagoitseope Mmopelwa , Piotr Wolski
      Globally, water security is negatively affected by factors that include climatic and hydrological conditions, population growth, rural-urban migration, increased per-capita water use, pollution and over-abstraction of groundwater. While Botswana has made strides in providing safe and clean water to its population since independence in 1966, over the years a combination of factors have contributed to water security problems in different settlement categories of the country (i.e., primary, secondary, tertiary and ungazetted settlements) in general and in the district of Ngamiland in particular. To study water security problems differentiated by settlement category, this study employed quantitative data collection methods (i.e. household structured questionnaires) and qualitative data collection methods (i.e. key informant interviews, observation, focus group discussions and informal interviews), complemented by a review of relevant literature. Water security in all settlements is affected by status of the settlement, i.e. gazetted or ungazetted, climatic and hydrological factors and water governance challenges. In large villages such as Maun, factors threatening water security include population growth, urbanization, management challenges, old water supply and distribution infrastructure, increased demand for individual connections and changing lifestyles. Small gazetted and ungazetted settlements encounter problems related to limited sources of water supply as well as salinity of groundwater resources. In order to enhance water security in different settlement categories, Botswana has to develop a comprehensive water resources management strategy underpinned by integrated water resources management principles aimed at addressing factors contributing to water security problems. The strategy has to be settlement category specific. Large villages have to address factors related to demographic changes, urbanization, management challenges, water supply infrastructure and the introducing of water demand management activities. Households in small villages need provision of water from more sustainable sources while ungazetted settlements need better access to clean water.

      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
  • Remote sensing based water quality monitoring in Chivero and Manyame lakes
           of Zimbabwe
    • Abstract: Publication date: Available online 25 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M Chawira , T Dube , W Gumindoga
      Lakes Chivero and Manyame are amongst Zimbabwe’s most polluted inland water bodies. MEdium Resolution Imaging Spectrometry level 1b full resolution imagery for 2011 and 2012 were used to derive chlorophyll-a (chl_a) and phycocyanin (blue-green algae) concentrations using a semi-empirical band ratio model; total suspended matter (TSM) concentrations were derived from the MERIS processor. In-situ measured chl_a was used to validate the remotely sensed values. Results indicate that remote sensing measurements are comparable with in-situ measurements. A strong positive correlation (R2 = 0.91; MAE = 2.75 mg/m3 (8.5%)) and p < 0.01 (highly significant)) between measured and modeled chl_a concentrations was obtained. Relationships between optically active water constituents were assessed. Measured chl_a correlated well with MERIS modeled phycocyanin (PC) concentration (R2 = 0.9458; p < 0.01 (highly significant)) whilst Chl_a and TSM gave (R2 = 0.7344; p < 0.05 (significant)). Modeled TSM and PC concentrations manifested a good relationship with each other (R2 = 9047; p < 0.001 (very highly significant)). We conclude that remote sensing data allow simultaneous retrieval of different water quality parameters as well as providing near real time and space results that can be used by water managers and policy makers to monitor water bodies.

      PubDate: 2013-09-26T14:00:43Z
  • Key Physical Characteristics used to Assess Water Harvesting Suitability
    • Abstract: Publication date: Available online 25 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): L.M. Bulcock , G.P.W. Jewitt
      Water harvesting (WH) techniques, which aim to increase water availability to crops, have long been used in arid and semi-arid areas to decrease the risk of reduced yields and crop failures due to dry spells. The landscape conditions dictate the type of WH system that can be implemented as well as the quantity and quality of water that will be collected. The measurement and understanding of how these landscape characteristics influence the hydrological function of WH systems is important and essential for further studies which seek to understand and enhance efficiency, extend uptake and model the impacts of WH within a catchment. However, commonly used guidelines often only prescribe optimal conditions for WH which results in many sites which may be suitable being over looked. Various statistical analyses was performed on 28 WH sites gathered from the available literature to try and identify whether the landscape conditions under which WH is currently taking place differs to the recommended guidelines. The results show that WH is taking place under a much broader range of conditions than those recommended by the guidelines. The recommendations for minimum and maximum slope in particular are too restrictive, with examples of successful WH taking place on slopes much steeper than the stipulated guidelines. A new set of guidelines are suggested, which take into account not only optimal conditions but also a range of suitable conditions on either side of the optimal range.

      PubDate: 2013-09-26T14:00:43Z
  • Calibrating a FDR sensor for soil moisture monitoring in a wetland in
           Central Kenya
    • Abstract: Publication date: Available online 20 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Beate Boehme , Mathias Becker , Bernd Diekkrüger
      The recent transformation of wetlands into farmland in East Africa is accelerating due to growing food-demand, land shortages, and an increasing unpredictability of climatic conditions for crop production in uplands. However, the conversion of pristine wetlands into sites of production may alter hydrological attributes with negative effects on production potential. Particularly the amount and the dynamics of plant available soil moisture in the rooting zone of crops determine to a large extent the agricultural production potential of wetlands. Various methods exist to assess soil moisture dynamics with Frequency Domain Reflectometry (FDR) being among the most prominent. However, the suitability of FDR sensors for assessing plant available soil moisture has to date not been confirmed for wetland soils in the region. We monitored the seasonal and spatial dynamics of water availability for crop growth in an inland valley wetland of the Kenyan highlands using a FDR sensor which was site-specifically calibrated. Access tubes were installed within different wetland use types and hydrological situations along valley transects and soil properties affecting soil moisture (organic C, texture, and bulk density) were investigated. There was little variation in soil attributes between physical positions in the valley, and also between topsoil and subsoil attributes with the exception of organic C contents. With a root mean squared error of 0.073 m3/m3, the developed calibration function of the FDR sensor allows for reasonably accurate soil moisture prediction for both within-site comparisons and the monitoring of temporal soil moisture variations. Applying the calibration equation to a time series of profile probe readings over a period of one year illustrated not only the temporal variation of soil moisture, but also effects of land use.

      PubDate: 2013-09-20T08:09:52Z
  • The aquaculture potential of Tilapia rendalli in relation to its feeding
           habits and digestive capabilities
    • Abstract: Publication date: Available online 16 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): S.N. Hlophe , N.A.G. Moyo
      Tilapia rendalli is a predominately macrophagous fish. However, it was able to colonize an oligotrophic dam (Flag Boshielo) with limited macrophytes. Therefore, the diet of T. rendalli in this dam was investigated; its stomach contents were examined over 12 months. A size related dietary shift was evident. Juveniles fed mainly on zooplankton while sub-adult and adult fish grazed on both macrophytes and marginal vegetation. T. rendalli’s ability to strive in an environment with limited food resources led to a subsequent study to determine its aquaculture potential. Its growth performance was compared to that of the commonly cultured Oreochromis mossambicus. Juveniles of both species were fed a commercial tilapia diet for 60 days. Specific growth rate and protein efficiency ratio was comparable to that of O. mossambicus (P>0.05, ANOVA). Feed conversion ratio was significantly higher (P<0.05) in T. rendalli (1.43) than in O. mossambicus (1.25) indicating a better efficiency in feed utilisation by O. mossambicus. At a physiological level, protease, lipase and cellulase activities did not differ significantly between the two fish species (P>0.05). Amylase activities were significantly higher (P<0.05) in T. rendalli than in O. mossambicus. The highest amylase activities were recorded in the proximal intestines as 26.34 and 22.00 μmol/min/mg protein in T. rendalli and O. mossambicus respectively. This may be an indicator that T. rendalli is better equipped to digest plant diets. T. rendalli may be the aquaculture species of choice for emerging fish farmers who cannot afford the highly priced fishmeal as a protein source in fish diets.

      PubDate: 2013-09-20T08:09:52Z
  • Remediation Studies of Trace Metals in Natural and Treated Water using
           Surface Modified Biopolymer Nanofibers
    • Abstract: Publication date: Available online 12 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Stephen Makali Musyoka , Jane Catherine Ngila , Bhekie B. Mamba
      In this study, remediation results of trace metals in natural water and treated water using three functionalized nanofiber mats of cellulose and chitosan are reported. The nanofiber materials, packed in mini-columns, were employed for the remediation of five toxic trace metals (Cd, Pb, Cu, Cr and Ni) from natural water samples. Trace metals in real water samples were undetectable as the concentrations were lower than the instrument’s detection limits of 0.27x10-3 (Cd) and 4.2x10-2 (Pb) μg mL-1, respectively. However, after percolation through the functionalised biosorbents in cartridges, detectability of the metal ions was enhanced. The starting volume of the natural water sample was 100 mL, which was passed through a column containing the nanofibers sorbent and the retained metals eluted with 5 mL of 2.0 M nitric acid. The eluate was analysed for metals concentrations. An enrichment factor of 20 for the metals was realized as a result of the preconcentration procedure applied to handle the determination of the metals at trace levels. The order of remediation of the studied metals using the nanofibers was as follows: chitosan/ PAM-g-Furan-2,5-dione < cellulose-g-Furan-2,5-dione < cellulose-g-Oxolane-2,5-dione. The modified biopolymer nanofibers were able to adsorb trace metals from the river water and treated water, thereby confirming their capability of water purification. These materials are proposed as useful tools and innovative approach for improving the quality of drinking for those consumers in small scale households.

      PubDate: 2013-09-16T09:32:15Z
  • Hydrochemical assessment of groundwater used for irrigation in Rumphi and
           Karonga districts, Northern Malawi
    • Abstract: Publication date: Available online 11 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Elijah M.M. Wanda , Lewis C. Gulula , Ambrose Phiri
      Irrigation water quality is an essential component of sustainable agriculture. Irrigation water quality concerns have often been neglected over concerns of quantity in most irrigation projects in Malawi. In this study, a hydrochemical assessment of groundwater was carried out to characterize, classify groundwater and evaluate its suitability for irrigation use in Karonga and Rumphi districts, Northern Malawi. Groundwater samples were collected during wet (January-April 2011) and dry (July-September 2011) seasons from 107 shallow wells and boreholes drilled for rural water supply using standard sampling procedures. The water samples were analysed for pH, major ions, total dissolved solids and electrical conductivity (EC), using standard methods. Multivariate chemometric (such as Kruskal Wallis test), hydrographical methods (i.e. Piper diagram) and PHREEQC geochemical modelling program were used to characterise the groundwater quality. Electrical conductivity, percentage sodium ion (% Na+), residual sodium carbonate (RSC), total dissolved solids (TDS), sodium adsorption ratio (SAR), Kelly’s ratio (KR) and permeability index (PI) were used to evaluate the suitability of water for irrigation. It was established that groundwater is neutral to alkaline and mostly freshwater (TDS <1000mg/l) of Ca-HCO3 - type. Groundwater is of low mineralisation which did not show statistically significant variations with respect to depth of shallow wells and boreholes, location and seasonality at 5 % significance level. Groundwater from Karonga District was largely oversaturated with respect to both calcite and dolomite, where as that from Rumphi District was undersaturated with respect to both calcite and dolomite. However, the calculated PCO2 values suggested that the groundwater system was open to soil CO2 and that there was possibility of degassing of CO2 during flow, which could increase the pH and subsequently result in the oversaturation of calcite in both districts. Groundwater water samples were stable towards calcite and kaolinite stability field. This suggested that equilibrium of the groundwater with silicates is an important indicator of the hydrogeochemical processes behind groundwater quality in the study area. The calculated values of SAR, KR and % Na+ indicated good and permissible quality of water for irrigation uses. However, samples with doubtful RSC (6% from Karonga district), unsuitable PI (5% and 3% from Karonga and Rumphi, respectively) and a high salinity hazard (56.2% and 20.3 % from Karonga and Rumphi, respectively) values restrict the suitability of the groundwater for agricultural purposes, and plants with good salt tolerance should be selected for such groundwaters. A detailed hydro-geochemical investigation and integrated water management is suggested for sustainable development of the water resources for better plant growth, long-term as well as maintaining human health in the study area.

      PubDate: 2013-09-12T09:39:50Z
  • Performance Evaluation Of Chicken, Cow And Pig Manure In The Production Of
           Natural Fish Food In Aquadams Stocked With Oreochromis Mossambicus
    • Abstract: Publication date: Available online 12 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M.M. Rapatsa , N.A.G. Moyo
      The main objective of this study was to characterize the ecological conditions that prevail after the application of chicken, cow and pig manure. Three treatments, chicken, cow, pig manure and a control were assigned to aquadams in a completely randomized design and each treatment was replicated three times. The aquadams were fertilized two weeks before the fish were stocked. One hundred Oreochromis mossambicus (mean weight ±40g) were stocked in each aquadam. Water physico-chemical parameters (temperature, dissolved oxygen, pH, electrical conductivity, salinity, turbidity, ammonia, nitrite, total alkalinity as calcium carbonate, and phosphorus) were determined once a week for the duration of the experiment. Zooplankton and phytoplankton in the different treatments were enumerated once every two weeks. The relationship between phytoplankton communities and the water physico-chemical parameters were evaluated using canonical correspondence analysis (CCA). The CCA indicated that the physico-chemical variables which best explain the distribution of phytoplankton were carbonate alkalinity, pH, phosphate, potassium, nitrogen and dissolved oxygen. Phytoplankton abundance was highest in chicken manure because the optimum nutrient conditions for the growth of phytoplankton were found in this treatment. Zooplankton abundance was also highest in the chicken manure treatment. The control was associated with one phytoplankton taxa, Chlorella. The numerical contribution of the different food items in the stomachs of O.mossambicus was determined. The diet of O.mossambicus was dominated by phytoplankton particularly Microcystis species. Total coliforms and Escherichia coli were used to assess the microbiological quality of the water in the different manure treatments. Chicken manure had the lowest total coliform and E.coli count. However, chicken manure had the highest Bacillus count. The implications of the microbial load in the chicken, cow and pig manure are discussed.

      PubDate: 2013-09-12T09:39:50Z
  • Comparison of the Hargreaves and Samani equation and the Thornthwaite
           equation for estimating dekadal evapotranspiration in the Free State
           Province, South Africa
    • Abstract: Publication date: Available online 2 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Mokhele Edmond Moeletsi , Sue Walker , Hamisai Hamandawana
      Eeference evapotranspiration (ET) is an important parameter that needs to be estimated accurately to enhance its utility in numerous applications. Although the widely recommended procedure for calculating this index involves using the FAO Penman-Monteith equation (ETo), the latter’s effectiveness is constrained by its considerable data requirements. To overcome this constraint, alternative methods using the limited data available have to be explored. In this study the ability of the Hargreaves and Samani (ETHS) and Thornthwaite (ETT) equations to estimate ET was investigated using multi-year data (1999-2008) from eight weather stations in the semi-arid Free State Province of South Africa. Results for non-calibrated equations are closely correlated, with ETHS tending to underestimate ET for the July-December period while ETT underestimates ET for all months of the calendar year. Although estimates from calibrated equations are also closely correlated, they have smaller deviations compared to the original equations with the calibrated Hargreaves and Samani equation (ETCHS) estimating reference evapotranspiration better than its calibrated Thornthwaite (ETCT) counterpart. The former’s better performance suggests that in data-scarce areas, the Hargreaves and Samani model is capable of giving results within acceptable ranges of accuracy.

      PubDate: 2013-09-04T09:30:18Z
  • Dechlorination of 3, 3’, 4, 4’ -tetrachlorobiphenyl (PCB77) in
           water, by Nickel/iron nanoparticles immobilized on L-lysine/PAA/PVDF
    • Abstract: Publication date: Available online 2 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Bonani Seteni , Jane Catherine Ngila , Keneiloe Sikhwivhilu , Richard Moutloali , Bhekie Mamba
      In this study, the dechlorination of chlorinated hydrocarbon 3, 3’, 4, 4’ -tetrachlorobiphenyl (PCB77) by bimetallic Ni/Fe nanoparticles immobilized on L-lysine /PAA/PVDF membrane was investigated at ambient conditions through the batch mode operation. The membrane support polyvinylidene fluoride (PVDF) was modified by in situ polymerization of acrylic acid in aqueous phase, then L-lysine was covalently bonded to the polymerized acrylic acid chains with the aid of a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC). The modification procedure involved cationic ion exchange with Fe2+, reduction to Fe0 with NaBH4 and finally deposition of Ni0. The scanning electron microscopic images showed that the Ni/Fe nanoparticles were successfully immobilized inside the membrane using the polyacrylic acid (PAA) as an inter-linkage between PVDF and L-lysine. A systematic characterization of the composite was performed using ATR-FTIR, HRSEM, EDX, HRTEM, XRD, and Contact Angle Measurement studies and a relatively uniform distribution of Ni/Fe was found in L-lysine/PAA/PVDF membrane because of its hydrophilic nature. The obtained Ni/Fe nanoparticles consist of Fe0 core surrounded by the Ni0 shell. The diameter of Ni/Fe nanoparticles was predominantly within the range 20-30 nm. The immobilized Ni/Fe nanoparticles exhibited a good reactivity towards the dechlorination of the chlorinated hydrocarbon since the concentration of the PCB 77 was decreased by catalytic dechlorination with Ni/Fe nanoparticles inside the L-lysine/PAA/PVDF membrane. Dechlorination efficiency of 98% was achieved within 9 hours.

      PubDate: 2013-09-04T09:30:18Z
  • Land use and land cover classification using phenological variability from
           MODIS vegetation in the Upper Pangani River Basin, Eastern Africa
    • Abstract: Publication date: Available online 3 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): J. Kiptala , Y. Mohamed , M.L. Mul , M.J.M. Cheema , P. Van der Zaag
      In arid and semi-arid areas, evaporation fluxes are the largest component of the hydrological cycle, with runoff coefficient rarely exceeding 10%. These fluxes are a function of land use and land management and as such an essential component for integrated water resources management. Spatially distributed land use and land cover (LULC) maps distinguishing not only natural land cover but also management practices such as irrigation are therefore essential for comprehensive water management analysis in a river basin. Through remote sensing, LULC can be classified using its unique phenological variability observed over time. For this purpose, sixteen LULC types have been classified in the Upper Pangani River Basin (the headwaters of the Pangani River Basin in Tanzania) using MODIS vegetation satellite data. Ninety-four images based on 8 day temporal and 250 m spatial resolutions were analyzed for the hydrological years 2009 and 2010. Unsupervised and supervised clustering techniques were utilized to identify various LULC types with aid of ground information on crop calendar and the land features of the river basin. Ground truthing data were obtained during two rainfall seasons to assess the classification accuracy. The results showed an overall classification accuracy of 85%, with the producer’s accuracy of 83% and user’s accuracy of 86% for confidence level of 98% in the analysis. The overall Kappa coefficient of 0.85 also showed good agreement between the LULC and the ground data. The land suitability classification based on FAO-SYS framework for the various LULC types were also consistent with the derived classification results. The existing local database on total smallholder irrigation development and sugarcane cultivation (large scale irrigation) showed a 74% and 95% variation respectively to the LULC classification and showed fairly good geographical distribution. The LULC information provides an essential boundary condition for establishing the water use and management of green and blue water resources in the water stress Pangani River Basin.

      PubDate: 2013-09-04T09:30:18Z
  • The effect of sewage effluent on the physico-chemical and biological
           characteristics of the sand river, limpopo, south africa
    • Abstract: Publication date: Available online 3 September 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): K.G. Seanego , N.A.G. Moyo
      Population growth in urban areas is putting pressure on sewage treatment plants. The improper treatment of sewage entering the aquatic ecosystems causes deterioration of the water quality of the receiving water body. The effect of sewage effluent on the Sand River was assessed. Eight sampling sites were selected, site 1 and 2 were upstream of the of the sewage treatment plant along the urbanised area of Polokwane, whilst sites 3, 4, 5, 6, 7 and 8 were downstream. The physico-chemical parameters and coliform counts in the water samples were determined. The suitability of the water for irrigation was also determined. Hierarchical average linkage cluster analysis produced two clusters, grouping two sites above the sewage treatment works and six sites downstream of the sewage effluent discharge point. Principal component analysis (PCA) identified total nitrogen, total phosphorus, conductivity and salinity as the major factors contributing to the variability of the Sand River water quality. These factors are strongly associated with the downstream sites. Canonial correspondence analysis (CCA) indicated the macroinvertebrates, Chironomidae, Belastomatidae, Chaoborus and Hirudinea being strongly associated with nitrogen, phosphorus, conductivity and temperature. Escherichia coli levels in the Polokwane wastewater treatment works maturation ponds, could potentially lead to contamination of the Polokwane aquifer. The Sodium Adsorption Ratio was between 1.5 and 3.0 and residual sodium carbonate was below 1.24 Meq/l, indicating that the Sand River water is still suitable for irrigation. The total phosphorus concentrations fluctuated across the different site.Total nitrogen concentrations showed a gradual decrease downstream from the point of discharge. This shows that the river still has a good self-purification capacity.

      PubDate: 2013-09-04T09:30:18Z
  • Decentralized water resources management in Mozambique: challenges of
           implementation at river basin level
    • Abstract: Publication date: Available online 29 August 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Ronaldo Inguane , Jordi Gallego-Ayala , Dinis Juízo
      In the context of the integrated water resources management implementation, decentralization of water resources management (DWRM), at river basin level, is crucial aspect for its success. However, decentralization requires creation of new institutions on the ground, to stimulate the enabling environment for stakeholder participation and integration in water management decision-making process. In 1991, Mozambique began restructuring its water sector toward operational decentralized water resources management. Within this context of decentralization, new legal and institutional frameworks have been created, e.g. Regional Water Administrations (RWAs) and River Basin Committees. This paper identifies and analyses the key institutional challenges and opportunities of the DWRM implementation in Mozambique. The paper uses a critical social science research methodology for in depth analysis of roots of the constraining factors for the implementation of the DWRM. Results obtained suggest that the RWAs should be designed considering the specific geographic and infrastructural conditions of their jurisdiction areas and select priorities in their institutional capacity building strategies that match the local realities. Furthermore, the results also indicates that RWAs have enjoyed limited support from basin stakeholders mainly in basins with less hydraulic infrastructures to secure water availability to their users and to minimize the effect of climate variability.

      PubDate: 2013-08-31T08:05:16Z
  • Preconcentration of trace multi-elements in water samples using Dowex
           50W-x8 and Chelex-100 resins prior to their determination using
           inductively coupled plasma atomic emission spectrometry (ICP-OES)
    • Abstract: Publication date: Available online 28 August 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Philiswa N. Nomngongo , J. Catherine Ngila , Titus A.M. Msagati , Brenda Moodley
      This work presents a solid phase extraction (SPE) method for simultaneous preconcentration of trace elements in water samples prior to their ICP-OES determination. Dowex 50w-x8 and Chelex-100 resins were used as SPE sorbent materials for preconcentration of trace Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn. The optimum sample pH, eluent concentration and sample flow rates were found to 6, 3.0 mol L-1 and 3.0 mL min-1, respectively. In terms of multi-element preconcentration capabilities, Dowex 50W-x8 appeared to be a better sorbent. The recoveries for all the tested analytes were >95%. However, Chelex-100 showed a better performance in terms of recovery (>95%) towards Cu, Fe and Zn. Under optimized conditions using Dowex 50W-x8, the relative standard deviations for different metals were < 3%. The limits of detection and limits of quantification ranged from 0.01-0.39 μg L-1 and 0.05-0.1.3 μg L-1, respectively. The accuracy of the preconcentration method was confirmed by spike recovery test and the analysis of certified reference materials. The SPE method was applied for preconcentration of the analyte ions in tap water, bottled water and wastewater samples.

      PubDate: 2013-08-31T08:05:16Z
  • A review of continental scale hydrological models and their suitability
           for drought forecasting in (sub-Saharan) Africa
    • Abstract: Publication date: Available online 25 July 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): P. Trambauer , S. Maskey , H. Winsemius , M. Werner , S. Uhlenbrook
      The aim of this review is to provide a basis for selecting a suitable hydrological model, or combination of models, for hydrological drought forecasting in Africa at different temporal and spatial scales; for example short and medium range (one to ten days or monthly) forecasts at medium to large river basin scales or seasonal forecasts at the Pan-African scale. Several global hydrological models are currently available with different levels of complexity and data requirements. However, most of these models are likely to fail to properly represent the water balance components that are particularly relevant in arid and semi-arid basins in sub-Saharan Africa. This review critically looks at weaknesses and strengths in the representation of different hydrological processes and fluxes of each model. The major criteria used for assessing the suitability of the models are (1) the representation of the processes that are most relevant for simulating drought conditions, such as interception, evaporation, surface water-groundwater interactions in wetland areas and flood plains and soil moisture dynamics; (2) the capability of the model to be downscaled from a continental scale to a large river basin scale model; and (3) the applicability of the model to be used operationally for drought early warning, given the data availability of the region. This review provides a framework for selecting models for hydrological drought forecasting, conditional on spatial scale, data availability and end-user forecast requirements. Among sixteen well known hydrological and land surface models selected for this review, PCR-GLOBWB, GWAVA, HTESSEL, LISFLOOD and SWAT show higher potential and suitability for hydrological drought forecasting in Africa based on the criteria used in this evaluation.

      PubDate: 2013-07-26T08:07:17Z
  • An analysis of the chemical and microbiological quality of ground water
           from boreholes and shallow wells in zimbabwe
    • Abstract: Publication date: Available online 5 July 2013
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): N.A.G. Moyo
      Groundwater from boreholes and shallow wells is a major source of drinking water in most rural areas of Zimbabwe. The quality of groundwater has been taken for granted and the status and the potential threats to groundwater quality have not been investigated on a large scale in Zimbabwe. A borehole and shallow well water quality survey was undertaken between January, 2009 and February, 2010 to determine the chemical and microbial aspects of drinking water in three catchment areas. Groundwater quality physico-chemical indicators used in this study were nitrates, chloride, water hardness, conductivity, alkalinity, total dissolved solids, iron, magnesium, manganese, potassium, calcium, fluoride, sulphates, sodium and pH. The microbiological indicators were total coliforms, faecal coliforms and heterotrophs. Principal component analysis (PCA) showed that most of the variation in ground water quality in all catchment areas is accounted for by Total Dissolved Solids (TDS), electrical conductivity (EC), sodium, bicarbonate and magnesium. The principal dissolved constituents in ground water are in the form of electrically charged ions. Nitrate is a significant problem as the World Health Organization recommended levels were exceeded in 36%, 37% and 22% of the boreholes in the Manyame, Mazowe and Gwayi catchment areas respectively. The nitrate levels were particularly high in commercial farming areas. Iron and manganese also exceeded the recommended levels. The probable source of high iron levels is the underlying geology of the area which is dominated by dolerites. Dolerites weather to give soils rich in iron and other mafic minerals. The high level of manganese is probably due to the lithology of the rock as well as mining activity in some areas. Water hardness is a problem in all catchment areas, particularly in the Gwayi catchment area where a value of 2550mg/l was recorded in one borehole. The problems with hard water use are discussed. Chloride levels exceeded the recommended levels in a few areas under irrigation. Most of the chloride is probably from agricultural activity particularly the application of potassium chloride. Fluoride levels were particularly elevated in the Gwayi catchment area and this is because of the geology of the area. There was no evidence of microbial contamination in all the boreholes sampled as the total coliform, faecal coliforms, heterotrophs count was nil. However, severe microbial contamination was found in the wells especially those in clay areas.

      PubDate: 2013-07-06T09:34:30Z
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