Scielo RSS <![CDATA[Water SA]]> vol. 37 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Improved sensitivity using liquid chromatography mass spectrometry (LC-MS) for detection of propyl chloroformate derivatised</b> <b>β</b><b>-<i>N</i>-methylamino-L-alanine (BMAA) in cyanobacteria</b>]]> β-N-methylamino-L-alanine (BMAA) is a difficult molecule to detect, primarily due to its presence in low concentrations in complex matrices. This has resulted in contradictory reports on the presence of BMAA in cyanobacteria. We report improved sensitivity of detection using propyl chloroformate derivatisation, liquid chromatographic (LC) separation, and single quadrupole mass spectrometry (MS) detection. Triple quadrupole mass spectrometry (MS/MS) was used to confirm the identity of BMAA in cyanobacteria based on product ions. We show a 10-fold increase in sensitivity with the LC-MS method compared to the previously published gas chromatography mass spectrometry (GC-MS) method with pre-column derivatised BMAA using a commercially available amino acid derivatisation kit. Clear chromatographic separation of BMAA from 2,4-diaminobutyric acid (DAB), as well as the 20 standard amino acids, was achieved. The analytical method was validated by multiple derivatisation of samples, multiple users, and multiple injections, as well as in various matrices. The quantifier ion used was [M + H]+ = 333 m/z. The MS/MS product ions 273 m/z and 245 m/z were used in identification and peak confirmation. Additionally, we confirm the presence of BMAA in cyanobacteria previously screened with GC-MS as well as the presence of BMAA in newly isolated cultures. <![CDATA[<b>The trigger-tube</b>: <b>a new apparatus and method for mixing solutes for injection tests in boreholes</b>]]> the trigger-tube apparatus and method was developed for mixing solutes and tracers for injection tests. The apparatus is a cap-trigger tube segment and the technique mixes solutes in boreholes in 2 min. Trigger-tube with solute/tracer is introduced into the well, the trigger is released, the tube is withdrawn and the solute/tracer mixes with well water instantaneously to give a homogeneous mixture. Field tests using this method and apparatus for point dilution tests gave a Darcy velocity of 4.06 m/d, seepage velocity of 122.89 m/d and effective porosity of 0.33. Natural gradient tests gave a Darcy velocity of 4.06 m/d and natural velocity of 123 m/d, using tracer, for the same fracture at 21 m in borehole UO5, University of the Free State campus test site. The apparatus enables a comparatively shorter time for carrying out SWIW tests than is possible using the pump mixing method. Field tests gave results of 13 min for the trigger-tube method and 25 min for the pump mixing method, for a point dilution test using NaCl as a conservative tracer. The trigger-tube apparatus can be used for any borehole test that requires the introduction of a homogenous mixture. <![CDATA[<b>Characteristics of local groundwater recharge cycles in South African semi-arid hard rock terrains - rainwater input</b>]]> Rainfall events in semi-arid regions of South Africa are characteristically erratic in terms of depths and recurrence rates. Chemical assessment of cyclic rainwater has recognised 3 intervals, spaced over the hydrological cycle, reporting diverse hydrochemical compositions of rainwater in winter and summer rainfall regions. Winter rainwater is generated over the south Atlantic maritime waters. This rainwater contains noticeably higher concentrations of oceanic aerosols (NaCl) than the summer rainwater generated in the Intertropical Convergence Zone/equatorial western Indian Ocean. Sporadic addition of terrigenous dust generated over the continent substantially elevates concentrations of non-oceanic nitrogenous and sulphurous aerosols in the summer rainwater. Prominent seasonal variations in the rainwater hydrochemistry signature coincide with cyclic rainfall depths, characteristic of the semi-arid climate. Macro-element concentrations during the summer dry period, April to September, are relatively high in relation to those recorded for the wet cycle, October to March. However, the latter period reports a noticeably depleted hydrochemical rainwater input into the local groundwater budget during the peak rainfall period (January to March). The October-December (early) period represents a phase between a dusty, dry winter atmosphere and a relatively flushed atmosphere in December, after the first regional rainfall manifests around middle September. Individual early rainfalls contain even higher hydrochemical concentrations than the previous dry period, which subsequently diffuses as the airborne moisture content increases towards the peak rainfall period starting in January. Continuous rainfall event monitoring in the summer semi-arid regions identified short-term wet cycles containing extraordinary high rainfall events, referred to as episodic events. These wet cycles are highly erratic in time and may last from 3 to 8 consecutive days with a recurrence rate of 1 in 5 years. The rainwater hydrochemistry signature differs significantly from the normal rainfall composition and represents a unique opportunity for tracing the infiltrating rainwater. For example, chloride concentrations from individual, high rainfall events (40 to 150 mm) may be as low as 0.4 mg·ℓ-1, whereas the background value varies around 0.8 mg·ℓ-1. Environmental chloride represents a conservative tracer for estimating the migration between rainwater and groundwater recharge. The concentration levels are not constant throughout the year and may lead to erroneous assumptions when performing groundwater recharge estimations using accumulated rainwater samples and uncontrolled groundwater sampling techniques. <![CDATA[<b>Influence of irrigation on the level, salinity and flow of groundwater at Vaalharts Irrigation Scheme</b>]]> In 1934, Act No. 38 of 1938 was approved, providing permission to construct the Vaal Dam and develop the Vaalharts Irrigation Scheme There are currently 1 200 plots varying in size from 25 to -75 ha and covering a total area of 35 302 ha. Water logging and salinisation are being experienced, leading to research being initiated in the area. The area researched stretches from Jan Kempdorp in the south to Taung (the Dry Harts River) in the north. A sampling network of 246 piezo-meters was installed to monitor the water levels and electrical conductivity (EC) over a period of 1 year. It was found that the leaching requirement to ensure sustainable irrigation is 611.5 mm/a. According to the water balance this requirement is 562 mm/a. Salt deposited through irrigation water amounts to 4.65 t/ha per annum. The total dissolved salts (TDS) aver aged 1 005 mg/ℓ in 1976 and 1 350 mg/ℓ in 2004, an average increase per annum of 13 mg/ℓ. At the time of this research TDS was 1 476 mg/ℓ, representing an increase of 96 mg/ℓ in 5 years, an average increase per annum of 19.25 mg/ℓ. Irrigated salt deposits not drained build up in the soil at a rate of 0.8 t/ha per annum. Results of this study suggest that upgrading of all infrastructure is essential. Suitable internal subsurface drainage should be cleaned, unsuitable drainage replaced and spacing decreased to drain the area more effectively. Effective drainage would minimise the salt build-up in the soil, have a positive influence on the sustainability of irrigation farming and improve crop yields and quality in the area. The drained water can be reticulated into an evaporation pond to confine the salt mass, thus preventing it from influencing the environment and other activities downstream. <![CDATA[<b>Effects of tillage on runoff from a bare clayey soil on a semi-arid ecotope in the Limpopo Province of South Africa</b>]]> Runoff constitutes one of the major water losses from agricultural fields in semi-arid areas. However, by adopting appropriate soil management practices, the runoff can be harnessed for improving crop yields. The main objective of this study was to quantify rainfall-runoff relationships under in-field rainwater harvesting (IRWH) using simulated rainfall, and to compare these results to those obtained with annually tilled conventional tillage (CON) (control). IRWH is a special type of no-till (NT) crop production practice that promotes runoff from a crusted runoff strip into basins where the water infiltrates beyond evaporation but is available for crop use. Runoff was related to time to runoff, total runoff, final runoff rate and runoff coefficient. This experiment demonstrated that by adopting IRWH production technique smallholder farmers could harness an additional 45.54 m³·ha-1 of water compared to the CON system. The extra water harvested could meet about 1% of maize water requirements. <![CDATA[<b>Investigation of the origin and distribution of heavy metals around Ebenezer Dam, Limpopo Province, South Africa</b>]]> This study was based on the outcome of the soil geochemical survey which was conducted by the Council for Geoscience around Ebenezer Dam during 1995-1996, the results of which indicated high concentrations of lead (Pb), zinc (Zn) and arsenic (As). The current study therefore focused on the origin and distribution patterns of Pb, Zn, Cu, As and Cr within the environs of Ebenezer Dam and their potential impacts on the environment and human health. The work involved soil, sediment, rock and water sampling and analysis. Atomic absorption and x-ray fluorescence spectrometry were used to determine the metal concentrations. The occurrence of anomalous concentrations of these metals in the study area was established. The anomalies registered maximum concentrations of (mg/g): 57 for Pb, 157 for Zn, 313 for Cu, 73 for As and 888 for Cr. The concentrations of these metals in sediments along the streams were high near the anomalies, but decreased downstream. Concentrations of heavy metals in water around the Ebenezer Dam were found to be less than 0.01 mg/g , except for As which was less than 1.0 mg/g. Thus Pb, Zn, Cu and Cr values were below the target water quality ranges for domestic, irrigation, livestock watering and aquatic ecosystem use. The study confirmed that the distribution of heavy metals in this area is localised within and around the source rocks that are felsic in nature, namely; granites and pegmatites that formed domes in the area. <![CDATA[<b>Uptake of selected metals in tissues and organs of <i>Clarias gariepinus</i> (sharptooth catfish) from the Vaal River System - chromium, copper, iron, manganese and zinc </b>]]> This paper discusses concentrations of 5 essential trace metals (chromium, copper, iron, manganese and zinc) in water, sediment and various fish (C. gariepinus) tissues. With the exception of high Zn concentrations in skin, the highest essential element metal concentrations were generally recorded in liver and gill arch tissues, followed by gill filaments and lastly skin and muscle. This general trend is in agreement with trends reported by other workers. Fe concentrations were found to be significantly higher at the Vaal Dam more often than at the Vaal Barrage. In comparison, Mn concentrations were higher at the Vaal River Barrage more often than at the Vaal Dam. No clear trends emerged with regard to differences between localities for the other metals, or between surveys/seasons for all essential trace metals examined. The likely reason for the lack of distinct trends is the amount of variability observed in tissue metal concentrations within localities and seasons in this study. Such variability is also reflected in current literature and accentuates the importance of both abiotic (e.g. physical water quality variables) and biotic (e.g. host physiological status, general biology and life history traits) factors influencing the concentrations and bioavailability of trace metals. <![CDATA[<b>Local and regional factors influencing zooplankton communities in the connected Kasseb Reservoir, Tunisia</b>]]> Associations between zooplankton community structure and abiotic (temperature, dissolved oxygen, turbidity, nutriments) and biotic factors (chlorophyll a and phytoplankton community) were examined, in Kasseb Reservoir, northern Tunisia. Samples were taken bimonthly from July to December 2002 at 3 sampling stations (deepest station: Station 1, Brik River: Station 2 and M'Zaz Stama River: Station 3). From our results it is evident that zooplankton exhibit seasonally and spatially heterogeneous distribution. The highest density of zooplankton was recorded in September at a depth of 5 m (10.8 × 10³ ind·ℓ-1). At Station 1 cyclopoid copepods (65% of total abundance) were the most abundant group followed by Cladocera (21% of total abundance). At Station 2 (93% of total abundance) and Station 3 (98% of total abundance) cyclopoid copepods were numerically dominant throughout the study period. Canonical correspondence analysis (CCA) was used to estimate the influence of abiotic and biotic factors in structuring the zooplankton assemblage. Zooplankton abundance was negatively correlated with turbidity (r= -0.381, P <0.05). The results also suggest that both local (environmental parameters, competition, and predation) and regional (hydrologic connections and dispersal) factors have a significant effect on both species richness and community structure of zooplankton in Kasseb Reservoir. The presence of zooplankton species con sidered to be indicators of eutrophic status confirmed the high trophic levels of Kasseb Reservoir. <![CDATA[<b>Removal of <i>Escherichia coli</i> from biological effluents using natural and artificial mineral aggregates</b>]]> Ability for disinfecting sterile biological effluents inoculated with Escherichia coli ATCC 25922 at concentrations of 10(5) CFU/mℓ, using a natural mineral aggregate (NMA) and artificial mineral aggregates (AMA's) consisting of individual oxides as FeO, CuO y Ag2O and combined oxides as Fe2O3-Cu2O, Fe2O3-Ag2O, Cu2O-Ag2O, Fe2O3-Cu2O-Ag2O, contained alginate beads, was compared. The results indicate that Ag2O and Fe2O3-Ag2O, Cu2O-Ag2O combinations, as well as NMA, inactivated 100% of E. coli in 30 min, whereas the oxides mixture, Fe2O3-Cu2O-Ag2O, took 13 min. It was observed that redox potential values were closely related to the disinfection level achieved. The advantage resulting from using alginate beads was that these allow the formation of AMA, which has higher disinfectant ability relative to NMA. <![CDATA[<b>Theoretical and numerical analysis of the influence of the bottom friction formulation in free surface flow modelling</b>]]> Bottom friction modelling is an important step in river flow computation with 1D or 2D solvers. It is usually performed using energy slope based formulations established for uniform flow conditions, or using a turbulent regime based approach relying on turbulence analysis. However, these formulations are often applied under conditions of relative roughness which lie far outside of their validity fields. Furthermore, the theoretical definition of the roughness coefficients, defined by the different authors of both approaches, is not valid for usual numerical flow modelling, considering numerical approximations. The value of this coefficient becomes generally dependent on the flow conditions. Following the definition of the flow validity field of the main friction formulations proposed in literature, an original formulation has been developed. It combines 2 explicit turbulent regime based formulations smoothly linked by a polynomial expression, providing a continuous formulation covering the wide range of roughness usually encountered in river flows. The formulation is suitable to model, with a unique value of the friction coefficient, river flows with a wide range of hydrodynamic properties (water depth, discharge). The efficiency of this new formulation, fitted to explicit friction formulations and numerically adjusted, is demonstrated through various 1D and 2D practical applications. <![CDATA[<b>Multi-grid Beam and Warming scheme for the simulation of unsteady flow in an open channel</b>]]> In this paper, a multi-grid algorithm is applied to a large-scale block matrix that is produced from a Beam and Warming scheme. The Beam and Warming scheme is used in the simulation of unsteady flow in an open channel. The Gauss-Seidel block-wise iteration method is used for a smoothing process with a few iterations. It is also shown that the governing equations determine the type of prolongation and restriction operators for the multi-grid algorithm. <![CDATA[<b>Local energy losses at positive and negative steps in subcritical open channel flows</b>]]> Local energy losses occur when there is a transition in open channel flow. Even though local losses in subcritical open channel flow due to changes in channel width have been studied, to date no studies have been reported for losses due to changes in bed elevations. Steps are commonly used in engineering applications to stabilise the flow in open channels. Hence, it is important to estimate local losses for design purposes. The aim of this study was to formulate the local energy losses at positive and negative steps in subcritical open channel flows. Flow rates and water depths before and after the step were measured for varying step heights of abrupt and 45º inclined steps. Empirical equations relating the local losses to the Froude number on the step and the relative step height are proposed for positive and negative steps. In addition, practical values of local loss coefficients are determined. <![CDATA[<b>Experimental and numerical investigations of flow through free double baffled gates</b>]]> Studying the flow patterns and behaviour of double baffled gates under different flow heads is important to improve their performance, which could help in widening the range of their application. In the present study, physical and numerical investigations were conducted on the double baffled gate. A 3D Acoustic Doppler Velocity Meter (ADV) was used for laboratory measurements of the instantaneous velocity fields in the physical gate model. In parallel with this, the CFD Fluent package was adopted to carry out a sensitivity analysis for a matrix of geometric parameters of the double baffled gate. The outcomes of the laboratory and CFD numerical investigations were incorporated in a spreadsheet with the purpose of informing the design of double baffled gates under conditions of non-submergence. <![CDATA[<b>Investigating the cooperative strategies between China and North Korea for the Tumen River Area Development Programme</b>]]> Addressing the equitable management of an international boundary river, this study aims to find the optimal strategy with regard to how to build multi-purpose dams and allocate the benefits and costs thereof. The interests of the riparian countries (North Korea and China) are defined in terms of the cooperative 2-person nonzero-sum game, and the Nash product is then calculated for various alternative strategies. The results reveal that the Kangkudong Dam and the Simpo Dam should be collaboratively constructed, and that the benefits of the 2 dams should be allocated according to relative demand in order to provide North Korea and China with sufficient benefits and to equitably address their conflicting interests. Furthermore, the suggested strategy was found to be optimal or at least quasi-optimal when the North Korean economy, which is regarded as a crucial source of uncertainty in this case, moved from a low-growth scenario to a high-growth scenario. <![CDATA[<b>Industrial effluent treatments using heavy-metal removing bacterial bioflocculants</b>]]> Bioflocculants produced by Herbaspirillium sp. CH7, Paenibacillus sp. CH11, Bacillus sp. CH15 and a Halomonas sp. were preliminarily evaluated as flocculating agents in the treatment of industrial wastewater effluents. Industrial (1 local chemical-industry and 2 textile-industry: Biavin 109-medium blue dye and Whale dye) effluent (9 mℓ) containing various heavy metals was vortexed with 1 mℓ of bioflocculant in a 25 mℓ test tube. One mℓ of water (Millipore Elix purification system, 17 megaΩ) was substituted for the bioflocculant in the control. After 5 min, the heavy metal concentrations, the microbial population and the turbidity of the top layer of the industrial effluent were determined using ICP-OES, spread-plate technique and a turbidity meter respectively. The flocculating activity was calculated based on absorbance at a wavelength of 550 nm. Bioflocculants produced in this study were capable of removing several heavy metals from industrial effluents simultaneously and effectively. This was significant (p < 0.05) when applied to Biavin medium blue dye, with 95% of Cr2+ and 94% of Ni2+ removed by the presence of bioflocculants. Bioflocculants also removed almost all of the bacteria and reduced 50-80% of the turbidity of the chemical effluent sample, simultaneously. Bacterial bioflocculants may provide an alternative means of treating industrial wastewater resulting in environmental and economical benefits. However, our findings suggest that the treatment of industrial effluents using bioflocculants might be effluent-dependent. In order to explore the potential of bioflocculants in the treatment of industrial effluents, a preliminary study to determine the optimal conditions is crucial.