Scielo RSS <![CDATA[Water SA]]> vol. 34 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Application of satellite-derived rainfall estimates to extend water resource simulation modelling in South Africa</b>]]> Spatially interpolated rainfall estimates from rain-gauges are widely used as input to hydrological models, but deriving accurate estimates at appropriate space and time scales remain a major problem. In South Africa there has been a gradual decrease in the number of active rain-gauges over time. Satellite-based estimates of spatial rainfall are becoming more readily available and offer a viable substitute. The paper presents the potential of using Climate Prediction Center African daily precipitation climatology (CPCAPC) satellite-based datasets (2001-2006) to drive a Pitman hydrological model which has been calibrated using gauge-based rainfall data (1920-1990). However, if two sources of rainfall data are to be used together, it is necessary to ensure that they are compatible in terms of their statistical properties. A non-linear frequency of exceedance transformation technique was used to correct the satellite data to be more consistent with historical spatial rainfall estimates. The technique generated simulation results for the 2001 to 2006 period that were greatly improved compared to the direct use of the untransformed satellite data. While there remain some further questions about the use of satellite-derived rainfall data in different parts of the country, they do seem to have the potential to contribute to extending water resource modelling into the future. <![CDATA[<b>Prediction of salt balances in irrigated soils along the lower Vaal River, South Africa</b>]]> In arid and semi-arid regions irrigation tends to degrade soil and water quality through salt accumulation with devastating effects on some crops. This is, according to irrigators, also the case along the lower Vaal River in South Africa. Properly calibrated and tested salinity models could assist the agricultural community in improving salinity management under irrigation. This paper reports on, firstly, salt balances of soils in this region being irrigated for different time periods, and secondly, salt content changes that can be expected as a consequence of future irrigation. Two empirical models, viz. a general and specific salt-balance model were used together with existing water- and soil-quality data to generate such information. The soils selected for this study had been irrigated for periods of between 17 to 53 years. Over these periods addition of salts as a result of farming practices varied between 79 and 280 t∙ha¹, with irrigation water being the major contributor. Between 78% to 87% of the salts added to the soils had been leached from the root zone Despite these large amounts of salts that have been removed, certain irrigation practices have promoted the buildup of salts in some of the soils. The freely drained sandy soils irrigated by centre pivot are of particular interest. Poor management of this system can reduce crop yields. On account of inadequate leaching salts are building up to levels that impair the potential evapotranspiration level of maize. Predictions also show that irrigation should rather be withdrawn from soils with poor internal drainage properties, such as the Arcadia soil at Spitskop. In contrast, flood irrigation on certain duplex soils, such as the Valsrivier at Vaalharts, with relatively good internal drainage properties, can improve their quality. <![CDATA[<b>Construction and evaluation of a <i>gfp</i>-tagged <i>Salmonella</i> Typhimurium strain for environmental applications</b>]]> Salmonella enterica ser. Typhimurium was isolated from freshwater sediments and chromosomally labelled with a stable variant of the green fluorescent protein (GFP). The pUT mini-Tn5 Km transposon was used to introduce the gfp gene onto the chromosome of the S. Typhimurium strain by tri-parental mating. Southern Blot hybridisation confirmed that the gene had integrated into the chromosome. The gfp gene was stably maintained and the labelled strain was not growth-rate impaired. The incorporation of the gfp gene did not convey any significant loss of phenotype which would affect the survival and behaviour of the tagged strains. The tagged S. Typhimurium strain was used to spike an established drinking water biofilm and was able to colonise and persist within the biofilm. The tagged strain was also successfully used to study the survival of S. Typhimurium in natural sediments under different temperatures. These tagged strains can therefore be used to study the fate and survival of different Salmonella strains in water environments. <![CDATA[<b>The application of a Fish Assemblage Integrity Index (FAII) in a Southern African river system</b>]]> The Fish Assemblage Integrity Index (FAII) was used to determine the status of the fish assemblage in relation to human-induced factors in 3 segments of the Nyagui River, Zimbabwe. The 1st and upstream segment, with a relative score of 56.5%, was classified as largely modified. The presence of exotic predators, Micropterus salmoides, that constituted >10% of the fish population sample, was linked to this low score in this segment that had low habitat diversity. The 2nd and middle segment had a relative score of 91.6% and was classified as unmodified. Species that are intolerant to habitat modification, which included Opsaridium zambezense, Chiloglanis neumanni and Zaireichthys rotundiceps, were collected. Habitat diversity increased while the proportional abundance of M. salmoides decreased in this segment. The 3rd and downstream segment, with a score of 81.5%, was classified as largely natural. This score was mainly obscured by rare and migratory species that were expected at low altitude but were not collected. Nevertheless, intolerant species were collected from this segment. Habitat diversity was highest while the proportional abundance of largemouth bass, Micropterus salmoides, was lowest. It is recommended that more studies be carried out to test the consistency of the FAII in determining the impact of introduced species on native species, and to test the impact of other human activities on fish communities in Zimbabwean rivers. <![CDATA[<b>Klein River Estuary (South Africa): 2D numerical modelling of estuary breaching</b>]]> 2D numerical modelling of the breaching process of the Klein River Estuary in South Africa was carried out. The model was calibrated on field data and performs reasonably well, and is able to simulate the ebb and flood channels that form upstream of the mouth. The focus of the simulations was to determine the effectiveness of flushing of sediments during breaching, by investigating the breaching process at different water levels in the estuary, as well as at two different areas along the berm. Breaching at higher water levels increases the effectiveness of flushing as the discharge through the mouth increases significantly at higher water levels. Flushing towards the middle or south-east side of the berm is much more effective than towards the north-west side. <![CDATA[<b>The effects of increased freshwater inflow on metal enrichment in selected Eastern Cape estuaries, South Africa</b>]]> The concentrations of select metals (Cd, Co, Cu, Fe, Pb, Ni and Zn) within the water column and sediment of the permanently open Kariega Estuary and temporary open/closed Riet and East Kleinemonde Estuaries were investigated during a dry and a wet season. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs Fe were used to assess the extent of metal enrichment in the sediments. The results of the study indicate that Cd, Co Ni and Pb were enriched above baseline concentrations (1.0 < EF < 4.1) in the sediments of all three estuaries. Co, Pb and Ni enrichment in the Kariega Estuary sediments was significantly higher during the dry season, and the mean concentrations of Pb and Cd in the water column were 19-fold and 66-fold higher in the dry season. The elevated concentration of metals during the dry season could be related to accumulation of diffuse pollution from human activities within the catchment area. Conversely, inflow of freshwater into the estuary had the net effect of reducing the concentration and enrichment of these metals within the Kariega Estuary due to scouring and outflow of estuarine water and sediment into the marine environment. The temporal variations in metal concentrations and enrichment factors were less pronounced in the temporary open/ closed estuaries than the Kariega Estuary. The observed trend can probably be related to the low anthropogenic impact within the catchment areas of these systems, and the relatively smaller size of the catchments. Significant spatial variations existed in metal enrichment in the sediment of both the East Kleinemonde and Riet Estuaries, with the highest degrees of enrichment occurring in the sediments from the marine environment and lower reaches. <![CDATA[<b>On the use of diatom-based biological monitoring Part 1: A comparison of the response of diversity and aut-ecological diatom indices to water quality variables in the Marico-Molopo River catchment</b>]]> Two main approaches have been followed in using diatoms as bio-indicators in the past few decades namely species diversity indices and aut-ecological indices. This study, based on 102 water quality and epilithic diatom samples from the Crocodile Groot-Marico catchment in South Africa, evaluated both types of indices by establishing how well they reflect changes in water quality. It was found that less of the variation in diversity indices could be attributed to changes in water quality variables than was the case for the aut-ecological indices. Furthermore it was found that species diversity indices tend to be higher at intermediate levels of pollution, rather than at low levels of pollution. <![CDATA[<b>On the use of diatom-based biological monitoring Part 2: A comparison of the response of SASS 5 and diatom indices to water quality and habitat variation</b>]]> Due to the fact that South Africa is a water-scarce country, integrated water resource management based on sound information is essential. Bio-indicators have provided valuable information for water resource management in recent years and have enjoyed increasing popularity. Bio-indicators especially stepped to the forefront with the realisation that aquatic eco-systems are not only a source of water but also deliver several goods and services, as well as being essential for industrial growth and quality of life of many South Africans. This study aimed to quantitatively test two kinds of biomonitoring tools namely diatom-based (SPI and BDI) and macro-invertebrate based (SASS 5) in order to assess their applicability in South African River systems; and whether any additional information can be gained by using the two tools in tandem. The results showed that diatom indices are affected more by changes in water quality than SASS 5, while SASS 5 displayed a higher dependency on habitat quality, as measured by IHAS, than the diatom indices. It is therefore suggested that the two indices be utilised as complementary indicators for integrated assessment of river health. <![CDATA[<b>Maximum growth and decay rates of autotrophic biomass to simulate nitrogen removal at 10°C with municipal activated sludge plants</b>]]> The present study aims at determining most likely values for the maximum growth rate (µA, max) and the endogenous decay rate (bA) of nitrifiers for activated sludge processes treating municipal wastewater operated at low temperature (10°C). The work used nitrification rate data measured on 10 full-scale plants and 2 pilot plants fed with domestic sewage. This set of data was combined with a modelling and a theoretical approach. The unified values (µA, max = 0.45-d-1 and bA = 0.13-d-1) were obtained at 10°C for the kinetic parameters of the autotrophic biomass in the SRT range 10 to 50 d. In addition, the factors affecting the expected nitrification rate (r v, nit) were established by a theoretical approach and confirmed by experimental results. For a given SRT, a linear relationship with the nitrogen volumetric loading rate was shown. The COD/TKN ratio of the influent on the nitrification rate was demonstrated. Finally, an operational tool for the verification of the nitrification rate in the design procedure of activated sludge processes is proposed. <![CDATA[<b>Groundwater discharges to aquatic ecosystems associated with the Table Mountain Group (TMG) aquifer: A conceptual model</b>]]> This paper reports on a conceptual model that was developed to describe the different groundwater discharge 'types' from the Table Mountain Group (TMG) aquifer, that contributes to the different components of the flow regime in each of the recognised river reaches for streams and rivers associated with the TMG. This model integrates hydrogeological, ecological and geomorphological understandings into an ecohydrological perspective linking ground- and surface water systems. Through geospatial intersections of existing GIS layers a GIS model was also developed to highlight the quaternary catchments containing sensitive aquatic ecosystems that could be vulnerable to groundwater use from the TMG. The conceptual model demonstrates the intimate link between groundwater from the TMG aquifer and aquatic ecosystems in the mountain and foothill reaches of streams and rivers in the Cape Folded Mountains in particular. It also identifies two primary zones of interaction between groundwater and surface water in the TMG, namely, the 'TMG aquifer daylight-domain', located in the recharge zone, and the 'TMG aquifer surface water interface-domain', located at the discharge end of the aquifer. The conceptual model clearly indicates the difference between real groundwater, and perceived groundwater contributions to streamflow in the TMG. It is the lower flows of the flow regime that will be most vulnerable to groundwater use from the TMG aquifer in the 'TMG aquifer daylight-domain', which are unfortunately also the most important flows from an ecological perspective. However, any groundwater use from the TMG aquifer will also affect the discharge end of the aquifer, located far from the higher elevation recharge areas, or the point of groundwater abstraction, in lowland settings in the 'TMG aquifer surface water interface-domain'. The GIS model integrated the conceptual understanding into a management tool by highlight all quaternary catchments associated with TMG containing sensitive aquatic ecosystems and gave the variable vulnerability for each. <![CDATA[<b>Pollution menacing Lake Victoria: Quantification of point sources around Jinja Town, Uganda</b>]]> Lake Victoria is Africa's largest tropical freshwater lake, important as a source of drinking water and as a source of food for the population in the surrounding region. Due to increased human activities in agriculture and industry during the past decades a continuously increasing inflow of agricultural runoff has been observed, and lately there have also been increased discharges of municipal effluents and industrial wastewater into Lake Victoria. This paper summarises the results of a one-year (1997 to 1998) environmental and ecological study of industrial wastewater point sources in the Jinja (Uganda) catchment area. Main industries concern food processing, textile, leather and paper production and metallurgy. One fish- filleting factory showed the highest annual nutrient loads with 0.13 t NO3-N, 0.20 t NH4-N and 0.77 t PO4-P, while another disposed of annual loads that amounted to 0.10 t NH4-N and 0.49 t PO4-P. From food-processing industries, the highest annual load of organic matter (COD) discharged to the lake amounted to 36.8 t. A tannery in Jinja released effluent with an extremely high mean concentration of the very toxic chromium+6 of 264 mg-t-1, which results in an estimated annual load of 2.2 t of Cr+6. Concentrations of nitrogen and phosphorus from fish-filleting industries and chromium+6 from the tannery were far above the allowed effluent limits in Uganda, leading to enhanced eutrophication and bioaccumulation of Cr+6 in Napoleon Gulf, Lake Victoria. The study provides information on point sources of effluent derived from Jinja's industrial sector in an effort to force resource users to move towards a more sustainable pattern of environmental management. The most appropriate way to reduce the ongoing eutrophication and pollution of Lake Victoria would be to reduce the releases of nitrogen, phosphorus, organic compounds and chromium into Napoleon Gulf by on-site pretreatment, so that they remain within non-critical levels. Industries must be required to monitor their effluents before these are discharged into Kirinya National Water and Sewerage Corporation oxidation ponds and finally into Kirinya West urban wetlands. <![CDATA[<b>Biological nitrate removal in a laboratory-scale slow sand filter</b>]]> This research evaluated removal of nitrates from drinking waters in a slow sand filter (SSF). Batch experiments were performed to determine optimum carbon to NO3-N (C/N) ratio for the filtration experiments. The filter column was filled with filter sand of an effective diameter of 0.5 mm and uniformity coefficient of 1.23. The filter was operated at filtration rates of between 0.02 to 0.120 m/h and 0.01 to 0.25 m/h with concentrations of 22.6 and 45.2 mg NO3-N/l, respectively, and effluent samples of the SSF were taken at 6 depths of 10, 15, 20, 40, 60, 80 cm, and the bottom. Optimum C/N ratio was found to be 1.5 when using ethanol in batch tests when the removal efficiencies of NO3-N and C were higher than 90%. Although increasing filtration rates decreased NO3-N removal, effluent NO3-N concentration at the effluent port of the SSF was lower than the limit value. Most of the NO3-N removal was carried out at the upper layer of (10 cm) the filter bed. Concentration of NO3-N, NO2-N, and C were not detected at the 60 cm depth of the SSF through the study for the inlet concentrations of 22.6 mg NO3-N/ℓ As expected, increasing influent NO3-N concentration to 45.2 mg/ℓ increased NO3-N, NO2-N, and C concentrations in the effluent water. The SSF process was unable to provide NO3-N removal rate of more than 228 g N/m³·d (0.2 m/h flow rate, 217g N/m²·d of surface loading rate). The NO3-N removal efficiency dropped slightly from 96 to 95% when the loading rate increased from 228 to 285 g/m³·d, but the effluent water contained higher concentrations of NO2-N (8.4 mg/ℓ) than the standard value. The results of the SSF experiment demonstrated that averaged nitrogen conversion to volatile solids was about 0.77 mg VS/mg NO3-N. <![CDATA[<b>The genetic relatedness of <i>E. coli</i> associated with post-collection drinking water contamination in rural households</b>]]> Rural households are often dependent on rivers, springs, boreholes or standpipes some distance from their homes for their daily water requirements. Water for drinking and domestic use is consequently stored in containers in-house which are prone to post-collection contamination. The objective of the study was to determine the most likely origin or place of introduction of E. coli associated with post-collection contamination in rural households, by assessing the degree of genetic relatedness of E. coli present in the stored water and other environmental samples. E. coli isolates were obtained using either mFC agar with confirmation of indole production (44 isolates) or Colilert®-18 (52 isolates). Amplified fragment length polymorphism (AFLP) fingerprinting was applied to determine the genetic relatedness of E. coli isolated from in-house storage containers, drinking cups, hand-swab samples, cattle dung and from the source water (spring water). DNA fingerprints of E. coli produced a number of clusters (>85% similarity scores calculated with the cosine coefficient). Identical E. coli genetic patterns were observed at closely linked points within the domestic pathway of water handling, such as between hand-swab and drinking-cup samples, between storage container and source isolates, and between drinking cups, source water and storage containers. The results indicated that AFLP fingerprinting could be applied to determine the genetic relatedness of E. coli isolated from closely linked points within the domestic pathway of water use within a household. However, the high genetic diversity observed for E. coli bacteria isolated from the different water and environmental samples tested in this study, hampered the identification of post collection points of contamination. <![CDATA[<b>Cyclodextrin polyurethanes polymerised with carbon nanotubes for the removal of organic pollutants in water</b>]]> Organic compounds are some of the major pollutants of water worldwide. They can be toxic or carcinogenic even at low concentrations. The non-reactivity of these species makes it difficult to remove them from water, particularly when present at concentration levels of nanograms per litre (ng·ℓ-1) or lower. Reasonably inexpensive yet effective methods for the removal of these organic pollutants to below ppb levels are therefore required. Insoluble cyclodextrin polyurethanes have demonstrated the ability to remove organic species from water at concentration levels of nanograms per litre. Carbon nanotubes have also been reported to efficiently adsorb some organic molecules such as dioxins and polychlorinated dibenzo-furans. However, these nanotubes are currently too expensive to be used on their own in water treatment. An investigation into the use of cross-linked cyclodextrin polyurethanes copolymerised with functionalised multiwalled carbon nanotubes as adsorbents for organic pollutants has yielded very useful results which may have an impact in future water treatment applications. <![CDATA[<b>Fatty acids composition in South African freshwater fish as indicators of food quality</b>]]> Lipid classes and fatty acid composition of three commercially important freshwater fish species Oreochromis mossambicus (Mozambique tilapia), Clarias gariepinus (African catfish) and Cyprinus carpio (carp) obtained from an aquaculture, different river systems and fish markets from different provinces in South Africa were investigated. Fatty acids were extracted from the fish fillets through the Folch extraction method (using chloroform: methanol at the ratio of 2:1). Generally, tilapia fish species was found to be the richest in fatty acid composition. In all fish species analysed, palmitic acid (16:0) was found to be the most abundant fatty acid ranging from 18.24 to 21.84%. Appreciable quantities of essential polyunsaturated fatty acid such as docosahexaenoic (DHA) (22:6 n-3, 3.92 to 6.16%), eicosapentaenoic acid (EPA) (20:5 n-3, 1.91 to 2.92%) and arachidonic acid (20:4 n-6, 7.19 to 8.50%) were also found. Observations show that fish species obtained from Gauteng Province are richer in fatty acids compared to those in Limpopo Province. The study points out that all fish species investigated contain appreciable levels of Omega-3 (n-3) polyunsaturated fatty acids (PUFA) and are therefore suitable for an unsaturated low-fat diet. This is important especially for poor communities who cannot afford to get a balanced diet, rich in some essential fatty acids.Therefore, it is important to determine the nutritional value of local fish, since it significantly contribute to a healthy diet in rural communities. <![CDATA[<b>Full-scale modelling of food industry WWTP: Model evaluation and reuse</b>]]> This study aimed at testing a mathematical model for an industrial WWTP. This model was developed in a previous study. The characterisation of the influent wastewater was repeated and results revealed that the composition of the wastewater was somewhat changed compared to the previous study. In order to account for varying wastewater composition in the future, the influence of this composition on the effluent concentration was calculated based on relative sensitivity functions. This calculation revealed that the effluent COD concentration is most affected by the inert COD fraction in the influent and that the effluent ammonium concentration is most affected by the biodegradable COD fraction in the influent. As such experimental efforts can be conducted towards determination of the fraction that is most influential on the required result. The model was further evaluated with new data. It could be shown that agreement between simulated and measured data was very good and that no model recalibration or extension will be necessary. As such the industrial WWTP model passed the model evaluation test. In the future this model will be used for potential further upgrades. <![CDATA[<b>A laboratory simulation of <i>in situ</i> leachate treatment in semi-aerobic bioreactor landfill</b>]]> In this study, two laboratory-scale simulated landfill bioreactors were established, of which Reactor A was operated only with leachate recirculation and served as the control, and Reactor B was operated as semi-aerobic bioreactor landfill with leachate recirculation. In situ leachate treatment and accelerating organic decomposition in semi-aerobic bioreactor landfill was investigated. The results indicated that the introduction of air into the landfill was favourable for optimising the micro-organism growth environment and accelerating the degradation of organic matter. It can be seen clearly from the results that NH4+-N can be removed in situ in the semi-aerobic bioreactor landfill with leachate recirculation. Moreover, semi-aerobic bioreactor landfill showed lower emissions for leachate than those in leachate from anaerobic landfill, with low concentrations of COD, VFA, NH4+-N and TKN, and which saved the disposing process of the discharged leachate. The three-dimensional excitation-emission matrix fluorescence spectroscopy (EEMs) of dissolved organic matter (DOM) in Reactor B changed greatly, and fluorescence peak changed from protein-like fluorescence at Day 60 to humic-like fluorescence at Day 95 and 250, while in Reactor A, fluorescence peak of DOM was always protein-like fluorescence. The comparison of the EEMs indicated that the semi-aerobic landfill accelerated the organic decomposition.