Showing papers in "Water SA in 1997"

Preliminary empirical models to predict reductions in total and low flows resulting from afforestation

Abstract: Mathematical models to predict runoff reductions due to afforestation are presented. The models are intended to aid decision-makers and planners who need to evaluate the water requirements of competing land uses at a district or regional scale. Five afforestation catchment experiments were analysed by the paired catchment method to determine the reductions in both total (annual) and low flows. The percentage reduction in flow after afforestation with both eucalypts and pines was determined for each post-treatment year relative to the expected flow based on a calibration relationship with an untreated (control) catchment. We fitted curves to these data points to predict the effects of afforestation under optimal and sub-optimal growing conditions. Eucalypt plantations were found to deplete both total and low flows sooner and in larger quantities than pine stands.

The need for guidelines to bridge the gap between ideal drinking-water quality and that quality which is practically achievable and acceptable

Abstract: Classically a distinct boundary is made between ideal and non-ideal water. Such a distinct boundar is not in keeping with resource water quality conditions, especially in a semi-arid climate. To facilitate the decision processes around the supply of quality drinking water, a classification system was devised to give a clearer picture of expected effects on the domestic user. The classification system, which divides water quality into four classes from 0 (ideal) to Ill (unsuitable for use as drinking water without prior treatment), based on the 2nd, 1996 edition, of the South African Water Quality Guidelines for Domestic Use. The classification, however, differs in several respects from the latter: (i) The definition of the user as drinking water for human use, rather than the wider definition for domestic water; (ii) the concept that non-ideal water may be used for short periods only rather than for a lifetime without significant ill effects, as in Class II; and (iii) the emphasis on health effects from drinking-water use, especially in sensitive individuals, such as bottle-fed infants. In the selection of constituents the classification is biased towards those constituents that commonly are of concern in borehole water in rural areas where there is little or no pollution from heavy industry. The present constituent list is not nearly as extensive as that contained in the 2nd edition of the South African Water Quality Guidelines for Domestic Use.

Chromium, copper, iron and manganese bioaccumulation in some organs and tissues of Oreochromis mossambicus from the lower Olifants River, inside the Kruger National Park

Abstract: The bioaccumulation of chromium, copper, iron and manganese by Oreochromis mossambicus was investigated at two localities (Mamba and Balule) in the lower Olifants River, inside the boundaries of the Kruger National Park. The Cr, Cu, Fe and Mn concentrations, recorded in the tissues of O. mossambicus at Mamba and Balule, did not differ much from each other. However, it was generally found that the highest accumulation of metals by the fish occurred at Mamba, except for iron, where the opposite occurred. The metals investigated during this study mainly accumulated in the liver and gills, followed by the skin, and lastly the muscle.

The effects of supplied water quality on human health in an urban development with limited basic subsistence facilities

Abstract: Domestic unavailability of water supply in South Africa often leads to improper use of supplied or other unsafe sources of water. The relationship between water quality, water availability, water accessibility, water use and incidence of diarrhoea due to these factors, was investigated in this study. The study was conducted in a large low socio-economic developing urban settlement. Reported diarrhoea cases were followed up to establish the water usage pattern of consumers in these particular households. Water was generally obtained from supply at public standpipes and stored in various forms of containers in households. Microbiological indicators were used to assess possible contamination of the water supply. Tests indicated limited instances of faecal and other forms of microbiological contamination in sections of the water-supply network. Indications were also found that the network in this area could intermittently be subjected to pollution from unknown sources although incidences were limited and not prolonged. Tests on the bulk water supply from the utility to the consumer water network indicated no faecal contamination in the bulk supply. In general the supply quality tested indicated no risk to consumers. However, the insanitary condition of containers as well as the manner of storing and handling of the containerised water led to contamination of water supplies. By implication, the system of water supply through public standpipe was conducive to conditions that could lead to contamination of stored water supply in households within the target consumer group.

Two-phase anaerobic digestion of three different dairy effluents using a hybrid bioreactor

Abstract: The South African dairy industry is a major water user and as a result has to reconsider current effluent treatment and disposal methods The effluents from three dairy factories (cheese, fresh milk and milk powder/butter factories) were analysed and the chemical oxygen demand (COD), pH and effluent volumes were found to be highly variable over short time intervals during the daily production cycles The pH was found to vary between 22 and 118 units and the COD values ranged from 800 to 15 000 mgt 1 over a period of 2 h The average COD of the effluents emerging from the three factories varied between 1 908 and 5 340 mgt 1 Significant differences were also found in the composition of the effluents from the three factories In this study, a mesophilic laboratory-scale hybrid bioreactor was used in conjunction with a pre-acidification step to treat the three dairy factory effluents It was clear from the data obtained on the cheese, fresh milk and milk powder/butter waste waters that dairy effluents are suitable for treatment by means of the anaerobic digestion process and the use of a hybrid anaerobic bioreactor can be seen as a viable treatment option The COD values of the three pre-digested dairy waste waters were reduced by between 91 and 97% at organic loading rates of between 097 and 282 kgCODm 3 d -1 and subsequent methane yields varied from 0287 to 0359 m 3 CH 4 kg -1 COD removed (73 and 91% of the theoretical maximum yield) during anaerobic digestion The pH values of all the digester effluents were >75 units The data clearly indicated that anaerobic treatment of the different dairy effluents was successful and that this particular type of bioreactor would be suitable for the anaerobic treatment of dairy effluents An important consequence of the data from this study is that a two-phase set-up will be required to protect the methanogens in the bioreactor from prohibitively low pH values and high VFA concentrations produced during the acidogenic phase The two-phase system will allow pH control in the acidogenic phase should it be needed in a full-scale or pilot-scale treatment plant

A strategy for evaluating the environmental impact of on-site sanitation systems

Abstract: In order to ensure that all South Africans are provided with access to adequate sanitation within the constraints of limited national resources, policies currently being considered by the South African government envisage a significant amount of on-site sanitation in use in the urban areas of the country for the foreseeable future. However, concerns exist that widespread use of these systems will cause subsurface migration of contaminants which may have adverse impacts on human health and on the natural environment. This paper provides an overview of the problem, reviews existing guidelines and presents a more rigorous strategy for evaluating the impact of on-site sanitation on human health and the natural environment. The suggested strategy, which permits account to be taken of a multitude of variables encountered, is as follows: . define compliance requirements in terms of both physical location (point of compliance) and allowable contaminant concentration; . estimate risk of pollution by viruses and bacteria using a 'residence time' approach; . estimate pollution risk by nitrates using a mass balance approach ; . for both microbiological and chemical contaminants, use a probabilistic approach (as far as the available data allow), allowing appropriate margins of safety in design, such margins of safety still to be determined . carry out field monitoring of on-site sanitation schemes (if water resources are to be protected) to provide early warning of contaminant build-up. The establishment of a set of general principles for compliance requirements together with the application of these principles to the different water bodies (both surface water and groundwater) in South Africa is the most urgent requirement for the implementation of the above strategy. It is also suggested that evaluation of environmental impact of sanitation systems should not be confined to on-site sanitation alone, but should be extended to all forms of sanitation system, including water-borne sanitation systems as well.

Partial replacement of fish meal with either soybean meal, brewers yeast or tomato meal in the diets of African sharptooth catfish Clarias gariepinus

Abstract: As intensively cultured fish usually require high protein feeds, and since feeds are normally the largest variable cost item in commercial production, the profitability of intensive aquaculture is closely related to the world supply and cost of feed protein. Traditionally fish meal has been the major component of all fish feeds. However, its high cost has necessitated a search for alternative protein sources, especially those that are not suitable for human consumption. This study investigated the partial replacing of fish meal with alternative protein sources (tomato waste, soybean meal, brewers yeast) in iso-nitrogenous diets of C. gariepinus. The tomato used consisted of sun-dried pips and skins from ripe tomatoes used in the production of tomato pastes. The soybean consisted of either dehulled, solvent-(hexane) extracted soybean meal (Soy-2) or the same soy meal that had undergone a further extrusion process (Soy-1). The yeast used was a waste product from a local brewery. A final diet consisting of a mixture of the various ingredients was also prepared. Twenty-five catfish (30 to 45 g live mass (LM) were randomly allocated to 24 500 l tanks and four tanks were allocated to each diet. The tanks were then connected to a recirculating system (13 000 l total volume) and each had a flow rate of 7 ± 1 l·min. The water temperature was maintained at 25 ± 1 °C. The total biomass in each tank was measured weekly and the feed adjusted accordingly. The catfish were fed at 5% of total biomass for the first 4 d and 6% for the last 3 d of the week. The experiment was terminated after a 60 d feeding period. A statistical comparison of the final mean mass showed that all the diets differed significantly from each other (p=0.05), with the exception of the yeast and mixture diet and the yeast and Soy-1 diet. The descending ranking order of the mean final body mass (LM ± standard error, g) of the various diets was as follows: fish meal (284.6 ± 5.2), tomato (261.9 ± 5.3), yeast (222.2 ± 5.7), Soy-1 (220.5 ± 5.2), mix (201.4 ± 5.51), and Soy-2 (115.3 ± 5.5). The relatively strong growth experienced by fish receiving the tomato diet could possibly be caused by the high fish meal content of this diet. The poor growth of the Soy-2 diet is attributed to a high urease activity index (1.73). Soy-1 had an index of 0.07. The growth experienced by catfish fed the various protein sources indicates that C. gariepinus are able to utilise alternative protein sources successfully.

Development of an operating rule model to simulate time series of reservoir releases for instream flow requirements

Abstract: The output from many of the instream flow assessment workshops, currently being held in South Africa whenever a major water resource development is proposed, is a matrix of monthly flow rates that describe the recommended nature of a river's modified regime (IFR) that will maintain the river in a pre-determined ecological condition after the development has been implemented. This paper describes a technique that may be used to translate the IFR information into reservoir release operating rules for both low-flow and flood event releases and that can generate a time series of releases. The technique is based upon the use of a reference time series of daily flow data to represent the prevailing climate and trigger the various releases. To avoid the necessity of having a reference-flow time series available for the specific IFR site, the release trigger is based on duration curve percentage point data. These values are believed to be more closely equivalent across adjacent catchments than are weighted flows. Ultimately, the technique is expected to be used for planning purposes, to illustrate the effect of a given IFR on the likely day-to-day pattern of releases, as well as operationally, to control releases. This paper explains the technique and how it has been incorporated into a preliminary version of a model to simulate the pattern of releases that is expected to occur. The definition of the operating rules and the application of the model are illustrated using an example from the Luvuvhu River, Northern Province.

Determination and partitioning of heavy metals in sediments of the Vaal Dam System by sequential extraction

Abstract: The partitioning of 12 heavy metals in sediments of the Vaal Dam system was determined by applying a sequential extraction procedure. Environmental risks associated with the potential remobilisation of these metals, the capacity of the sediment to continue functioning as a sink and the possible origin of the metals were assessed. Despite the fact that the water level was at record lows; ca, 13% in the Vaal Dam. the extractable metal content of the sediments was low indicating a relatively unpolluted system. Major proportions of most metals seemed to be associated with the inert phase and could therefore be classified as of geochemical origin.

Kinetic-based model for mixed weak acid/base systems

Abstract: This paper describes the development of a simple kinetic model for mixed weak acid/base systems. In the model, the weak acid/ base equilibria are formulated in terms of the kinetics of the forward and reverse reactions for the dissociation of the weak acid/ bases. The parameter (compound) H + is also explicitly included in the model, so that pH can be calculated directly. The weak acid/ bases included are water, carbonate, ammonium, phosphate and short-chain fatty acids. However, the approach used to develop the model is general, and can be applied to include any other weak acid/base of importance. Precipitation of CaCO 3 and gaseous exchange of CO 2 also have been included. The model and the approach on which it is based have been validated by comparing model predictions to those obtained from equilibrium-chemistry-based models; good correlation was obtained. Compared to the equilibrium chemistry approach to modelling mixed weak acid/base systems, the kinetic approach offers several advantages. In particular, the use of kinetics will facilitate integration of the weak acid/base model with other kinetic models (biological, chemical or physical). For example, the model presented here can be readily integrated with the existing biological kinetic models for waste-water treatment systems, to extend application of these models to situations where an estimate for pH is essential. Furthermore, by providing an estimate for pH and for the species making up the weak acid/bases, the model will simplify inclusion of chemical and physical processes, where these are of importance.

Activated sludge mixed liquor heterotrophic active biomass

Abstract: In the current steady state design and kinetic simulation models for activated sludge systems, the heterotrophic active biomass is a key parameter. However, this parameter remains hypothetical within the structure of the models; it has not been measured directly, primarily due to the lack of suitable simple experimental techniques. In this paper a simple batch test procedure is used to quantify the heterotrophic active biomass concentrations of mixed liquor samples drawn from a well-defined anoxi/aerobic activated sludge system. The measured heterotrophic active biomass concentrations are in close agreement with those calculated theoretically using the steady state design and kinetic simulation models. This agreement provides substantive direct evidence supporting both the models and the experimental method.

Water demand and population growth

Abstract: The contribution of population growth in water demand projections is often obscured, since only the increase in domestic water demand is usually taken as an indication of the increase in water demand due to population growth. This paper aims to quantify direct (domestic) and indirect water requirements (e.g. for food production, energy etc.) to sustain an individual at a particular lifestyle level. The average domestic water demand projected to the year 2015 accounts for only about 20% of the average full demand while the water demand for the production of food and consumer goods and for employment accounts for 80% of the full water demand to sustain an individual. The full water demand of the 1995 increase in the South African population of about I million people, projected to the year 2015 when the newborns reach adulthood, is conservatively estimated at 638 MUd or about 23% of the current average daily water supply of Rand Water, indicating the tremendous pressure on water resources as a direct consequence of the high current levels of population growth.

A botanical importance rating of selected Cape estuaries

Abstract: A formula has been developed which allows a single numerical botanical importance score to be calculated for estuaries. The formula includes the area cover of each estuarine plant community type, its association with the estuary, its condition and the plant community richness. This study focused on temporarily and permanently open estuaries along the Cape coast, which for convenience was divided into four regions: Western Cape; South-Western Cape; Southern Cape and South-Eastern Cape. Thirty three temporarily and permanently open estuaries were studied and rated according to importance within the whole Cape coast, regional importance (i.e. Southem Cape or South-Eastern Cape), as well as against other estuaries of their type (i.e. temporarily or permanently open). The Olifants Estuary on the west coast received the highest importance score for the whole Cape coast. It has extensive marshes in its lower reaches that are in good condition. Reed and submerged macrophyte beds are also a feature of this estuary. Two False Bay estuaries, the Lourens and the Sir Lowry's Pass, had the lowest scores. These estuaries are severely impacted as a result of residential and industrial proximity, and rehabilitatory steps would be necessary to restore any botanical significance to them. Not all the regions' estuaries were used to obtain these scores and more need to be included to make the importance rating relevant to all estuaries along the whole South African coast. This rating can be used to identify estuaries which are worthy of receiving a high conservation status.

The fluvial dynamics of the Maunachira Channel system, northeastern Okavango Swamps, Botswana

Abstract: This study was undertaken to investigate the role and function of secondary channels (those that arise within the swamps and carry no externally derived bedload sediment) in the Okavango Delta, and focused on the Maunachira Channel of the north-eastern swamps. Three reaches were identified: an erosive upper reach; a depositional middle reach; and a stable lower reach where no sediment movement occurring and the channel bed is vegetated. The erosive reach is confined to the most proximal section of the channel and is associated with inflow into the channel from tributaries and from the surrounding swamp. Downstream of this reach, the channel becomes aggradational. The aggradational reach is associated with a marked rise in the channel water level relative to the surrounding swamps, which promotes water loss from the channel. Some of the water leaked from the channel supplies the Mboroga Channel to the south. Cyperus papyrus grows vigorously along the aggrading reach, and partially constricts the channel. Aggradation results in a decrease in channel gradient and flow velocity declines to below 0.4 m/s, when bottom-rooted vegetation is able to colonise the channel bed, terminating sediment movement. Channel margins in these lower reaches are characterised by Miscanthus junceus, a non-invasive plant species, which promotes long-term stability. The zone of aggradation is migrating upstream at about 170 m/a. The study suggests that secondary channels arise due to local oversteepening of the regional gradient, and their role is to redistribute sediment down this gradient.

Hepatitis viruses in water:Update on risk and control

Abstract: Three different hepatitis viruses, designated hepatitis A (HAV), hepatitis E (HEV) and hepatitis F (HFV) are now known to be transmitted by water. HAV has a long history of water-borne transmission in all parts of the world. HEV has been discovered only recently, and is now known to cause outbreaks of clinical disease in certain parts of the world. Indications are that HFV causes sporadic cases in restricted areas. Although the mortality of infections caused by all three viruses is relatively low, clinical disease may be severe and incapacitating. Case fatality rates of 20 to 40% are on record for HEV infections in pregnant women. HAV is endemic in most of the population of South Africa. Recent evidence indicates that HEV is also endemic, with high incidence in some communities. Although HFV has not yet been recorded in the country, it could be imported rapidly. The risk of waterborne hepatitis in South Africa should, therefore, not be underestimated. The risk can be expected to increase as a result of population growth and escalating demands on limited water resources. Since vaccines are available only for HAV, and no meaningful treatment is available for any of the viruses, control of the diseases depends on prevention of transmission. This implies a major responsibility for the water industry and related health authorities. No practical methods are available for direct detection of any of the viruses. Monitoring of the safety of water supplies does, therefore, continue to rely on the meticulous application of indirect methods. Shortcomings of these indirect methods emphasise the need for practical techniques to detect the viruses.

Review of recent developments in seasonal forecasting of rainfall

Abstract: General circulation models generally provide underestimates of the seasonal forecastabiliiy of the atmosphere as a result of their inability to simulate adequately the atmospheric response to sea-surface temperature anomalies and because of their exaggeration of the effects of the chaotic behaviour of the atmosphere. As a result, statistical forecast models will continue to provide a useful supplement to the dynamic models, although there is a need for the statistical models to capture explicitly the non-linear behaviour of the ocean-atmosphere system. Of concern, however, is the observation that forecast skill in many areas of the world appears to have decreased since the late 1980s. Careful validation of this possibility is required for South Africa.

A comparison of two sets of primers for the RT-PCR detection of astroviruses in environmental samples

Abstract: Human astroviruses (HAstV) are associated with sporadic cases and outbreaks of diarrhoea. The faecal-oral route is the predominant mode of transmission and contaminated drinking water and shellfish have been implicated as vehicles of transmission. Conventional diagnostic techniques have limited sensitivity and in this study two primer pairs, designated Jon and Mon, were compared for the detection of HAstV in environmental specimes by the reverse transcriptase-polymerase chain reaction (RT-PCR). Both primer pairs yielded positive RT-PCR products for the cell culture adapted HAstV-1 positive control. The Jon primers, however, also yielded positive results for other viruses as well as for a number of water samples. These data suggest that the regions amplified by the Jon primers are not unique to HAstV. The Mon primer pair yielded positive RT-PCR results only for HAstV serotypes 1 to 4 and some environment samples. The results obtained using the Mon primer pair could be confirmed by either hybridisation with an oligonucleotide probe specific for HAstV or a HAstV specific enzyme immunoassay (EIA). RT-PCR. using the Mon primers, proved more sensitive than electron microscopy (EM), immune electron microscopy (IEM) and EIA for the direct detection of HAstV in river water. Cell culture amplification using the PLC/PRF/5 human primary liver carcinoma cell line improved the sensitivity of HAstV detection by EIA and RT-PCR, but not EM and IEM. The sensitivity of the RT-PCR assay system was enhanced by prior viral recovery by a glass wool adsorption-elution technique.

Potentiometric measurement of chemical oxygen demand

Abstract: Measurement of the COD of an aqueous solution involves firstly digestion of a test sample with dichromate solution, and secondly measurement of the dichromate remaining either by titration by ferrous ammonium sulfate (FAS) to a color indicator endpoint, or via colorimetric determination using a spectrophotometer. In this paper, a potentiometric end-point determination (using FAS titrant) is proposed as a third option for measuring the dichromate remaining. The potentiometric method is based on the observation that the titration end point corresponds to a region of minimum redox buffer. That is, the end point to the titration is sharp and easily identified. Furthermore the platinum-calomel electrode system used in this method responds quickly to potential changes within the (Fe 2+ /Fe 3+ ):(Cr 2 O 7 2. /Cr 3+ ) solution producing stable readings. These factors allow rapid and accurate COD measurement. Furthermore the method is based firmly on theoretical considerations allowing extension into a region of low COD. The method is applied to a broad spectrum of waste waters and dilutions of these, using both macro- and semi-macro techniques. Results are compared with data determined using colorimetric and color indicator end-point methods. It is shown that the potentiometric end-point titration (with FAS titrant) can be used with equal or better facility.

A brief assessment of a weather data generator (CLIMGEN) at Southern African sites

Abstract: Weather data generators usually consist of two parts - a section that derives site-specific data-generation coefficients, and a routine that creates the actual observations themselves. In this study, the two CLIMGEN routines were integrated into a single PASCAL program, together with a radiation estimator, and then tested at sites in Southem Africa which had more than 50 years of concurrent daily air temperature and rainfall data. Annual figures were compared for all sites, while monthly statistics were compared for best and worst cases. Additionally, CLIMGEN daily data were used with the crop yield model CERES-Maize. Yield estimates obtained were compared with those using real observations over a similar 25-year period. CLIMGEN appears to work satisfactorily over much of Southern Africa. Its representation of climatic means and day to day variability are good. However, it requires more testing at places with shorter climatic records. Also, additional research using other crop yield models at other sites would be invaluable.

The diet of juvenile Sillago sihama (Forsskal, 1775) from three estuarine systems in KwaZulu-Natal

Abstract: The diet of Sillago sihama, a species whose juveniles occur regularly in KwaZulu-Natal estuaries, was investigated in Richards Bay, Durban Bay and Mlalazi Estuary. The species was is carnivorous in all three systems, with a distinct size-related change in diet being noted. Small individuals (<60 mm SLj consumed primarily planktonic prey (mainly larvaceans and copepods) whilst larger specimens fed on benthic crustaceans, polychaetes and bivalve Siphon tips. Although the prey consumed by S.sihama from different systems was similar, the trends of increasing reliance on benthic food sources with the size differed. Fish from Mlalazi began feeding on benthos at a smaller size than those from Richards Bay and Durban Bay. This is ascribed to potentially higher plankton densities in the harbours duc to animals from the marine environment king swept in through the deep entrance channels.

Water quality guidelines for livestock watering in Southern Africa

Abstract: The validity of the water quality guidelines for livestock watering is questionable as these are based largely on international guidelines and lack locally established water quality constituent lists, levels of acceptability and reference to Southern African livestock production systems. The water quality constituents fluoride, chloride, total dissolved solids and sulphate were identified in a review of subterranean water samples from non-hydrogauging stations from the Northern Province, North-Western Province and the Northern Cape Province as being the primary constituents of concern for livestock watering. Biological trials investigating toxicological and palatability aspects regarding the constituents fluoride, chloride, total dissolved solids, sulphate, nitrate and nitrite were conducted in sheep, cattle and poultry. The results indicated that the guidelines in use were too conservative for specific categories of livestock within Southern African livestock production systems, and that the guideline format used was inadequate in assessing the effects of water quality over the diverse range of livestock production systems found in Southern Africa. For more accurate assessment of the effects of water quality, for a given livestock production system the format should be based on ingestion levels, as opposed to a mg/l basis, and should take into account site-specific synergistic and antagonistic interactions within and external to the water to a greater extent. The results led to the compilation of the interim water quality guidelines currently in use and to the formulation of a water quality guideline index system.

Salt-water intrusion from the Mzingazi River and its effects on adjacent swamp forest at Richards Bay, Zululand, South Africa

Abstract: Drought conditions in the Richards Bay area coupled with abstraction for domestic and industrial use caused freshwater outflow from Lake Mzingazi to cease in February 1992. This led to the tidal intrusion of saline water from Richards Bay into the Mzingazi River. The extent of the intrusion up the river and into the groundwater was determined and the impact on the adjacent flora recorded. Results showed that saline water penetrated the groundwater for up to 20 m from the river bank and that this had caused the death of a number of swamp forest trees as well as the defoliation of others. Spring tides and particularly a very high equinox tide had further aggravated the situation causing damage to, and the death of, numerous plants in herbaceous swamp areas.

The use of oxygen evolution to assess the short-term effects of toxicants on algal photosynthetic rates

Abstract: O 2 -production using either Selenastrum capricornutum or Chlorella vulgaris as indicator organisms to assess the presence or not of toxic compounds, was measured in a small oxygen chamber. These measurements were done at predetermined I k irradiancies. At EC 50 and EC 90 levels, the response of S. capricornutum and C. vulgaris to atrazine toxicity was opposite to the response as determined at the EC 10 level. Chlorella vulgaris is more sensitive than S. capricornutum to high atrazine concentrations, but S. capricornutum is more sensitive than C. vulgaris at the EC 10 level. It was shown that the heavy metals Hg, Cd and Cu and the herbicide, atrazine, influenced the photosynthtic rates but the organophosphate, gusathion, had no effect. The oxygen evolution assay may be useful as a rapid preliminary screening method for the presence or absence of toxic substances.

A laboratory evaluation of Watermarkelectrical resistance and Campbell Scientific 229 heat dissipation matric potential sensors

Abstract: There is much interest in continuous recording of soil matric potential with porous matrix sensors for irrigation scheduling purposes. Watermark electrical resistance and Campbell Scientific 229 heat dissipation matric potential sensors were simultaneously tested in a modified pressure chamber. Both sensors are suitable for automatic recording of changes in soil water content or matric potential. Initial indications are that individual sensor calibration will be unnecessary for irrigation scheduling purposes. The electrical resistance measurement was shown to be affected by soil salinity and temperature and to be dependent on wetting history. Moderate hysteresis of heat dissipation sensors was recorded. Both the electrical resistance and the heat dissipation measurement provided reliable estimates of soil matric potential in the range from - 100 to 0 J-kg -1 at various salinity levels. A minimum reading interval of 3 min is recommended for the heat dissipation sensor to allow the block temperature to re-equilibrate.

Ultrafiltration in potable water production

Abstract: A low-pressure membrane technology for the one-step clarification and disinfection of water for potable use is described. The membranes are operated at net driving pressures of between 30 and 4kPa. The filtered product ol low turbidity was produced continuously and there was no correlation between the turbidity of feed and that of the product. The membrane process appears to be an effective means for filtering out coliforms, to render a good quality potable water upstream of final breakpoint chlorination.

Effect of gold-mine related operations on the physical and chemical characteristics of sediment texture

Abstract: The gold-mining process is unique as it not only has effects on the water quality and related environmental impacts. but also on the physical characteristics of the sediment in the area of the mining activities. The texture of the sediment in streams inside the mining area differs from the sediment texture in streams outside the mining area. The impact on the sediment in the gold-mining area is not uniform hut area specific. It became clear that certain sections of the gold-mine environment might be common to most gold mines in South Africa. Internal recirculated waterways/streams which are not diverted into watland areas. and also do not discharge to the outside boundaries of the mine, normally have fine graded sediment particles (≤63 pm). These streams are also close to the actual gold-mining activities. On the other hand, the sediment texture of the streams which do discharge to the outside boundaries of the gold mine and which, in some instances, also flow through wetland areas, is coarser closer to the mining activities than the texture some distance away. This suggests a deposition of coarse sand in the area closest to the mining activities and that fine sand, as a result of a fairly strong stream velocity, is transported through the wetland areas to the outside boundaries of the mine. Wetland vegetation (e.g. Typha latifolia and hragmites australis) may also act as a physical barrier to the transport of coarse sand. Each section has its own characteristics regarding the metal concentrations in the various grain tractions; however, certain similarities exist. In the sections represented by streams, all metals, except into, have the highest concentration in the size fractions ≤ 63 μm. The lowest concentrations were found in the coarser fractions, which can possibly be ascribed to the presence of quartz in these fractions.

Seasonal fluctuations in gonadotropin levels in the plasma and gonads of male and female tilapia, Oreochromis mossambicus

Abstract: Syferkuil Dam is situated 8 km NW of the University of the North and comprises a series of eight interconnected rectangular dams. having cement sides and mudbottoms. Throughout the experimental period, male and female adult specimens of the mouthbrooding tilapia, Oreochromis mossambicus were collected for further analysis. Aspects of the reproductive physiology of O. mossambicus that were investigated included the role of gonadotropin hormones in reproduction. There are two distinct gonadotropins in O. mossambicus, luteinizing-like hormone (LH-like), and follicle stimulating-like hormone (FSH-like). Both of these hormones are secreted in response to increased water temperature and both are involved in enhancing spawning. The gonadotropins also provide the impetus for steroid hormone secretion to occur. Human chorionic gonadotropin (HCG) plays a role in the final maturation of the oocytes within the female ovary. The results imply a close interaction between environmental cues and endocrine control of reproduction. Endocrine control cannot be sustained without the appropriate environmental cues required to stimulate reproduction.

The use of Aspergillus niger (Strain 4) biomass for lead uptake from aqueous systems

Abstract: The potential of Aspergillus niger Strain 4 pellets to remove lead (Pb 2+ ) from solution was determined. Aspergillus niger Strain 4 was cultured in Currie's liquid medium as mycelial pellets for 5 d. Pellets were washed in water, and some were dried before exposure to varying concentrations of lead (Pb 2+ ) ion solutions. Various masses of dried mycelial material were exposed to different concentrations of Pb 2+ solutions to determine the effect of biomass concentration on lead uptake. A mycelial biomass of 2 mg.mt 1 was found to be optimal for Pb 2+ uptake at all the lead concentrations tested. Drying of the mycelial pellets did not affect the uptake of Pb 2+ . Scanning electron microscopy and energy dispersive X-ray micro-analysis of the fungal biomass, indicated that the lead was more or less evenly distributed within both the dried and undried mycelial pellets, and transmission electron microscopy confirmed that lead was present in the cell surface layers of the hyphal strands, i.e. the mechanism of uptake was determined to be biosorption onto the cell surface layers. Aspergillus niger Strain 4 pellets show potential for use in the removal of lead from industrial waste waters.

Treatment of a high-strength leachate from a closed co-disposal landfill site in South Africa

Abstract: A high-strength leachate from a closed co-disposal landfill site was characterised to determine its chemical composition and susceptibility to biological treatment. The leachate required dilution to 25% (v/v) before it responded to aerobic catabolism. Complete anaerobic treatment was ineffective even with a final dilution of 90% (v/v) of the original leachate. Indirect inhibition of methanogenesis by the high sulphate concentration was the probable cause. Following phosphate addition, aerobic biological treatment effected a significant chemical oxygen demand (COD) reduction but did not lower the ammoniacal-N concentration. Scaling and precipitation occurred which did not adversely affect the biological process but could cause operational problems in full-scale leachate treatment plants. Ion exchange, with soil and lime addition, was, therefore, considered to effect inorganic content reductions prior to biological treatment.

Vertical structure of the atmosphere during wet spells over Southern Africa

Abstract: Vertical sections of atmospheric structure during wet spells over Southern Africa are analysed in terms of ECMWF meteorological variables. Six cases occurring between December and March 1986 to 1992 are averaged to form a single composite pattern and the mean is subtracted to highlight structure. Vertical uplift is vigorous over Southern Africa and compensated by sinking motions over the surrounding oceans and Congo basin. Temperature departures indicate predominantly barotropic easterly wave conditions and a cool dome near the surface. A warm region to the south is coincident with easterly wind anomalies. Evidence points to the need for both a mid-latitude ridge and tropical Hadley overturning. The requisite convergence of airstreams from the southern Mozambique Channel and Congo basin are viewed as a brief southward excursion of the ITCZ over Southern Africa. The wet spells help overcome large moisture deficits built up in the preceding winter and spring, and enable adequate crop yields and water resource replenishment over the dry sub-continent of Southern Africa.