Scielo RSS <![CDATA[Water SA]]> http://www.scielo.org.za/rss.php?pid=1816-795020120002&lang=es vol. 38 num. 2 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Regional-scale risk assessment methodology using the Relative Risk Model (RRM) for surface freshwater aquatic ecosystems in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200001&lng=es&nrm=iso&tlng=es To maximise the long-term use of limited ecosystem services in South Africa, managers continually require approaches to optimise the establishment of balances between the use and protection of ecosystems to ensure sustainability. Surface freshwater aquatic ecosystems are dynamic and difficult to manage effectively. Sound management protocols that can identify and rank threats to these ecosystems are urgently required. The Regional-Scale Risk Assessment approach is carried out on a spatial scale and allows for the consideration of multiple sources of multiple stressors affecting multiple endpoints, with the inclusion of local ecosystem dynamics and the characteristics of the landscape that may affect the risk estimate. This paper presents an integrated approach to carry out regional-scale ecological risk assessments using a Relative Risk Model (RRM) adapted for South African conditions. The RRM consists of 10 procedural steps that are relatively easily applied. The use and application of the RRM within South Africa has the potential to provide resource users, resource conservators and regulators of surface aquatic ecosystems with a range of benefits. These benefits include the establishment of a validated, structured methodology that is sensitive to the dynamics of individual case studies, extremely informative, locally applicable and internationally comparable with other RRM assessments. The use of the RRM approach in South Africa has many advantages that outweigh some disadvantages. This approach has the potential to substantially contribute towards the ease and effectiveness of management of the balance between the use and protection of aquatic ecosystems in South Africa. <![CDATA[<b>Prediction of water temperature metrics using spatial modelling in the Eastern and Western Cape, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200002&lng=es&nrm=iso&tlng=es Key aspects of a river's temperature regime are described by magnitudes, timing and durations of thermal events, and frequencies of extreme exceedance events. To understand alterations to thermal regimes, it is necessary to describe thermal time series based on these statistics. Classification of sites based on their thermal metrics, and understanding of spatial patterns of these thermal statistics, provides a powerful approach for comparing study sites against reference sites. Water temperature regime dynamics should be viewed regionally, where regional divisions have an inherent underpinning by an understanding of natural thermal variability. The aim of this research was to link key water temperature metrics to readily-mapped environmental surrogates, and to produce spatial images of temperature metrics: 37 temperature metrics were derived for 12 months of sub-daily water temperatures at 90 sites in the Eastern Cape and Western Cape provinces, South Africa. These metrics were correlated with 16 environmental variables. Correlations enabled development of multiple regression models which facilitated mapping of temperature metrics over the study area. This approach has the potential to be applied at a national scale as more thermal time series are collected nationally. It is argued that the appropriateness of management decisions in rivers can be improved by including guidelines for thermal metrics at a regional scale. Such maps could facilitate incorporation of a temperature component into management guidelines for water resources. <![CDATA[<b>The response of microalgal biomass and community composition to environmental factors in the Sundays Estuary</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200003&lng=es&nrm=iso&tlng=es The Sundays Estuary is permanently open to the sea and experiences regular freshwater inflow in the form of agricultural return flows with large supplies of nutrients. The objectives of this study were to measure microalgal biomass and community composition and relate these to freshwater inflow, water quality and other environmental variables. These data can then be used in setting the ecological water requirements of the estuary. Surveys in August 2006, March 2007, February, June and August 2008 showed that salinity less than 10, expressed in practical salinity units, mostly occurred from 12.5 km from the mouth in the middle reaches of the estuary, which was also where the highest water column chlorophyll a (>20 μg.ℓ-1) was found. The study showed that different groups of microalgae formed phytoplankton blooms during individual sampling sessions. These included blooms of green algae (August 2006), flagellates (March 2007), dinoflagellates (June 2008) and diatom species (February and August 2008). The estuary was then sampled over 5 consecutive weeks from March to April 2009 to identify environmental factors that support different microalgal bloom species. Phytoplankton blooms were found during Weeks 1, 4 and 5 from the middle to the upper reaches of the estuary. It was shown that diatoms occurred in blooms during warm, calm conditions whereas wind-mixing and reduced temperature, as a result of a cold front during 17 to 19 March 2009, promoted the dominance of flagellates throughout the estuary although they were present at all times. Dominant diatom species (Cylindrotheca closterium, Cyclotella atomus and Cyclostephanus dubius) indicated brackish, nutrient-rich water. Nanoplankton (2.7 - 20 μm) was dominant during each week sampled and contributed 55 - 79% to the phytoplankton biomass. Maximum benthic chlorophyll a was found 12.5 km from the mouth. This study is the first to show successive chlorophyll a blooms consisting of different phytoplankton groups in an estuary, an indication of the eutrophic state of the system. <![CDATA[<b>Synthetic monthly flow duration curves for the Cape Floristic Region, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200004&lng=es&nrm=iso&tlng=es A flow duration curve (FDC) provides a valuable planning and management tool since it describes the entire flow regime of a river. Water resource planning in South Africa is often based on monthly river flow data and synthetic FDCs are required for applications in ungauged catchments. The objective of this study was to derive 11 monthly FDC percentile flows and the mean annual flow (MAQ) for catchments in the Cape Floristic Region of South Africa using regression equations with readily measureable catchment variables, including vegetation indices from Moderate Resolution Imaging Spectrometer (MODIS) satellite imagery. An 'all-models' approach with 10-fold validation was adopted to identify the 'best' regression models. Predictions of percentile flows above the median flow and MAQ were generally good but poor for low flows. Overall predictive uncertainty had a tendency to be larger in drier catchments. The most important predictive variables were catchment mean annual precipitation, physiography and soils. MODIS vegetation indices were significant predictors in equations for 6 percentile flows and MAQ, and predictive uncertainty increased if the MODIS indices were excluded from model development. The regression approach implemented in this study may be appropriate for other regionalisation studies that are based on a small sample of gauged catchments. <![CDATA[<b>The water balance of a seasonal stream in the semi-arid Western Cape (South Africa)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200005&lng=es&nrm=iso&tlng=es A detailed water balance and conceptual flow model was calculated and developed for the Sandspruit catchment for the period 1990 to 2010 on a winter rainfall water-year (1 April - 31 March) basis. The Sandspruit catchment (quaternary catchment G10J) is located in the Western Cape Province of South Africa and is a tributary of the Berg River. It contributes significantly to the salinisation of the mid- to lower-reaches of the Berg River and thus the hydrological drivers need to be quantified and conceptualised in order to develop salinity management strategies. Various components of the water balance, i.e. precipitation, evaporation, streamflow, recharge, etc., were monitored and quantified. In addition, stable environmental isotopes and water balance modelling were used to perform hydrograph separation as well as to quantify components of the water balance. Annual streamflow in the catchment during the period of observation was variable, ranging between 0.026 mm-a-1 and 75.401 mm-a-1. Streamflow volumes also exhibit high variability between water years. Catchment annual rainfall varied between 351 and 655 mm-a-1, averaging at 473 mm-a-1. On average, 6.5% of rainfall was converted to streamflow during the period of observation. Evapotranspiration was found to be the dominant component of the water balance, as it comprises, on average, 94% of precipitation in the catchment. Groundwater recharge was calculated to average at 29 mm-a-1. The water balance model (J2000) performed well during the simulation period with all measures of performance exhibiting acceptable values. Simulation results indicate that streamflow is driven by interflow from the soil horizon (94.68% of streamflow), followed by overland flow (4.92% of streamflow). These results, together with the physiographic conditions evident in the catchment, were used to develop a conceptual flow model. Streamflow is interpreted to be driven by quickflow, i.e. overland flow and interflow, with minimal contribution from groundwater, and is also more dependent on the rainfall distribution in time rather than on the annual volume. The correlation between average annual streamflow and average rainfall was observed to be poor, suggesting that alternative factors, e.g. the spatial distribution of winter wheat, the temporal distribution of rainfall, climatic variables (temperature), etc., exert a greater influence on streamflow. The water balance and conceptual flow model will form the basis for the application of distributed hydrological modelling in the Sandspruit catchment and the development of salinity management strategies. Results from this investigation, e.g. ET estimates, methods to quantify groundwater recharge, hydrograph separation, etc., could potentially be extrapolated to other semi-arid areas. <![CDATA[<b>Identification of sources and infiltration regimes of nitrate in the semi-arid Kalahari</b>: <b>Regional differences and implications for groundwater management</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200006&lng=es&nrm=iso&tlng=es The Kalahari region of southern Africa offers much potential for nitrogen input into its groundwater. High nitrate concentrations in Kalahari groundwater are therefore quite common and are caused by both anthropogenic and natural sources. Forecasting groundwater nitrate concentrations remains challenging. Source identification of nitrate contamination in groundwater is an important first step for groundwater management and quality prediction, and is aided by isotope analysis of nitrate in the water. Comparative data from 3 groundwater study sites in the Kalahari of Botswana and Namibia with widely different characteristics are presented. Two of the sites (Ghanzi and Gobabis) have shallow water tables in fractured quartzite. These aquifers were affected by pollution from cattle wastes (manure) and septic tank outflows resulting in groundwater nitrate levels exceeding 1 000 mg NO3/ℓ and in δ15N values of between +7 and +20 %o AIR. Short-term increases of groundwater nitrate concentrations were triggered by exceptional rainfall events occurring every 10-20 years. At the third site (Serowe in Botswana) there is similar land use and land cover, yet the aquifers are deeper, groundwater dates to Late-Pleistocene age and borehole levels do not show a response to present-day high-rainfall episodes. Nitrate levels up to 219 mg/ℓ are found, but lower 15N content (δ15N of +3 to +8 0/00) indicates a natural origin of the nitrate. In this area pollution nitrate is sufficiently delayed in the vadose zone, reaching the saturated zone much later. The data from all 3 sites suggest that nitrogen management options can only be evaluated once an understanding of sources, processes and flow patterns has been established. <![CDATA[<b>Quantifying rainfall-runoff relationships on the Mieso Hypo Calcic Vertisol ecotope in Ethiopia</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200007&lng=es&nrm=iso&tlng=es Droughts are common in the semi-arid areas of Ethiopia and adversely influence the wellbeing of many of the 80% of the population involved in agriculture. The introduction of any strategy that could increase crop yields would therefore be advantageous. The objective of the study was to attempt to assess the benefit that the in-field rainwater harvesting (IRWH) crop production technique would have, compared to conventional tillage, on increasing soil water, and therefore the yield of a crop, on a semi-arid ecotope at Mieso. The mean annual rainfall at Mieso is 738 mm. The soil is a Hypo Calcic Vertisol with a high clay and silt content and is very susceptible to crusting. To achieve the objective of the study, rainfall-runoff measurements were made during 2003 and 2004 on 2 m x 2 m plots provided with a runoff measuring system, and replicated 3 times for each treatment. There were 2 treatments: conventional tillage (CT) that simulated the normal local CT; and a flat surface simulating the no-till IRWH technique (NT). Rainfall intensity was measured at 1-min intervals and runoff was measured after each storm. The Morin and Cluff runoff model was calibrated and validated using measured rainfall-runoff data. Appropriate values for final infiltration rate (If), surface storage (SD) and the crusting parameter (y) were found to be: 10 mm-hr-1; 2 mm for NT and 5 mm for CT; 0.4 mm-1; respectively. The runoff (R)/rainfall (P) ratio (R/P) gave values of 0.43 and 0.34 for the NT and CT treatments, respectively. There was a statistical difference between the runoff on the 2 treatments. The first estimated yield benefit of IRWH compared to CT is 455 kg-ha-1. Based on the average long-term maize yield of 2 000 kg-ha-1 at Melkassa, this is an estimated yield increase of 23%. <![CDATA[<b>Infiltration and runoff losses under fallowing and conservation agriculture practices on contrasting soils, Zimbabwe</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200008&lng=es&nrm=iso&tlng=es Fallowing and conservation agriculture are sustainable farming practices that can be used for soil and water conservation. The objectives of the study were to evaluate the effects of different conservation agriculture practices on rainfall infiltration and soil and water losses across 4 sites, using simulated rainfall. The study was carried out at Domboshawa and the Institute of Agricultural Engineering and Chikwaka smallholder farming areas, 4 sites with different soil types. Conservation agriculture practices evaluated were mulch reaping (MR) and clean reaping (CR) at Domboshawa with 5% clay and the Institute of Agricultural Engineering (IAE) with 50% clay. The study also evaluated runoff losses from fallow plots subjected to no tillage (NT) and conventional tillage (CT) at ICRAF Domboshawa site (20% clay) and fallows subjected to CT in Chikwaka smallholder farming areas (4% clay). Infiltration rates were greater under conservation agriculture practices (>35 mm-h-1) when compared to CT (<27-29 mm-h-1). On fallows infiltration rates ranged from 24-35 mm-h-1 when compared to <15 mm-h-1 in maize under CT. Runoff losses were highest under CT at both Domboshawa and IAE sites, and were 21.5 and 15% respectively, while there was no runoff under MR and CR. At the ICRAF Domboshawa site, runoff ranged between 0-31% in fallows and was 57% in maize under CT. At Chikwaka runoff in CT maize was 58%, while in fallow plots runoff ranged 37-44%. Soil losses ranged from 0.2-0.3 t-ha-1 per rainfall event in maize, while in fallows, soil loss ranged from 0-0.1 t-ha-1. The results showed that CT resulted in reduced infiltration rates, increased soil and water loss when compared to fallowing and conservation agriculture across different range of soils. Conservation agriculture practices and fallowing are potential sustainable cropping practices that reduce soil and water loss and increase water use efficiency. <![CDATA[<b>Monetary valuation of salinity impacts and microbial pollution in the Olifants Water Management Area, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200009&lng=es&nrm=iso&tlng=es This paper estimates costs associated with water pollution in the Olifants River Water Management Area (WMA) in South Africa, and, more specifically, the area represented by the Loskop Dam Water User Association. We focus on the impacts of salinisation on commercial irrigated agriculture, and of microbial pollution on the general population of the WMA, many of whom do not have access to municipal water and sanitation services, leaving them vulnerable to microbial pollution in the water resource. Costs associated with salinity are estimates based on the impacts of increased salinity on the value of marginal product of certain irrigated crops. Costs associated with microbial pollution are estimated based on the direct and indirect costs of human health impacts as a result of microbial pollution in the study area. These monetary value estimates give an indication of the magnitude of the cost of water pollution to society in the WMA. It is concluded that the once-off cost required to provide some pollution prevention infrastructure will be lower than the current annual cost burden of pollution on society in the WMA, and that pollution prevention is therefore cost effective. <![CDATA[<b>The perceptions of research values and priorities in water resource management from the 3<sup>rd</sup> Orange River Basin Symposium</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200010&lng=es&nrm=iso&tlng=es Research has played an important role in water resource management and a consensus on research objectives would increase the efficiency of these practices. In this paper we aimed to elicit the views of attendees of the 3rd Orange River Basin Symposium regarding water-related research, by using both quantitative and qualitative responses to a questionnaire survey, and purposeful sampling methods. Overall, research was perceived to play an important role in water resource management and there was significant agreement on which sectors are responsible for carrying out this research. Although clear strengths in water resource management in southern Africa were identified, we found that most perceived weaknesses related to the lack of enforcement or to human resource constraints. Despite this fact, the identified research priorities, which were aligned to those of the Water Research Commission, tended to be technical in nature and would not address these perceived weaknesses. Our recommendations were that, by incorporating previously ignored sectors into research, such as private consultants and non-governmental organisations, and addressing human capacity and enforcement issues, unique and unexplored research opportunities could improve water resource management. <![CDATA[<b>An ion-imprinted polymer for the selective extraction of mercury(II) ions in aqueous media</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200011&lng=es&nrm=iso&tlng=es A double-imprinted polymer exhibiting high sensitivity for mercury(II) in aqueous solution is presented. Polymer particles imprinted with mercury(II) were synthesised by copolymerising the functional and cross-linking monomers, N'Â-[3Â- (Trimethoxysilyl)-propyl]diethylenetriamine (TPET) and tetraethylorthosilicate (TEOS). A double-imprinting procedure employing hexadecyltrimethylammonium bromide (CTAB), as a second template to improve the efficiency of the polymer, was adopted. The imprinted polymer was characterised by FTIR, scanning electron microscopy (SEM) and the average size determined by screen analysis using standard test sieves. Relative selective coefficients (k') of the imprinted polymer evaluated from selective binding studies between Hg²+ and Cu²+ or Hg²+ and Cd²+ were 10 588 and 3 147, respectively. These values indicated highly-favoured Hg²+ extractions over the 2 competing ions. The results of spiked and real water samples showed high extraction efficiencies of Hg²+ ions, (over 84%) as evaluated from the detected unextracted Hg²+ ions by ICP-OES. The method exhibited a dynamic response concentration range for Hg²+ between 0.01 and 20 μg/mℓ, with a detection limit (LOD, 3o) of 0.000036 μg/mℓ (36 ng/ℓ) that meets the monitoring requirements for the USA EPA of 2 000 ng/ℓ for Hg²+ in drinking water. Generally, the data (n=10) had percentage relative standard deviations (%RSD) of less than 4%. Satisfactory results were also obtained when the prepared sorbent was applied for the pre-concentration of Hg2+ from an aqueous certified reference material. These findings indicate that the double-imprinted polymer has potential to be used as an efficient extraction material for the selective pre-concentration of mercury(II) ions in aqueous environments. <![CDATA[<b>Optimal synthesis of a Ni(II)-dimethylglyoxime ion-imprinted polymer for the enrichment of Ni(II) ions in water, soil and mine tailing samples</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200012&lng=es&nrm=iso&tlng=es A Ni(II)-dimethylglyoxime ion-imprinted polymer {Ni(II)-DMG IIP} was optimised by the uniform design experimental method and used to adsorb Ni(II) ions from water, soil and mine tailing samples. This aimed to improve the performance of this ion-imprinted polymer in trapping Ni(II) ions from soil and mine tailing samples which are characterised by complex matrices. The optimisation was carried out by varying the molar ratios of monomer to crosslinker to porogen and template to ligands, as well as by keeping these parameters constant and varying the concentrations of initiator, 2,2'-azobisisobu-tyronitrile (AIBN). The optimal molar ratios of crosslinker to monomer, monomer to template and nickel(II) sulphate hexahydrate (NiSO4.6H2O) to 4-vinylpyridine to dimethylglyoxime were found to be 3.3:1.0, 0.6:1.0 and 1.0:0.6:3.6, respectively, with 30 mg and 8 mℓ as the optimum amounts of initiator and porogen, respectively. Through this optimisation, extraction efficiency for Ni(II) increased from 98 to 100% in aqueous samples. The extraction efficiencies for the soil and mine tailing samples were 98-99% and 99%, respectively, with an enrichment factor of 2 in mine tailing samples and ranging from 27 to 40 in soil samples. The method displayed good accuracy, as it was validated with certified reference materials (SEP-3 and BCR-142R) and the values obtained were close to the certified ones. The improved quality of results obtained from water, soil and mine tailing samples showed that the uniform design experimental method is effective and efficient for optimising imprinted polymers using a lower number of experiments performed. <![CDATA[<b>The influence of pH on the adsorption of lead by Na-clinoptilolite</b>: <b>Kinetic and equilibrium studies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200013&lng=es&nrm=iso&tlng=es The objectives of this study were, firstly, to establish the mechanism by which modified clinoptilolite (in Na form) adsorbs lead ions and, secondly, to assess the extent of influence of pH on the adsorption capacity. To this end, the experimental data have been fitted by adsorption isotherms, thermodynamic and kinetic models. Based on the standard errors obtained during experiments, it was determined that the accuracy of prediction of the isotherm models considered for adsorption decreases in the order: Dubinin-Raduschkevich (4.63%, average normalised standard deviation error); Langmuir (7.90%); and Freundlich (15.98%). For the kinetic models, the accuracy of prediction decreases in the order: intra-particle Weber-Morris (with an average normalised standard deviation error of 5.53%); heterogeneous diffusion (5.67%); pseudo-second order kinetic model (10.47%); diffusion through the particle surface (41.73%); and the pseudo-first kinetic model (47.51%). The mechanism of adsorption of lead ions by Na-clinoptilolite was found to occur in a monolayer and heterogeneous surface. The pH of contact solutions played an important role owing to competition by hydrogen ions. As the pH of the solution decreased, the maximum monolayer adsorption capacity established theoretically, based on the Langmuir isotherm, also decreased. Thus, if, for instance, the pH decreases from 4 to 1, the maximum adsorption capacity decreases from 0.3569 to 0.1604 mol-kg-1. At high pH of the contact solution, the adsorption process occurs by ion exchange and at low pH; i.e., it is physical. The variation of the Gibbs free energy demonstrates that adsorption occurs spontaneously. The process was also observed to occur at a higher rate at low acidity. Diffusion through the internal structure of macro- and micropores is the stage taking place with the lowest speed during the adsorption process and plays an important role in the mechanism of adsorption. The intra-particle diffusion coefficient depends on pH, which can modify the shape and concentrations of the hydrated metal complexes in solutions, thus affecting the adsorption process. The decrease of pH from 4 to 1 resulted in a decrease of the intra-particle diffusion coefficient from 4.0610-11 to 1.9610-11 m²min-1. The film diffusion coefficients were found to be 10 times larger than the intra-particle coefficients, suggesting that diffusion to the external surface cannot be the rate-limiting step in the adsorption mechanism. <![CDATA[<b>Fluoride removal performance of phosphoric acid treated lime</b>: <b>breakthrough analysis and point-of-use system performance</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200014&lng=es&nrm=iso&tlng=es Fluoride in drinking water above permissible levels is responsible for dental and skeletal fluorosis. In this study, removal of fluoride ions from water using phosphoric acid treated lime was investigated in continuous and point-of-use system operations. In the continuous column operations, fluoride removal performance was investigated as a function of the fluoride concentration, flow rate and amount of adsorbent mass. Early saturation and lower fluoride removal were observed at higher flow rate and initial concentration, and at lower mass. Two domestic defluoridation point-of-use systems operated intermittently to process 20 ℓ.day-1 of water were used. High fluoride uptake capacity (FUC) from groundwater was observed depicting the suitability of the new media in defluoridation. However, further research is required to optimise the point-of-use systems performances. <![CDATA[<b>Sensitivity study of reduced models of the activated sludge process, for the purposes of parameter estimation and process optimisation</b>: <b>benchmark process with ASM1 and UCT reduced biological models</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200015&lng=es&nrm=iso&tlng=es The problem of derivation and calculation of sensitivity functions for all parameters of the mass balance reduced model of the COST benchmark activated sludge plant is formulated and solved. The sensitivity functions, equations and augmented sensitivity state space models are derived for the cases of ASM1 and UCT reduced biological models. Matlab software for sensitivity function calculation and sensitivity model simulation is developed. The results are described and discussed. The behaviour of the sensitivity functions is used to determine which parameters of the reduced model need to be estimated in order to fit the reduced model behaviour to the real data for the process behaviour. <![CDATA[<b>Effects of tailwater depth on spillway aeration</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200016&lng=es&nrm=iso&tlng=es Hydraulic structures such as spillways or weirs with their water-air controlling mechanisms are not only important for their structural properties but also for their effects on downstream ecology. Tailwater depth is an important factor affecting dissolved oxygen transfer and aeration rates of spillways. In this study, effects of tailwater depths and discharge values on the aeration efficiencies of laboratory-model smooth and stepped spillways were investigated. Changes of tailwater depths affect the dissolved oxygen transfer rates and aeration efficiencies are affected more than 100%, resulting in supersaturated dissolved oxygen concentrations. Tailwater depth is a significant parameter in the design of the spillway and the stilling basin of dams. Therefore, this value should be estimated correctly. <![CDATA[<b>Catchment management agencies as crucibles in which to develop responsible leaders in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200017&lng=es&nrm=iso&tlng=es During the past 17 years in South Africa, far-reaching policy, legislation and institutional changes in water-related governance have occurred. Responsible leaders have ensured that a paradigm of integrated water resource management (IWRM) is firmly entrenched in the above policy, legislation and institutional arrangements. IWRM in turn demands a level of interaction between individuals, disciplines and organisations such that multi-sector, multi-level stakeholders can collectively, timeously, wisely and cost-effectively visit the consequences of their proposed, present and past actions. Such social learning processes demand leadership and the ongoing development of leaders at all levels. This paper is structured around the propositions for leadership development in the field outlined by Scharmer (2009a). The principal aim of the paper is to reveal the extent to which the multi-sector catchment management agency (CMA) phenomenon is an ideal crucible for leadership development in the field. It is argued that the complex adaptive system that embodies the water realm needs to be engaged by developing complex adaptive systems of governance and that the CMAs have the potential to meet this requirement. Furthermore, it is argued that processes to achieve this required leadership are also ideal for developing leadership. At a time when worldwide developments in communication and computer technology have spawned an exponential growth in successful endeavours related to self-organising around common challenges, the CMA provides a unique and nourishing context for self-organising that simultaneously connects to South Africa's water governance mainstream of policies, laws, institutions and administrative procedures. <![CDATA[<b>The use of water resources for inland fisheries in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200018&lng=es&nrm=iso&tlng=es The contribution of inland fisheries to food security, livelihood provision, poverty alleviation, and economic development in developing African countries is well documented, but there is surprisingly little literature on the history, current status and potential of South Africa's inland fishery resources. This presents a constraint to the management and sustainable development of inland fisheries. A literature review of peer-reviewed and grey literature was thus undertaken which is presented as a synthesis of knowledge on inland fisheries in South Africa. We track the chronology of literary themes on inland fisheries from the colonial era to the present, provide an overview of the recreational, subsistence and commercial sub-sectors, the production potential of inland waters, interventions to promote fishery development, and attempts to value inland fisheries. The review summarises the current state of knowledge on fisheries resources, outlines potential sources of data, highlights relevant and important information, and identifies knowledge gaps. The literature survey reveals an urgent need for research covering the biological, social, economic and governance aspects, if inland fisheries are to be developed in a rational and sustainable manner which promotes South Africa's national policy goals. <![CDATA[<b>Impacts of invasive alien plants on water quality, with particular emphasis on South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502012000200019&lng=es&nrm=iso&tlng=es We review the current state of knowledge of quantified impacts of invasive alien plants on water quality, with a focus on South Africa. In South Africa, over 200 introduced plant species are regarded as invasive. Many of these species are particularly prominent in riparian ecosystems and their spread results in native species loss, increased biomass and fire intensity and consequent erosion, as well as decreased river flows. Research on the impact of invasive alien plants on water resources has historically focused on water quantity. However, although invasive alien plants also affect the quality of water, this aspect has not been well documented. Alien invasive plants increase evaporation rates, and reduce stream flow and dilution capacity. The biomass inputs of alien invasive plants, especially nitrogen fixers such as Acacia spp., alter nutrient cycles and can elevate nutrient concentrations in groundwater. Alien plant invasions alter the fire regimes in invaded areas by changing the size, distribution and plant chemistry of the biomass. More intense fires increase soil erosion and thereby decrease water quality. In contrast to riparian invasions, aquatic invasive plants have been more extensively studied in South Africa and their impacts on water quality have been relatively well monitored. Water quality in South Africa is rapidly deteriorat-ing, and all factors that influence this deterioration need to be taken into account when formulating actions to address the problem. The changes in water quality brought about by alien plant invasions can exacerbate the already serious water quality problems.