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Artificial neural networks (ANNs) are powerful data-oriented "black-box" algorithms capable of assessing and delineating linear and multifaceted non-linear correlations between the dependent and explanatory variables. Through the years, neural networks have proven to be effective and robust analytical techniques for establishing artificial intelligence-based tools for modelling, estimating, and projecting spatial and temporal variations in water bodies. Accordingly, ANN-based algorithms gained increased attention and have emerged as practical alternatives to traditional approaches for hydro-chemical analysis. ANNs are among the widely used computer systems for modelling surface water quality. Considering their wide recognition, resilience, flexibility, and accuracy, the current study employs a neural network-based methodology to construct a novel water quality index (WQI) model suitable for analysing South African rivers. The feed-forward, back-propagated multilayered perceptron model has three parallel-distributed neuron layers interconnected with seventy weighted links orientated laterally from left to right. First, the input layer includes thirteen neuro-nodes symbolising thirteen explanatory variables, including NH3, Ca, Cl, Chl-a, EC, F, CaCO3, Mg, Mn, NO3, pH, SO4, and turbidity (NTU). Second, the hidden layer consists of eleven neuro-nodes accountable for computational tasks. Lastly, the output layer features one neuron responsible for conveying network outcomes using a single-digit WQI rating extending from zero to one hundred, where zero represents substandard water quality and one hundred denotes exceptional water quality. The AI-based model was developed using water quality data obtained from six monitoring locations within four drainage basins under the management of the Umgeni Water Board in the KwaZulu-Natal Province of South Africa. The dataset comprises 416 samples randomly divided into training, testing, and validation sets using a proportional split of 70:15:15%. The Broyden–Fletcher–Goldfarb–Shanno (BFGS) technique was utilised to conduct backpropagation training and adjust synapse weights. The dependent variables are the WQI scores from the universal water quality index (UWQI) model developed specifically for South African river basins. The ANN demonstrated enhanced efficiency through an overall correlation coefficient (R) of 0.985. Furthermore, the neural network attained R-values of 0.987, 0.992, and 0.977 for the training, testing, and validation intervals. The ANN model achieved a Nash–Sutcliffe efficiency (NSE) value of 0.974 and coefficient of determination (R2) of 0.970. Sensitivity analysis provided additional validation of the preparedness and computational competence of the ANN model. The typical target-to-output error tolerance for the ANN model is 0.242, demonstrating an adequate predictive ability to deliver results comparable with the target UWQI, having the lowest and highest index ratings of 75.995 and 94.420, respectively. Accordingly, the three-layer neural network is scientifically sound, with index values and water quality evaluations corresponding to the UWQI results. The current research project seeks to document the processes used and the outcomes obtained. [ABSTRACT FROM AUTHOR]

The quality of surface water has a significant impact on human health and the entire ecological system. Sewer spillages from the surrounding informal settlements discharging into the river, carrying high concentrations of fecal coliforms, are one of the major causes of extreme pollution in the rivers of South Africa. These informal settlements are common in many developing countries, and they are usually located near waterways to compensate for basic demands for water, sanitation, and recreational space, where municipal infrastructure lags behind urban growth. One major problem has been poor sanitation and poor waste disposal practices in the informal settlements, which has led to the contamination of water resources. This study aims to assess the extent to which poor sanitation in informal settlements impacts the water quality of South African rivers, given the rapid rise in population and unemployment rate. The study also highlights health and environmental issues in the local regions caused by poor sanitation. Contamination of water bodies is associated with serious health problems and fatalities. Therefore, there is a need for frequent monitoring and management of waste products discharged into the neighboring aquatic environments. [ABSTRACT FROM AUTHOR]

With water quality deteriorating rapidly at a global scale, river sections suited to serve as reference sites are being increasingly lost. It thus becomes critical to develop rapid methods to confirm that previously monitored sites continue meet the requirements of reliable reference sites. In the absence of pristine sites, 9 near-natural sites, as defined by the Kleynhans (1996) classification, were used as reference sites for the Luvuvhu River catchment to compare the quality of physico-chemical factors against a biological metric. Baetid mayfly community structure at a site was chosen as an index of water quality, since this family is common in all types of freshwaters, highly diverse and adapted to unpolluted running water. Baetid larvae were sampled monthly from stones-in-current biotopes across 9 sites for over 1 year, between December 2016 and January 2018. A Spearman’s correlation test was used to evaluate the relationship between physicochemical factors and identify redundant variables. Water quality standards were measured against the national water quality guidelines for aquatic ecosystems. We used a generalized linear model to determine the effect of physico-chemical variables on baetid species, and canonical correspondence analysis to show the relationships between baetid species, sites, and physico-chemical variables. A total of 3 039 individuals belonging to 12 mayfly species were recorded. Our findings indicated that while the physico-chemical factors were highly variable, they were within favourable ranges to reflect reference site conditions. While water temperature was the most important driver of baetid community structure in general, as it negatively affected their abundances, a subset of species (Pseudoponnota sp., Pseudocloeon sp., Acanthiops varius and Demoulinia crassi) showed clear responses to changes in TDS and stream width. We conclude that specific baetid species show good potential as biological indicators of reference sites and chronic water temperature stress, making assessment of reference sites easier. [ABSTRACT FROM AUTHOR]

The operationalization of water resource protection initiatives for surface water resource quality and equitable water quality allocation is critical for sustainable socio-economic development. This paper assessed Blesbokspruit River Catchment's water quality status, using the South African Water Quality standards and Water Quality Index (WQI). Protection levels for quality, and waste discharge for point sources were set and evaluated using the total maximum daily loads (TMDLs) and chemical mass balance (CMB) techniques, respectively. The study found that the water quality results for the analysed physico-chemical parameters (Na+, Ca2+, Mg2+, Cl−, F−, pH, EC, SO42−) of the data collected from 2015 to 2022 were within the limits of the water quality standards, except for NO3− and PO42−. The water quality from the study area was categorized as acceptable for drinking purposes with the WQI of 54.80. The application of the TMDL approach resulted in the 77.96 mS/m for electrical conductivity (EC), 9.92 mg/L for phosphate (PO42−), and 15.16 mg/L for nitrate NO3− being set as the protection levels for the catchment. The CMB was found to be a useful tool for the evaluation of point source discharges into water resources. The study recommends the application of TMDL and CMB techniques in water resource protection practice. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are facing degradation from human activities in the form of alterations of flow regimes, changes in land-use, and intensive water abstraction, in turn generating adverse effects on biodiversity and ecological functionality. Efficient assessment of river/stream ecosystem response to such anthropogenic changes is urgently needed. Many human activities that have an effect on water quality and river health are increasing along the Mohlapitsi River, which used to be one of the rivers with good water quality in South Africa. The aim of the study was to assess spatial variation in macroinvertebrate assemblages in relation to water quality of the Mohlapitsi River. A combination of canonical correspondence analysis and univariate analyses were used to examine the macroinvertebrate assemblages at six different sites of the Mohlapitsi River. The spatial difference in macroinvertebrate abundance was mostly related to changes in water quality. The number of taxa and the diversity of macroinvertebrates remained relatively high across the river as compared to other rivers in the Olifants River System. The midstream and downstream sites were mostly dominated by macroinvertebrates tolerant to disturbance/pollution. The most abundant family was the Thiaridae (about 60%) and mainly occurred in the midstream and downstream sites of the river (more disturbed sites). The study showed a higher evenness index in the upstream than the midstream and downstream sites which is an indication of good water quality at the upstream sites of the river. The results suggest that the river is being subjected to a moderate environmental pollution, which requires continuous assessment and monitoring to determine causes and initiate remedial measures. [ABSTRACT FROM AUTHOR]

The Hartbeespoort Dam is a discharge point of a catchment that is characterized by urbanization, mining, industrial, and agricultural activities. These activities coupled with fluxes of heavily polluted wastewater from informal settlements, wastewater treatment works, as well as runoff from golf courses have led to the development of recurring harmful algal blooms (HABs). The predominant cyanobacteria scum that is largely covering the Dam water is toxic to fish and poses serious public health risks. Phosphorus is the limiting nutrient in terrestrial aquatic systems and excess concentration in the waters usually results in eutrophication. The productivity level in Hartbeespoort Dam is also a function of total phosphorous (TP) level, showing a positive correlation with chlorophyll-a, an index for phytoplankton which are predominantly HABs in this Dam. Analysis of long-term in situ water quality data (1980–2020) show that TP is not the only driver, changes in surface water temperatures also affect the productivity level, especially, when TP levels are below a threshold of approximately 0.4 mg/L. Chlorophyll-a was retrieved from current generation high resolution satellite (Landsat and Sentinel) at 5-year interval. Standard band ratio-based ocean color model applied to satellite data produced an accuracy of R2 = 0.86 and RMSE of 5.56 µg/L. Time series analysis of in situ and satellite data show similar trends including capturing the effect of biocontrol on productivity levels between the late 1980s and the early 1990s, after which productivity increased with an increased flux of TP. Since 2015, the average annual surface temperature in the Dam has decreased leading to the decline in productivity level despite increasing levels of TP. The spatial dynamics of the HABs is a function of the discharges levels of the various rivers draining into the Dam as well as its geometry. Relatively higher concentrations are observed near river discharges and in areas of restricted water circulation. [ABSTRACT FROM AUTHOR]

Benthic macroinvertebrates play a vital role in ecosystem functioning, such as nutrient cycling, primary production, decomposition and material translocation. A study was done to determine the functional feeding groups (FFGs) distribution along two streams of the Olifants River System, South Africa. There were longitudinal differences of the functional groups but were more pronounced in the Dwars River than in the Spekboom River. Collector-gatherers and collector-filterers were the most abundant groups recorded in both rivers. The least abundant groups were the shredders and scrapers in both rivers. The highest abundance of shredders in both rivers was at upstream sites (DS1 and SS1), more scrapers were found at midstream sites (DS3 and SS2), collector-gatherers and collector-filterers increased in the downstream (SS4) of the Spekboom River and predators were nearly constant in relative abundance at all sites. The relative abundance and richness of the FFGs did not conform completely to the river continuum concept (RCC). This could be related to the degradation of the catchment resulting from human activities which affected the quality of the water. [ABSTRACT FROM AUTHOR]

Background: The understanding of the impact of land-use on the dynamics of phytoplankton assemblages during varying climate conditions on rivers is limited. Objective: To determine the impact of land-use types and flow on phytoplankton assemblages in the Sabie River. Methods: The relationships between land-use patterns, water quality and phytoplankton assemblages were analysed using canonical correspondence analyses (CCA). Results: Six main land-use types could be distinguished in the eight identified sub-catchments of the river. The CCA results showed that the land-use had a stronger correlation with phytoplankton classes during the higher flow conditions than during low flow conditions. The forestry land-use type had the strongest correlation with nitrate-nitrite concentrations in the Sabie River. Chlorophyll-a concentrations were higher during 2016, and a slightly lower number of genera were observed for the class Chlorophyceae. During 2017 the number of genera of the class Cyanophyceae decreased together with chlorophyll-a and total cell concentrations. Conclusion: Low flow conditions favoured filamentous genera that are common to mesotrophic conditions while higher flow conditions favoured single-celled small genera more common to oligotrophic waters with higher disturbance. This study showed that flow has the potential to enhance the impact of land-use on phytoplankton community dynamics in a river system and thereby may have further impacts on the health and activities of surrounding communities. [ABSTRACT FROM AUTHOR]

Wetlands within the catchments of water supply dams have potential to make important contributions to water-related ecosystem services, particularly water quality enhancement. Wetlands are facing growing threats and continuing degradation. There have been limited attempts at evaluating the contribution of South African wetlands, and their rehabilitation, for water quality enhancement and other water-related ecosystem services. A comprehensive and integrated wetland services economic assessment determined the value of the Vyeboom Wetland in the catchment of the Theewaterskloof Dam. The water of this dam is a significant contributor to the City of Cape Town's water supply. The economic valuation model integrates hydrological, catchment status and economic models, with a long-term (80-year monthly) wetland water balance from a calibrated hydrological model as a driver for the nutrient removal aspect. The economic valuation builds on a water quality enhancement model, based on the minimisation of indirect use replacement cost principle, supplemented by a sediment retention and carbon storage assessment. The capability of the economic valuation model is illustrated by assessing the rehabilitation of a 25-ha area in the Vyeboom Wetland, which is currently intact, but is under threat of being severely degraded by the advancing erosion headcut. It was assumed that the current state of the Vyeboom Wetland is almost pristine (only 1 ha degraded), but that a further 24 ha would degrade over a period of 50 years, following spatial changes over time. By balancing the total investment in offsetting the potential loss in benefits, it is evident that an amount of 2.5 million ZAR could be afforded for rehabilitation. If, instead of a logistic degradation profile, the wetland is assumed to already be in a state of accelerated deterioration, the rehabilitation project budget for Vyeboom Wetland will increase once the other intrinsic benefits described are considered in the analysis. [ABSTRACT FROM AUTHOR]

This paper presents the levels of detection of selected agricultural pesticides in river and tap water in the Letsitele, Lomati and Vals–Renoster catchments, South Africa. Agriculture plays a major role in the development of communities through job creation and poverty eradication. However, exposure to agricultural pesticides can result in serious human health and environmental effects. This study, therefore, identified critical areas where specific pesticides might result in high environmental and human health risks. Three water catchment areas, namely, Letsitele, Lomati and Vals–Renoster, were identified for raw and tap water analysis. The results confirmed the presence of selected agricultural pesticides: atrazine, terbuthylazine, imidacloprid, metolachlor, simazine and alachlor. Although low concentrations of most of these pesticides were detected, pesticides such as atrazine, alachlor and simazine are known for endocrine disruption. A critical finding of this study is the detection of these pesticides in tap water (drinking water) of a primary school in the Lomati catchment. This reveals a high exposure potential for human health. It is thus recommended that further research be conducted to determine the potential health risks associated with these pesticides among vulnerable communities, through epidemiological studies. [ABSTRACT FROM AUTHOR]

Diatoms are siliceous micro-algae and have been used with increasing frequency as bioindicators in aquatic ecosystems. Typically, European diatom indices have been modified and augmented with data on taxa endemic to and commonly found in other parts of the world. In order to further test the application of diatom indices, water quality and diatom sampling were performed in the Bloukrans River system, Eastern Cape Province of South Africa. Nine sites with contrasting water quality were sampled along the length of the river in February, May and July 2018. Multivariate statistical analysis (Canonical Correspondence Analysis) was employed to elucidate spatiotemporal differences in diatom community structure. Canonical correspondence analysis indicated that differences in diatom community assemblages were best explained by dissolved oxygen, temperature, nitrate, conductivity and phosphate. Diatom-based indices incorporated in OMNIDIA software were also applied to assess the integrity of the water quality as indicated by diatom communities. Several foreign indices (e.g. the trophic diatom index (TDI), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. The SADI demonstrated that the Bloukrans River was impacted and had significant correlations with water quality variables (p <.05). We therefore recommend the wider use of the SADI as an indicator of water quality conditions in South African lotic systems. • Anthropogenic perturbations in Bloukrans River system can be assessed using diatom indices and multivariate analysis. • High levels of nitrate, phosphate and conductivity were recorded in downstream urban sites. • Patterns of diatom assemblages were different between sites. • The South African Diatom Index (SADI) showed significant strong correlations with all water quality variables considered. • The South African Diatom Index (SADI) is also applicable for the Eastern Cape river systems. [ABSTRACT FROM AUTHOR]

Bacterial communities in human-impacted rivers and streams are exposed to multiple anthropogenic contaminants, which can eventually lead to biodiversity loss and function. The Wonderfonteinspruit catchment area is impacted by operational and abandoned gold mines, farms, and formal and informal settlements. In this study, we used 16S rRNA gene high-throughput sequencing to characterize bacterial communities in the lower Wonderfonteinspruit and their response to various contaminant sources. The results showed that composition and structure of bacterial communities differed significantly (P<0.05) between less (downstream) and more (upstream) polluted sites. The taxonomic and functional gene dissimilarities significantly correlated with each other, while downstream sites had more distinct functional genes. The relative abundance of Proteobacteria, Bacteroidetes and Actinobacteria was higher at upstream sites, while Acidobacteria, Cyanobacteria, Firmicutes and Verrucomicrobia were prominent at downstream sites. In addition, upstream sites were rich in genera pathogenic and/or potentially pathogenic to humans. Multivariate and correlation analyses suggest that bacterial diversity was significantly (P<0.05) impacted by pH and heavy metals (cobalt, arsenic, chromium, nickel and uranium). A significant fraction (~14%) of the compositional variation was explained by a combination of anthropogenic inputs, of which mining (~6%) was the main contributor to bacterial community variation. Network analysis indicated that bacterial communities had non-random inter- and intra-phyla associations and that the main taxa showed both positive and negative linkages to environmental parameters. Our results suggest that species sorting, due to environmental parameters, was the main process that structured bacterial communities. Furthermore, upstream sites had higher relative abundances of genes involved in xenobiotic degradation, suggesting stronger removal of polycyclic aromatic hydrocarbons and other organic compounds. This study provides insights into the influences of anthropogenic land use on bacterial community structure and functions in the lower Wonderfonteinspruit. [ABSTRACT FROM AUTHOR]

Many rivers in the southern coastal region of the Western Cape Province, South Africa, are known to be in a poor state. Since the 1990s, the river water quality of this coastal region has been affected by increasing populations and by intensifying land use activities. Simplified risk assessment approaches are critical to identify in a timely manner areas where land use activities may impact water quality, particularly for regions with limited data. For this study, a simple assessment approach to estimate the impacts of land use activities on river water quality was improved by incorporating landscape potentials that take into account environmental factors. The methods were applied to two regions experiencing intensive land use along the southern coast. The findings indicate that the incorporation of the landscape potentials, (i) the landscape sediment generation potential and (ii) the diffuse nitrate potential, to estimate the impacts of sediment and nutrient inputs on river water quality need to be considered. Agricultural activities and informal settlements contribute to the increasing sediment and nutrient inputs of the river reaches. Areas with high proportions of river reaches at increasing pollution risk need to be managed on a large scale to ensure that all the potentially affected sub-catchments are included. [ABSTRACT FROM AUTHOR]

The water-energy-food nexus has emerged as a useful concept to understand the multiple interdependencies that exist between the water, energy and food sectors. The nexus is an ambitious attempt to work across disciplines and scales to understand the workings of these complex systems. It is, however, criticised for being more of a general framework than a practical methodology because of the vast amount of data it would need to make real-life contributions to sustainable development. We show how the nexus approach, when used within a farm budget model, can transform the problem focus in water governance. By changing the relationship among water, energy and food production of a farm, profitability is significantly changed. The water-energy-food nexus debate is discussed within the context of the South African water sector, particularly the Breede River Catchment. Working from within the farm budget model, we demonstrate the impact of moving from an irrigation canal system that requires electricity for pumping, to a gravity-fed piped irrigation system in the Middle Breede River. The finding is that the water-energy-food nexus has the potential to unlock groundbreaking solutions to complex problems in agricultural water management when used in appropriate modelling systems. [ABSTRACT FROM AUTHOR]

A monthly to daily streamflow disaggregation method is presented as part of an emerging water quality model designed to link with established monthly hydrology and yield models. The daily time step is assumed necessary for simulating water quality dynamics. The method is tested on two catchments in South Africa where observed daily flow data are available. The model includes a volume correction process to ensure daily sums are equal to input monthly flows and this reduces the sensitivity of the results to some model parameters. The sequences of events in the input daily rainfall must be representative of the catchment. Model validation against observed flows achieved Nash-Sutcliffe efficiency values ranging from 0.75 to 0.94 and initial applications of a water quality component suggested little difference between using observed and disaggregated flows. The main practical advantages are simplicity and the fact that the method builds on the experience of existing monthly models.Editor D. Koutsoyiannis; Guest editor G. Mahé [ABSTRACT FROM PUBLISHER]

Electrical conductivity (EC) is a useful surrogate for total dissolved solids (TDS). EC is more rapidly and easily measurable with reasonably-priced equipment. However, as an indirect measure EC is subject to uncertainties that are not always apparent to the user. We set out to investigate the relationship between TDS and EC in 144 643 sample results available on the Department of Water Affairs water quality database. TDS is calculated as the sum of the major solutes determined by laboratory analysis and EC is a measurement in a flow cell. The median TDS:EC ratio for 332 high priority sites was 7 mg/l: 1 mS/m. Regional differences ranged from 4.8 to 8.6. Investigation of 38 of these sites using Maucha diagrams suggested that the differences are related to the dominant major ions, with sodium chloride waters having a lower TDS:EC conversion factor than calcium bicarbonate waters. The practical application of these findings is that users of EC meters should not simply apply a blanket conversion factor, but need to select an applicable factor for the river system in which they are measuring. [ABSTRACT FROM AUTHOR]

Vegetation cover in catchments in semi-arid environments with distinct rain seasons is important in influencing water quality and availability through its effect on runoff and groundwater recharge. This study assessed catchment-scale vegetation cover and condition, indicated by land degradation and vegetation vigour, using recent rain season Landsat TM/ETM+ images supplemented by dry season images for comparison. Image classification into vegetation density categories was used in mapping land degradation, the bare land category used as indicator. Vegetation vigour indicates vegetation productivity levels, and has been shown to correlate with the NDVI in similar previous studies. The 30 savanna biome vegetation types in the catchment were used as strata for assessing relative vigour using NDVI values. The NDVI frequency distributions per vegetation stratum were normal (Gaussian), the location of whose peaks enabled comparisons. Land degradation could be mapped with certainty mainly in the vicinity of settlements. Rivers draining through degraded areas had elevated colour and turbidity values. As the NDVI profiles per vegetation type could be explained by the land use and landscape position context of the vegetation types, NDVI profiling proved useful for assessing vegetation condition. NDVI profiling of vegetation types is potentially useful in monitoring savanna vegetation condition using remotely sensed images. [ABSTRACT FROM AUTHOR]

The ACRU agrohydrological model, in the form of ACRU2000 and its salinity module, ACRUSalinity, was employed in catchment-scale assessment of widespread irrigation with low quality mine-water in undisturbed (un-mined) and rehabilitated soils in the Upper Olifants basin of South Africa. The study area comprised a small catchment of 4.7 km² located in a coal-mine environment, known as the Tweefontein Pan catchment. The catchment drained to a surface reservoir (Tweefontein Reservoir) of maximum capacity and surface area 4000 Mℓ and 1.5 km², respectively. The catchment was instrumented to measure hydrodynamic responses and simulated as a hydrological system. Consideration was given to run-off, groundwater storage, evapotranspiration, baseflow, interception, irrigation water supply and rainfall, thereby accounting for all the dominant hydrological components of the system. Three scenarios were simulated using the available records for 5 years (1999 to 2004). The first was a baseline scenario representing the prevailing condition in the study area and the other 2 scenarios represented widespread irrigation with the mine-water on undisturbed and rehabilitated soils. In simulating the widespread irrigation on rehabilitated soils, a distinction was made between a rehabilitated irrigated area before and after the re-establishment of the equilibrium water table. Comparison of the results from the simulated scenarios indicated that a greater undisturbed area (max of 160 ha) than rehabilitated area (max of 120 ha) could be irrigated with mine-water from the Tweefontein Reservoir. Irrigation on rehabilitated soils depleted the water in the reservoir more rapidly than irrigation on undisturbed soils, due to lower runoff and higher ingress to groundwater in rehabilitated areas. [ABSTRACT FROM AUTHOR]

A lake-wide bloom of the dinoflagellate Ceratium hirundinella, discovered in Albert Falls Dam in October 2006, exposed a significant ecological change indicative of reduced water quality in this historically mesotrophic reservoir. The spatial distribution of the bloom was examined synoptically in October 2006 and January 2007; these surveys revealed generally higher dinoflagellate densities in inshore reaches of the lake, and especially in the discharge plume of the inflowing Mgeni River. Ceratium totally dominated the phytoplankton assemblage, accounting almost completely for coincident chlorophyll levels, which generally increased with depth to generate a `deep' chlorophyll maximum. Vertical oxygen profiles during the bloom differed substantially from corresponding profiles during non-bloom conditions historically typical in this reservoir. Direct count data and ordination analysis using non-metric multidimensional scaling exposed marked changes in zooplankton community structure compared to seasonally congruent non-bloom conditions in other years. Changes included the effective replacement of Moina by Bosmina, substantial reductions in Daphnia and Ceriodaphnia, and smaller but definite increases iii abundance especially of calanoid copepods, as well as cyclopoid copepods and of Chaoborus, although not all of these differences were apparent in both survey months. These compositional changes are attributable to intrinsic differences in feeding biology among taxa and their associated susceptibility to the altered food environment, which was commensurate with Ceratium's emergence. In addition, chydorid cladocerans appeared as a new (but spatially restricted) eutrophic bio-indicator component of the zooplankton, and the species diversity of cyclopoid copepods was enriched. The historical incidence of Ceratium in the lake since 1995 coincided with low NO3-N:TP values (used here as an N:P ratio proxy), particularly of inflow waters, and with broadly coincident values in the open lake. Ceratium was present but sparse in 1995, at average N:P ratios around 5.5. It disappeared in 1996 when the ratio increased radically to >10, and reappeared in 2004 after an erratic decline of the ratio to <5 in the lake. The decline in N:P ratio of inflow waters since 1996 was clearly associated with a consistent rise in TP levels in inflows, most plausibly attributable to inputs of (Howick) wastewater treatment (WWT) plant origin. The appearance of Ceratium blooms is accordingly related to progressive elevations in mean annual P concentrations in inflows from -40 μg/ℓ in 1995 to 120 μg/ℓ in 2007 (broadly mirrored in annual TP loadings), suggesting that improved operational efficiency (and capacity) of the WWT plant offers a plausible prospect for mitigation and reversal. [ABSTRACT FROM AUTHOR]

The concept of water neutrality, based on its carbon equivalent, was first coined during the World Summit on Sustainable Development in 2002. Since then the term has been loosely used, with little quantitative validation. Here we present a first quantitative framework for a water-neutral scheme that allows a private water user to balance its water account through both demand- and supply-side interventions. Such innovative voluntary mechanisms can provide benefits in a chronically water stressed and developing country, such as South Africa. This scheme seeks to harness private sector investment in water security, by allowing investors to balance quantitatively their water account based on sound scientific rationale. Investors are required to engage in a three-step process of: reviewing their water usage, implementing a reduction strategy, and replenishment of water to hydrological systems through the investment in watershed services, equivalent to their water usage. Initially, the scheme allows participants to replenish quantitatively their water usage through investment in the clearing of water-intensive invasive alien plants. The project, however, encourages the innovation and development of further quantitative mechanisms for investing in watershed services, and proposes an operational model for the promotion of a water-neutral market in South Africa. [ABSTRACT FROM AUTHOR]

Understanding the spatial and temporal patterns of water quality is central to its management as it provides information essential to the restoration as well as protection of water resources. The main objectives of this study were (i) to analyze the spatial and temporal trends of water quality and (ii) to identify the critical sources of pollution in the Klip River catchment (KRC). Water samples were collected at 12 sampling points along the Klip River, monthly from February 2016 to January 2017 and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and spectrophotometry for heavy metals and nutrients, respectively. Multivariate statistical techniques (cluster analysis and discriminant analysis) were used to delineate homogeneous water quality zones and seasons, and principal component analysis was used to identify pollution sources. Comprehensive pollution index (CPI) was also computed to classify the overall pollution of the river. The spatial grouping yielded two homogenous water quality zones namely upstream and downstream. Temporal grouping yielded two clusters, which were attributed to the effects of the El Nino (2015/16 season) and La Nina phenomena (2016/17 season). The CPI revealed that the KRC was critically polluted in the upstream for domestic (162.16–323.28) and aquatic uses (617.70–837.09) in both the 2015/2016 and 2016/2017 seasons. It can be concluded that pollutants, which influence water quality in the KRC in one season and/or location, may not necessarily be the same in the other season or location. Therefore, there is need to develop a water quality management plan in the KRC that targets the most impaired uses, pollutants of priority, and the critically polluted areas. [ABSTRACT FROM AUTHOR]

Floodplain ecosystems in Africa are under threat due to direct anthropogenic pressure and climate change. The lower Phongolo River and associated floodplain is South Africa's largest inland floodplain ecosystem and has been regulated by the Pongolapoort Dam since the 1970s. The last controlled flood release from the dam occurred in December 2014, after which a severe drought occurred and only a base flow was released. The central aims of this study were to determine the historic and present water quality state of the middle and lower Phongolo River and assess the possible effects of the most recent drought may have had. Historic water quality data (1970s to present) were obtained from monitoring stations within the Phongolo River catchment to assess the long-term water quality patterns. Using multivariate statistical analyses as well as the Physicochemical Driver Assessment Index (PAI), a water quality index developed for South African riverine ecosystems, various in situ and chemical water variables were analysed. Key findings included that the water quality of the middle and lower Phongolo River has degraded since the 1970s, due to increased salinity and nutrient inputs from surrounding irrigation schemes. The Pongolapoort Dam appears to be trapping nutrient-rich sediments leading to nutrient-depleted water entering the lower Phongolo River. The nutrient levels increase again as the river flows through the downstream floodplain through input from nutrient rich soils and fertilizers. The drought did not have any significant effect on water quality as the PAI remained similar to pre-drought conditions. [ABSTRACT FROM AUTHOR]

Ensuring food security is becoming increasingly difficult due to limited freshwater resources. Low-quality irrigation water also poses a severe threat to crop yield and quality. The aim of this study was to evaluate the water quality associated with the Crocodile (West) and Marico catchments, which represent one of South Africa’s most developed regions. Sources of irrigation water include the hypertrophic Hartbeespoort Dam, as well as the heavily impacted Crocodile (West) River. Analysis of historical irrigation water quality data (from January 2005 to December 2015) revealed that the Hartbeespoort and Crocodile (West) irrigation schemes were exposed to calcium sulfate enrichment, likely as a result of extensive mining activities in the Bushveld Igneous Complex. Also, significant differences in water quality parameters occurred between these irrigation schemes and the reference system (Marico-Bosveld Irrigation Scheme), while important salt (chloride and sodium) and nutrient (inorganic nitrogen and orthophosphate (as phosphorus)) concentrations exceeded threshold values provided by irrigation water quality guidelines. The Hartbeespoort and Crocodile (West) irrigation schemes also presented distinctive temporal (long-term and seasonal) patterns in water quality. Seasonal variation in pH levels at the Hartbeespoort Irrigation Scheme is likely caused by excessive algae growth and cyanobacteria blooms (Mycrocystis sp.), which also pose an important threat to human and animal health. Despite mitigation efforts by government and other stakeholders, some of South Africa’s major irrigation schemes remain highly impacted as a result of water quality deterioration. [ABSTRACT FROM AUTHOR]