Scielo RSS <![CDATA[Water SA]]> vol. 44 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>3-D numerical modelling of groundwater flow for scenario-based analysis and management</b>]]> In recent years, extensive competition for groundwater use among different consumers has exploited major freshwater aquifers in Pakistan. There is an urgent need for appraisal of this precious resource followed by some mitigation strategies. This modelling study was conducted in the mixed cropping zone of the Punjab, Pakistan. Both remote sensing and secondary data were utilized to achieve objectives of this study. The data related to piezometric water levels, canal gauges, well logs, meteorological and lithological information were collected from Punjab Irrigation Department (PID), Water and Power Development Authority (WAPDA). Groundwater flow models for both steady and transient conditions were set-up using FEFLOW-3D. Water balance components and recharge were estimated using empirical relations and inverse modelling approaches. Both manual and automated approaches were utilized to calibrate the models. Moreover, sensitivity analysis was performed to see the response of model output against different model input parameters. Followed by calibration and validation, the model was run for different management scenarios, including lining of canal sections, minimization of field percolation, and change of groundwater abstraction. The study results show a drop in groundwater levels for almost all scenarios. The highest negative change was observed for the 4th scenario (i.e. 25% increase in groundwater pumping over a 10-year period), with a value of 3.73 m, by ignoring very wet summer and winter seasons. For normal weather conditions, the highest negative change was observed for the 4th scenario with a value of 2.91 m followed by 2.68 m for the 3 scenario (i.e. 50% reduction in canal seepage and field percolation over a 10-year period). For very wet summer and winter seasons, only one positive change was observed, for the 5th scenario (i.e. 25% decrease in groundwater pumping during 10 years period), with a value of 1.17 m. The changes for all other scenarios were negative. The mitigation strategy may include less groundwater pumping, by supporting cultivation of low delta crops and adjusting cropping patterns considering canal water supplies. It is further suggested to support current modelling results by incorporating more detailed information on cropping and by exploring the effect of climate change. <![CDATA[<b>Effects of a polymeric organic coagulant for industrial mineral oil wastewater treatment using response surface methodology (RSM)</b>]]> In this study, treatment of a local South African oil refinery effluent using a coagulation flotation process is designed using response surface methodology (RSM). A Box-Behnken design (BBD) implementing the RSM is applied to evaluate the effects and interactions of three operating parameters, viz., pH, coagulant dosage and flotation time, on the treatment of mineral oil wastewater (MOW). Polyacrylamide (Zetag-FS/A50), which is a water-soluble compound, is applied to enhance the adsorption mechanism and intermolecular bridging to minimise the amount of oil droplets. In addition, due to the monomeric nature and the charge density of the Zetag-FS/A50, its efficiency was evaluated to serve as an alternative coagulant for the pre-treatment of the MOW. The removal of chemical oxidation demand (COD), soap oil and grease (SOG), total suspended solids (TSS) and turbidity from the MOW were used as the response variables for the coagulation flotation process. This was done with a standard dissolved air flotation jar test. The results show that the actual COD, SOG, TSS and turbidity percentage removal at optimised conditions with a coagulant dosage of 50 mg/L were 82%, 83%,70% and 83% respectively, while the predicted response was 92%, 96%, 73% and 87% for COD, SOG, TSS and turbidity, respectively. The analysis of variance (ANOVA) showed that the proposed models are significant at a 95% confidence level. A quadratic model was generated for response variables COD and SOG, while TSS and turbidity produced a linear model. The models fitted well with the experimental data with correlation coefficients (actual R2) of 0.94 for COD, 0.91 for SOG, 0.81 for TSS, and 0.75 for turbidity. The outcome of the study shows that the RSM has merit to optimise and identify the most important factor to control and the Zetag-FS/A50 coagulant has the potential to adsorb the oil droplets in order to enhance the treatment efficiency of the process. <![CDATA[<b>Applications of the PyTOPKAPI model to ungauged catchments</b>]]> Many catchments in developing countries are poorly gauged/totally ungauged which hinders water resource management and flood prediction in these countries. This study explored the application of the PyTOPKAPI model to South African (Mhlanga) and Ethiopian (Gilgel Ghibe) case study catchments to test its suitability for simulating stream flows from ungauged catchments. The aim is to extend the model application to poorly gauged/totally ungauged catchments in developing countries. The model uses digital elevation data and other spatial data sources to set up the model parameters and the forcing files. To generate reliable stream flows, models generally need to be calibrated, which typically relies on the availability of reliable stream flow data. We show how application of simple lumped models for average runoff ratios, such as that proposed by Schreiber in 1904, can be used as an alternative to detailed calibration with gauged flows. This approach seems to be new; and we show how the proposed method, together with the PyTOPKAPI model, can be used to predict runoff responses in ungauged catchments for water resource applications and flood forecasting in developing countries. <![CDATA[<b>Control of hydrogen sulphide in full-scale anaerobic digesters using iron (III) chloride: performance, origin and effects</b>]]> The study presents the results of sulphide control using iron (III) chloride in full-scale anaerobic digesters (ADs) at a large-scale municipal wastewater treatment plant (WWTP). Iron (III) ('ferric') chloride was applied at a range of 24-105 mg FeCl3/L with and without alkali solution using different strategies. Introduction points were implemented at the feeding line and the sludge thickener unit. Response of the ADs in terms of biogas H2S reduction over time, solid loading rates (SLR), feed sludge flow rate and pH level were investigated. Reduction of H2S in the biogas reached 4 035 μg/L in directly-dosed AD versus a 1 345 μg/L drop in non-dosed ADs, as a result of internal recirculation among the digesters, where actual values were possibly higher as volatile solid (VS) degradation increased in all ADs during the dosing period. No noticeable effect on biogas production and pH was observed. The degree of H2S production was found to be correlated to the volatile SLR, where primary sludge solids contributed mostly to the organic and proteinaceous content of the thickened sludge and presented a high variation and a strong relationship with H2S production. Correlation analysis based on data for the 17-month period that followed supported the significant role of primary SLR in H2S production. <![CDATA[<b>Review of available data for a South African Inventory of Inland Aquatic Ecosystems (SAIIAE)</b>]]> The National Biodiversity Assessment of 2011 found freshwater ecosystems to be highly threatened and poorly protected. However, a number of studies have shown that the National Wetland Map (NWM) Version 4 represents less than 54% of wetlands mapped at a fine scale. A more comprehensive South African Inventory of Inland Aquatic Ecosystems (SAIIAE) would greatly improve the assessment of wetland ecosystem types and their condition and conservation status, and is crucial for monitoring trends to inform decision making and planning. In preparation for the third National Biodiversity Assessment of 2018, a review was undertaken to identify possible data sources that could contribute to the SAIIAE. The objectives of the study were to (i) assess which type of information is available for developing a SAIIAE; and (ii) list and understand the availability of fine-scale wetland data for updating the NWM. A variety of data related to species occurrence and distribution, extent and type of inland wetlands and rivers, as well as datasets which describe regional settings of inland aquatic ecosystems, were found across a number of institutions. Fine-scale spatial data amounted to more than double the extent of inland wetlands mapped by remote sensing at a country-wide scale. Nearly 5 million ha of fine-scale data were collected from a diverse number of institutions, with the majority (73%) of these data mapped by Government (3 681 503 ha or 3% of South Africa). It is estimated that < 8% of the sub-quaternary catchments of South Africa had complete wetland data sets, primarily in the Gauteng, Mpumalanga and Western Cape Provinces. Accuracy assessment reports and confidence ratings were however not consistently available for the wetland datasets. Inland wetlands in the majority of South Africa (84%) therefore remain poorly represented. We recommend future steps to improve the SAIIAE, including improving the representation of inland wetland ecosystem types and focusing on accuracy assessment. <![CDATA[<b>Decolourization of Direct Blue 2 by peroxidases obtained from an industrial soybean waste</b>]]> In this work the decolourization of Direct Blue 2 dye (DB2) using an industrial soybean waste as a source of peroxidases was studied. Temperature, pH, amount of H2O2 and concentration of dye were evaluated to determine the maximum catalytic activity of the enzyme during the dye degradation process. It was observed that a temperature of 40°C, a pH of 5 and a concentration of 40 mg/L for the dye in aqueous phase, play a significant role in the overall enzyme-mediated reaction. The maximum decolourization efficiency achieved under optimal conditions was 70% ± 4%. HPLC studies were carried out to confirm dye degradation and analyse the intermediate metabolites. The oxidation products quantified during the reaction were benzidine and 4 aminobiphenyl. Also, an increase in toxicity, determined by Vibrio fisheri, was observed after the enzymatic oxidation of the dye. Results suggest that the oxidation of DB2 with peroxidases can be recommended as a pretreatment step before a conventional treatment process. <![CDATA[<b>Influence of temperature on the performance of anaerobic treatment systems of municipal wastewater</b>]]> Anaerobic sewage treatment systems, especially upflow anaerobic sludge blanket (UASB) reactors, have found wide application over the past decades, particularly in regions with a warm climate. A low sewage temperature is generally considered as a factor contributing to poor performance, characterized by an increase of the COD fractions in the effluent and the generated sludge, and decreasing the fraction that is transformed into methane. An experimental investigation was carried out at pilot scale to establish the values of the three COD fractions for different values of temperature and the applied organic load. The sludge age of the anaerobic treatment, together with temperature, was identified as the main operational variable that affects the efficiency of anaerobic treatment. An empirical expression was derived for the values of the three factions as a function of these two variables. From the results of the experimental investigation it was apparent that there is no point in applying a sludge age of more than 100 d, when the reactor is near its best performance. An expression was derived to establish the hydraulic retention time for maximum digestion efficiency as a function of temperature, concentration and composition of organic material and sludge mass. It was established that the main limit to the sludge hold-up in UASB reactors treating sewage is not the sludge settleability, but rather the break-up of flocs leading to loss of small, poorly-settling particles. <![CDATA[<b>Comparison of the chemical quality of rainwater harvested from roof and surface run-off systems</b>]]> Despite numerous studies, little is known about the quality of rainwater harvested (RWH) from roofs or overland flow by smallholder farmers of Africa. Thus, the main objective of this study was to compare the physical and chemical quality of the rainwater harvested from both dwelling roofs and yards situated in a smallholder community in KwaZulu-Natal (South Africa). Rainwater samples were collected at 51 households during a dry period for assessment of the concentration of specific chemical elements. The water harvested from metallic roofs and yards did not meet the World Health Organization (WHO, 2011) guidelines for drinking water, as it exceeded recommended levels of Se, Al, B and Cd in at least 75% of the roof water samples, and of Al in the case of yard RWH. Compared to yard water, RWH from metallic roofs exhibited higher B, Se, Ni, Pb, Cu, As, Cd, and Cr but lower dissolved organic carbon (DOC), NO3-, Fe, SO4(2-), Na, Mg, Ca, K, Fe concentrations. The content of nutrients and DOC in the water harvested from the surface correlated with the number of pigs per household (with r = 0.78 for SO4(2-), r = 0.74 for DOC and r = 0.52; NO3). These results are expected to inform improved design and implementation of RWH. Further investigations should consider both physicochemical and microbiological aspects of water quality to provide a more holistic understanding of potential health risks. <![CDATA[<b>Partition distribution of selected organochlorine pesticides in water, sediment pore water and surface sediment from uMngeni River, KwaZulu-Natal, South Africa</b>]]> Organochlorine pesticides (OCPs) were analysed in surface water, pore water and surface sediment samples collected from the uMngeni River, which is one of the largest rivers in the province of KwaZulu-Natal, South Africa. Liquid-liquid extraction was used to extract the analytes from water and pore water samples and soxhlet extraction was used to extract sediment samples with subsequent florisil clean-up and gas chromatography-mass spectrometry (GC-MS) analysis. Twelve selected OCPs were analysed and their total concentrations were found to range from 8.04-21.06 ng/mL, 36.06-188.43 ng/mL and 148.17-554.73 ng/g in unfiltered surface water, unfiltered pore water and surface sediment (dry weight (dw)), respectively. The results indicated that the concentrations of these selected pesticides were far higher in sediment (72%) than in pore water (25%) and water (3%). The most polluted sites were Northern Wastewater Treatment influent (NWTI) for water (Z12OCP = 19.41 ± 1.43 ng/mL) and Northern Wastewater Treatment effluent (NWTE) for pore water (Σ12 OCP = 166.23 ± 7.16 ng/mL) and sediment (Σ12 OCP = 495.21 ± 32.38 ng/g). The most abundant individual OCPs and their average concentrations in general in the river were p,p′-DDE in unfiltered water (1.62 ±0.22 ng/mL) and unfiltered sediment pore water (17.09 ±7.96 ng/mL), and endrin in surface sediment (55.57 ± 19.01 ng/g, dw). <![CDATA[<b>Decentralised wastewater treatment effluent fertigation: preliminary technical assessment</b>]]> The Decentralised Wastewater Treatment System (DEWATS) can provide a potential sanitation solution to residents living in informal settlements with the effluent produced being used on agricultural land. This paper reports on a first step to assess the technical viability of this concept. To do so a pilot DEWATS plant was connected to 83 houses in the eThekwini Municipality. An experiment was conducted in a randomised complete block design with 2 treatments (DEWATS effluent irrigation and tap water irrigation + fertiliser) and 3 blocks. Banana and taro crops were irrigated using an automated drip irrigation system. Data on the weather, crop growth, nitrogen and phosphorus uptake and soil chemical properties were collected. Irrigation with DEWATS effluent was comparable to tap water + fertiliser especially for banana growth and biomass production. Banana and taro required 3 514 mm of irrigation effluent. About 0.0117 ha-household-1 (23.3 m²-person-1) was found to be an adequate area for effluent reuse. Wet-weather storage requirements were calculated to be about 9.2 m³-household-1. DEWATS effluent, after passing through a horizontal flow wetland, was unable to meet banana and taro nitrogen and phosphorus requirements. Nutrient monitoring is required when using anaerobic filter effluent from a DEWATS for irrigating banana and taro. <![CDATA[<b>Potential of dyes as draw solutions in forward osmosis for the South African textile industry</b>]]> The textile industry produces large volumes of wastewater that requires appropriate treatment before being released into the environment. Research globally has focused on advanced desalination technologies to augment the limited freshwater resources. Forward osmosis (FO) technology has gained substantial interest as a possible lower-energy desalination technology. However, challenges such as the availability of effective draw solutions (DS) have limited its implementation. This study evaluated alternative feed water resources and assessed the potential of dye solutions as DS. The aim is to dilute a concentrated dye DS to a target concentration for direct dye-batch use, thereby reclaiming water resources. The measured osmotic pressure (OP) of the alternative feed solutions (synthetic brackish water; syntethic seawater; seawater from the Atlantic and Indian Oceans; and wastewater from two textile factories) were 414, 2 761, 2 580, 2 614; 1 716 and 7 822 kPa, respectively. Three basic dyes (Maxilon Turquoise, Red and Blue) and three reactive dyes (Carmine, Olive Green and Black) were selected based on common use in the South African textile industry. The dye samples were prepared without and with salt at different concentrations and different dye-to-salt mass ratios ranging from 1:10 to 1:60. The OP trends for the basic dyes followed Blue >> Red > Turquoise and for the reactive dyes Black >> Olive > Carmine. The overall OP trend was Black > Olive > Carmine > Blue > Red > Turquoise. The OP at different dye concentrations and different dye-to-salt ratios was mostly influenced by the dye chemistry and molecular weight (Mw) rather than the type of dye, i.e., reactive vs basic.The OP trend for the dye-to-salt ratios was 1:60 > 1:50 > 1:40 > 1:30 > 1:20 > 1:10. For both the basic and reactive dyes a linear relationship exists between OP and dye concentration; as well as between OP and Mw. The dye DS exhibited larger OP compared to that of the FS evaluated, thus rendering them suitable DS. <![CDATA[<b>Driving factors of temporary and permanent shallow lakes in and around Hwange National Park, Zimbabwe</b>]]> Small aquatic ecosystems in semi-arid environments are characterised by strong seasonal water level fluctuations. In addition, land use as well as artificial pumping of groundwater to maintain water resources throughout the dry season may affect the functioning of aquatic ecosystems. In this study, we investigated pans situated in and around Hwange National Park, Zimbabwe, where certain waterholes are artificially maintained during the dry season for conservation purposes. We monitored 30 temporary and permanent waterholes for 7 months across the wet and dry seasons in 2013, and analysed them for standard parameters to investigate seasonal variations, assess the effects of land use and pumping on lake functioning, and determine the driving factors of these aquatic systems. Results show an increase in conductivity, hardness, and turbidity when temporary pans dry up and permanent ones are filled with groundwater. Prominent parameters explaining the diversity of aquatic ecosystems are water hardness, conductivity, turbidity, and the presence of vegetation. Seasonality differences in certain parameters suggest the influence of water level fluctuations associated with rainfall, evaporation, and pumping activities. Further, the distinction between turbid pans and those with clear water and vegetation suggests the alternative functioning of pans. Land use had no significant effects, while the effects of pumping are discussed. In times of water scarcity, animals gather around artificially maintained waterholes and foul water with faeces and urine, thus inducing water eutrophication. <![CDATA[<b>High-frequency monitoring of stream water physicochemistry on sub-Antarctic Marion Island</b>]]> Given the remoteness and challenging environmental conditions on sub-Antarctic Marion Island, continuous high-resolution studies of the island's natural water systems are rare. Subsequently, current understanding of the island's hydrochemistry is based entirely on manual point-based measurements. To address this research gap we analysed continuous, in-situ high-frequency physicochemical measurements (pH, water temperature, dissolved oxygen (DO), and electrical conductivity (EC)) from the Soft Plume River over the period 21 April 2015-26 April 2015. We observed a sharp, short-term response from all measurements to a precipitation event that was superimposed on consistent but subtle diel (i.e. 24 h) cycles throughout the study. Total variation in pH and electrical conductivity amounted to 1.3 units and 27.7 μS/cm respectively. Stream water temperature was less variable (6.2°C) than air surface temperature (14.2°C). Total variation in DO was 2.0 mg/L. Aside from the precipitation-induced response, diel oscillations were small and only visible through the use of continuous, high-resolution monitoring. Findings highlight the advantages of continuous high-frequency monitoring in capturing the range of daily variation and elucidating diel cycles in stream water physicochemistry on sub-Antarctic Marion Island that have not previously been accounted for. <![CDATA[<b>Variation of runoff source areas under different soil wetness conditions in a semi-arid mountain region, Iran</b>]]> Runoff source areas can serve as focus areas for water quality monitoring and catchment management. In this study, a conceptual form of the Soil Conservation Service Curve Number method (SCS-CN) is used to define variable-source runoff areas in a meso-scale catchment in the Zagros mountain region, southwest of Iran. The analysis indicates that for the average and dry antecedent soil wetness (the dominant soil moisture conditions), the original SCS-CN criterion that assumes the initial abstraction of rainfall to be equal to 20% of the maximum potential soil water retention fails to predict runoff source areas correctly, suggesting the ineffectiveness of the original form of the method for the study region. However, the determination of the initial abstraction based on hydrograph-hyetograph matching technique provides reasonable results, outperforms the original form of the SCS-CN based method and, more importantly, highlights the significance of having localized rainfall and runoff data. Under wet soil conditions, both techniques provide similar results; the robustness of the SCS-CN based method is thus supported only for wet soil conditions. <![CDATA[<b>Climate trends across South Africa since 1980</b>]]> Observed and simulated climate trends across South Africa in the period 1980-2014 are studied. Observed CRU3/CAMS (Climate Research Unit v3 / Climate Analysis and Monitoring System) air temperatures have increased by 0.02°C-yr-1 while NOAA/SODA sea temperatures have risen by 0.03°Gyr-1 in the Agulhas Current. A poleward expansion of the South Atlantic high in NCEP2/MERRA (National Center for Environmental Prediction v2 / Modern-Era Retrospective analysis for Research and Applications) has produced a trend toward south-easterly flow which contributes to a moist-east/dry-west pattern. Observed CHIRPS2 rainfall and NDVI vegetation fraction show no appreciable trend except near Cape Town where drier conditions in the period 1980-2014 correspond with enhanced coastal upwelling. CMIP5 model projections for rainfall up to 2050 reflect drying, except in the eastern coastal plains. While inter-annual fluctuations of South African rainfall overshadow linear trends, temperature increases account for 32% of observed variance. <![CDATA[<b>Investigating the effects of different physical and chemical stress factors on microbial biofilm</b>]]> Microorganisms that adhere to surfaces in order to protect themselves from many adverse environmental conditions form a layer called biofilm. Biofilms protect bacteria from changing environmental conditions such as starvation, antibiotics, disinfectants, pH and temperature fluctuation, dryness and UV rays. In this study, biofilms were formed on surfaces of glass coupons in a cooling tower model system over a period of 180 days. The biofilms were treated with various stress factors monthly. These stress factors were: exposure to temperatures of 4°C and 60°C, pH of 3, 5, and 11, 3 M aqueous NaCl and distilled water, as well as, monochloramine at 2, 500, and 1 000 mg/L (ppm). Following the treatment with stress factors, both the numbers of actively respiring bacteria and the total bacteria in the biofilms were determined by CTC-DAPI staining. The aerobic heterotrophic plate counts (HPC) in the biofilms were determined by the conventional culture method of spread plating on R2A agar. The aim of this study was to determine the impact of these stressors on the model cooling-tower biofilms. Of the stressors tested, those that had the greatest impact were a temperature of 60°C, pH of 3, 3 M NaCl, and monochloramine at both 500 and 1 000 mg/L. However, when using a non-culture-based viability assay (CTC-DAPI staining), an extremely high number of live bacteria were detected even after applying the most effective stress factors (with the exception of pH 3) of 60°C, 3 M NaCl, monochloramine at 500 and 1 000 mg/L. Results showed that biofilm protects the bacteria from extreme physical and chemical stress conditions. Additionally, the conventional culture technique cannot detect the presence of bacteria that have entered the viable but non-culturable (VBNC) phase; the use of different techniques, such as microscopy and cytometry (flow and solid-phase), is therefore important to obtain more accurate results. <![CDATA[<b>Oxidative stress biomarkers in <i>Oreochromis niloticus </i>as early warning signals in assessing pollution from acid mine drainage and diffuse sources of pollutants in a subtropical river</b>]]> This study investigated the use of an exotic fish species Oreochromis niloticus as a bio-indicator organism in active biomonitoring of Yellow Jacket and Mazowe rivers, Zimbabwe, receiving acid mine drainage from Iron Duke Mine. The Yellow Jacket River flows through Iron Duke Pyrite Mine while the Mazowe River passes through the Mazowe factory and estate shop that receives runoff from intensive agricultural activities. Active biomonitoring (ABM) exposures were conducted for 6 weeks in effluent-contaminated sections of the rivers during high flow, from February to March 2013. A set of biomarkers of exposure and effect (glutathione S-transferase, catalase and metallothioneins) were selected and their responses determined in O. niloticus liver, gills and muscle. We hypothesized that the increase in activities of GST, CAT and MT in exposed fish, in comparison to control fish, can be used to assess river water quality using O. niloticus. Biomarker expression was measured after 4 and 6 weeks and compared against control fish kept under laboratory conditions without contaminants. Concentrations of zinc, cadmium, chromium, nickel, lead, copper, manganese, arsenic and iron were measured in flowing water, riverbed sediments and muscle tissue of actively biomonitored O. niloticus. Key water quality parameters, including dissolved oxygen and conductivity, clearly showed a pollution gradient from Iron Duke Mine. Expression of CAT and GST was highest in the liver, compared to gills and muscles, after 4 and 6 weeks of exposure, and their expression was lower (p < 0.05) in control fish. The expression of the enzymes was not significantly different after 6 weeks compared to 4 weeks. Increased enzyme expressions at Site 1, which is upstream from Iron Duke Mine, were comparable to enzyme expressions at Sites 3, 4, 5 and 6, which correlated with increased zinc concentrations in the exposed fish muscle tissue. The general order of metal concentrations was sediments &gt; water &gt; fish, except for zinc, which had the highest bioconcentration factors. Using the GST, CAT and MT we concluded that Mazowe and Yellow Jacket rivers are contaminated and that these oxidative stress biomarkers can successfully be used in assessing pollution from point sources such as acid mine drainage, as well as diffuse sources of pollutants such as commercial agriculture. <![CDATA[<b>Characterising the water use and hydraulic properties of riparian tree invasions: A case study of <i>Populus canescens </i>in South Africa</b>]]> Invasive alien plants (IAPs) pose a serious threat to the already limited water resources in dry countries like South Africa which are facing increasing water shortages. Much of South Africa is expected to get drier in future due to climate change. In addition, the future climatic conditions are also predicted to accelerate the rate at which IAPs will spread, due to favourable growing conditions, further disrupting the provision of goods and services. Previous studies on tree water use in South Africa focused on commercial forests of introduced genera mainly Pinus, Eucalyptus, and Acacia. This study sought to expand these observations by quantifying water use and its drivers in riparian Grey Poplar (Populus canescens) invasions in the Berg River catchment of South Africa. Whole tree hydraulic resistance ranged from ~ 1.4 MPa-h-g-1 for large trees to ~14.3 MPa-h-g-1 for the small ones. These resistances are higher than those found for poplars in temperate climates, suggesting substantial hydraulic constraints to transpiration. Daily peak transpiration varied from 5 to 6 L-tree-1 in small trees (~9.2 cm DBH) to between 35 and 40 L-tree-1 for large trees (~24 cm DBH). Stand-level transpiration peaked at ~4 mm-d-1 in summer (Jan-Feb). However, the annual total transpiration was only 338 mm due to the deciduous nature of the species and also the high hydraulic resistance in the transpiration stream. Daily transpiration was strongly correlated to solar radiation (R² > 0.81) while the air vapour pressure deficit (VPD) constrained transpiration at high VPD values. We conclude that the water use of the poplar invasions is significantly lower than that of other riparian invasions. The impact of these invasions on the water resources is therefore likely quite low, warranting less priority in alien plant clearing operations aimed at salvaging water.