Scielo RSS <![CDATA[Water SA]]> http://www.scielo.org.za/rss.php?pid=1816-795020170002&lang=pt vol. 43 num. 2 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Phytostabilization of metals by indigenous riparian vegetation</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200001&lng=pt&nrm=iso&tlng=pt Given the increasing pressure of man-made activities on riparian zones, the capacity of the riparian vegetation along the Upper Olifants River, South Africa, to phytoextract and phytostabilize aluminium (Al), manganese (Mn) and iron (Fe) from the soil was investigated. The aim of the study was to gain better understanding of the capacity of indigenous vegetation in riparian zones to immobilize metals in the soil, thereby improving river water quality and ecosystem services. Seven commonly-occurring pollution-tolerant riparian plant species were evaluated to establish their potential as bioaccumulators for Fe, Al and Mn. Species included: Cyperus haspan, Schoenoplectus corymbosus, Typha capensis, Phragmites australis, Cynodon dactylon, Cyperus marginatus and Juncus effusus, which were sampled in five riparian areas in the Upper Olifants catchment. The bioconcentration factor (BCF) for Mn was > 1 for all species investigated with a maximum of 5 for Typha capensis, which also showed the highest accumulation of Al (10.26) and Fe (7.03). The remaining species presented with Al and Fe BCF between 0.11 and 2.00, with minimal transfer from root to shoot. When measured against an ideal hypothetical buffer zone, the buffer zones under investigation varied between intact and severely compromised. Intact riparian zones showed elevated metal concentrations in the soil, yet significantly lower concentrations in the river water compared to areas with insufficient vegetative cover. A polluted riparian area overgrown by P. australis effectively phytoextracted 204 960 g/m² Al, 204 400 g/m² Fe and 27 887 g/m² Mn. The two indigenous Cyperus spp. were not ideal for metal immobilization with low bioaccumulation and transfer factors as well as low biomass. High biomass and Al, Fe and Mn phytostabilizing species: P. australis, T. capensis, S. corymbosus and J. effusus, should be considered in the rehabilitation of South African buffer areas. <![CDATA[<b>Carbapenem-resistant bacteria in a secondary wastewater treatment plant</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200002&lng=pt&nrm=iso&tlng=pt Bacterial resistance to carbapenems is an emerging problem of this century. A carbapenem-resistant bacterial population (CRBP) grown at 42°C was monitored in the influent and effluent of a secondary municipal wastewater treatment plant over 10 months. The municipal wastewater consisted of domestic, industrial, hospital and storm wastewaters. Median numbers of CRBP in influent and effluent water were 3.5 and 1.3 log CFU/mL, with its prevalence among total heterotrophic bacteria at 47% and 26%, respectively. Correlation of CRBP with physico-chemical and other bacteriological parameters of wastewater was estimated. Higher numbers of CRBP in influent and effluent were found in cases of nutrient-rich wastewater with higher concentrations of total heterotrophic bacteria and intestinal enterococci. Reduction of CRBP in the wastewater treatment process of 54% was comparable to the reduction of intestinal enterococci. Despite the significant elimination of CRBP in the secondary type of wastewater treatment plant, substantial numbers of CRBP are released through the effluent into the natural receiving waters. Since the CRBP grown at 42°C was not found in natural water samples beyond the vicinity of hospitals, these bacteria may be used as an indicator of hospital wastewaters. <![CDATA[<b>Trophic state categorisation and assessment of water quality in Manjirenji Dam, Zimbabwe, a shallow reservoir with designated multi-purpose water uses</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200003&lng=pt&nrm=iso&tlng=pt Intermittent, dire droughts and water abstraction pressures impact shallow man-made reservoirs with multiple designated water uses, often leading to water quality deterioration, and loss of biological integrity and utility value of a lake, threatening the livelihoods of lake shore communities. Thus, water quality information is crucial in setting up guidelines for freshwater resources management. In this study we investigated the water quality, determined the trophic state and assessed the influence of lake zones on the physical-chemical parameters of the Manjirenji Dam, Zimbabwe. Furthermore, we tested the applicability of two customary temperate water quality indices, the Canadian Council of Ministers of the Environment (CCME) Water Quality Index and the Carlson Trophic State Index, for a tropical lake system. Ten littoral and seven pelagic sites were sampled monthly over 9 months for the following water parameters: pH, conductivity, turbidity, total dissolved solids, suspended solids, chlorophyll a, temperature, dissolved oxygen, water transparency, ammonia, nitrogen, nitrates, total and reactive phosphorus. Despite slight fluctuations/variations, water quality in the Manjirenji Dam was generally fair, with a CCME value averaging 78.1, and the Carlson Trophic State Index reflecting oligotrophy. Non-significant differences in water quality parameters between pelagic and littoral sites in the Manjirenji Dam reflect the high connectivity of different spatial zones in a shallow lentic system. Index scores of the adapted temperate water indices detect similar water quality conditions for the Manjirenji Dam, thus perhaps indicating their potential applicability. The current water quality data set for the Manjirenji Dam is vital for formulating prudent management strategies to formulate/ensure adequate multi-purpose water usage and service for this aquatic ecosystem. <![CDATA[<b>Sensitivity to selected contaminants in a biological early warning system using <i>Anodonta woodiana</i> (Mollusca)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200004&lng=pt&nrm=iso&tlng=pt Several early warning systems for the monitoring of water quality are based on the assessment of valve opening/closing in bivalves. Tests were conducted to assess the sensitivity of the mussel Anodonta woodiana, installed on the Mosselmonitor, to seven contaminants and evaluate the usefulness of these sensors for detecting pollution events in the Po River (Italy). Mussels were exposed for 30 min to increasing concentrations of chromium (range 0.01-5 mg/L); arsenic (range 0.05-2.5 mg/L); sodium dodecyl sulphate SDS (range 0.25-50 mg/L); phenol (range 0.1-100 mg/L); oxadiazon (range 0.001-5 mg/L); trichloroethylene (range 0.01-100 mg/L); and crude oil (range 0.5-50 mg/L). Treatment with the highest concentration of SDS elicited two types of alarm response. In a second set of tests, the bivalves were exposed for 6 h to a selected concentration of each chemical. Only SDS led to a dramatic alteration of valve opening, resulting in alarms. This system would have limited applications for monitoring drinking water influent. <![CDATA[<b>Calibration and testing of AquaCrop for selected sorghum genotypes</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200005&lng=pt&nrm=iso&tlng=pt Predicting yield response to water is important in rainfed agriculture. The objective of this study was to calibrate and test AquaCrop for simulating yield of 3 sorghum genotypes (PAN8816, a hybrid; Macia, an open-pollinated variety; and Ujiba, a landrace) grown during the 2013/14 and 2014/15 planting seasons (early, optimal and late planting dates). Variables considered during model evaluation included canopy cover (CC), biomass (B) and yield (Y). The model was able to simulate CC (R² ≥ 0.710; root mean square error (RMSE) ≤ 22.73%; Willmott's d-index (d) ≥ 0.998), biomass accumulation (R² ≥ 0.900; RMSE ≤ 10.45%; d ≥ 0.850), harvest index (R² ≥ 0.902; RMSE ≤ 7.17%; d ≥ 0.987) and yield (R² ≥ 0.945; RMSE ≤ 3.53%; d ≥ 0.783) well for all genotypes and planting dates after calibration. AquaCrop over-estimated biomass and crop yield. The relatively good simulations produced by the minimum data input calibration confirm AquaCrop's simplicity and suitability for use in places where extensive datasets may be unavailable. Biomass and yield overestimation resulting from the use of the minimum data input calibration suggests that other parameters (water productivity, canopy sensitivity to water stress and water stress coefficient) are required to improve canopy and yield predictions for sorghum genotypes. <![CDATA[<b>Impacts of supplemental irrigation as a climate change adaptation strategy for maize production: a case of the Eastern Cape Province of South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200006&lng=pt&nrm=iso&tlng=pt Dry spells and climatic hazards are responsible for maize output decline, sometimes to levels below potential yield levels. There is a pressing need to reduce the gap between actual and potential maize yield/ha, especially among farmers in semi-arid regions. This present study examines the potential role of supplemental irrigation and its differential impact on maize yield in the Eastern Cape Province of South Africa. In this study, maize yield data were generated from information recorded over a period of 20 years by farmers in Ntabankulu through cross-sectional interviews with 124 randomly-selected farming households. Maize yields for interviewed farmers were analysed for each of the experienced climatic hazards, for yield decline per ha and preferable adaptation strategies. Maize yield analyses show a maximum ceiling/attainable yield of 0.234 t/ha and average farm yield of 0.146 t/ha. Floods or hailstorms cause 75% decline in maize yield/ha and there was no significant difference between farmers practising irrigation and those practising dryland farming (P > 0.05). Low/no rains throughout the season; delay or low onset of rainfall and a rain-break for a week or more in a season results in 75%; 54% and 50.5% decline in maize yield/ha, respectively. On a scale of 1 to 10, farmers highly rank practicing supplementary irrigation (8.4) and change of planting date (7.8) as important adaptation strategies. Rescheduling planting date from the traditional planting times to earlier or later planting dates, assisted by use of weather reports and forecasting, to some extent curbs the impact of delays or slow onset of rainfall on yield. Supplemental irrigation is instrumental in reducing the impact of mid-season drought (rains break for a week) and light rainfall throughout the season. Analyses of actual yields and yield decline against each of the experienced climatic hazards provided insight into management possibilities to stabilize maize output. <![CDATA[<b>Determinant of farmers' ability to pay for improved irrigation water supply in rural KwaZulu-Natal, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200007&lng=pt&nrm=iso&tlng=pt The aim of this study was to determine smallholder farmers' ability to pay (ATP) for improved irrigation water supply, using their gross margins, in rural KwaZulu-Natal, South Africa. The analysis was conducted on a sample of 161 irrigators. Production data were collected from the irrigators and the residual imputation method (RIM) was used to calculate the gross margins that the farmers realised. An ordinary least squares regression was used to investigate factors affecting ATP. Results indicate that factors such as labour, training, household assets and road conditions positively influence ATP. The study highlights the importance of support to farmers and their institutions. The study also concludes that farmers are making profits from their irrigated crops, especially tomatoes, and therefore recommends that farmers start paying for the water used for their crops. <![CDATA[<b>Application of the activated sludge model to aerated lagoons</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200008&lng=pt&nrm=iso&tlng=pt The different kinds of aerated lagoons, which exclude anaerobic pre-treatment ponds, are described and the design approach for aerated lagoons is explained. This hinges around ensuring that the 1st lagoon is suspension mixed and the second and any additional are facultative. Selection of the retention time for the 1st lagoon is important to ensure complete utilization of the influent biodegradable organics. Minimum retention times to achieve this at 14°C and 22°C were determined with the general activated sludge kinetic simulation model for (i) readily biodegradable soluble organics (BSO) only, (ii) slowly biodegradable particulate organics (BPO) only, (iii) real municipal wastewater (20% BSO and 80% BPO) and (iv) real municipal wastewater with 5% OHO active VSS mass seed. The minimum hydraulic retention times for these four cases are: at 14°C 1.3, 3.0, 2.0 and 1.5 d, respectively, and at 22°C 0.3, 2.0, 1.2 and 1.0 d, respectively. From a comparison of the simulation results with the steady-state model calculations, washout of OHOs takes place at about 75% of these retention times. Approximate equations to estimate the power requirements for aeration by mechanical surface aerators and mixing are given. These equations are combined with those of the steady-state activated sludge lagoon model for calculating the oxygen requirements and the aeration power density (W/m³) in each lagoon. With these equations, it is shown that influent COD concentration needs to be between an upper and lower limit band to ensure that the 1st lagoon is suspension mixed and the second lagoon is facultative. This COD concentration band decreases as the influent flow increases. The important conclusion arising from this is that if the aerated lagoon system is applied for small rural communities, where land for these large systems is likely to be available, then additional mixing energy above that for aeration will need to be provided to ensure that the 1st lagoon is suspension mixed - this additional aeration cost makes it unlikely that aerated lagoons will be applied for municipal wastewater treatment. Matching mixing and aeration power requirements for industrial organic wastewaters is easier because these usually are significantly stronger than municipal wastewaters. <![CDATA[<b>Distribution and habitats of <i>Burnupia trapezoidea </i>(Boettger, 1910) (Gastropoda: Ancylidae) in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200009&lng=pt&nrm=iso&tlng=pt This paper deals with the geographical distribution and habitat preferences of B. trapezoidea, the third most widespread species of the 14 species of Burnupia currently on record in the database of the National Freshwater Snail Collection (NFSC) of South Africa. Although the 121 loci (¹/16 square degrees) from which the 445 samples of B. trapezoidea were collected are much fewer than the number reported for B. capensis, the range of its geographical distribution is almost as widespread as that of B. capensis. The limited distribution of B. trapezoidea in the Limpopo, Northern Cape and Western Cape Provinces can most probably be attributed to the paucity of perennial water bodies in these areas and the fact that Burnupia spp. in general have poor abilities to overcome conditions of desiccation prevalent in these areas. It is therefore not surprising that the majority of samples were collected in perennial rivers and streams. A Random Forest statistical analysis selected water bodies, the presence or absence of marginal and aquatic vegetation, and type of substratum as the most important variables that played a significant role in determining the presence and numbers of specimens of B. trapezoidea in a specific area. In this respect, temperature and turbidity, respectively, played a moderate and minor role. Little is known regarding the conservation status of Burnupia spp, in general, but habitat degradation and climatic warming could be reasons for concern. However, in extensive on-going biodiversity surveys in two rivers and selected tributaries in the North-West Province, many new distribution records of B. trapezoidea are still being created and therefore this species could probably be considered for listing as not endangered. In view of its wide distribution, largely sessile, benthic lifestyle, and ability to bioaccumulate various substances, the feasibility to utilise it as indicator of river ecosystem health in South Africa should be explored. <![CDATA[<b>Simultaneous determination of naproxen, ibuprofen and diclofenac in wastewater using solid-phase extraction with high performance liquid chromatography</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200010&lng=pt&nrm=iso&tlng=pt The occurrence and removal efficiency for naproxen, ibuprofen and diclofenac in two of eThekwini Municipality's wastewater treatment plants (WWTPs), Kingsburgh and Umbilo, were investigated. This paper describes a simple method that can be used routinely for the simultaneous determination of such compounds in the influent and effluent of the WWTPs. Target compounds were extracted from wastewater and pre-concentrated using the optimized Oasis MAX solid-phase extraction (SPE) method. During SPE, the pH of wastewater samples was adjusted to 2.5; then 100 mL of each sample was loaded onto a pre-conditioned cartridge. The SPE cartridge was rinsed with methanol:water (10:90%, v:v) prior to sequential elution of retained analytes with 2 mL methanol, followed by 2 mL methanol and acetic acid (90:10, v:v) and 2 mL of 2% (v:v) formic acid diluted using a mixture of methanol and acetic acid (40:60, v:v). The eluted analytes from the SPE cartridge were quantified using high performance liquid chromatography (HPLC) equipped with photo diode array detection. The analytical method was validated by spiking deionized water with 5 and 50 µg·L-1 of target compounds, for which the recovery range of 76 to 98% was achieved with good precision. The instrument quantification limits obtained were 0.1 µg·L-1, for naproxen and 0.4 µg·L-1 for both ibuprofen and diclofenac. The detected concentrations for naproxen, ibuprofen and diclofenac in the influent of both WWTPs were in the ranges of 15-20 µg·L-1, 55-69 µg·L-1 and 6.4-16 µg·L-1, respectively. In effluent, the detected concentrations for naproxen, ibuprofen and diclofenac were in the ranges of 0.6-1.1, 2.1-4.2 and 1.4-2.0 µg·L-1, respectively. Overall, the employed SPE-HPLC method led to rapid pre-concentration of target compounds prior to their trace quantification in wastewater samples. <![CDATA[<b>Modelling the effect of land use change on hydrological model parameters via linearized calibration method in the upstream of Huaihe River Basin, China</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200011&lng=pt&nrm=iso&tlng=pt Conceptual rainfall-runoff models have become a basic tool for evaluating effects of land use/cover changes on the hydrologic processes in small-scale as well as large watersheds. The runoff-producing mechanism is influenced by land use/cover changes. In this study, we analysed the effect of land use change on hydrological model parameters by calibrating the model parameters of different time periods with different land use via a linearized calibration method. The parameter calibration of a conceptual model usually involves the construction of objective function and optimization methods for good performance of observed data. However, the objective function of the minimum-sum-squared error will introduce an unrelated optimum solution for the parameter calibration problem of a conceptual model, which belongs to a highly complex nonlinear system. Thus, a linearized parameter calibration method, which searches for the optimal value on a parameter surface, is presented, based on the analysis of the problems of the objective function of the minimum-sum-squared error. Firstly, an ideal model is shown that illustrates the efficiency and applicability of this method. Secondly, the novel method is demonstrated for solving the Xinanjiang daily model parameter calibration. Finally, 50 years of data are divided into 4 different periods for parameter comparison, through which the effects of land use/cover changes on runoff in Dapoling watershed are evaluated. The results show that the linearized parameter calibration method is convergent, reasonable and effective. For example, the model parameter of evapotranspiration coefficient KC varied considerably, from 0.658 to 0.922, in response to land use/cover change within the watershed. <![CDATA[<b>Historical rainfall trends in South Africa: 1921-2015</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200012&lng=pt&nrm=iso&tlng=pt The aim of this study is to update the analysis of historical rainfall trends with reference to the work from previous studies, through optimizing the highest spatial resolution with the longest possible period of analysis, i.e., 1921-2015. Two interlinked datasets, namely the district rainfall and individual rainfall stations datasets were used for the trend analyses, namely, daily time series of 60 individual rainfall stations and the daily district rainfall of 88 of 94 rainfall districts in South Africa. The extreme precipitation indices defined by the World Meteorological Organization Expert Team on Climate Change Detection and Indices were applied. In general, the results show an increase in rainfall for most rainfall stations in the southern interior of South Africa, and indications of decreases in rainfall in the far northern and north-eastern parts. The increase in the annual rainfall in the south is reflected in the seasonal trends, where summer rainfall shows a similar increase, but also extends into the central interior. For other seasons, most of the country shows no significant historical trends in annual total rainfall. From the extreme rainfall analyses, an increase in daily rainfall extremes in the southern to western interior is apparent. Also, most of the country experienced increases in the intensity of daily rainfall, which confirms global results in general. Decreases in rainfall from wet spells were noted in most places over the east and north-east, while the southern and eastern parts along the escarpment experienced shorter annual dry spells. This study improves on previous studies in the region by more than doubling the analysis period, largely eliminating the influence that decadal-scale cycles might have on analyses over shorter periods. However, some differences in the trend results compared to previous studies are apparent, e.g., less pronounced drying in the east and the previously observed increase in rainfall in the western and southern interior not extending as far as the south-western Cape. The observed trends broadly confirm those of projected changes in summer rainfall, i.e., an increase in the west and decrease in the east. <![CDATA[<b>Aqueous solubility of Cr(VI) compounds in ferrochrome bag filter dust and the implications thereof</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200013&lng=pt&nrm=iso&tlng=pt The production of ferrochrome (FeCr) is a reducing process. However, it is impossible to completely exclude oxygen from all of the high-temperature production process steps, which may lead to unintentional formation of small amounts of Cr(VI). The majority of Cr(VI) is associated with particles found in the off-gas of the high-temperature processes, which are cleaned by means of venturi scrubbers or bag filter dust (BFD) systems. BFD contains the highest concentration of Cr(VI) of all FeCr wastes. In this study, the solubility of Cr(VI) present in BFD was determined by evaluating four different BFD samples. The results indicate that the currently applied Cr(VI) treatment strategies of the FeCr producer (with process water pH ≤ 9) only effectively extract and treat the water-soluble Cr(VI) compounds, which merely represented approximately 31% of the total Cr(VI) present in the BFD samples evaluated. Extended extraction time, within the afore-mentioned pH range, proved futile in extracting sparingly-soluble and water-insoluble Cr(VI) species, which represented approximately 34% and 35% of the total Cr(VI), respectively. Due to the deficiencies of the current treatment strategies, it is highly likely that sparingly water-soluble Cr(VI) compounds will leach from waste storage facilities (e.g. slimes dams) over time. Therefore, it is critical that improved Cr(VI) treatment strategies be formulated, which should be an important future perspective for FeCr producers and researchers alike. <![CDATA[<b>SuDS for managing surface water in Diepsloot informal settlement, Johannesburg, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200014&lng=pt&nrm=iso&tlng=pt Sustainable drainage systems (SuDS) imitate natural water management processes in catchments that have been degraded due to urbanisation. The aim is to reduce the quantity of stormwater runoff and improve water quality. Management of rainwater in the informal settlement of Diepsloot in Johannesburg is compounded by domestic wastewater discharged into the informal lanes. These lanes fall outside the mandate of the City of Johannesburg's stormwater management system; hence residents need to rely on their own initiatives to address surface-water problems. This preliminary study investigated the introduction of SuDS to enhance existing surface-water interventions, as a low-cost flexible approach. Using action research methods, small-scale interventions were designed, constructed and refined by residents and researchers at two sites close to the Jukskei River. While the primary intention of the research was to reduce standing water in the public areas, water quality testing indicates that the SuDS reduced some pollutants. Nitrate and phosphate concentrations were slightly lowered through the introduction of permeable channels and soakaways, while these interventions had a moderate effect on chemical oxygen demand. The involvement of residents at the two sites was markedly different, reflecting divergent priorities and social dynamics. Spontaneous continuation of the SuDS system at one of the sites indicates successful knowledge and skills exchange. This study was of limited duration with only two sets of water quality tests; therefore, longer term monitoring is strongly advised to be able to give more robust assessment of this type of intervention. <![CDATA[<b>A comparison between <i>Daphnia pulex</i> and <i>Hydra vulgaris</i> as possible test organisms for agricultural run-off and acid mine drainage toxicity assessments</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200015&lng=pt&nrm=iso&tlng=pt Bioassays, consisting of a diverse selection of organisms, aid in assessing the ecotoxicological status of aquatic ecosystems. Daphnia pulex and Hydra vulgaris are commonly used test organisms belonging to different trophic levels. The current study focused on comparing the sensitivity of H. vulgaris to D. pulex when exposed to geometric dilutions of two different water sources, the first (Site 1) from a source containing agricultural run-off and the second (Site 2), acid mine drainage. These sources were selected based on the contribution that the agricultural and mining sectors make to water pollution in South Africa. The bioassay method followed in this study was a modified version of the method described by the USEPA and additional peer-reviewed methods. The mortalities as well as morphological changes (H. vulgaris) were analysed using Microsoft Excel. The LC50-values were statistically determined using the EPA Probit Analysis Model and the Spearman-Karber analysis methods. Prior to being used, analysis of the physico-chemical properties, nutrients and metals of both water samples was performed. These results showed a relationship to the results obtained from the D. pulex and H. vulgaris bioassays, as Site 1 (lower concentration of contaminants) was less hazardous to both test organisms than Site 2 (higher concentration of contaminants). Both organisms can be used for ecotoxicity testing, with D. pulex being a more sensitive indicator of toxicity with regards to water sampled from the acid mine drainage site. Due to the sensitivities of sub-lethal endpoints observed over time, H. vulgaris may be used for chronic toxicity testing and D. pulex for acute toxicity testing. <![CDATA[<b>Some attributes of snow occurrence and snowmelt/sublimation rates in the Lesotho Highlands: environmental implications</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200016&lng=pt&nrm=iso&tlng=pt We present attributes of snow occurrence and dissipation rates (melt and sublimation) for the Lesotho Highlands, based on remotely-sensed MODIS images from 2003-2016. Multi-temporal imagery is used, with SNOMAP and NDSI algorithms applied to MODIS Rapid Response images. The spatial extent of snow loss was determined by daily repeat measurements of snow coverage, which was calculated from each filtered and trimmed MODIS SNOMAP image using the ArcGIS Spatial Analyst tool. Results indicate an average of 11.5 snowfalls per annum for the years 2003-2016; with snow longevity averaging ca. 10 days following individual snowfalls in mid-winter. Snow cover on the highest south-facing slopes persists longest during the months of June to August, in particular along the southern Drakensberg where it averages ca. 58 days during these 3 months. Mean daily melt increases by 1.6% per 1°C rise during the first 5 days post-snowfall, and by 3.3% per 1°C rise for 6 to 10 days post-snowfall. However, snowmelt rates are spatially highly variable given other factors such as wind deflation and wind-induced sublimation. The observed snow trends have important implications for biosystem functioning, regional climate and hydrology, earth surface processes, and rural livelihoods in the Lesotho Highlands. <![CDATA[<b>A technological and economic exploration of phosphate recovery from centralised sewage treatment in a transitioning economy context</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200017&lng=pt&nrm=iso&tlng=pt Phosphate is one of the substances which wastewater treatment works (WWTW) have to lower in order to meet the South African regulatory discharge standard of 1 mg/L. Wastewater is increasingly viewed as a 'water-carried waste', presenting opportunities for resource recovery. South Africa has commenced its transition to a low-carbon and resource-efficient economy, all whilst it struggles to provide universal access to basic needs and is faced with massive infrastructure maintenance as well as upgrading backlogs in the sanitation sector in particular. Although phosphate recovery methods exist, there is little evidence to indicate that these techniques would be economically viable or socially accepted in South Africa. This paper explores the potential for centralized recovery of nutrients, through the conceptual design and techno-economic pre-feasibility assessment of two phosphate recovery options, at the largest WWTW in the Western Cape, South Africa. This assessment revealed that the digestate stream at the 200 ML/d Cape Flats WWTW (CFWWTW) has the potential to produce ~470 kg/d of struvite fertilizer, whilst recovering 4-8% of the plant's costs in 20 years. When contrasted with the more familiar, yet less sustainable, chemical precipitation process, low-grade and high-grade struvite production establishment costs are 10 and 25 times higher, respectively. Still, to reduce effluent phosphate loading to within regulated standards, the low-grade struvite production option at an estimated net present cost of R25.4 million over a 20-year lifetime is more affordable than chemical precipitation at a net present cost of R51.2 million. Low-grade struvite production is thus concluded to be technically feasible and the economically most affordable option from a lifecycle-costs perspective. Although it is a simple process, it is not cheap. Municipalities will need to consider the lower operating costs, as well as the environmental benefit of producing a useful phosphate fertilizer, over the immediate capital investment, if they decide to install such an operation. <![CDATA[<b>Automated irrigation systems for wheat and tomato crops in arid regions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502017000200018&lng=pt&nrm=iso&tlng=pt Automated irrigation systems (AISs) are critical for the sustainability of irrigated farming systems, considering the present water crisis in Saudi Arabia. This study investigated whether electronic controllers in irrigation systems effectively save water. The study also assessed the effect of these controllers on crop yield using drip and sprinkler irrigation systems in severely arid climate conditions. Evapotranspiration (ET) controllers were installed in experimental fields of wheat (Triticum aestivum) and tomato (Solanum lycopersicum Mill.) crops for 2 successive seasons. The results revealed that the water use efficiency (WUE) and irrigation water use efficiency (IWUE) were typically higher in the AIS than in the conventional irrigation control system (CIS). Under the AIS treatment, the WUE and IWUE values were 1.64 and 1.37 k·gm-3 for wheat, and 7.50 and 6.50 kg·m-3 for tomato crops; under the CIS treatment the values were 1.47 and 1.21 kg·m-3 for wheat and 5.72 and 4.70 kg·m-3 for tomatoes, respectively. Therefore, the AIS provided significant advantages in both water savings and crop yields by utilising up to 26% less water than the CIS, and simultaneously generating higher total yields. The automated irrigation system technique may be a valuable tool for conserving water and scheduling irrigation for wheat and tomato crops, and may be extendable to other similar agricultural crops.