Water SA

Aquatic macroinvertebrate community colonisation and succession in macadamia orchard and communal area reservoirs: a case study of Luvuvhu River valley, South Africa

Tue, 07 May 2024 00:00:00 +0000

The demand for macadamia nut production worldwide has led to increased use of pesticides and chemicals for pest and disease control. Reservoirs in these macadamia farming sectors are at risk, since these chemicals can enter and contaminate the water through direct application, runoff, and atmospheric deposition, subsequently negatively affecting aquatic organisms. The current study investigated macroinvertebrate colonisation and succession associated with two macadamia orchards and two communal area reservoirs. The potential effects of stressors from these land uses was tested for and compared using stone substrates over a 6-week period. Stone substrates from both reservoir types were abundantly colonised over time and the total macroinvertebrate taxa and abundance showed an increasing trend across the sampled weeks, with macadamia orchards having the highest number of macroinvertebrate taxa. Strong ecological succession was observed across reservoirs, with the initial succession of early colonisers – i.e., Chironominae (collectorgatherers), Ostracoda (collector-filterers) and Anax sp. (predator) within communal area reservoirs, and Chironominae, Ostracoda and Radix natalensis (scrapers) in macadamia orchard reservoirs – followed by predatory colonisers such as Gyrinidae larvae, Trithemis sp. (macadamia orchard reservoirs), and Ranatra sp. (communal area reservoirs). Macroinvertebrate community structure differed significantly across sites and weeks, with no similarity being observed for communities across the different reservoirs. Redundancy analyses further highlighted 11 sediment chemistry variables (i.e., pH, resistivity, P, K, Na, Ca, Mg, Cu, B, Fe and S) which were significantly related to macroinvertebrate community structure. Thus, sediment variables were found to be better predictors of macroinvertebrate community structure in macadamia orchard reservoirs than communal area reservoirs. Consequently, we concluded that differences in colonisation ability among taxa and environmental stressors were important factors driving succession. These results add to the understanding of the macroinvertebrate colonisation processes and environmental stressors within agricultural landscapes, which can aid in the development of conservation management of freshwater ecosystems.

Antimicrobial susceptibility patterns of Listeria monocytogenes isolated from fresh produce in KwaZulu-Natal Province, South Africa

F Tshabuse, NK Cele, AR Opoku, A Basson, MS Mthembu, MF Swalaha — Tue, 07 May 2024 00:00:00 +0000

Fresh, ready-to-eat produce is frequently irrigated with untreated water, making it a leading cause of foodborne illness outbreaks worldwide. This study investigated the presence of Listeria monocytogenes in fresh produce that was grown using river water. Standard biochemical tests were used for the identification of L. monocytogenes isolated from river water used for irrigation, and from fresh produce including lettuce, spinach, and pumpkin. The inlA gene of L. monocytogenes was molecularly identified using PCR amplification. The susceptibility of L. monocytogenes isolates to antimicrobial agents was assessed using the Kirby-Bauer disc diffusion method. The presence of the amplified inlA gene (800 bp) indicated that all of the fresh produce and river water samples were contaminated with virulent L. monocytogenes. Lettuce and spinach exhibited higher quantities of L. monocytogenes, with lettuce ecording 87 CFU/g and spinach recording 71 CFU/g. The L. monocytogenes isolates from spinach and lettuce sources showed significant resistance to colistin (56.2% and 53.3%, respectively) as well as ampicillin (68.8% and 53.3%, respectively). Moreover, lettuce (40%) and spinach (31%) exhibited a common resistance pattern of AMP-CHL-CT-KAN-PIP-ERY-TET, with a maximum MAR index value of 0.54. Our research demonstrates the transmission of multidrug-resistant L. monocytogenes from irrigation river water to fresh produce. Hence, the ingestion of ready-to-eat fresh produce carries the potential for human listeriosis, particularly among individuals with compromised immune systems.

Integrated treatment of stormwater using multistage filtration (MSF) for domestic application (reuse)

Chekwubechukwu V Chibueze, Chidozie C Nnaji, Cordelia N Mama, Ekene J Nwankwo — Tue, 07 May 2024 00:00:00 +0000

Stormwater harvesting is a promising solution for global freshwater depletion, particularly in tropical regions with abundant rainfall. However, it is not widely used due to the lack of suitable treatment technologies for domestic applications. Multi-stage filtration (MSF) is an effective integrated treatment technology that provides a cost-effective alternative for stormwater treatment. This study investigated MSF’s capacity for treating stormwater at different stages. The MSF designed and built comprised the down-flow roughing filter (DRF) and slow sand filter (SSF). The results achieved by the MSF for the treated effluents were: pH (7.1–8.1), temperature (27.6–29.4°C), electrical conductivity (EC) (100–190 μS/cm) and total dissolved solids (TDS) (70–130 mg/L). Turbidity removal efficiency of the MSF was in the range of 36–99% (5.825–164.05 NTU) and the overall average removal efficiency of the MSF was 74%, 90% and 86% for total coliforms (TC) (360–11 800 CFU/ 100 mL), faecal coliforms (FC) (0–1 300 CFU/100 mL) and Enterococcus spp. (120– 1 400 CFU/100 mL), respectively. The study identified stormwater reuse potentials based on international guidelines and benchmarks. For the treated effluent, pH, temperature, EC and TDS were all within the permissible limits for toilet, laundry, bathing, recreational and agricultural water reuse, while turbidity suited agricultural (non-food crop) and restricted urban reuse. 46% of the effluent was suitable for recreational purposes as this satisfied the 50 NTU standard. 62.5% of the effluent satisfied the FC standard for toilets and urinals and agricultural reuse (non-food crop) purposes, while 87.5 % of the effluent satisfied urban reuse purposes (restricted access). 66.67% of the effluent satisfied the Enterococcus spp. standard for agricultural reuse (non-food crop). All treated effluents satisfied the TC bathing standard. This study shows that after minimal disinfection, stormwater effluents offer potential reuse in household applications, thereby reducing potable water demand.

Degradation of methyl orange by the Fenton-like reaction of pyrite-activated hydrogen peroxide forming the Fe(III)/Fe(II) cycle

Wenlong Bi, Ruojin Du, Hui Liu, Peng Fu, Zhenguo Li — Tue, 07 May 2024 00:00:00 +0000

In this study, the typical azo dye methyl orange (MO) was degraded by pyrite (FeS₂) activated by hydrogen peroxide (H₂O₂). When [MO] = 0.1 mM, [FeS₂] = 2.0 g/L and [H₂O₂] = 22 mM, 96.4% MO was removed in 120 min and the TOC removal rate was higher than 50%. HO• was the primary radical responsible for MO degradation. In addition, the acid condition promoted the degradation of MO in the FeS₂/H₂O₂ system. MO in tap water and river water was not effectively degraded, whereas acidification could weaken the inhibitory effect on the FeS₂/H₂O₂ system to enable the degradation of MO in tap and river water. The OD₆₀₀ indicated that the solution was environmentally friendly after the reaction, and three degradation pathways of MO were discussed. In summary, Fe(II) could be dissolved from FeS₂, which activated H₂O₂ to generate Fe(III) and HO•. FeS₂ could reduce Fe(III) into Fe(II), thus realizing the Fe(III)/(II) cycle and efficiently activating H₂O2 to degrade MO.

Optimization of irrigation (ETc) and nitrogen levels under drip fertigation in okra (Abelmoschus esculentus L.) using response surface methodology (RSM)

C Lokesh, B Balaji Naik, M Uma Devi, M Venkateswara Reddy — Tue, 07 May 2024 00:00:00 +0000

A comprehensive field investigation was conducted to enhance the productivity, profitability, and water use efficiency (WUE) of summer okra through the optimization of irrigation and nitrogen fertilizer application. The study involved 3 irrigation levels – 0.75 E_pan (pan evaporation) as I₁, 1.00 E_pan as I₂, and 1.25 E_pan as I₃ – as the main plot factors, and 4 nitrogen concentrations – 75% recommended nitrogen dose (RDN) as N1, 100% RDN as N2, 125% RDN as N3, and 150% RDN as N4 – as the subplot variables. The results of the study revealed a significant influence of irrigation and nitrogen levels on various key parameters. Above- round dry matter, yield, plant height, WUE, net returns, and benefit-to-cost ratio (B:C) exhibited an incremental trend with increasing irrigation and nitrogen levels, up to a certain threshold. Beyond this threshold, further increments in irrigation and nitrogen led to diminishing returns. The models developed for estimating crop yield, above-ground dry matter, plant height, WUE, net returns, and B:C demonstrated impressive accuracy, with high coefficients of determination (R²) and satisfactory precision. The optimized irrigation level (crop evapotranspiration, ET_c) ranged from 418.39– 441.23 mm. At the same time, the ideal nitrogen application rate was found to be in the range of 167.04–176.13 kg N/ha. These optimal conditions resulted in peak crop yield of 28 295 kg/ha, aboveground dry matter of 6 709.1 kg/ha, plant height of 66.3 cm, WUE of 5.26 kg/m³, B:C of 4.54, and net returns amounting to 441 133 INR/ha. In conclusion, the application of response surface methodology facilitated the identification of the impact of each factor on individual responses, as well as the determination of optimal conditions that simultaneously maximize multiple desirable outcomes. These findings hold significant promise for improving the cultivation of summer okra while optimizing resource use and economic returns.

Comprehensive performance analysis of training functions in flow prediction model using artificial neural network

Tue, 07 May 2024 00:00:00 +0000

Higher Himalayan catchments are often poorly monitored for hydrological activities involving flood flow
prediction for the safety of riverside communities and the successful operation of hydropower projects. This study aimed to estimate the comparative performance of artificial neural network (ANN) based flow prediction models using 10 years of daily river flow data of Kaligandaki catchment at Kotagaun, Nepal, which is a snow-fed catchment in the Himalayan region. The flow prediction models were trained and tested at a hydrological station using the previous 3 days’ river flow data to predict the 1-day ahead flow data. Eight different training functions were employed in an ANN model for comprehensive statistical assessment of accuracy and precision of each training function. The most significant and validated result obtained in this study is the comprehensive comparison of various training functions’ performance, and identification of the most efficient training function for the study case. Among the training functions investigated, the Levenberg- Marquardt backpropagation function exhibits the best performance for the model having Nash-Sutcliffe efficiency, root mean square error and mean absolute error values of 0.866, 209.578 and 75.422, respectively. This study provides a fundamental basis for accurate flow prediction of topographically challenged catchments where hydrological monitoring and data collection may be limited. In particular, this model will help to improve early warning system, hydrological planning, and the safety of riverside communities in the Himalayan region.

Stability of boulders on cobble streambeds

K Stols, CS James — Tue, 07 May 2024 00:00:00 +0000

The placement of boulders in streams enhances aquatic habitat by increasing the heterogeneity of flow conditions. Practical design must ensure the stability of individual boulders, requiring calculation of their incipient movement conditions. The stability of a boulder on a cobble bed is shown experimentally to depend on its size, the bed material size, the degree of embedment of the boulder, the slope of the bed and the flow velocity and depth. An equation is derived through a pivoting analysis for predicting the relationship between the critical ambient depth-averaged velocity and the critical flow depth; this, together with a resistance equation, can be used to predict the flow conditions for boulder stability. The equation is used to develop a simpler form for unsubmerged spherical boulders and cobbles. The stability equation is tested against the experimental data, using an experimentally determined drag coefficient relationship.

Review of soil form and wetness indicators for wetland delineation in South Africa

Tue, 07 May 2024 00:00:00 +0000

Wetland delineation in South Africa incorporates soil form and soil wetness indicators, requiring formal soil classification and description of soil redox morphology. The current wetland definition used administratively in South Africa focuses on saturated (hydric) soil signatures within plant root zones. Saturated soil horizons deeper than plant root zones fall outside the 50 cm criterion in the local approach as well as the accepted zone in USA literature. The field of hydropedology accommodates the classification of the various hydrologically active horizons and provides a tool for the handling of horizons with ephemeral wetness. This approach has been variably accepted by mandated authorities in South Africa. The South African soil classification system has evolved through three editions over the past 50 years while retaining the same redox morphology understanding. However, despite the concepts and context of redox morphology having been thoroughly technically adopted by soil scientists, this is not the case within the wetland research and management environment. This especially because the classification system is structured differently from other international systems, and the South African landscape is geologically ancient with mature soils, introducing challenges to resource assessment specialists who rely on international norms and approaches for wetland assessment. This paper reviews the various components of soil classification and redox morphology based on Fe and Mn minerals within the context of the South African soil classification system, the field of hydropedology and wetland delineation indicators. We provide a qualitative correlation between the various diagnostic horizons and materials in the system and their related redox morphology contexts that are relevant to wetland assessment, delineation, and protection in South Africa. This paper therefore aims to serve as a reference point for the description and correlation of various soil hydrological parameters used in formal assessments.

Impacts of the Covid-19 pandemic on the South African water sector

Nikki Funke, Audrey de Wet, Ayanda Mafunda, Lisa Schaefer, Wouter le Roux — Tue, 07 May 2024 00:00:00 +0000

An analysis of the impacts of the Covid-19 pandemic on the South African water sector is presented. The study identified and focused on three main themes: water revenue collection, water service delivery, and water sector operations. The Covid-19 pandemic negatively impacted these aspects and exacerbated pre-existing problems in the water provision landscape of South Africa. Business continuity management was identified as a top priority for water sector institutions in South Africa to ensure the continued provision of critical water services. In-depth case study research is recommended to establish how water sector institutions in South Africa dealt with the Covid-19 pandemic and how this can inform their disaster preparedness and management going forward.

Hydropedology of South African soil forms and families

JJ van Tol, D Bouwer — Tue, 07 May 2024 00:00:00 +0000

Hydropedology is an interdisciplinary field that studies the interactions between soil and water, recognizing that soils influence hydrological processes through their hydraulic properties, and serve as indicators of hydrological behaviour through their morphological properties that are shaped by water regimes. Given the practical implications of hydropedology and its integration into South Africa’s latest soil classification system, an updated categorization of soil forms and 1 657 (1 629 + 28) families was necessary, organizing them into three overarching response groups based on their predominant hydrological responses: recharge, interflow, and responsive. Within these groups, recharge soils are further classified into deep, shallow, and slow subgroups, interflow soils encompass soil/bedrock, shallow, and slow categories, while responsive soils are subdivided into responsive shallow and responsive wet. This paper aims to enhance the reader’s comprehension of hydrological responses and simplify the intricacies integrated into South Africa’s official soil classification system.