Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The consumption of fresh produce has increased over the past few decades, but it has also resulted in an increase in foodborne outbreaks. Once fresh produce gets contaminated, microbes can survive or even multiply on the produce. There is, however, very little information available on what impact environmental conditions will have on the survival and growth of potential pathogens. Thus the purpose of the first phase of the study was to determine the impact of different environmental factors: carbon levels; temperature; incubation time; and initial microbial load on the growth of E.coli and other "indigenous" microbes present in the Plankenburg river water. Water from the Plankenburg River was incubated at 10° to 35°C and the E.coli and aerobic (ACC) loads determined at 0, 6, 12 and 24 h. The impact of different COD:N:P ratios on growth were also evaluated by altering the water values. It was found that in non-sterile river water the E.coli levels increased with increase in incubation temperature. Minimal growth took place between 10° and 20°C and the largest growth increases at 35°C. The data showed that E.coli dieoff was rapid when the nutrient levels were low. It was concluded that the carbon (COD) level is a major growth limiting factor in river water. The impact of adjusted carbon levels on the growth of E.coli present was then evaluated. The E.coli was found to die-off faster at the higher temperatures when the carbon levels were low (COD = <10 mg.L-1), possibly due to nutrient limitations. At higher carbon levels (COD = >100 mg.L-1), the growth profiles of E.coli showed major growth increases with no die-off during the 24 h period, probably because of the availability of sufficient nutrient levels. Even though standard methods can be used to identify if irrigation water is faecally contaminated it is important to confirm that organisms on fresh produce are from the faecally polluted irrigation water. The purpose of the second study was to determine the effect of daily irrigation on carry-over, the effect of “once-off” irrigation on the survival of E.coli on the produce, identifying types of E.coli in the irrigation water and those on irrigated fresh produce, and then linking the E.coli types. In the first trial, green beans planted in a tunnel and irrigated on a daily basis (14 days) with Plankenburg water and a “pure wild-type” E.coli at a concentration of 106 cfu.mL-1 were evaluated. The results showed that E.coli is carried over from irrigation water to the irrigated green beans, especially when the E.coli levels in the river water were high. After the enumeration steps, colonies from both the irrigation water and from the irrigated beans were selected (67 isolates from the green beans and 72 from the irrigation water). Unique phenotypic (API) profiles were generated for each isolate. The first indication of linking was confirmed based on the degree of phenotypic similarity using numerical clustering systems. The results showed that these isolates were related and originated from the same pollution source. The use of PCR further confirmed (uidA positive) that all the phenotypically identified strains were E.coli. With multiplex PCR, further linking confirmation was shown when strains tested positive for the mdh gene. The presence of EPEC strains in the irrigation water was also revealed. Thirteen E.coli isolates, which showed positive carry-over links between the irrigation water and the green beans, were further analysed using triplex PCR. However, no direct phylogenetic link to the three main phenotypic E.coli clusters was found. However the triplex PCR could be of value in identifying the source of faecal pollution. For further linking confirmation, DNA sequencing was done on selected phenotypically clustered strains. The oriC-locus sequencing was unsuccessful in distinguishing between the different E.coli strains while the dnaJ sequences showed clear differences and similarities between E.coli strains and some E.cloacae and K.pneumoniae strains respectively from the river water and from the beans. The probability of faecal coliforms being carried-over from irrigation water to fresh produce was shown. This showed the importance of a "multi-method" approach to confirm carryover. / AFRIKAANSE OPSOMMING: Tydens die afgelope paar dekades het die verbruik van vars groente en vrugte vermeerder, maar dit het ook gepaard gegaan met ‘n toename in voedselverwante uitbrekings. Indien vars groente of vrugte gekontamineer word, kan die mikrobes daarop oorleef en ook vermeerder. Daar is min informasie beskikbaar oor die impak van omgewingskondisies op die oorlewing en groei van potensiële patogene. Dus was die doel van die eerste fase van die studie om die impak van verskillende omgewingsfaktore te bepaal: koolstofvlakke; temperatuur; inkubasietyd; en aanvanklike mikrobiese lading op die groei van E.coli en ander “inheemse” mikrobes wat teenwoordig is in die Plankenburg Rivier water. Water van die Plankenburg Rivier was geïnkubeer by 10° tot 35°C en die E.coli en aërobe kolonie tellings (AKT) was bepaal by 0, 6, 12 en 24 h. Die impak van verskeie CSB:S:F verhoudings op groei, was ook geëvalueer deur die waarders van die rivierwater te verander. Dit was gevind dat in die nie-steriele rivierwater, die E.coli vlakke vermeerder het soos die inkubasie temperatuur vermeerder het. Minimale groei het plaasgevind by 10° en 20°C en die meeste groei by 35°C. Die data het gewys dat die E.coli vinnig afgesterwe het as die nutriënt vlakke laag was. Die gevolgtrekking was dat die koolstofvlakke (CSB) die hoof faktor is wat die groei beperk in rivierwater. Die impak van die aangepasde koolstofvlakke op die groei van E.coli teenwoordig was ook geevalueer. Daar was gevind dat die E.coli vinniger afsterf by die hoër temperature as die koolstofvlakke laag is (CSB = <10 mg.L-1), omdat die nutriente moontlik beperk is. Tydens die hoë koolstofvlakke (CSB = >100 mg.L-1), het die E.coli groeiprofiele baie groei getoon met geen afsterwe tydens die 24 h periode nie, omrede dat daar moontlik genoeg nutriente beskikbaar was. Al kan standaard metodes gebruik word om fekale kontaminasie in besproeiingswater te identifiseer, is dit belangrik om te kan bevestig of die organismes op vars groente of vrugte van fekale gekontamineerde besproeiingswater is. Die doel van die tweede fase van die studie was om die effek van daaglikse besproeiing op oordrag te bepaal, effek van eenkeer se besproeiing op die oorleweing van E.coli op groenboontjies, identifisering van E.coli tipes in die besproeiingswater en op die groenboontjies, asook die koppeling van E.coli tipes. In die eerste proef was groenboontjies geplant in ‘n tonnel en daagliks besproei (14 dae) met Plankenburg water en ‘n “suiwer wilde-tipe” E.coli met ‘n konsentrasie van 106 cfu.mL-1. Die resultate het getoon dat E.coli oorgedra was van die besproeiingswater na die besproeide groenboontjies, veral toe die E.coli vlakke in die rivierwater hoog was. Na al die isoleringsstappe, is kolonies van die besproeiingswater en van die besproeide groenboontjies geselekteer (67 isolate van die groenboontjies en 72 van die besproeiingswater). Unieke fenotipiese (API) profiele was gegenereer vir elke isolaat. Die eerste indikasie van koppeling was bewys deur die graad van soortgelyke fenotipiese profiele deur numeriese groepering. Die resultate het gewys die isolate was verwant en oorspronklik van dieselfde bron van kontaminasie. Die gebruik van PKR het verder bewys (uidA positief) dat al die fenotipiese geidentifiseerde isolate E.coli was. Verdere koppeling was geidentifiseer met die multiplex PKR deurdat die isolate positief getoets het vir die mdh geen. Die teenwoordigheid van die EPEC isolate in die besproeiingswater was ook gevind. Dertien E.coli isolate, wat positiewe oordrag verbinding getoon het tussen die besproeiingswater en die groenboontjies, was verder geanaliseer deur triplex PKR. Geen direkte fenotipiese verbinding met die drie hoof fenotipiese E.coli groepe was egter gevind nie. Die triplex PKR kan wel van waarde wees om die bron van die fekale besoedeling te identifiseer. Vir verdere koppeling bevestiging, was DNA volgorde gedoen op isolate van geselekteerde fenotipiese groepe. Die oriC-locus volgorde was onsuksesvol om te onderskei tussen die verskillende E.coli tipes, terwyl die dnaJ volgordes duidelike verskille en ooreenstemmings getoon het tussen die E.coli asook party E.cloacae en K.pneumoniae tipes, onderskeidelik van die rivierwater en boontjies. Die waarskynlikheid van oordrag van fekale kolvorme vanaf besproeiingswater na vars goedere was getoon. Dit wys die belangrikheid van ‘n “multi-metode” benadering om oordrag te bewys.

Made available in DSpace on 2014-06-11T19:23:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-15Bitstream added on 2014-06-13T20:11:00Z : No. of bitstreams: 1 beraldo_rm_me_arafcf.pdf: 282816 bytes, checksum: 5801e8fb514fd0197781c52154b68859 (MD5) / Universidade Estadual Paulista (UNESP) / O consumo de alimentos frescos como frutas e hortaliças representa riscos à saúde humana, uma vez que tais alimentos podem estar contaminados, constituindo veículos de transmissão de várias doenças. A água utilizada na irrigação de hortas representa umas das possíveis fontes desse tipo de contaminação, comprometendo a qualidade do produto e, principalmente, a saúde humana. Assim, o controle da qualidade bacteriológica de águas utilizadas para tal finalidade torna-se de vital importância para a saúde pública. O objetivo deste trabalho foi avaliar a qualidade bacteriológica de amostras de águas utilizadas na irrigação de 40 hortas dos municípios de Araraquara, Boa Esperança do Sul e Ibitinga, SP. Foram colhidas em cada horta duas amostras de águas destinadas à irrigação. Tais amostras foram colhidas no mesmo ponto e em diferentes meses, caracterizando dois grupos de coleta com 40 amostras cada, totalizando 80 amostras. Foi determinado o número mais provável (NMP/100 mL) de coliformes totais, coliformes termotolerantes e enterococos, através da técnica dos tubos múltiplos (APHA, 2005). Foi utilizado o padrão de qualidade estabelecido pela Resolução n°357 do Conselho Nacional do Meio Ambiente- CONAMA, que determina um limite de 200 coliformes termotolerantes em 100 mL de amostra de água utilizada para irrigação de hortaliças consumidas cruas (CONAMA, 2005). Após a análise das amostras referentes à primeira coleta, os proprietários das hortas, cujas águas utilizadas na irrigação não atenderam ao padrão de qualidade estabelecido pela Resolução CONAMA n°357 foram orientados quanto à necessidade de medidas de desinfecção das mesmas ou suas fontes. A segunda coleta das amostras ocorreu somente após terem sido tomadas as providências para a melhoria da qualidade da água, nos casos em que isso foi necessário. Após a primeira análise observou-se... / The consumption of fresh foods such as fruits and vegetables represents risks to human health, since these foods may be contaminated, behaving as sources of various diseases. The water used for irrigation of vegetables gardens represents one of the possible sources of contamination, which may compromise the quality of the product and, mainly, the human health. Thus, the bacteriological quality control of water used for such purposes becomes vitally important for public health. The objective of this paper was to evaluate the bacteriological quality of water used for irrigation of 40 vegetables gardens in the municipalities of Araraquara, Boa Esperança do Sul and Ibitinga, SP. Were collected in each vegetables garden two samples of water for irrigation. The samples were collected in different months at the same point, featuring two groups collection with 40 samples each, totaling 80 samples. It was determined the most probable number (MPN/100 mL) of total coliforms, termotolerants coliforms and enterococcus using the multiple tube technique (APHA, 2005). It was used the quality standard established by Resolution n°357 of Environmental National Council - CONAMA, which determines a limit of 200 termotolerants coliforms in 100 mL of sample of water used for irrigation of vegetables consumed raw (CONAMA, 2005). After the analysis of the samples from the first collects, the owners of the vegetables gardens, whose waters used in irrigation not satisfy the quality standard established by CONAMA Resolution n°357, were instructed about the necessary disinfection measures of the water or its sources. The second collects of the samples occurred only after been taken steps to improve water quality, when it was necessary. After the first analysis it was observed the presence of termotolerants coliforms, in quantities above the permitted by law, in nine samples (22,5%). The owners of these vegetable... (Complete abstract click electronic access below)

Orientador: Rodrigo Máximo Sánchez Román / Banca: Ricardo Molto Pereira / Banca: Célia Regina Lopes Zimback / Resumo: O presente trabalho teve por objetivo desenvolver um modelo em dinâmica de sistemas, propondo assim, uma ferramenta que permitisse a análise da sustentabilidade dos recursos hídricos do município de Promissão, interior do estado de São Paulo. Este modelo para gestão de recursos hídricos auxiliará gestores da bacia hidrográfica do Córrego Gonzaga e à companhia municipal responsável pelo planejamento e gestão de sistema de abastecimento e distribuição de água tratada e esgotamento sanitário, à tomada de decisões com maior embasamento já que permite uma visão sistêmica do processo de abastecimento do município. Para desenvolver o modelo, foi utilizada a metodologia sistêmica que é uma ferramenta de grande valia para os gestores de recursos hídricos, pois permite a previsão de cenários futuros de abastecimento e tratamento de efluentes e viabiliza a elaboração e implementação de políticas públicas. O programa STELLA (Structural Thinking Experimental Learning Laboratory with Animation), versão 9.1.3, foi utilizado para desenvolver o modelo dinâmico. Para elaboração e validação da mecânica do modelo desenvolvido, foram utilizados dados da atual gestão de recursos hídricos do município. O modelo desenvolvido foi o "Modelo de Recursos Hídricos de Promissão (MRH-PROMI)". Para analisar a sustentabilidade dos recursos hídricos do município de Promissão através dos resultados gerados pelo MRH-PROMI, foram elaborados cinco cenários com situações adversas e analisou-se o comportamento dos ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study aimed to develop a model usinf dynamic systems, thus proposing a tool that allows the analysis of water resources sustainability at Promissão, state of São Paulo. This water management model will help managers of the Gonzaga Stream watershed and the municipal company responsible for the management and distribution of treated water and sewage, to decision making with better basis as it allows a systemic view the municipality of supply process. To develop the model, systemic methodology was used which is a valuable tool for water resources managers, it allows the prediction of future scenarios of supply and wastewater treatment and enables the development and implementation of public policies. STELLA software (Structural Learning Laboratory Experimental Thinking with Animation), version 9.1.3, was used to develop the dynamic model. To design and mechanical validation of the developed model, the current water resources management in the municipality data were used. The model was the "Water Resources Model Promissão (WRM-PROMI)." To analyze the water resources sustainability Promissão municipality through the results generated by the MRH-PROMI were prepared five scenarios with adverse situations and analyzed the behavior of the elements involved in the offer process and municipal demand in every situation. The model allows water managers make plans to avoid potential problems related to the new scenario or develop projects with information generated by the model for maintaining and improving the use of these resources ... / Mestre

Master of Science / Department of Agricultural Economics / Jeffrey M. Peterson / Understanding irrigation water demand is vital to policy decisions concerning water scarcity. This thesis evaluates irrigation water-use responses to changes in prices, while accounting for cross-sectional characteristics of irrigators’ resource settings. An irrigator’s profit-maximizing decision is modeled in two stages. In the first stage, he decides which crop to plant, and in the second stage he decides how much water to apply given the crop choice. This thesis employs an econometric modeling technique not previously used in the irrigation water demand literature, a multinomial logit selectivity model. This econometric technique allows the intensive (change in water use for each crop in the short run) and extensive (change in water use in the long run due to changes in crop-choice) margin effects to be computed in a simultaneous equation system. A multinomial logit selectivity model has applications to many resource issues in production agriculture where the two-stage decision process is common. The model is estimated from field-level data on water use and crop-choice for a 25-county region in western Kansas over the period 1991-2004. Water use was found to be highly inelastic to the price of natural gas, but becomes more elastic as the price increases. The intensive margin effect was significant for natural gas price. The extensive margin effect only comprised half the total effect under high natural gas prices and was negligible for low prices. However, the extensive margin effect under high natural gas prices declined over time due to more efficient irrigation systems and improved crop varieties. The intensive margin effect explained most of the water use response from changes in other variables, including corn price. An increase in corn price has a negligible extensive margin effect because corn is most often substituted with alfalfa, which has a similar water requirement. Inelastic demand implies that policies aiming to conserve the Ogallala Aquifer by increasing the price of water will not accomplish their purpose and will affect irrigators’ incomes. More effective policies would be voluntary or mandatory quantity restrictions. However, efficient restrictions would need to account for spatial variation in the rate of depletion and the remaining saturated thickness.

Magister Scientiae (Biodiversity and Conservation Biology) / Heavy metal contamination tends to be a problem in inner city agricultural areas and gardens. High levels of certain heavy metals have been found in the soil and vegetables in the Cape Town Metropolitan area. The aim of this project was twofold. Firstly to ascertain whether water (ground or surface) was responsible for the heavy metal problem found in vegetables in the Philippi and Kraaifontein-Joostenbergvlakte farming areas in Cape Town; and secondly to evaluate the efficacy of two possible remediation methods, namely chelation (with EDTA) and precipitation (using phosphate), aimed at tackling the problem. In order to achieve this a water survey and greenhouse experiment were conducted. The water survey involved collecting a number of samples; both from surface dams and boreholes, from the two farming areas. Results showed minimal heavy metals in both, and therefore ruled this out as the source of the heavy metal problem. The greenhouse sand culture experiment tested the effects of the two remediation methods on the growth, development and elemental content of turnip and spinach plants treated with two cadmium and lead concentrations. In summary, Cd reduced growth more than Pb; Cd accumulated in roots and leaves, and Pb in roots. Several treatments, both metal and mitigation enhanced the chlorophyll content. The difference between the EDTA and phosphate mitigation treatments were not significant in the case of cadmium but in the case of lead, high phosphate resulted in increased growth. The large variation of results in this study, and indeed those of the available literature, indicate that the remedial treatments investigated here are not necessarily the most effective and that other treatments should be investigated to control the uptake of either cadmium or lead, as agricultural soils in future become more contaminated with either or both of these heavy metals.

Although a wide range of flow measurement devices and methods already exist for the measurement of irrigation water, water users and water management officials still claim there is a need for more appropriate devices that are non-intrusive, reliable, easy to install and maintain, and cost effective. Meters that are typically used for irrigation water measurement were tested in a laboratory as an initial part of the research and measurement errors larger than ±10 % of the actual discharge was recorded. This study was aimed at evaluating an experimental measuring method that may meet the requirements of the users. The experimental method is based on the unique relationship between the differential pressure and the discharge of a specific pump. By determining this relationship for a specific pump over a range of operating conditions (but for specific installation conditions), a curve similar to the pump curve as developed by the pump manufacturer can be established. If this relationship is inversed (into a discharge-differential pressure relationship), it can be used to calculate the discharge of the pump by measuring the differential pressure. The volume of water discharged by the pump over a period of time can then be determined by integrating the calculated discharge over time. Laboratory tests were conducted to evaluate the validity of the proposed measuring method. The tests entailed the development of the discharge-differential pressure relationship for the specific pump being used, by simultaneously measuring the system discharge, and pressure at both the suction and delivery sides of the pump. Once the relationship had been developed, a set of independent tests was conducted and the pressure measurements used to calculate the discharge through the system. The calculated discharge values were then compared with the measured values. The experimental measuring method was also evaluated in the field through empirical testing of its application in the field. The necessary equipment was installed and calibrated at an irrigation system pump station at the Orange-Riet Water User Association, and data collected over a two week period. The laboratory evaluation of the proposed measurement method produced favourable results, with the analyses showing that discharge can be "measured" with this method at errors smaller than ± 5.4 % of the reference reading within a specified range of flow rates, which is better than the errors produced by the conventional meters evaluated during the initial part of the research. The field tests showed that the method can be applied successfully to monitor pump abstractions. The method's results were compared to two reference measurements and it was found that the volume of water abstracted according to the experimental method was within ± 2.6 % of the reference measurements. The field work also showed that from a practical application point of view, the method has definite advantages over the conventional meters, although it is not less expensive than other measuring devices. The advantages include easier installation, high turn-down ratios, low maintenance requirements, no additional head loss, and suitable for telemetric data collection. Further work that is required include investigations on the use of a differential pressure transducer (rather than two separate suction and delivery side transducers), since this may reduce costs and the number of recorded data points, as well as evaluations of the validity of the discharge - differential pressure relationship over a long period of time, since it may change due to wear on the pump or motor. / Dissertation (M Eng (Agricultural Engineering))--University of Pretoria, 2005. / Civil Engineering / unrestricted

Current irrigation scheduling technologies are limited to refilling the root zone based on measured or predicted amount of water stored within the root zone. This needs measurement of soil-water status and specifying soil field capacity that make this approach expensive and challenging. The FullStopTM wetting front detector (FS) was specifically developed to be a simple and affordable technology to help farmers manage water, nutrients and salts in the root zone. This device responds to a strong wetting front, but research has shown it is less sensitive to weak redistributing wetting fronts, and this may compromise its efficacy in certain situations. The objectives of this study were to recommend a modified version of the FS that responds to weak redistributing wetting fronts and to develop guidelines for the deployment of these detectors to schedule irrigation. The research described herein comprises of two phases: the first phase focused on literature review, field evaluation of wetting front detector of varying sensitivities (WFD) and laboratory measurements of hydraulic properties of soil and wick materials. The second phase validates the HYDRUS-2D/3D for the development of guidelines on how to use WFD to schedule irrigation. The first phase includes: i) a literature review on passive lysimetry that relates design features to the sensitivity of WFD and how prototypes of WFD operate; ii) hydraulic characterization of soil and wick materials to describe the functioning of the different WFD designs; iii) an empirical investigation to determine whether the wick characteristics limits the attainment of equilibrium between the opening of the outer tube and the water table in the inner tube; iv) field evaluations of five types of WFD under sprinkler and natural rainfall to examine the accuracy and sensitivity of the different WFD designs; and v) analysis of the equilibrium between the WFD and the surrounding soil, and recommendations for the best design options based on the sensitivity requirement for different situations. The second phase of the study used observed data sets to validate the Hydrus-2D/3D model. After validation, the model was used to simulate different irrigation scenarios to develop guidelines for the deployment of WFD to schedule irrigation. Field evaluations of various WFD designs showed that length has significant effect on the sensitivity of WFD (P ≤ 0.05). The 90-cm-long Tube wetting front detector (90TD) was significantly more sensitive than the original FS design. The hydraulic conductivity function of two wick materials (Diatomaceous Earth and Fine sand) were not limiting for the attainment of the equilibrium between the Tube Detector and the surrounding soil, and the opening of the Tube Detector and the water level in the inner tube. The Hydrus-2D/3D model performed well in simulating the measured responses of FS or 90TD and the experimental sensitivity thresholds of these detectors. This model was deployed to link WFD responses to different simulated irrigation scenarios to generate monitoring protocol such as detector placement depth, irrigation amount or interval. The model simulations showed that FS can be used to schedule irrigation objectively for sprinkler or drip irrigations, i.e. adjusting irrigation amount or interval based on the response of a detector. Though further study is warranted, model simulation has indicated that 90TD can be used to improving furrow irrigation management. It is envisaged that WFD technology can guide farmers to make informed irrigation decisions and alerting farmers to percolation losses below the root zone. / Thesis (PhD)--University of Pretoria, 2014 / gm2015 / Plant Production and Soil Science / PhD / Unrestricted

A deteriorating trend has been noted in the bacteriological quality of surface irrigation water sources in South Africa. In a bid to compare the bacteriological quality of two irrigation water sources as well as whether irrigation water was a source of bacterial pathogens on irrigated lettuce, this study was designed and divided into two phases. Phase one involved determination of physico-chemical parameters and bacterial indicators in the Loskop canal, the Skeerpoort river and lettuce irrigated with water from the Skeerpoort river over 10 months. Co-currently the study further determined the diversity of the most prevalent bacterial microflora in the 3 sample sources over the same time period. Aerobic colony counts (ACC), Aerobic spore formers (ASF), Anaerobic spore formers (AnSF), Faecal coliforms (FC), Intestinal enterococci (IE) and Staphylococcus aureus (S. aureus) as well as prevalence of Escherichia coli (E. coli), Salmonella spp and Listeria monocytogenes (L. monocytogenes) were determined. Additionally the most prevalent aerobic bacterial species isolated from the three sources were determined. Higher mean rainfall was noted in areas surrounding the Skeerpoort river (74.7mm) than the Loskop canal (0.1mm). Mean temperature was 15.4˚C and 18.2˚C while mean pH was 7.4 and 8.4 in the Loskop canal and the Skeerpoort river respectively. Low mean bacterial counts of less than 3.4 log10cfu/ml, were noted for ACC, ASF, AnSF, S. aureus and IE at both irrigation sites. Higher mean ACC of 5.9 log10cfu/g and S. aureus counts of 3.0 log10cfu/g were noted on lettuce. Although low mean counts of FC (1.3 log10cfu/100ml) were noted for all three sources, high incidence of E. coli was observed during bacterial composition studies on nonselective media. This suggested underestimation of faecal contamination possibly indicating that identification of specific pathogens provided a better measure of assessing bacterial contamination than bacterial indicators. E. coli, Bacillus spp and Enterobacter spp were the most prevalent bacteria in the Loskop canal, the Skeerpoort river and on lettuce. Prevalence of E. coli, Bacillus spp and Enterobacter spp in the Loskop canal was 23%, 33% and 26% respectively. Similarly prevalence in the Skeerpoort river was 36%, 26%, 16% respectively. On lettuce prevalence of the same bacteria was 36%, 30% and 6% respectively. E. coli O157:H7 was isolated at both irrigation sites while Salmonella enterica (gp 1) ST paratyphi A was isolated from the Skeerpoort river. High prevalence of similar bacterial species within the Loskop canal and the Skeerpoort river suggested similar sources of contamination in the two water sources inspite of different geographical location and surrounding land use practices. Additionally, similar bacterial species in irrigation water from the Skeerpoort river and on irrigated lettuce suggested water as a source of contamination on produce. Additionally it suggests ability of bacterial pathogens to withstand environmental conditions under field conditions which may pose a risk to food safety and public health among individuals consuming irrigated fresh produce. Phase 2 aimed at determining the prevalence of antibiotic resistant and virulent E. coli collected from the Loskop canal, the Skeerpoort river and lettuce irrigated with water from the Skeerpoort river. Forty one (41) E. coli isolates: (19) Loskop canal; (12) the Skeerpoort river; (10) lettuce were tested with 11 antibiotics at single concentrations and screened for Shigatoxin 1 (stx 1), Shigatoxin 2 (stx 2) and intimin (eae) genes. Antibiotic resistance was also used as a means of clustering E. coli isolated from the 3 sources. In the Loskop canal 84% and 83% of strains in the Skeerpoort river were resistant to at least one antibiotic. There was a significant difference (p≤0.05) in resistance to antibiotics between isolates from the Loskop canal and the Skeerpoort river. Additionally the combined effect of isolate source (irrigation water site) and antibiotics for isolates from the Skeerpoort river was significant (p≤0.05). From lettuce, 90% of isolates were resistant to at least one antibiotic and resistance significantly differed (p≤0.05) from isolates in the Skeerpoort river. The highest resistance to single antibiotics in all three samples was to cephalothin and ampicillin. Higher resistance was noted to multiple (more than 2) antibiotics in the Skeerpoort river (33%) than Loskop canal (5%). Most isolates from the same source showed close relatedness. Close relatedness was noted between isolates from the Loksop canal (10.5%) and the Skeerpoort river (16%). From irrigated lettuce 40% of isolates showed close relatedness to isolates in irrigation water from the Skeerpoort river. In the Loskop canal 15% and 41% of isolates in the Skeerpoort river possessed virulence genes. From lettuce, 20% of isolates possessed virulence genes. In the Loskop canal as well as from lettuce all isolates with virulence genes were antibiotic resistant while 80% of isolates with virulence genes in the Skeerpoort river were antibiotic resistant. In the Loskop canal 10% and 25% of isolates in the Skeerpoort river were positive for stx1/stx2 and eae, genes synonymous with Enterohaemorrhagic E. coli (EHEC). Results from this study show that E. coli from the two irrigation water sources as well as on irrigated lettuce were resistant to antibiotics and potentially pathogenic. This may increase risk of contaminating irrigated fresh produce which may compromise food safety and public health of consumers. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Food Science / unrestricted

Marginal values of water us ed in irrigation are needed if water is to be optimally allocated among alternative uses. Cobb- Douglas production function analysis and linear programming methods were studied in this investigation to find their fruitfulness in predicting these marginal values. The theoretical properties of both methods indicate that they are conceptually capable of yielding valid marginal value estimates for irrigation water. Further investigation of the two methods was carried out as an empirical test in the Milford area of Utah . Marginal values of water used for irrigation in that area were estimated by both procedures. Although inviolable criteria for testing the validity of the estimates are not available, imperfect standards or' measure imply that they are sound. Linear programming and Cobb -Douglas production function anal ysis are therefore concluded to be fruitful methods of es timating marginal values of water used for irrigation.

No description available.