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Consumption threshold used to investigate stability and ecological dominance in consumer-resource dynamics
(Elsevier, 2015) Collins, Obiora Cornelius; Duffy, Kevin Jan
Understanding consumer resource population dynamics can be important to an understanding of the overall ecology of systems. For example, the tree-grass continuum dynamics of savannas, an important ecological biome, is inﬂuenced by the population dynamics. Here we investigate herbivory driven popu-lation dynamics of a savanna using a simple model of the interactions of the dominant players, namely: trees, grasses, browsers, grazers and mixed browsers-grazers. We introduce a consumption threshold that summarises some of the parameters and this is used as a guide to understanding the dynamics. This number is used in investigating system stability and sensitivity to parameter ﬂuctuations. It is also used to identify degrees of ecological dominance.
Contribution of wastewater irrigation to Soil Transmitted Helminths infection among vegetable farmers in Kumasi, Ghana
(National Centre for Biotechnology Information, 2016-12-06) Amoah, Isaac Dennis; Abubakari, Amina; Stenstrom, Thor Axel; Abaidoo, Robert Clement; Seidu, Razak
Wastewater irrigation is associated with several benefits but can also lead to significant health risks. The health risk for contracting infections from Soil Transmitted Helminths (STHs) among farmers has mainly been assessed indirectly through measured quantities in the wastewater or on the crops alone and only on a limited scale through epidemiological assessments. In this study we broadened the concept of infection risks in the exposure assessments by measurements of the concentration of STHs both in wastewater used for irrigation and the soil, as well as the actual load of STHs ova in the stool of farmers and their family members (165 and 127 in the wet and dry seasons respectively) and a control group of non-farmers (100 and 52 in the wet and dry seasons, respectively). Odds ratios were cal-culated for exposure and non-exposure to wastewater irrigation. The results obtained indi-cate positive correlation between STH concentrations in irrigation water/soil and STHs ova as measured in the stool of the exposed farmer population. The correlations are based on reinfection during a 3 months period after prior confirmed deworming. Farmers and family members exposed to irrigation water were three times more likely as compared to the con-trol group of non-farmers to be infected with Ascaris (OR = 3.9, 95% CI, 1.15–13.86) and hookworm (OR = 3.07, 95% CI, 0.87–10.82). This study therefore contributes to the evi-dence-based conclusion that wastewater irrigation contributes to a higher incidence of STHs infection for farmers exposed annually, with higher odds of infection in the wet season.
Identifying stability conditions and Hopf bifurcations in a consumer resource model using a consumption threshold
(Elsevier, 2016) Duffy, Kevin Jan; Collins, Obiora Cornelius
The existence, or not, of cyclic dynamics is one of the pivotal aspects of ecological populations. This work considers a consumer resource model found in ecology that can describe both cyclic and non-cyclic dynamics depending on parameter conditions. A threshold consumption number C0 is introduced, similar to the basic reproduction in epidemiological models. It is shown that consumer survival requires C0 > 1 and that a Hopf bifurcation occurs at , where is defined here and is greater than 1. This result is discussed with an example and extensions to other more complicated models.
Microbiological water quality along Vaal Gamagara’s potable water distribution system
(Business Perspectives, 2015) Mokhosi, Agnes; Dzwairo, Bloodless
Safe drinking water is essential to all life forms. Thus analysis for microbiological parameters is critical as this assists in declaring the fitness of potable water for human consumption, among other sustainable and “green uses”. The aim of this paper is to investigate the microbiological quality of potable water along Vaal Gamagara Water Treatment Plant’s (VGWTP) distribution system. A total of 10 samples were collected weekly along the system. The samples were col-lected from January to December 2013 in order to analyze for Escherichia coli (E.coli), total coliforms (TC) and Hete-rotrophic plate counts (HPC). The results showed that only 0.1% and 0.4% of samples analyzed were positive for E. coli and total coliforms, respectively. However, HPC results showed that 40% of the samples analyzed from June to December 2013 had higher counts than the recommended standard limit. The chlorine residual showed an increase from June to December 2013. An assessment of the results indicated that the integrity of the system was compromised for the research period. Water quality failures in a distribution system are unacceptable because they threaten human health and sometimes result in loss of life. Thus the assessment called for an urgent need to boost chlorine residual especially at points further away from the treatment plant. This was envisaged to provide a safety net for microbial compliance while the system was critically and continuously monitored, and further investigations were performed. Studies on chlorine decay were recommended as a priority in order to optimize disinfection and maintain good quality drinking water throughout the system.
A probabilistic assessment of the contribution of wastewater-irrigated lettuce to Escherichia coli O157:H7 infection risk and disease burden in Kumasi, Ghana
(IWA Publishing, 2015-03) Seidu, Razak; Abubakari, Amina; Amoah, Isaac Dennis; Heistad, Arve; Stenström, Thor-Axel; Larbi, John A.; Abaidoo, Robert Clement
Wastewater use for vegetable production is widespread across the cities of many developing countries. Studies on the microbial health risks associated with the practice have largely depended on faecal indicator organisms with potential underestimation or overestimation of the microbial health risks and disease burdens. This study assessed the Escherichia coli O157:H7 infection risk and diarrhoeal disease burden measured in disability-adjusted life years (DALYs) associated with the consumption of wastewater-irrigated lettuce in Kumasi, Ghana using data on E. coli O157:H7 in ready-to-harvest, wastewater-irrigated lettuce. Two exposure scenarios – best case and worst case – associated with a single consumption of wastewater-irrigated lettuce were assessed. The assessment revealed wastewater-irrigated lettuce is contributing to the transmission of E. coli O157:H7 in Kumasi, Ghana. The mean E. coli O157:H7 infection risk and DALYs in the wet and dry seasons, irrespective of the exposure scenario, were above the World Health Organization tolerable daily infection risk of 2.7 × 10−7 per person per day and 10−6 DALYs per person per year. It is recommended that legislation with clear monitoring indicators and penalties is implemented to ensure that farmers and food sellers fully implement risk mitigating measures.
A theoretical approach to using faecal indicator data to model norovirus concentration in surface water for QMRA : Glomma River, Norway
(Elsevier, 2016) Petterson, Susan R.; Stenström, Thor-Axel; Ottoson, Jakob
Monitoring of faecal indicator organisms, such as Escherichia coli, in environmental and drinking waters is inadequate for the protection public health, primarily due to the poor relationship between E. coli and the occurrence of human pathogens, especially viruses, in environmental samples. Nevertheless, measurements of faecal indicator organisms within the risk based approach, can provide valuable information related to the magnitude and variability of faecal contamination, and hence provide insight into the expected level of potential pathogen contamination. In this study, a modelling approach is presented that estimates the concentration of norovirus in surface water relying on indicator monitoring data, combined with specific assumptions regarding the source of faecal contamination. The model is applied to a case study on drinking water treatment intake from the Glomma River in Norway. Norovirus concentrations were estimated in two sewage sources discharging into the river upstream of the drinking water offtake, and at the source water intake itself. The characteristics of the assumed source of faecal contamination, including the norovirus prevalence in the community, the size of the contributing population and the relative treatment efficacy for indicators and pathogens in the sewage treatment plant, influenced the magnitude and variability in the estimated norovirus concentration in surface waters. The modelling exercise presented is not intended to replace pathogen enumeration from environmental samples, but rather is proposed as a complement to better understand the sources and drivers of viruses in surface waters. The approach has the potential to inform sampling regimes by identifying when the best time would be to collect environmental samples; fill in the gaps between sparse datasets; and potentially extrapolate existing datasets in order to model rarer events such as an outbreak in the contributing population. In addition, and perhaps most universally, in the absence of pathogen data, this approach can be used as a first step to predict the source water pathogen concentration under different contamination scenarios for the purpose of quantifying microbial risks.
Understanding multiple species ecosystem dynamics using a consumer resource model
(Wiley, 2016) Collins, Obiora Cornelius; Duffy, Kevin Jan
Most ecological systems comprise multiple species coex-isting and the dynamics of these multiple species can be important for understanding, management, and conservation. One method to study such ecological system dynamics is the use of heterogeneous models. Here we for-mulate and analyze a multiple species (n patches or groups) consumer re-source model. Initial insights are gained by analyzing the special cases n =1 and n = 2. A threshold consumption number C0 is used to investigate system stability and hence the long-term dynamics of the system. It is shown how this threshold consumption number can measure the eﬀects and extent of multiple species coexistence in the system.
Water quality modelling to assess sources and transport of pathogens within uMsunduzi catchment, South Africa
(2022-05) Ngubane, Zesizwe; Bergion, Viktor; Dzwairo, Bloodless; Troell, Karin; Amoah, Isaac; Stenström, Thor Axel; Sokolova, Ekaterina
Water quality modelling is essential to integrated water resources management and decision-making, as it improves the understanding of the spatial and temporal dynamics of chemical and microbial pollution in a river system. Understanding of the spatio-temporal dynamics of pollution and accurate prediction of its pollution hotspots are vital to improving the microbial quality of surface water. South African rivers generally receive waste from inadequate wastewater infrastructure, mines, and farming activities, among others. The uMsunduzi River in KwaZulu-Natal, South Africa, is among rivers with recorded poor to very poor water quality. To identify parts of the uMsunduzi River that are polluted by Escherichia coli (E. coli) and Cryptosporidium, chosen to represent bacteria and protozoan parasites respectively, this study mapped out pollutants emanating from point and non-point sources using the Soil and Water Assessment Tool (SWAT) model. SWAT uses a combination of empirical and physically based equations that use readily available inputs and enables users to study long term impacts. Streamflow calibration in the upper and lower reaches of the catchment showed good performance with R² of 0.64 and 0.58, respectively. The SWAT module for predicting microorganism loads and concentrations in the river was used. The main faecal sources in the uMsunduzi catchment can be summarised as: wastewater treatment plant (WWTP), broken sewers in the urban area, and faecal droppings from grazing livestock. The microorganism loads from these sources were described in SWAT using data from different local water authorities and stakeholders. With respect to E. coli, the output from SWAT was compared to observed data from four points within the catchment representing upper rural, upper urban, lower urban, and lower rural parts. The output from the SWAT model showed slightly low variability, however, the trend in the SWAT model simulations followed the observed data patterns in most subbasins. The trend with Cryptosporidium was such that concentrations are higher downstream the WWTP than upstream, though insufficient data exists to compare the model Cryptosporidium output with observed data. Overall, the model microbial output showed that in rural areas, animals contribute more to pathogen loads than human sources. Human sources were more prominent in urban areas owing to the major contributions from wastewater infrastructure. The microbial output data from the SWAT model were used as input for quantitative microbial risk assessment (QMRA). Considering that not all E. coli are pathogenic, 8% of E. coli was assumed as pathogenic following various studies. The exposure routes investigated were direct ingestion of the uMsunduzi River water during recreational swimming, canoeing training, and drinking. The exposed population was categorised as children (<18 years old) and adults (>18 years old). The probability of infection for most users exceeds the acceptable level for drinking and recreation as outlined in the South African water quality guidelines and by the World Health Organisation (WHO).
The results of this study can be used as a baseline to assess the economic and health implications of different management plans, resulting in better-informed, cost-effective, and impactful decision-making.