Bayesian Network Applications for Sustainable Holistic Water Resources Management: Modeling Opportunities for South Africa.

Anthropogenic transformation of land globally is threatening water resources in terms of quality and availability. Managing water resources to ensure sustainable utilization is important for a semiarid country such as South Africa. Bayesian networks (BNs) are probabilistic graphical models that have been applied globally to a range of water resources management studies; however, there has been very limited application of BNs to similar studies in South Africa. This article explores the benefits and challenges of BN application in the context of water resources management, specifically in relation to South Africa. A brief overview describes BNs, followed by details of some of the possible opportunities for BNs to benefit water resources management. These include the ability to use quantitative and qualitative information, data, and expert knowledge. BN models can be integrated into geographic information systems and predict impact of ecosystem services and sustainability indicators. With additional data and information, BNs can be updated, allowing for integration into an adaptive management process. Challenges in the application of BNs include oversimplification of complex systems, constraints of BNs with categorical nodes for continuous variables, unclear use of expert knowledge, and treatment of uncertainty. BNs have tremendous potential to guide decision making by providing a holistic approach to water resources management.

Risk Assessment of Water Quantity and Quality Stressors to Balance the Use and Protection of Vulnerable Water Resources.

In developing regions of the world, valuable and vulnerable water resources are being used excessively. Through water resource development, multiple water quality, flow, and other stressors threaten the sustainable use and protection of these resources. Few attempts have been made to evaluate the synergistic effects of multiple water quality and flow stressors to socioecological attributes of systems that we care about in integrated water resource management. Regional scale ecological risk assessments evaluate the probable negative effects of multiple stressors, affecting dynamic ecosystems on multiple spatial scales. The present study demonstrates how multiple water quality, flow, and other stressors that cumulatively affect the sustainability of the lower Thukela River, South Africa, can be evaluated using the relative risk model, Bayesian network (RRM-BN) approach. This risk assessment facilitated the establishment of minimum water quality and flow requirements to maintain the sustainability of this system and make water resource use and protection trade-off decisions. In this case study, the risk of 10 water resources use and protection scenarios were evaluated in a regional scale ecological risk assessment of the socioecological attributes of the lower Thukela River. In addition we evaluated the consequences associated with these scenarios based on risk pathways of multiple sources, stressors, and receptors to endpoints that represent the sustainable vision of multiple stakeholders of the system. The outcomes of the present study have contributed to new evidence to improve the water resource use efficiency and protect important resources of the lower Thukela River, to ensure sustainability. Integr Environ Assess Manag 2021;17:110-130. © 2020 SETAC.

Implications of the movement behaviour of African tigerfish Hydrocynus vittatus for the design of freshwater protected areas.

African tigerfish Hydrocynus vittatus (n = 35) were tagged with external radio-transmitters in the Kavango River, Namibia, to determine whether freshwater protected areas could be an effective tool for the management and conservation of this species. They were manually tracked in the core study area of 33 km every c. 12 days from July-October 2016 to May 2017 for between 123 to 246 days. In addition, 14 extended surveys were carried out for up to 680 km to determine the total area use of the tagged individuals. Tigerfish displayed at least two behavioural patterns either having high site fidelity with shorter movements or using larger areas with longer movements. Twenty-three (66%) of the tigerfish had high site fidelity using an area of less than 33 km of river, whereas 12 tigerfish (34%) undertook long distance movements of up to 397 km upstream and 116 km downstream from their tagging locations. During the long-distance movements tigerfish crossed the territorial boundaries of Angola, Namibia and Botswana. Of the 35 fish that were monitored, 14 (40%) spent more than 80% of the monitored time in the 33 km study area and 18 (51%) stayed within the study area for at least 50% of the monitored time. These findings suggest that freshwater protected areas may be a useful management tool and we predict that a protected river area of 2-5 km river length could protect 25.9-34.6% of the population for at least 75% of the time whereas protection of 10 km river length could protect at least 50% of tigerfish for at least 75% of the time.