Exploring the Water-Nutrient-Food Nexus for an African City Region: Linking the Chivero Lake and Harare City Region, Zimbabwe

Abstract

Some of the most important challenges in the city regions of Africa are related to food, energy, water, and nutrients. To meet these challenges, arguments have emerged that cities should become regenerative, resource-efficient and arrest the decline of ecosystems. Therefore, a case study was performed by considering the linkage between Lake Chivero, and the Harare city region to conceptualize a framework of the water-nutrient-food nexus and to examine how nutrients from the wastewater that is disposed to Lake Chivero can assist in contributing to the food production in the Harare city region. An Applied Systems Analysis (ASA) linked System Dynamics (SD) modelling methodology was used. It is observed that the water supply in the city region, wastewater generation and disposal to Lake Chivero, nutrients, food production, food consumption and wastewater generated from consumption in the city, all work in a feedback mechanism. Premised upon the feedback mechanism, the ASA linked SD model estimates that Lake Chivero has already accumulated about 19,800 tonnes of Nitrogen (N) in its sediments, of which over half can be extracted. To comprehend the significance, it is estimated that 100 tonnes of N might assist in the production of over 35,000 tonnes of food if extracted and utilised in the city region. Therefore, the waste generated in the city region needs to be considered as a resource and recovered, which might turn a recalcitrant problem of pollution into the benefits of resource recovery and environmental and socio-economic wellbeing of the city region.