Short-cutting the Phosphorus Cycle in Urban Ecosystems

This dissertation presents a methodology of short-cutting the phosphorus cycle in urban ecosystems. In nature, the P-cycle is a circular, closed-loop system, but human activities use and dispose P in a linear, open-ended system leading to the customary environmental problems. Lake Chivero in Zimbabwe is used as a case study to illustrate the unsustainable practice of discharging valuable and finite phosphorous into drinking water resources. Short-cutting or closing the P-cycle in the urban environment is closely related to the closure of water cycles. Closing the P-cycle is dependent on the adoption of ecological sanitation and eco-city concepts. These concepts lead to solutions, which are source orientated (local and small scale), non-mixing, ecologically sound, closed-loop systems. Recycling of P in urban ecological agriculture (without synthetic fertilisers) is used in this dissertation to test the feasibility of these concepts. A phosphorus calculator has been developed, based on studies of monthly P-fluxes and stocks, in a high-density suburb of Harare in Zimbabwe, where agriculture is an established activity.