Short-cutting the Phosphorous 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 finitephosphorous 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 conceptslead tosolutions, 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 isan established activity.

Chapter 1 Introduction Chapter 2 Biogeochemistry of phosphorous global transfers and cycles Chapter 3 Description of study area Chapter 4 Establishing fluxes and stocks in an urban-shed Chapter 5 Options for short-cutting the phosphorus cycle Chapter 6 Conclusions Chapter 7 Epilogue

Bekithemba Gumbo was born in Bulawayo, Zimbabwe. He studied civil engineering at the University of Zimbabwe, and later obtained his Masters Degree in Water and Waste Engineeringat Loughborough University in the UK. He worked as Acting Project Manager in the programme Capacity Building in the Water Sector of Zimbabwe, beginning a collaboration with staff of UNESCO-IHE in the Netherlands which culminated in his PhD research at the IHE inDelft.