Arcadius, Ahogle Agassin Martinien2024-10-022024-10-022024-04https://ir-library.ku.ac.ke/handle/123456789/29015A Thesis Submitted in Fulfilment of the Requirements for The Award Of The Degree Of Doctor Of Philosophy In Environmental Planning And Management In The School Of Agriculture And Environmental Sciences Of Kenyatta University, April 2024. Supervisors 1. Sammy Letema 2. Nicholas K. Korir 3. Gertrud SchaabPeri-urban agriculture is increasingly becoming important to cities of developing countries for food security, household livelihoods and income generation. However, peri-urban agriculture is often associated with heavy metals, trace elements and bacterial pathogens contamination, which poses serious human and environmental health risks. This study, therefore, assesses the dynamics of peri-urban agrosystems and their implications on land suitability for vegetable farming in Nairobi-Machakos counties interface. The objectives of the study in Nairobi-Machakos counties interface are to 1) to explore the diversity of peri-urban agrosystems and their determinants, 2) to assess irrigation water suitability and the contamination of peri-urban agrosystems, 3) determine the ecological and health risks of peri-urban agro-systems contamination, and 4) model land suitability for vegetable farming. The study used a descriptive correlational research design. Very High Resolution Google Earth imagery analysis and semi-structured questionnaire administered randomly to 130 farming units was used to characterise peri-urban agrosystems. A stratified random sampling method was used to collect irrigation water, soil and vegetable samples in ten vegetable production zones. The samples were processed following standard protocol and tested for water quality parameters, heavy metals and trace elements, and bacterial. Ecological risks were estimated using Hakanson Ecological Index and health risks were estimated using the USEPA framework for human exposure. Land suitability analysis was based on land use, irrigation water quality and accessibility, soil suitability, health risk, landform, and market accessibility considering a current situation (2022) and a future scenario (2030). The findings show that peri-urban farming in Nairobi-Machakos counties interface takes various forms and configurations characterised by different farming scales and diversified resource endowment as influenced by the type of actors, land tenure, irrigation water sources, and market orientations. Irrigation water across the site exhibits high concentrations of dissolved materials and bacterial load, making water quality degraded and thus of marginal suitability for vegetable irrigation. Soil and vegetables show above permissible threshold concentrations of heavy metals and trace elements, with arsenic, cadmium, mercury, and lead exhibiting the highest ecological risks. The potential health risks related to vegetable consumption indicate significant carcinogenic risks. Heavy metals and trace elements contamination in peri-urban farmlands correlate with irrigation water sources and farmland location across the peri-urban interface. Land suitability analysis shows that land use, irrigation water accessibility and quality, and soil suitability are key factors determining land suitability for vegetable farming in the interface. Land suitability modelling show that the current (2022) suitable to highly suitable lands account for 38.3% in dry season and 45.3% in wet season and is expected to drop to 25.2% and 26% in dry season and wet season in the 2030 scenario. The findings imply that there is a non-negligible potential for production of healthy and safe vegetable in Nairobi-Machakos counties interface. However, this potential is undermined by current land development, in which the situation of land use for 2022 has already overruled the expected situation in 2030 for some areas. Considering high peri-urban contamination and increasing reliance on urban hydrological flows for irrigation, there is an urgent need for rational zoning of peri-urban agricultural lands based on land use, water accessibility and quality, and soil suitability, coupled with regular monitoring of public and environmental risks and regulatory enforcement in urban and peri-urban landscapes. Furthermore, the sensitization of the different actors including farmers, urban population, leaders, and experts is important for efficient alleviation of ecological and public health risks.enThesis