Peri-Urban Agrosystems Dynamics and their Implications on Land Suitability for Vegetable Farming in Nairobi Machakos Counties Interface, Kenya
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Date
2024-04
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Peri-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.
Description
A 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 Schaab