Design, Implementation and Evaluation of Urban Soil Carbon Sequestration Toolkit

Thesis Abstract

Urban soils play a critical yet underutilized role in mitigating climate change within dense cityscapes, where impervious surfaces and limited green space constrain natural carbon storage. This study addresses the persistent gap between theoretical potential for urban soil carbon sequestration and practical, scalable implementation by designing, implementing, and evaluating a context-sensitive toolkit for urban soil carbon management. The aim is to develop a transferable framework that enables city authorities, planners, and community groups to quantify, enhance, and monitor soil carbon stocks across diverse urban land uses. Specific objectives include (1) identifying soil carbon stock variability across representative urban land uses (paved surfaces, lawns, parks, community gardens, and green roofs) in three metropolitan districts, (2) developing an operational toolkit comprising standardized soil sampling protocols, a carbon accounting calculator, and decision-support guidelines for soil amendments, mulching, and green infrastructure design, (3) validating the toolkit through a pilot implementation in 20 sites with pre- and post-intervention measurements, and (4) evaluating cost-effectiveness and social acceptance of toolkit deployment among stakeholders. A mixed-methods approach was employed, drawing on pragmatic philosophy to integrate quantitative soil data with qualitative stakeholder insights. The population comprises urban soils within a stratified random sample of 60 sites, from which 40 sites were selected for the pilot toolkit implementation. Soil cores (0–15 cm and 15–30 cm) were collected to determine organic carbon (OC), total nitrogen, bulk density, pH, and electrical conductivity, with analyses conducted via dry combustion (Elemental Analyzer) and loss-on-ignition as supplementary validation. The toolkit includes an OC calculator based on regression models linking soil texture, land-use class, and management practices to carbon stock changes, and decision-support modules guided by the Theory of Planned Behavior and the Social-Ecological Systems framework to promote adoption and sustained management actions. Data collection instruments comprise standardized soil sampling templates, a field-data app for geotagged measurements, a user-friendly carbon-tracking dashboard, semi-structured interviews with municipal planners, community leaders, and residents, and focus group discussions to elucidate perceived barriers and enablers. Validity and reliability of instruments were established through pilot testing, inter- and intra-laboratory calibration, and member-checking of qualitative transcripts. Quantitative analysis employed descriptive statistics, one-way ANOVA to compare carbon stocks across land uses and depths, multivariate regression to identify predictors of carbon change, and paired t-tests to assess pre–post intervention differences. The qualitative component utilized thematic analysis to extract stakeholder perspectives, with triangulation performed against quantitative results to strengthen inference. Expected findings indicate measurable gains in soil organic carbon at 12–18 months post-implementation, particularly in community gardens and green roofs where mulching and soil amendments were applied, with average deep-soil OC increase of 0.8–1.2 Mg C ha?1 and surface-layer gains of 2.5–4.0 Mg C ha?1 across pilot sites. Regression analyses are anticipated to identify soil texture, organic amendment type, and canopy cover as significant predictors of carbon accumulation, while ANOVA is expected to reveal statistically higher gains in managed green spaces relative to unmanaged urban soils. The study anticipates positive stakeholder acceptance with identified enablers including perceived co-benefits (biodiversity, heat island mitigation) and robust governance mechanisms, and notable barriers such as initial cost and knowledge gaps. The research contributes to knowledge by operationalizing an urban soil carbon toolkit grounded in empirical field data, incorporating both biophysical measurements and socio-technical considerations, and demonstrating a scalable model for integrating soil carbon sequestration into urban planning and climate action frameworks. The main conclusion is that a carefully designed and context-responsive toolkit can meaningfully augment urban soil carbon stocks while fostering stakeholder collaboration and policy integration. Recommendations include scaling the pilot to additional districts with diverse socio-ecological contexts, integrating toolkit outputs into city climate action plans, establishing ongoing monitoring and adaptive management protocols, and capacity-building programs for municipal staff and community partners to sustain engagement and carbon accounting accuracy.