Impact of Simulated Physical Weathering on the Chemical Properties and Nutrient Availability of Extensive Green Roof Substrates Amended with Biochar and Porous Concrete

This study examines the effect of simulated physical weathering on the chemical properties and nutrient availability of extensive green roof substrates amended with nutrient-rich sewage sludge biochar and adsorptive components (wood-derived biochar and porous concrete). The amendments improved water-holding capacity and air-filled porosity in fresh substrates. After laboratory ageing via wetting/drying and freezing/thawing cycles, amended substrates showed reduced total dissolved solids and nutrient leaching. Aged biochar-amended substrates (SB and SBP) retained more nitrogen and exhibited gradual phosphorus release, highlighting the slow-release potential of sewage sludge biochar. These results suggest that simulated weathering provides a useful, controlled method for evaluating substrate degradation and nutrient dynamics and may help predict long-term substrate performance under rooftop conditions.