Time (Years) | Physical Changes | Chemical Changes | Biological / Other Effects | Impact on Contaminants | Key Controlling Factors |
|---|---|---|---|---|---|
2 | Retains original structure and porosity; labile components react with water and oxygen. | Formation of initial hydroxyl and carboxyl functional groups; pH increase due to alkalinity. | Early microbial colonization; slight modification by root exudates. | Immobilization of heavy metals and organics through adsorption, cation exchange, surface complexation. | Abiotic: moisture, temperature, oxygen; Biotic: microbial colonization, root exudates; Biochar properties: feedstock, porosity, alkalinity. |
5 | Partial collapse of pores; formation of micro-aggregates; colloidal/nanoscale particle formation begins. | Increase in oxygen-containing functional groups (OFGs), cation exchange capacity (CEC) and polarity; partial reduction in aromaticity. | Biochar aggregates with soil; microbial activity enhances functionalization; light-driven radical formation begins. | Stabilization of metals in aggregates; some metals may start mobilizing due to organic acids. | Abiotic: wet-dry and freeze-thaw cycles, light exposure; Biotic: microbial and root activity; Biochar: surface area, aromaticity, CEC. |
20 | Significant surface oxidation; collapse of porous structure; colloidal/nanoscale particle detachment and movement. | Advanced oxidation; carboxyl-rich functional groups; persistent free radicals; partial carbon loss. | Biochar fully integrates into soil aggregates; ongoing microbial and root interactions. | Mixed effects: continued immobilization via aggregates and OFGs; partial remobilization from pH decline, structural degradation, and colloid transport. | Abiotic: long-term oxidation, acid rain, UV, moisture fluctuations; Biotic: ongoing microbial and root processes; Biochar: stability, initial porosity, chemical composition. |