Evaluation of carbon sequestration potential and biogeochemical driving mechanisms in contaminated land under long-term nature-based restoration

Abstract As the global community pursues net-zero emissions by 2050, identifying innovative carbon sinks beyond traditional forest and agricultural sectors has become a strategic imperative. Contaminated land and brownfields represent a significant yet historically overlooked resource for terrestrial carbon sequestration. This study evaluates the capacity of a long-term nature-based restoration project in a cadmium-contaminated agricultural area in Taiwan to function as a verifiable carbon sink. Utilizing high-resolution grid sampling, microbial metabolic profiling with Biolog EcoPlates, and the FAO’s EX-Ante Carbon-balance Tool (EX-ACT), the study quantified the cumulative impacts of phytoremediation on soil organic carbon (SOC) and tree biomass carbon stocks. The net carbon balance is governed by a complex interplay among heavy metal toxicity, shifts in microbial functional activity, and rhizosphere priming effects. The results indicate that cadmium stress has been selected for tolerant microbial consortia with high metabolic rates. In addition, rhizosphere priming effects in the subsoil led to trade-offs that enhanced biomass accumulation under specific soil pH, bulk density (BD), electrical conductivity (EC) conditions. This study provides compelling evidence that brownfields possess substantial potential to function as terrestrial carbon sinks through long-term nature-based restoration. Transforming cadmium-contaminated land into a naturalized forest system resulted in a significant net sequestration potential of 4.36 tC/ha/year, driven primarily by vegetation growth. Overall, the regeneration of contaminated land offers a high-performance pathway for carbon sequestration, extending greenhouse gas mitigation benefits beyond those provided by conventional land-use systems.