Evolution towards functional stability of buried wood in an anoxic Lab Wood Vault for durable carbon dioxide removal

Wood harvesting and storage (WHS) via Wood Vaulting is an emerging carbon dioxide removal method. Its effectiveness hinges on long-term wood preservation but currently our process understanding is limited. A major type of Wood Vault aims to create anoxic (oxygen-free) condition to stop biological degradation. Here we study wood preservation inside a ‘Lab Vault’ where wooden discs are buried under a layer of clay to seal off air with subsequent monitoring of gas concentrations. Our results show 3 stages of gas evolution: (1) Aerobic decomposition: O 2 decreased from 21 to 0% by the consumption of a small amount of organic matter in 10 days, replaced by CO 2 ; (2) Anaerobic decomposition in the next 1.5 months, with CH 4 increased from 0.0002% to 0.2%; (3) A ‘deep anoxic state’ where both aerobic and anaerobic decomposition stop or slow down drastically with zero oxygen and negligible CH 4 generation while CO 2 remains high. The third stage signifies a ‘functional stability’ where wood degradation stops completely. However, long-term maintenance requirement of anoxic condition on millennial timescales cannot be directly inferred from the short-term experiment because anoxic condition was initially created by wood decay. Our experiment suggests that Wood Vault is fundamentally different from landfill, which is often used as a reference in commercial implementation standards. Our results provide direct observational evidence of the initial biophysical processes underlying durable wood preservation, as well as targets for engineering design and monitoring and verification for biomass burial as a climate solution.