Biomass Burial as a Permanent Carbon Removal Strategy

Biomass burial, also known as woody biomass carbon sequestration, is emerging as a scalable and verifiable carbon dioxide removal (CDR) solution. The technique involves harvesting biomass—typically from invasive species or forestry residues—and burying it in low-oxygen, geologically stable conditions to avoid decomposition and CO₂ release. When executed properly, biomass burial offers permanence, verifiability, and co-benefits for land restoration.

Conceptual Basis and Carbon Sequestration Logic

Photosynthesis captures atmospheric CO₂ and stores it in plant biomass in the form of lignocellulosic carbon (Zeng, 2008). Under natural conditions, this carbon would return to the atmosphere via microbial decomposition or combustion. However, if biomass is buried in anaerobic, dry, and low-permeability conditions (e.g., clay-capped chambers), microbial activity is dramatically reduced, stabilizing the carbon for centuries to millennia (Gooding, 2023).

Scientific modeling confirms that anaerobic burial of woody biomass can retain over 95% of the original carbon for 1,000 years (Zeng et al., 2022). Moreover, the burial of recalcitrant biomass—such as Acacia melanoxylon, known for high lignin content—enhances permanence due to its natural resistance to microbial breakdown (Zummo & Friedland, 2011).


Process Implementation: From Harvest to Carbon Storage

Based on the photographic sequence provided, the process can be divided into the following technical steps:

Step 1: Biomass Harvesting
Tree species such as Acacia melanoxylon are felled using conventional chainsaws or mechanical harvesters. This species is a target for removal in regions like Chile due to its invasiveness and high growth rate (Fuentes et al., 2014), offering a low-cost, high-volume feedstock.

Step 2: Trench Excavation
Trenches are dug to depths between 2 to 5 meters using excavators. The sides are often compacted or reinforced to prevent collapse. Soils with low permeability (e.g., clay loam) are preferred for minimizing gas and water exchange (Gooding, 2023).

Step 3: Log Placement
Logs are stacked tightly to maximize volume efficiency and minimize voids that could allow air infiltration. According to Zeng (2008), packing density is a critical factor in determining the oxygen availability and thus the decay rate.

Step 4: Sealing
The trench is sealed with a clay capping layer, followed by a mound of topsoil. The clay acts as a diffusion barrier to oxygen and moisture—two critical drivers of microbial decomposition (Zummo & Friedland, 2011). In some cases, trenches are lined or backfilled with bentonite or other engineered barriers to enhance impermeability.

Step 5: Vegetative Cover and Monitoring
Native grasses or shallow-rooted species are planted to restore the surface. Shallow root systems prevent disturbance of the buried biomass while offering aesthetic, ecological, and soil erosion control benefits. Remote sensing, soil probes, and microbial monitoring can be used to verify stability and permanence (Spokas, 2010).


Environmental and Climatic Benefits


  • Permanence: Estimates suggest lifespans exceeding 1,000 years for carbon stored under controlled burial (Zeng et al., 2022).

  • Co-benefits: Includes invasive species control, avoided methane emissions, and soil health restoration (Fuentes et al., 2014).

  • Verification potential: Burial projects can be verified via mass balance calculations, MRV protocols (e.g., Isometric's BiCRS), and carbon isotope analysis (Gooding, 2023).

References

  • Fuentes, N., Ugarte, E., Kühn, I., & Klotz, S. (2014). Alien plants in Chile: Inferring invasion periods from herbarium records. Biological Invasions, 16(2), 555–567. https://doi.org/10.1007/s10530-013-0609-3

  • Gooding, J. L. (2023). Geologic perspective for carbon sequestration by woody biomass burial. Science and Technology for Energy Transition, 78, 17.

  • Spokas, K. A. (2010). Review of the stability of biochar in soils: Predictability of O:C molar ratios. Carbon Management, 1(2), 289–303. https://doi.org/10.4155/cmt.10.32

  • Zeng, N. (2008). Carbon sequestration via wood burial. Carbon Balance and Management, 3(1), 1. https://doi.org/10.1186/1750-0680-3-1

  • Zeng, N., Zaitchik, B. F., Wang, G., Koarashi, J., & Smith, P. (2022). The potential and risks of carbon removal with enhanced biomass burial. Nature Climate Change, 12(3), 249–257. https://doi.org/10.1038/s41558-022-01274-y

  • Zummo, L. M., & Friedland, A. J. (2011). Soil carbon release along a gradient of physical disturbance in harvested northern hardwood forests. Forest Ecology and Management, 261(6), 1016–1026.