A novel life cycle impact assessment method on biomass residue harvesting reckoning with loss of biomass productivity

Second generation bioenergy such as cellulosic bioethanol is expected to become commercially available in the near future. Large scale production of this bioenergy will require secure and continuous supplies of raw materials. One promising source of materials is biomass residues that currently remain on the fields following harvest, a feedstock that does not compete with food. However, unsustainable removal of these residues may adversely affect soil quality and hamper future harvests. In order to assess this effect, an impact assessment method was developed within the life cycle assessment framework based on a specific system definition, i.e. decomposed biomass residues above soil surfaces resulted in net carbon flow into soil compartment. This soil organic carbon functions as an elementary flow to complete the overall carbon balance. The assessment method considers effects of soil organic carbon on soil biomass-productivity. This impact is expressed as loss of net primary production, a midpoint indicator. The impact assessment method follows the ISO-standard format, comprising a characterization factor and an input term representing changes in elementary flows. The operation of the proposed method was illustrated with a small case study. At 10% biomass removal, the impact is 7.16 g-carbon/m