Are biomass feedstocks sustainable? A systematic review of three key sustainability metrics.

Biomass feedstocks are growing in importance due to their ability to serve as a renewable alternative to fossil fuels for large scale energy generation, with bioenergy projected to be a growing part of the UK's energy mix. Combined with technologies such as carbon capture and storage, sustainable bioenergy has the potential to produce negative emissions with including counterbalancing residual emissions. This paper presents a systematic review of the sustainability impacts of wood biomass (forestry/SRC) and Miscanthus, which are grown as energy fuels, comparing the three key indicators of sustainability: soil organic carbon sequestration rates, biodiversity, and water use efficiency (WUE). Analysis has shown significant influence from primary soil composition (p < 0.001) and previous land use (p < 0.001) on soil organic carbon sequestration rates following conversion to biomass feedstock production. Conversion from arable to forestry can have positive rates of sequestration of 1.4 ± 0.3 Mg C ha−1 year−1 on mineral soils, while similar conversions on a highly organic soils can lead to losses of −25 Mg C ha−1 year−1. This indicates a strong need for careful site selection for future forestry plantations. Miscanthus showed no preference under mineral or organic soils for carbon sequestration rate. Biodiversity at different trophic scales is impacted differently by biomass feedstock production. No significant impact on invertebrates was demonstrated between feedstocks but there is a significant difference between crops (p < 0.001) for vertebrates at higher trophic levels. A limited dataset was collected for WUE from the review, but analysis showed comparable WUE rates for Miscanthus and short rotation coppice, while forestry had significantly lower (p < 0.001) WUE. With global temperatures increasing and changes to climate, water stress is likely to increase. WUE will play an important role in the considerations dfor long term biomass feedstock planning and sourcing. [ABSTRACT FROM AUTHOR]