Impacts of Enhanced Weathering on biomass production for negative emission technologies and soil hydrology

Abstract. Limiting global mean temperature changes to well below 2 °C likely requires a rapid and large-scale deployment of Negative Emission Technologies (NETs). Assessments so far showed a high potential for biomass based terrestrial NETs, but only few included effects of the commonly found nutrient deficient soils on biomass production. Here, we investigate the deployment of Enhanced Weathering (EW) to supply nutrients to phosphorus (P) deficient areas of Afforestation/Reforestation and naturally growing forests (AR) and bio-energy grasses (BG), besides the impacts on soil hydrology. Using stoichiometric ratios and biomass estimates from two established vegetation models, we calculated the nutrient demand of AR and BG. By comparing the inferred AR P demand to different geogenic P supply scenarios, we estimated that 3–98 Gt C of the predicted biomass accumulation cannot be realized due to insufficient soil P supply for an AR scenario considering natural N supply. An amount of 2–362 Gt basalt powder applied by EW would be needed to cover P gaps and completely sequester projected amounts of 190 Gt C during years 2006–2099. The potential carbon sequestration by EW is 0.6–97.8 Gt CO2 for the same scenario. For BG, 8 kg basalt m−2 a−1 might, on average, replenish the exported K and P by harvest. Using pedotransfer functions, we show that the impacts of basalt powder application on soil hydraulic conductivity and plant available water, for closing predicted P gaps, would depend on basalt and soil texture, but in general the impacts are marginal. We show that EW could potentially close the projected P gaps of an AR scenario, and exported nutrients by BG harvest, which would decrease or replace the use of industrial fertilizers. Besides that, EW ameliorates soil capacity to retain nutrients, soil pH, and renew soil nutrient pools. Last, EW applications could improve plant available water capacity depending on deployed amounts of rock powder – adding a new dimension to the coupling of land-based biomass NETs with EW.