Impacts of enhanced weathering on biomass production for negative emission technologies and soil hydrology

Wagner De Oliveira Garcia,Kristine Karstens,Pete Smith,Lena R Boysen,Alexander Popp,Daniel Goll,Jens Hartmann,Thorben Amann

doi:10.5194/bg-17-2107-2020

Abstract

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 have shown a high potential of biomass-based terrestrial NETs, but only a few assessments have 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 areas of afforestation–reforestation and naturally growing forests (AR) and bioenergy grasses (BG) that are deficient in phosphorus (P), 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. Insufficient geogenic P supply limits C storage in biomass. For a mean P demand by AR and a low-geogenic-P-supply scenario, AR would sequester 119 Gt C in biomass; for a high-geogenic-P-supply and low-AR-P-demand scenario, 187 Gt C would be sequestered in biomass; and for a low geogenic P supply and high AR P demand, only 92 Gt C would be accumulated by biomass. An average amount of ∼150 Gt basalt powder applied for EW would be needed to close global P gaps and completely sequester projected amounts of 190 Gt C during the years 2006–2099 for the mean AR P demand scenario (2–362 Gt basalt powder for the low-AR-P-demand and for the high-AR-P-demand scenarios would be necessary, respectively). The average potential of carbon sequestration by EW until 2099 is ∼12 Gt C (∼0.2–∼27 Gt C) for the specified scenarios (excluding additional carbon sequestration via alkalinity production). For BG, 8 kg basalt m−2 a−1 might, on average, replenish the exported potassium (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, to close 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 nutrients exported by BG harvest, which would decrease or replace the use of industrial fertilizers. Besides that, EW ameliorates the soil's capacity to retain nutrients and soil pH and replenish soil nutrient pools. Lastly, EW application 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.

Highlights

To limit temperature increase due to climate change to well below 2 ◦C compared to preindustrial levels by the end of the century, research efforts on negative emission technologies (NETs; i.e., ways to actively remove CO2 from the atmosphere) intensify
We show that enhanced weathering (EW) could potentially close the projected P gaps of an AR scenario and nutrients exported by bioenergy grass (BG) harvest, which would decrease or replace the use of industrial fertilizers
The calculated P budgets according to Eq (4) for the AR time of 2006–2099 (Fig. 5) considered different geogenic supply scenarios and the average and range of the N-stock-based P demand for the AR simulation from Kracher (2017)

Summary

Introduction

To limit temperature increase due to climate change to well below 2 ◦C compared to preindustrial levels by the end of the century, research efforts on negative emission technologies (NETs; i.e., ways to actively remove CO2 from the atmosphere) intensify. Terrestrial NETs encompass bioenergy with carbon capture and storage (BECCS); afforesta-. W. de Oliveira Garcia et al.: Impacts of enhanced weathering tion, reforestation and naturally growing forests (AR); enhanced weathering (EW); biochar; restoration of wetlands; and soil carbon sequestration. From these land-based NET options, BECCS, AR, biochar, and EW can potentially be combined to increase atmospheric carbon dioxide removal (CDR; Smith et al, 2016; Beerling et al, 2018; Amann and Hartmann, 2019). BECCS combines energy production from biomass and carbon capture at the power plant with subsequent storage. The biomass yields of AR and agricultural bioenergy crops directly correlate with fertilizer application, which in turn could reduce CDR efficiency due to related emissions of N2O (Creutzig, 2016; Popp et al, 2011) and initiate unwanted side effects like acidification of soils (Rockström et al, 2009; Vitousek et al, 1997), streams and rivers, and lakes (Vitousek et al, 1997)

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Conclusion