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

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.

Potential CO2 removal from enhanced weathering by ecosystem responses to powdered rock

“…The silicate grains chemically react with CO 2 to form bicarbonate dissolved ions; these are transported by rivers to the oceans and potentially stored for hundreds years and longer, depending on calcium carbonate sedimentation processes 13 . In addition to this abiotic carbon dioxide removal (CDR) pathway, amending soils with BD enhances soil fertility by releasing nutrients, buffering low soil pH, stabilizing soil organic matter 14 , and can improve soil water retention 15 , thereby promoting plant growth and CDR in agriculture [16][17][18] and forestry 11 . This biotic CDR pathway for enhanced weathering 19,20 has so far been omitted in assessments of the climate mitigation potential of this NET 6,21 .…”

“…A source of concern is the environmental impact of massive BD deployment in natural systems: although positive impacts have been suggested 8,15 , the effects of BD application on eutrophication of aquatic systems, on biodiversity, on biosphere-atmosphere feedbacks, and on air-, water-and soil pollution still requires thorough assessment. Moreover, application of fine (<10 µm) particles may also pose health risks 32 .…”

Intensity and Duration of Nitrogen Addition Jointly Alter Soil Nutrient Availability in a Temperate Grassland

“…However, an unexpected finding was also observed that short‐term N addition significantly increased the total contents of base cations and exchangeable Ca (Figure 2). Such finding is mainly because the impacts of external disturbance in this natural ecosystem, such as the excessive N supply in the closed system, may accelerate weathering process and physical fragmentation of rocks (Doetterl et al., 2018; Oliveira Garcia et al., 2020; Rafiei & Kennedy, 2020). Nevertheless, some other processes may also cause changes in the total and exchangeable contents of base cations, including plant uptake, binding and dissolution with soil organic materials, and leaching out from the soil system (Bünemann et al., 2018; Cameron et al., 2013; R. Wang et al., 2018).…”

Is the climate change mitigation effect of enhanced silicate weathering governed by biological processes?

“…Few modeling studies have yet addressed interactions between ESW and biota. Most studies are limited to the dissolution reactions, removal of weathering products, abiotic CO 2 drawdown (e.g., Rinder & von Hagke, 2021;Strefler et al, 2018), and impact on soil hydrology ( de Oliveira Garcia et al, 2020). Nonetheless, first models are emerging which include interactions between biota and weathering rates.…”