Increased carbon capture by a silicate-treated forested watershed affected by acid deposition

Abstract. Meeting internationally agreed-upon climate targets requires carbon dioxide removal (CDR) strategies coupled with an urgent phase-down of fossil fuel emissions. However, the efficacy and wider impacts of CDR are poorly understood. Enhanced rock weathering (ERW) is a land-based CDR strategy requiring large-scale field trials. Here we show that a low 3.44 t ha⁻¹ wollastonite treatment in an 11.8 ha acid-rain-impacted forested watershed in New Hampshire, USA, led to cumulative carbon capture by carbonic acid weathering of 0.025–0.13 t CO₂ ha⁻¹ over 15 years. Despite a 0.8–2.4 t CO₂ ha⁻¹ logistical carbon penalty from mining, grinding, transportation, and spreading, by 2015 weathering together with increased forest productivity led to net CDR of 8.5–11.5 t CO₂ ha⁻¹. Our results demonstrate that ERW may be an effective, scalable CDR strategy for acid-impacted forests but at large scales requires sustainable sources of silicate rock dust.

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