Impacts of enhanced rock weathering on soil sponge function: a global synthesis of soil physical and hydrological responses

Enhanced rock weathering (ERW) involves the application of finely ground silicate minerals to soils, where mineral dissolution can alter soil chemistry, structure, and hydrological functioning. While ERW research has largely focused on geochemical CO2 removal, its effects on soil physical and hydrological properties remain poorly constrained. Here, we present the first structured evidence synthesis evaluating whether ERW modifies components of the soil sponge function, defined as the capacity of soils to infiltrate, store, redistribute, and gradually release water. A systematic literature search identified 17 studies comprising 261 treatment–control observations. Relative changes were calculated for key soil physical and hydrological variables and classified as increase, decrease, or no change using a ± 5% threshold. Given the heterogeneity of experimental designs and non-independence of observations within studies, results were interpreted descriptively and primarily at the study level. ERW effects were variable across soil properties. Bulk density had no median response (0.0%; n = 72 observations from 10 studies), while aggregate stability had a weak positive response (+1.9%; n = 35 from 6 studies). Penetration resistance declined (−18.1%), but this response was based on one study only. Soil water indicators provided modest evidence for increased storage capacity, with positive responses in field capacity (+9.4%; n = 23 from 5 studies) and plant available water (+10.1%; n = 15 from 3 studies), but only a small increase in soil moisture (+4.4%; n = 21 from 4 studies). Hydraulic responses were mixed: saturated hydraulic conductivity declined (−27.5%; n = 10 from 2 studies), porosity declined (−6.3%; n = 34 from 7 studies), and infiltration rate had no median response (0.0%; n = 13 from 3 studies). Overall, available data suggest that ERW does not uniformly enhance the soil sponge function; its effects are context-dependent, and the apparent contrast between increased water-storage indicators and reduced flow-related properties may reflect differences among study contexts because these variables were not consistently co-measured within the same experiments.