Effects of Enhanced Rock Weathering (ERW) on primary productivity and evapotranspiration rates estimated via satellite remote sensing

Enhanced Rock Weathering (ERW) holds significant potential to achieve substantial, durable carbon storage at a global scale. As ERW continues to grow as a commercially deployed carbon dioxide removal technology, there is a critical need to identify and quantitatively assess its effects on ecosystem processes beyond measures of carbon storage. Previous studies have examined the effects of ERW on soil, plants, and animals; however, few studies have explored potential effects on the water cycle. In particular, observations that the application of crushed rocks may increase plant biomass raise important questions as to whether there is a concomitant increase in plant water use, which would alter ecosystem water balance.  

We compared primary productivity and evapotranspiration between control and treatment plots in two independent trials where crushed rock (basalt) was applied for enhanced rock weathering. The trials comprise 4 different crop combinations (miscanthus, maize, soybean/corn, and hay) totaling 59 plots with an average size of ~2 ha. Basalt was applied at a rate of 44.8 t ha^-1in one trial and 50 t ha^-1in the second trial. We used the Normalized Difference Vegetation Index (NDVI) from Sentinel-2 as one measure of productivity and estimates of gross primary productivity and evapotranspiration were obtained from NASA’s ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS). 

Both trials found evidence for significant increases in grain yield in plots where crushed rock was applied, although we found no significant differences in NDVI or GPP between control and treatment plots over the course of the time series. Notably, we found no significant differences in evapotranspiration between control and treatment plots, even when specifically comparing times where peak biomass would be expected to lead to peak water use. Crops followed typical seasonal patterns of productivity and water use, indicating the utility of high-resolution satellite remote sensing for monitoring ERW.  

A change in evapotranspiration associated with ERW deployment would have important implications for ecosystem water balance in these commercial agricultural systems, as well as for the water available for exporting dissolved inorganic carbon from the system. We find no evidence for a change in evapotranspiration. Our results serve as the foundation for studying how ERW may affect different parts of the terrestrial water cycle.