CO2 Sequestration and Ion Transport from Enhanced Rock Weathering at a Northern California Cropland Site

Abstract:

Field-level quantification of carbon (C) sequestration from enhanced rock weathering (ERW) must be robust to assess this technology’s potential in agricultural systems or as a tool in C offset programs. Moreover, determining the fate of weathered ions from ERW, particularly if they are lost through runoff or percolation, is essential to evaluating the potential of ERW as a nutrient source for crops. Operating under the umbrella of the Working Lands Innovation Center, I investigate the proportion of soil C stored via ERW that occurs as bicarbonate or carbonate production in a corn cropping system and the fraction of weathered ions that is lost to leaching. The five-acre Northern California field site is characterized by circumneutral pH and young soils (Xerofluvents) and is currently planted with conventionally managed, drip-irrigated corn. Tension-controlled lysimeters were installed in plots amended with meta-basalt alone and a meta-basalt and olivine mix, as well as in unamended plots. Alkalinity titrations plus elemental analysis of leachate are used to track carbonate and bicarbonate production, as well as the release of other ERW-derived ions into the system. These measurements, coupled with analyses of inorganic soil C, soil base saturation and exchange complex ions, and plant nutrient content, allow for detailed accounting of weathered ion fluxes and C sequestration associated with the rock-amended plots. Here, preliminary results are discussed, and next steps are proposed to better quantify ERW potential in the field.