The role of hydrology on enhanced weathering for carbon sequestration II. From hydroclimatic scenarios to carbon-sequestration efficiencies

Effects of precipitation seasonality, irrigation, vegetation cycle and soil type on enhanced weathering – modeling of cropland case studies across four sites

“…The rates of carbon sequestration presented in Beerling et al (2020) at the global scale are about 3 orders of magnitude higher than those achieved in this study. However, these are derived using a one-dimensional vertical reactive transport model that considers the CO 2 captured by EW as the dissolved inorganic carbon due to the weathering reaction (apart from the CO 2 emissions due to logistic operation), which is similar to the one that we called CO 2,sw in Cipolla et al (2021b), which represents the amount of extra bi(carbonate) anions dissolved in soil water due to olivine weathering. In effect, even in our previous work we obtained about a 3-order-of-magnitude difference between the CO 2,sw and the CO 2 leached, but we believe that the latter is better connected to the actual sequestered CO 2 , given that some HCO − 3 and CO 2− 3 dissolved in soil water due to olivine dissolution may react with H + forming the carbonic acid, thus potentially releasing CO 2 back to the atmosphere.…”

“…For these areas, the most common crops according to the USDA crop production maps (https://ipad.fas.usda.gov/rssiws/al/global_ cropprod.aspx, last access: 29 July 2022), namely the wheat for Sicily and California and the corn for the Padan plain and Iowa, are considered. As in Cipolla et al (2021b), all simulations are related to a unit ground area of homogeneous soil, vegetation and rainfall characteristics, vertically delimited by the active root zone depth of the involved crop, i.e., 40 and 60 cm for the corn and wheat, respectively (Fan et al, 2016).…”

“…Irrigation, applied here only during the summer season for corn planted in Sicily and California, leads to a decrease in soil pH and a faster olivine dissolution. Larger MAP differences would likely result in bigger changes of EW dynamics (Cipolla et al, 2021b), emphasizing the effect of rainfall seasonality and climatic conditions on olivine dissolution and EW.…”

“…12. This is calculated, as in Cipolla et al (2021b), as the leaching of the extra HCO − 3 and CO 2− 3 produced by olivine dissolution, considering a time window of 10 years after olivine amendment. In particular, for each time step, the loss of HCO − 3 and CO 2− 3 to groundwater is derived by the product of the leaching rate and the concentration of these ions in soil water, taking into account only the extra amount produced by the weathering reaction.…”

“…Many of the model parameters are obtained from measurements (i.e., pH and cation exchange), and achieved weathering rates are then compared with those of Amann et al (2020), which is currently one of the experiments closest to field conditions. Extending the work of Cipolla et al (2021b), where the influence of statistically stationary precipitation with different mean annual precipitation (MAP) on EW is analyzed, in this study we focus on the effect of the seasonal variation of the meteorological forcing, irrigation, soil type and crop cycle on EW dynamics. These four regions are characterized by very similar MAP values but much different rainfall seasonality.…”