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

Abstract

Abstract. Enhanced weathering (EW) is a promising strategy for carbon sequestration, but several open questions remain regarding the actual rates of dissolution in conditions of natural hydroclimatic variability in comparison to laboratory experiments. In this context, models play a pivotal role, as they allow exploring and predicting EW dynamics under different environmental conditions. Here a comprehensive hydro-biogeochemical model has been applied to four cropland case studies (i.e., Sicily and the Padan plain in Italy and California and Iowa in the USA) characterized by different rainfall seasonality, vegetation (i.e., wheat for Sicily and California and corn for the Padan plain and Iowa), and soil type to explore their influence on dissolution rates. The results reveal that rainfall seasonality and irrigation when applied are crucial in determining EW and carbon sequestration dynamics, given their effect on hydrological fluxes, soil pH and weathering rate. The carbon sequestration rate was found to be strongly affected also by the background weathering flux, which is one of the main factors controlling soil pH before the olivine amendment. Regarding the US case studies, Iowa sequesters the greatest amount of CO2 if compared to California (4.20 and 2.21 kg ha−1 yr−1, respectively), and the same happens for Sicily with respect to the Padan plain (0.62 and 0.39 kg ha−1 yr−1, respectively). These low carbon sequestration values suggest that an in-depth analysis at the global scale is required to assess EW efficacy for carbon sequestration.

Nano- to Global-Scale Uncertainties in Terrestrial Enhanced Weathering

“…For EW in croplands, a previous analysis suggests that irrigation may be an important factor affecting EW effectiveness. 54 Especially in arid and semiarid regions, the additional water input during the crop-growing season can bring the weathering rate to levels typical of wetter regions (with a lower dryness index). This is illustrated in Figure 2B, where the specific weathering rate clearly increases with irrigation, particularly for a higher dryness index, while the effect of irrigation is negligible in already wet climates.…”

“…For EW in croplands, a previous analysis suggests that irrigation may be an important factor affecting EW effectiveness . Especially in arid and semiarid regions, the additional water input during the crop-growing season can bring the weathering rate to levels typical of wetter regions (with a lower dryness index).…”

“…However, precisely predicting the efficiency of EW (i.e., the rate of atmospheric CO 2 consumption by weathering reactions) and determining a suitable soil amendment (e.g., type of silicate material, application amount and frequency) requires accurate enhanced weathering models. Current modeling approaches to estimate EW CO 2 removal potential vary from simple expressions dependent only on mineral surface area to more complex reactive transport , and ecohydrological ,, models fully integrating environmental conditions. Yet, their estimated rates all rely on a formalism based on results of experiments conducted under controlled laboratory conditions .…”

Constraining the Capacity of Global Croplands to CO2 Drawdown via Mineral Weathering

“…The silicate dissolution reaction (eq ) is the weathering rate-limiting step controlled by reaction kinetics and mass transport, whereas the carbonate precipitation/dissolution reactions are thermodynamically controlled . The release of Ca and Mg from the silicate minerals in soil depends on the weathering/dissolution rate, which in turn, depends on several parameters, including temperature and soil pH . With the aim of further acceleration of the weathering rate, the specific surface area of the mineral, directly related to particle size, is also critical. , In our previous work, the weathering rate of silicate minerals was used to assess the CO 2 sequestration potential of alkaline minerals applied to agricultural soils using an idealized shrinking core model.…”

The environmental controls on efficiency of enhanced rock weathering in soils

“…While existing dedicated experiments on enhanced rock weathering in soils are few, and more (laboratory and field) experiments are needed to uncover the mechanisms underlying in situ weathering rates, reactive transport modeling provides a valuable tool to complement experimental studies 5 , 28 . It has the advantages of expanding the spatial scales and extending beyond the duration of current experimental investigations which are typically carried out on monthly time scales, and thus to better inform field studies and engineering practices.…”