THE ROLE OF HYDROLOGICAL PROCESSES ON ENHANCED WEATHERING FOR CARBON SEQUESTRATION IN AGRICULTURAL SOILS

Abstract

With the aim to face climate change, some NCS (Natural Climate Solutions) are currently studied given their capability to sequester carbon from the atmospheric CO2, by means of some natural processes, and to store it within oceans, plants, soil, or other terrestrial environments. Among all the existing NCS, Enhanced Weathering (EW) acts in speeding up the chemical weathering that naturally occurs in soils. This is achieved by amending soils with crushed highly reactive silicate minerals, such as forsterite, better known as olivine. In general, EW reactions are faster at high temperature and soil water content and low soil pH, demonstrating that the most suitable places in the world to apply this technique are those characterized by hot and humid climates. Vegetation has a positive effect for EW reactions, given its acidifying action on soil water, due to the displacement of H+ ions consequent to the uptake of cations used as nutrients (i.e., Mg2+, Ca2+ and K+). Furthermore, it has been demonstrated that olivine dissolution leads to the increase of the above-listed nutrients concentration in soil water, resulting in a fertilizing effect for plants. For these reasons, various studies affirm that it may be realistic to apply EW technique in forested or cultivated areas, but only after reliably quantifying its carbon sequestration rate and other beneficial/detrimental effects. This study presents a dynamic mass balance model that explores ecohydrological, biogeochemical and olivine dissolution dynamics. The model allows to explore the role of hydrological processes on long term olivine dissolution and, therefore, to compute carbon sequestration and the increase of nutrients in soil water upon olivine dissolution. The model is composed of different interconnected components and the resulting scheme consists of an explicit system of eight mass balance total differential equations and an implicit part with 22 algebraic equations in as many unknown variables. The main purpose of the present study is to apply the model to two different sites in Italy (i.e., Sicily, in the south and the Padan plain, in the north) and two other sites in the USA (i.e., California, in the south-west and Iowa, in the north-central area). Furthermore, crops that are very common and occupy a huge area in correspondence of the considered sites, namely the wheat crop for Sicily and California and the corn crop for Padan plain and Iowa, are here taken into account. This allows to explore the EW dynamics under different climate conditions and crop and soil types, with the aim to assess the importance of such factors in the EW application. This study could be helpful for decision makers to identify which parts of the globe, among those presented, are more suitable for amending soil with olivine, in perspective to put EW into practice.