The role of hydrology on enhanced weathering for carbon sequestration in soils

Natural climate solutions are attracting considerable research effort with the aim of reducing greenhouse gas emissions or sequestering carbon within the oceans or terrestrial environments. In this context, enhanced weathering can be a powerful means of increasing the natural weathering reaction rates, by adding some highly reactive minerals to the soil. The present study evaluates the effects of hydrologic fluctuations on Forsterite dissolution, a silicate mineral also known as Mg-olivine. This mineral is available in many parts of the world and its reaction rates with CO2 are much higher than those of other minerals. Toward this goal, we developed a mathematical model coupling biogeochemical and ecohydrological aspects of a soil treated with olivine. The model can be forced with a stochastic rainfall, in order to understand the role of hydrological processes on long-term enhanced weathering dynamics. The results under different climate scenarios quantify the dependence of weathering rates on wetness. High soil water contents are linked to higher reactive surface area and lower pH levels, resulting in higher dissolution rates. The weathering rate shows a hysteretic behavior with respect to soil moisture since its variability does not immediately lead to a change in weathering rate. Plants play a relevant role in this context since they may further increase the weathering rate by releasing H+ ions in soil water. In addition, we explore the twofold role of organic matter on enhanced weathering; while its decomposition is a source of CO2, organic matter also increases the soil CEC, thus buffering changes in soil pH. In conclusion, by shedding light on the interaction between olivine dissolution and ecohydrological processes, this study paves the way for the inclusion of enhanced weathering in agroecosystem management practices.