Silicate Weathering Dynamics in the Kasaï Basin and Implications for Enhanced Rock Weathering Applications in the Tropics

Yi Hou , Lissie W de Groot, Travis Drake, José Nlandu Wabakanghanzi, Alfred Ludjwera Bahati, Marijn Bauters, Chris Seitz, Antoine de Clippele, Johan Six, Kristof Van Oost, Jordon D Hemingway

Silicate weathering is one of the ultimate geologic sinks of atmospheric CO2. Enhanced rock weathering (ERW), aiming at accelerating this natural process to mitigate anthropogenic warming, has received significant attention due to high projected CO2 removal potential and possible agricultural co-benefits applications in the tropics. Yet, the natural baseline of chemical weathering in low-relief, tropical landscapes, especially central Africa, remains poorly characterized. Here, we systematically sampled river and suspended sediments in the Kasaï Basin, the largest tributary of the Congo River. We constrained chemical weathering dynamics with river solute data and other hydro-chemical/physical observations. We show that organic acids contribute substantially to the alkalinity budget, and, through a mass-balance model, we demonstrate that dry deposition and canopy exchange processes are important solute sources in Kasaï rivers and can bias silicate weathering flux estimates. These complications point to particular challenges in quantifying carbon sequestered through ERW applications in tropical Africa.