Quantifying the impact of CO2 transport and transient hydrological flow on basalt weathering at the Biosphere 2 Landscape Evolution Observatory
Jianwen Du1, Bo Guo1, Guo-Yue Niu1, Katerina Dontsova2,3, Peter A. Troch1,3, Jon Chorover2,3
1Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA
2Department of Environmental Science, University of Arizona, Tucson, AZ, USA
3Biosphere 2, University of Arizona, Tucson, AZ, USA
Transient hydrological flow and the transport of gases play important roles in controlling soil formation in the critical zone. In the present work, we apply a two-dimensional reactive transport model (RTM) to simulate basalt weathering at Biosphere 2 Landscape Evolution Observatory for one mini zeroth-order replicated artificial hillslope (having 1 m2 area and a 1 m deep crushed basalt soil). The RTM accounts for transient variably saturated flow, transport of aqueous species and gases, and mineral-water reactions including precipitation and dissolution. We constrain and calibrate the RTM using high-resolution temporal and spatial observations of water discharge rates, outflow water chemistry, soil moisture, and porewater chemistry. The model simulations and comparisons with outflow water chemistry and other datasets allow us to identify the dominant processes controlling chemical weathering under different conditions. Our results suggest that transient hydrological flow and CO2 transport both enhance the spatial heterogeneity of mineral dissolution and precipitation. The heterogeneity of mineral species distributions further influences the flow path and residence time of soil water and subsequently affects reactions. Overall, the present work considering both the transient hydrological flow and CO2 transport in modeling chemical weathering provides a reliable tool for analyzing and quantifying basalt weathering.