Reactive Transport Modeling Of Basalt Weathering And Early Soil Formation Within A Highly-Controlled, Sloping Lysimeter
Presenter: Jianwen Du1
Co-Author(s): -
Advisor(s): Dr. Bo Guo
1Department of Hydrology and Atmospheric Sciences, University of Arizona
Understanding and quantifying the feedback among chemical weathering, soil formation, and hydrological processes in the subsurface is critical for predicting how landscapes respond to climate change. In the present work, we employ a transient two-dimensional reactive transport model to simulate hydrogeochemical processes for basalt weathering in a highly-controlled sloping lysimeter at Biosphere 2 in Tucson, AZ, USA. Hydrographs and discharge water chemistry measured over one period were used to calibrate the reactive transport model, while data from another two experimental periods were used for model evaluation. The comparison between modeled results and measurements shows that, though there are some discrepancies in the local patterns of porewater chemistry, the simulations have captured the dynamic changes of water chemistry in the outflow. The model predictions and additional numerical experiments reveal that the basalt glass dissolution was fast and homogeneous resulting from its far-away-from-equilibrium state, while the precipitation of secondary minerals was relatively heterogeneous and varied with rainfall intensity. In addition, the transients of rainfall infiltration had a minimal impact on the reaction of basalt glass, iron oxidation and manganese oxidation, but strongly affected the precipitation rates of minerals that are transport-controlled, especially calcite and hydroxyapatite and proto-imogolite allophane. Overall, the present work demonstrates that transient hydrological processes and reaction kinetics strongly control basalt glass weathering during early soil formation.