Solid phase evolution in the Biosphere 2 hillslope experiment as predicted by modeling of hydrologic and geochemical fluxes

摘要

A reactive transport geochemical modeling study was conducted to helppredict the mineral transformations occurring over a ten year time-scalethat are expected to impact soil hydraulic properties in the Biosphere 2(B2) synthetic hillslope experiment. The modeling sought to predict the rateand extent of weathering of a granular basalt (selected for hillslopeconstruction) as a function of climatic drivers, and to assess the feedbackeffects of such weathering processes on the hydraulic properties of thehillslope. Flow vectors were imported from HYDRUS into a reactive transportcode, CrunchFlow2007, which was then used to model mineral weatheringcoupled to reactive solute transport. Associated particle size evolution wastranslated into changes in saturated hydraulic conductivity using Rosettasoftware. We found that flow characteristics, including velocity andsaturation, strongly influenced the predicted extent of incongruent mineralweathering and neo-phase precipitation on the hillslope. Results were alsohighly sensitive to specific surface areas of the soil media, consistentwith surface reaction controls on dissolution. Effects of fluid flow onweathering resulted in significant differences in the prediction of soilparticle size distributions, which should feedback to alter hillslopehydraulic conductivities.