Evaluating sensitivity of silicate mineral dissolution rates to physical weathering using a soil evolution model (SoilGen2.25)

[摘要] Silicate mineral dissolution rates depend on the interaction of a number offactors categorized either as intrinsic (e.g. mineral surface area, mineralcomposition) or extrinsic (e.g. climate, hydrology, biological factors,physical weathering). Estimating the integrated effect of these factors onthe silicate mineral dissolution rates therefore necessitates the use offully mechanistic soil evolution models. This study applies a mechanisticsoil evolution model (SoilGen) to explore the sensitivity of silicatemineral dissolution rates to the integrated effect of other soil-formingprocesses and factors. The SoilGen soil evolution model is a 1-D modeldeveloped to simulate the time-depth evolution of soil properties as afunction of various soil-forming processes (e.g. water, heat and solutetransport, chemical and physical weathering, clay migration, nutrientcycling, and bioturbation) driven by soil-forming factors (i.e., climate,organisms, relief, parent material). Results from this study show thatalthough soil solution chemistry (pH) plays a dominant role in determiningthe silicate mineral dissolution rates, all processes that directly orindirectly influence the soil solution composition play an equally importantrole in driving silicate mineral dissolution rates. Model resultsdemonstrated a decrease of silicate mineral dissolution rates with time, anobvious effect of texture and an indirect but substantial effect of physicalweathering on silicate mineral dissolution rates. Results further indicatedthat clay migration and plant nutrient recycling processes influence the pHand thus the silicate mineral dissolution rates. Our silicate mineraldissolution rates results fall between field and laboratory rates but wererather high and more close to the laboratory rates possibly due to the assumptionof far from equilibrium reaction used in our dissolution rate mechanism.There is therefore a need to include secondary mineral precipitation mechanismin our formulation. In addition, there is a need for a more detailed studythat is specific to field sites with detailed measurements of silicatemineral dissolution rates, climate, hydrology, and mineralogy to enable thecalibration and validation of the model. Nevertheless, this study is anotherimportant step to demonstrate the critical need to couple different soil-forming processes with chemical weathering in order to explain differencesobserved between laboratory and field measured silicate mineral dissolutionrates.

[学科分类] 地球化学与岩石