Abstract
Abstract. Silicate mineral dissolution rates depend on the interaction of a number of factors categorized either as intrinsic (e.g. mineral surface area, mineral composition) or extrinsic (e.g. climate, hydrology, biological factors, physical weathering). Estimating the integrated effect of these factors on the silicate mineral dissolution rates therefore necessitates the use of fully mechanistic soil evolution models. This study applies a mechanistic soil evolution model (SoilGen) to explore the sensitivity of silicate mineral dissolution rates to the integrated effect of other soil-forming processes and factors. The SoilGen soil evolution model is a 1-D model developed to simulate the time-depth evolution of soil properties as a function of various soil-forming processes (e.g. water, heat and solute transport, chemical and physical weathering, clay migration, nutrient cycling, and bioturbation) driven by soil-forming factors (i.e., climate, organisms, relief, parent material). Results from this study show that although soil solution chemistry (pH) plays a dominant role in determining the silicate mineral dissolution rates, all processes that directly or indirectly influence the soil solution composition play an equally important role in driving silicate mineral dissolution rates. Model results demonstrated a decrease of silicate mineral dissolution rates with time, an obvious effect of texture and an indirect but substantial effect of physical weathering on silicate mineral dissolution rates. Results further indicated that clay migration and plant nutrient recycling processes influence the pH and thus the silicate mineral dissolution rates. Our silicate mineral dissolution rates results fall between field and laboratory rates but were rather high and more close to the laboratory rates possibly due to the assumption of far from equilibrium reaction used in our dissolution rate mechanism. There is therefore a need to include secondary mineral precipitation mechanism in our formulation. In addition, there is a need for a more detailed study that is specific to field sites with detailed measurements of silicate mineral dissolution rates, climate, hydrology, and mineralogy to enable the calibration and validation of the model. Nevertheless, this study is another important step to demonstrate the critical need to couple different soil-forming processes with chemical weathering in order to explain differences observed between laboratory and field measured silicate mineral dissolution rates.
Highlights
Silicate mineral weathering is the major source of most plant nutrients in soils (Carey et al, 2005; Hartmann et al, 2014), and it is probably the foremost process controlling soil production rates (Anderson et al, 2007; Dixon and von Blanckenburg, 2012)
Silicate mineral dissolution rates depend on the interaction of a number of factors categorized either as intrinsic or extrinsic
Estimating the integrated effect of these factors on the silicate mineral dissolution rates necessitates the use of fully mechanistic soil evolution models
Summary
Silicate mineral weathering is the major source of most plant nutrients in soils (Carey et al, 2005; Hartmann et al, 2014), and it is probably the foremost process controlling soil production rates (Anderson et al, 2007; Dixon and von Blanckenburg, 2012). There is a need for mechanistic models capable of simulating the integrated effect of physical, biological, and chemical soil-forming processes on chemical weathering rates Such coupling will give the possibilities to determine the role played by intrinsic and extrinsic factors and explain the differences in dissolution rates observed in the laboratory and field experiments (Goddéris et al, 2006; Hartmann et al, 2014; Moore et al, 2012). A constant grain size distribution has been assumed when estimating weathering rates; this assumption could be invalid especially when looking at longer timescales This contribution applies a SoilGen model (a model that simulates evolution of soil properties as a function of several interactive soil-forming processes including water flow, chemical weathering, physical weathering, carbon-cycling, cation exchange, clay migration, nutrient uptake by plants, bioturbation, and leaching) to evaluate the sensitivity of silicate mineral dissolution rates to other soil-forming processes. Specific objectives are to (i) assess the effects of parent material composition on the silicate mineral dissolution rates, (ii) assess sensitivity of chemical silicate mineral dissolution rates to change in soil texture, (iii) assess the effect of physical weathering of primary minerals on their dissolution rates, (iv) assess the effect of interactive soil-forming processes on silicate mineral dissolution rates, and (v) compare our modelled silicate mineral dissolution rates to rates reported in literature
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