Stephens & Hering(2004)による〔『Factors affecting the dissolution kinetics of volcanic ash soils: dependencies on pH, CO2, and oxalate』（1217p）から〕

『火山灰土壌の溶解カイネティックスに影響を与える要因：pH、CO2、およびシュウ酸に対する依存性』

『Abstract
　Laboratory experiments were conducted with volcanic ash soils from Mammoth Mountain, California to examine the dependence of soil dissolution rates on pH and CO2 (in batch experiments) are on oxalate (in flow-through experiments). In all experiments, an initial period of rapid dissolution was observed followed by steady-state dissolution. A decrease in the specific surface area of the soil samples, ranging from 59％ to 80％, was observed; this decrease occurred during the period of rapid, initial dissolution. Steady-state dissolution rates, normalized to specific surface areas determined at the conclusion of the batch experiments, ranged from 0.03μmol Si m-2 h-1 at pH 2.78 in the batch experiments to 0.009μmol Si m-2 h-1 at pH 4 in the flow-through experiments. Over the pH range of 2.78-4.0, the dissolution rates exhibited a fractional order dependence on pH of 0.47 for rates determined from H+ consumption data and 0.27 for rates determined from Si release data. Experiments at ambient and 1 atm CO2 demonstrated that dissolution rates were independent of CO2 within experimental error at both pH 2.78 and 4.0. Dissolution at pH 4.0 was enhanced by addition of 1 mM oxalate. These observations provide insight into how the rates of soil weathering may be changing in areas on the flanks of Mammoth Mountain where concentrations of soil CO2 have been elevated over the last decade. This release of magmatic CO2 has depressed the soil pH and killed all vegetation (thus possibly changing the organic acid composition). These indirect effects of CO2 may be enhancing the weathering of these volcanic ash soils but a strong direct effect of CO2 can be excluded.』

1. Introduction
2. Materials and methods
　2.1. The volcanic ash soils of Mammoth Mountain
　2.2. Experimental
　　2.2.1. pH-stat batch experiments
　　2.2.2. Flow-through experiments
　2.3. Oxalate adsorption methods
3. Results and discussion
　3.1. Determination of weathering rates in batch reactors
　3.2. Decrease in specific surface area
　3.3. Comparison of dissolution rates
　3.4. pH dependence
　3.5. Lack of dependence on CO2
　3.6. Dependence on oxalate
　3.7. Surface concentration of oxalate
　3.8. Comparison of rates in batch and flow-through reactors
　3.9. Implications for weathering of Mammoth Mountain soils
4. Conclusions
Acknowledgements
References

戻る