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Elsevier, Geoderma, (237-238), p. 21-35, 2015

DOI: 10.1016/j.geoderma.2014.08.004

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The surface area and reactivity of granitic soils: I. Dissolution rates of primary minerals as a function of depth and age deduced from field observations

Journal article published in 2015 by Sa Parry ORCID, Me Hodson ORCID, Sj Kemp, Eh Oelkers
This paper is available in a repository.
This paper is available in a repository.

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Abstract

Surface area-normalised dissolution rates of the primary minerals in two distinct granitic soils located in 1) the Dartmoor National Park, England and 2) Glen Dye, Scotland were determined as a function of depth. Each soil was sampled to a depth of ~ 1 m. The maximum soil ages based on 14 C analysis of the humin fraction of the soil are 15,600 and 4400 years for the Dartmoor and Glen Dye soil profiles, respectively. The measured BET sur-face areas of the soil minerals are close to 5 m 2 /g in the B and C horizons, but decrease to less than 1 m 2 /g close to the surface. Retrieved geometric surface area normalised mineral dissolution rates are most rapid at the surface and at the bedrock–soil interface; this behaviour is interpreted to stem from a combination of the approach to equilibrium of the soil waters with depth and more rapid dissolution rates of fresh versus weathered surfaces. At the soil surface, the relative mineral dissolution rate order is found to be quartz N feldspar N mica, with quartz geometric surface area dissolution rates as fast as 2.6 to 4.1 × 10 −13 mol/m 2 /s. As observed in a number of past studies, field based rates obtained in this study are significantly slower than corresponding rates obtained from laboratory studies, suggesting that these latter rates may not accurately describe the reactivity of primary min-erals in soils. © 2014 Published by Elsevier B.V.