Inorganic sulphate extraction from SO2-impacted andosols
(2005) European Journal of Soil Science — Vol. 56, n° 1, p. 127-133 (2005)
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- Sulphate sorption on to the surface of short-range ordered minerals and precipitation of Al-hydroxy sulphate contribute to the acid neutralizing capacity of soils. The correct measurement of total inorganic sulphate is thus essential in soils that are accumulating SO42- anions. We extracted SO42- by various solutions, namely 0.005M Ca(NO3)(2), 0.016M KH2PO4, 0.5M NH4F and 0.2M acidic NH4-oxalate ( pH 3), from Vitric and Eutric Andosols exposed to prolonged deposition of acid and SO2 from an active volcano ( Masaya, Nicaragua). We attributed sulphate extractable by KH2PO4 (20 - 3030 mg kg(-1)) to anion-exchangeable SO42-, which was much smaller than NH4F- and oxalate- extractable SO42- (400 - 9680 and 410 - 10 480 mg kg(-1), respectively). Our results suggest the occurrence of a sparingly soluble Al-hydroxy-mineral phase extractable by both NH4F and oxalate. The formation of Al-hydroxy minerals would result from the combination of enhanced weathering caused by strong acid loading and simultaneous occurrence of large SO42- concentrations in soil solution. Oxalate extracted slightly more inorganic SO42- than did NH4F, this additional amount of SO42- correlating strongly with oxalate- extractable Si and Fe contents. Preferential occlusion of SO42- by short-range ordered minerals, especially ferrihydrite, explains this behaviour. If we exclude the contribution of occluded sulphate then oxalate and NH4F mobilize similar amounts of SO42- and are believed to mobilize all of the inorganic SO42- pool.
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Delfosse, T., Delmelle, P., Givron, C., & Delvaux, B. (2005). Inorganic sulphate extraction from SO2-impacted andosols. European Journal of Soil Science, 56(1), 127-133. https://doi.org/10.1111/j.1365-2389.2004.00647.x (Original work published 2005)