Soil and soil solution chemical composition at three sites within the Loch Dee catchment, SW Scotland

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Abstract
SUMMARY: Soil solution chemical composition was monitored over a 2–year period at three plots near the edge of an igneous intrusion in SW Scotland. Soil solutions were all strongly acidic with mean pH of approximately 4.0 at 0.20 m depth and 4.5 at 0.60 m. Chemical composition of the deeper soil solutions varied with geology. Greatest acidity and aluminium concentrations were found over metamorphosed Ordovician sedimentary rocks, with mean pH of 4.3 and A1 concentration of 22 mmol m−3 at 0.60 m. At a site on similar rocks nearer the intrusion, mean pH at 0.60 m was 4.8, with very low A1 (3 mmol m−3) and correspondingly greater Ca. At a peaty site on igneous rocks, increased pH with depth was associated with no change in base cations and A1 but a reduction in mean SO, from 41 mmolm−3 at 0.20m to 10mmol m−3 at 0.60m. Ion‐exchange selectivity coefficients calculated from soil and solution chemistry differed slightly from currently used values for peaty upland soils, with larger coefficients for A1/K exchange and smaller coefficients for A1/Ca and A1/Mg exchange. Relations between A1 and H ion concentrations confirmed under‐saturation of solutions with respect to gibbsite at 0.20 m. The differences between plots were consistent in different seasons, despite significant seasonal variability in Na, C1, dissolved organic carbon and Fe.

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