Hydrochemical Fluxes and their Effects on Stream Acidity in Two Forested Catchments in Central Scotland

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Abstract
The hydrochemical fluxes and budgets have been determined for two forested catchments, including inputs, tree throughfall and stemflow, soil water throughflow and output streams. The major vegetational induced differences are the enrichment of sodium, chloride, sulphate and particularly hydrogen by Sitka spruce compared to Norway spruce. These increased concentrations are primarily due to vegetation interception along with crown leaching, both of which contribute to sulphate enhancement. Soil throughflow and consequent stream chemistries reflect these species effects with additional enrichment both due to geological weathering of base cations as well as possible desorption or mineralization processes. Norway spruce vegetation and the associated podzolic soils show no net stream acidification (pH 4.61) of inputs (pH 4.65), whereas Sitka spruce on gleyed soils show considerable stream acidification (pH 4.02) compared with similar inputs (pH 4.50). Both streams have similar sulphate concentrations, but this important mobile anion is associated primarily with hydrogen in the Sitka spruce dominated Kelty catchment whereas at Chon it is associated with base cations as well as hydrogen.