Climatic influences on the leaching of dissolved organic matter from upland UK Moorland soils, investigated by a field manipulation experiment

The leaching of dissolved organic matter (DOM) from three acidic soils (brown earth, micropodzol, and peaty gley), under different climatic conditions, was investigated. Cores of undisturbed soil, taken from near the summit of Great Dun Fell (Cumbria, U.K.), were maintained at the summit (site A), and at three lower-altitude sites (B, C, and D) with higher mean temperatures and lower rainfall, for three years. Some cores at site A were heated, while some at site C received supplementary rain inputs. Leachate concentrations of dissolved organic carbon (DOC) increased in the order micropodzol < brown earth << peaty gley. Concentrations were highest in summer and autumn, and at the warmer, drier sites. Exported loads of DOC from the peaty gley at sites B, C, and D were approximately double that at site A, but the additional DOM was similar to that leached at site A, as judged by the hydrophilic/hydrophobic ratio and optical absorbance. Additional input water at site C significantly increased export from the brown earth and micropodzol. Exports were unaffected by heating at site A. It is concluded that warming and drying can accelerate the production of potential DOM within organic horizons, and that leaching is influenced by the adsorption of DOM in mineral horizons. (C) 1999 Elsevier Science Ltd.