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 (bro wn earth, micropodzol, and peaty gley), under different climatic conditions , was investigated. Cores of undisturbed soil, taken from near the summit o f Great Dun Fell (Cumbria, U.K.), were maintained at the summit (site A), a nd at three lower-altitude sites (B, C, and D) with higher mean temperature s and lower rainfall, for three years. Some cores at site A were heated, wh ile some at site C received supplementary rain inputs. Leachate concentrati ons 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 add itional DOM was similar to that leached at site A, as judged by the hydroph ilic/hydrophobic ratio and optical absorbance. Additional input water at si te C significantly increased export from the brown earth and micropodzol. E xports were unaffected by heating at site A. It is concluded that warming a nd drying can accelerate the production of potential DOM within organic hor izons, and that leaching is influenced by the adsorption of DOM in mineral horizons. (C) 1999 Elsevier Science Ltd.