Hydrochemical input-output budgets for a clean rain and drought experiment at Solling

In order to evaluate the response of an acidified forest ecosystem to reduced atmospheric deposition and seasonally limited water supply, hydrochemical fluxes were estimated for the roof experiments at Selling, Germany. The experiments were carried out in a 58 year-old spruce (Picea abies (L.) Karst.) plantation from 1990 to 1994. Clean rain was applied to the soil surface by reducing the nitrogen, sulphur and proton inputs to 67%, 56% and 74% of the loads in ambient throughfall. The drought/rewetting experiment was carried out by artificially modifying weather extremes of drought and rewetting events. Hydrochemical input-output budgets, based on element fluxes in throughfall and in soil seepage water, have been established for major elements. Results show that on this highly acidified soil, atmospheric deposition widely influenced element fluxes in the soil seepage water. Consequently, hydrochemical budgets altered when inputs of acidity and nitrogen were reduced. After one year of the clean rain treatment nitrate output was considerably reduced. The nitrate and proton budgets changed from surplus to deficit. The sulphur deficit was further increased by reducing sulphur input. In the course of the drought/rewetting experiment, a distinct increase of nitrate budgets was found. A possible nitrification or an acidification pulse was not observed. (C) 1998 Elsevier Science B.V.