DYNAMICS OF SOLUTES IN 2 SMALL FORESTED W ATERSHEDS IN THE FLYSCH ZONE - EFFECTS OF FOREST USE

In the interdisciplinary project ''Bodenforschung im Deutschen Alpenra um'' the dynamics of solutes were studied in different compartments of mountainous forested watersheds with special regard to the effects of a forest, cut. The input is characterized by high amounts of precipit ation, and high loads of acidity and nitrogen. An almost complete and rapid conversion or buffering of the deposited or internally produced acidity and nitrogen took place in the soils. The main buffering proce sses are cation exchange and hydrolysis of silicates. This leads to a strong export of alkali and alkaline earth cations, and of Si and bica rbonate. The watersheds are characterized by minor loads of organic (P AH) and inorganic (heavy metals) pollutants. The forest event, where 5 0% of the trees were subjected to tesselated cutting (Plenter-method), causes strong changes in the input situation of the manipulated water shed with a shift to an intermediate position between the open field p recipitation/deposition and the throughfall of the control watershed. The concentrations of almost all cations and anions increased in the s oil solution due to the cessation or reduction of the nutrient uptake by the roots, and to an increased mineralization. NH4 and NO3 showed t he strongest effects. These effects continue up to the receiving strea m and output The changes of the chemical composition in soil solution and runoff return to pre-event conditions one year after the tree cut.