AN INTEGRATED WATERSHED PLOT-SCALE STUDY OF ELEMENT CYCLING IN SPRUCE ECOSYSTEMS OF THE BLACK-FOREST

The research project ARINUS is the study of the effects of restabilization measures (fertilization with rapidly soluble Mg salts) and atmospheric deposition on the element cycling of typical spruce ecosystems in the Black Forest. The objective is to quantify the natural and anthropogenic components of element cycling at these sites which will provide a better estimation of the effects induced by external perturbations, e.g. increasing atmospheric deposition, fertilization, or biomass export. Interrelations between the terrestrial and aquatic system are assessed using an integrated approach which combines flux measurements in representative plots with balance of small experimental watersheds. This paper describes the approach, treatments, field installations, methods, and site conditions of one of the two research areas. Furthermore, preliminary results from element inventories and watershed input-output budgets are discussed. According to the distribution of Mg in the ecosystem, the experimental area Schluchsee is a typical Mg deficient site. Magnesium losses result from leaching both from the canopy and the superficially rooted top soil. Since atmospheric deposition is low, cation export is primarily controlled by the ecosystem's internal production of acids. This excess mineralization in the soil is attributed to a change from the original mixed forest to the present spruce monoculture.