Das Projekt "Vorhersage und Erklaerung des Verhaltens und der Belastbarkeit von Oekosystemen unter veraenderten Umweltbedingungen - Teilprojekt N16: Modellentwicklung zur Stickstoffdynamik von Waldstandorten" wird vom Umweltbundesamt gefördert und von Universität Bayreuth, Bayreuther Institut für Terrestrische Ökosystemforschung, Abteilung für Bodenphysik durchgeführt. This report summarizes the specific features of the numerical simulation code SIMFONI (SIMulation of FOrest NItrogen). The model takes into account the reactive transport of both inorganic (NHhoch4+, NOhoch3-) and organic nitrogen species in the soil compartment of forest ecosystems. Transport and reactive processes are modeled within a one-dimensional layered soil profile. Upper and lower boundaries of the model domain are represented by forest floor and parent material or groundwater table, respectively. Reactive transport of nitrogen species considers cation-exchange or generalized sorption isotherms. To provide the essential data for the transport module water and heat flow are calculated. Soil solution chemistry and acid/base reactions are considered to provide the data for the cation-exchange reactions. Nitrogen transformation due to soil microorganisms takes into account ammonification, nitrification and mineralization. Mobile sorbent influenced transport of ionic nitrogen species is considered, too.