Investigation of Nitrogen Fluxes and Pools, Model Approaches and Results : 36th Air Pollution Workshop Rhinelander, Wisconsin, USA, 26 - 29.April 2004

Wien

2004

Poster

SonderdruckMonographie

9592S

120944

Global emissions of nitrogen compounds (NOx, NHx, N2O) have been rising in the last decades due to combustion, agriculture and expanded fertilizing acitvites. In Europe, the resulting depositions are distributed inhomogeneously. In Austria, the nitrogen input exceeds the Critical Loads. Since the end of 1997 nitrogen pools and fluxed are continuously and detailed measured in the North Tyrolean Limestone Alps. This area, the main transit of Austria, gained special interest, because the forest condition (needle loss) was significantly higher than in other Alpine regions. Based on extensive investigations of natural and anthropogenic stress factors, intention has primarily been directed to interpret the N dynamics, the eutrophications as well as to assess the degree of nitrogen saturation. The input side (atmospheric deposition) pools and internal fluxes (nitrogen cycle) as well as the output by seepsage water and N2O losses, where the main components of the detailed flux investigations and models were evaluated. They made it possible to quantify the individual parts of the flux scheme and to make an assessment of their relevance. The annual rate of nitrogen deposition is moderate, compared to Central European forest ecosystems. So far, the soils have efficiently retained the incoming N. The major mechanism of nitrogen output is leaching during episodes of water flow in macro-pores. Soils are moist throughout the year and the frequent events of heay rainfall repeatedly occur in summer. So far, tree nutrition indicates no detectable signs of nitrogen europhication. The nitrogen content in needles remained in the range of insufficient supply. Apparently, the ecosystem has accumulated nitrogen over time, but it is tied up in the organic matter of the soil and inaccessible for plants and micro-organisms. Until now no immediate tendency to high leaching losses of nitrogen has occured and can thus be ruled out. The system is approaching nitrogen saturation because inputs still exceed the outputs, but the capacity of further nitrogen retention remains unknown. Therefore, the problem of nitrogen saturation deserves further attention because it is not yet possible to predict a critical level.