Versauerung und Stickstoffeutrophierung österreichischer Waldböden

Nitrogen deposition into forest ecosystems primarily occurs as nitrogen oxides, ammonia, nitrate and ammonium. Nitrogen is on the one hand an important nutrient, on the other hand elevated input: may lead to soil acidification, eutrophication, nutrient imbalances and elevated nitrogen lea ching into the groundwater. During pre-industrial periods Austrian forest soils were acidified by litter raking. Over the last 20 years gaseous emissions have decreased: SO emissions significantly, NO-emissions markedly and NH emissions insignificantly. Due to the reduction of these emissions the acid and nitrogen input decreased. The accelerated wood increment that requires an increasing nitrogen supply, the renunciation of litter raking and the increased exploitation of forest resources has led to fundamental changes of the acidification and eutrophication situation in forest ecosystems. Based on data of the Austrian monitoring grids the current situation and the trends during the last 20 years were investigated: The data set comprises pH values, C:N ratios of the soils, nitrogen and proton deposition rates as well as nitrogen contents of Norway spruce and Scotch pine needles and mosses. The pH-value of the soils has increased during the last 20 years. Reasons are decreasing acid emissions (esp. SO) and an aggradation of soils that were previously acidified by litter raking. The tendency towards wider C:N ratios is caused by a reduction of N inputs and the increased N uptake of the forests. The nitrogen depositions exceeded Critical Loads occasionally. The nitrogen supply of Norway spruces and Scotch pines is still insufficient as revealed by the nitrogen content of their needles. The examples of several catchment areas have shown that the deposited nitrogen is efficiently retained and the leachate into the groundwater does not pose a problem. Wood increment and productivity of Austrian forests will increase as long as the water and nutrient supply is sufficient.