Nitrogen deposition effects in Austrian forests

Excess Nitrogen (N) deposition from industrial, domestic and agricultural sources have led to increased nitrate leaching, the loss of biological diversity, and has affected C sequestration in forest ecosystems. Global mean N deposition is still increasing while in Europe, N deposition peaked during the mid 1980s and was slowly going down until today as a result of emission reductions (EU28) of NO x by 50% and NH 3 by 30% between the years 1990 and 2015. However, the amount of N deposition did not decrease in all areas in Europe and the currently legislated emission reduction targets are too low to save ecosystems and biodiversity from further effects. In order to assess the ecosystem effects of chronically high N deposition in the forests of the Austria, a unique four-decade data set of 16 single monitoring and research sites has been compiled. These measurements include air concentration, deposition, soil water chemistry, and foliage chemistry together with ancillary data on climate, soils, tree species, forest management and structure. The results underpin the tight relationship between N deposition, nitrate leaching, and nutrient deficiency in trees. Hence, the deposition pattern found in Austria (high in the north and southeast and low in the center) correlate with the N impacts. Furthermore, tree species and climate mediate the magnitude in the effects. In Austria, 56% of the nitrogen released into the environment comes from agriculture. In particular, emissions of ammonia, which are produced during livestock farming, the storage of slurry and manure and fertilisation, have been reduced comparatively little. As a result, forests, meadows, heaths and moors, which account for around 60% of the country's surface area, still receive nitrogen above the critical load. Protected areas for rare species and habitats are also affected. The Ammonia Reduction Ordinance has been in force since January 2023. Targeted measures such as the mandatory covering of manure storage facilities, the mandatory incorporation of fertilisers in arable farming and requirements for the use of emission-intensive urea fertilisers are intended to reduce nitrogen emissions.