Empirical Case Studies: Potentials of Global Risks: Risks of Chemical Substances. Gerald Busch, University of Göttingen, Institute for Soil Science and Forest Nutrition Büsgenweg 2, 37077 Göttingen, Germany; and Gerhard Lammel, Marx Planck Institute for Meteorology, Bundesstrasse 55, 20146 Hamburg, Germany
The common effect of the emission and subsequent deposition into terrestrial ecosystems which contribute most to acidification and nitrogen fertilization of the soils (NH3, NOx, SO2) is globally assessed for today (observations of the years 1980-1990) and for a szenario of future emissions (IS92a; years 2040-2050; IPCC 1992).
SOy (= SO2 + sulfate) and NOy (= NO2 + HNO3 + nitrate) deposition fields are taken from a general circulation model of the atmosphere, ECHAM4. NHy (=ammonia + ammonium) deposition fields are taken from a run of the global tracer transport model MOGUNTIA, the only model which describes reduced nitrogen compounds so far. The model simulates the sulfur and nitrogen atmospheric chemistry and sinks. Global atmospheric inputs to the continents and oceans amount today ( 1980-1990) to 4.2, 4.7 and 11.7 mequiv m-2 a-1 for NHy-N, Noy-N and SOy-N, respectively, with dry and wet depositional fractions contributing almost equally. These numbers are expected to increase by 70, 60 and 65% respectively within 60 years (2040-2050).
Large forested regions with the nitrogen input yet today exceeding 15kg N ha-1 a-1 - which has to be judged unsustainable - are identified in Europe, East and Southeast Asia (China, Japan, India, Myanmar), Russia and North America. Many of these forest ecosystems are located on acidified and nutrient deficient soils and receive actually an acid input over 1kmol H+ ha-1 a-1 which exceeds by far the buffering capacity of the soils. The deposition of nitrogen and acids in combination with increasing temperatures and CO2 leads to the risk of further destabilasation of the forest ecosystems. The probability of occurrence is high but the extent of damage is marked by great uncertainty. In view of the great delay effect and the high complexity of the involved processes this risk has to be assigned to the risk type"Pythia."
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