Sensitivity of European Ecosystems to Acid Deposition

Sensitivity of European ecosystems to acid deposition The calculation and mapping of CDs of acidity, sulfur and nitrogen form a basis for assessing the effects of changes in emission and deposition of S and N compounds. So far, these assessments have focused on the relationships between emission reductions of sulfur and nitrogen and the effects of the resulting deposition levels on terrestrial and aquatic ecosystems. 

Critical loads of sulfur and nitrogen, as well as their exceedances are derived with a set of simple steady-state mass balance (SSMB) equations. The first word indicates that the description of the biogeochemical processes involved is simplified, which is a necessity when considering the large scale application (the whole of Europe or even large individual countries like Russia, Poland or Ukraine) and the lack of adequate input data. The second word of the SSMB acronym indicates that only steady-state conditions are taken into account, and this leads to considerable simplification. These models include the following equations. 

This equation equals the net input of (sea-salt corrected) base cations minus a critical leaching of acid neutralizing capacity. 

All deposited N is consumed by sinks of nitrogen (immobilization and uptake), and only in this case CLmaxS is equivalent to a critical load of acidity. 

The maximum critical loads for nitrogen acidity represents a case of no S deposition. The value of CLmaxN not only takes into account the nitrogen sinks summarized as CLminN, but considers also deposition-dependent denitrification as a denitrification fraction fje- Both sulfur and nitrogen contribute to acidification, but one equivalent of S contributes, in general, more to excess acidity than one equivalent of N, since nitrogen is also an important nutrient, which is deficient in the most natural ecosystems. 

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