Effects and Empirical Critical Loads of Nitrogen for Europe

Empirical critical loads of nitrogen (N) were first presented in a background document for a workshop in 1992 in Sweden. Since their first presentation, the critical loads of N have been updated at regular intervals and for a large number of habitats. This chapter presents a brief history of the empirical critical loads and explains the process of determination of empirical critical loads for nitrogen and their reliability. For European habitats (defined as EUNIS and Natura 2000 habitat classes), current empirical critical loads for nitrogen are presented. For each of these habitats, the main effects of enhanced nitrogen inputs are discussed that have formed the basis for the determination of the empirical critical loads. Factors other than nitrogen, that may affect ecosystem processes or ecosystem functioning, are discussed as these may modify the nitrogen critical load under specific conditions.