Steady-State Models for Calculating Critical Loads of Acidity for Surface Waters

Three models for calculating critical loads of acidity forsurface waters, which have been used in several Europeancountries to map regions sensitive to deposition of acidifyingsulfur and nitrogen, are derived and their latest modificationsare presented. Using Norwegian lake data as an example, some ofthe methods are compared and discussed. While the Steady-StateWater Chemistry (SSWC) model and the Empirical Diatom model arebased on water chemistry alone, the First-order Acidity Balance(FAB) model also includes descriptions of the most importantsinks of nitrogen (and sulfur) in the catchment soils and thelake/sediment system. This is the first time that all currentlyused models as well as some new developments for calculatingcritical loads of acidity for surface waters are presented in a single paper.

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