COMPARING TRENDS IN LAKE ACIDIFICATION USING HYDROCHEMICAL MODELING AND PALEOLIMNOLOGY - THE CASE OF THE HERRENWIESER-SEE, BLACK-FOREST, GERMANY

We reconstruct the post-industrial acidification of a dystrophic headw ater lake in the Black Forest by (1) modelling past chemical change us ing MAGIC and (2) assessing past pH using diatoms from a sediment core . Both methods were consistent in indicating only a small pH decline b etween the mid 19th century and the 1980s, followed by a minor recover y around 10 years after peak sulphate deposition. However, the magnitu de and timing of pH change varied between the different diatom algorit hms (weighted averaging vs. multiple regression, maximum change 0.21 a nd 0.78 pH units, respectively), and between the most extreme diatom s cenario and MAGIC (0.15 pH units). We advocate further validation exer cises of this type to assess whether consistency is maintained or diff erences emphasised, where pH change has been larger. (C) 1998 Elsevier Science B.V. Ail rights reserved.