Comparing trends in lake acidification using hydrochemical modelling and paleolimnology: The case of the Herrenwieser See, Black Forest, Germany

We reconstruct the post-industrial acidification of a dystrophic headwater lake in the Black Forest by (1) modelling past chemical change using MAGIC and (2) assessing past pH using diatoms from a sediment core. Both methods were consistent in indicating only a small pH decline between the mid 19th century and the 1980s, followed by a minor recovery around 10 years after peak sulphate deposition. However, the magnitude and timing of pH change varied between the different diatom algorithms (weighted averaging vs. multiple regression, maximum change 0.21 and 0.78 pH units, respectively), and between the most extreme diatom scenario and MAGIC (0.15 pH units). We advocate further validation exercises of this type to assess whether consistency is maintained or differences emphasised, where pH change has been larger.