THE ACIDIFICATION OF THE HERRENWIESER-SEE, BLACK-FOREST, GERMANY, BEFORE AND DURING INDUSTRIALIZATION

Past trends in the biology and chemistry of the Herrenwieser See in th e base-poor Bunter Sandstone Black Forest were reconstructed from a se diment core. Diatom inferred pH indicated pre-industrial acidification periods with subsequent recovery. For the most recent acidification, multiple regression indicated a pH decline by 0.78 pH units to a minim um of pn 3.91 in the early 1980s; weighted averaging also indicated a pH minimum in the 1980s, but the lowest value was pH 4.58 and the over all decline only 0.30 units. The most important indicator species were Asterionella ralfsii for moderate acidification and Tabellaria quadri septata for extreme acidification. Community diversity H' and floristi c composition, as shown by cluster analysis, were sensitive to pH chan ges in the lake. Chlorophyll pigments offered another indicator for pH trends since periods of acidification were accompanied by higher conc entrations of chlorophyll derivatives. Acidic inputs into the lake wer e indirectly detected via analysis of persistent pollutants, metals an d polycyclic aromatic hydrocarbons. Characteristic chemical changes in dicated a metal burden from atmospheric deposition, and the release of base cations and aluminium from weathering, PAH concentrations rose s imultaneously with the pH decline in the 19th century. After the input maximum in the 1960s the Aux rates for PAHs decreased and are now <20 % of their peak value. The simultaneous trends in biological indicator s and persistent pollutants demonstrate that recent acidification was caused by atmospheric acid deposition. So far there has been no signif icant reverse trend despite signs of recent changes indicated by the d iatoms. However, pre-industrial acidification and recovery were also r elated to acid deposition, and indicate that reversal is possible in t his lake. (C) 1997 Elsevier Science Ltd.