Chronological relationship between eutrophication and reed decline in three lakes of southern Germany

Eutrophication is often considered to play an important role in reed decline. We decided to use a chronological comparison of the two phenomena as a useful aid in the search for a possible causal relationship between them. Eutrophication is usually documented by changes in phosphorus and nitrogen content in water but there are no such data older than 10 years available for most of the lakes in which reed decline has been observed. The entire historical record of eutrophication has been recently reconstructed from micropaleontological analysis of indicatory diatom frustules, deposited in sediments in three lakes in south Germany. In these lakes, reed decline was well documented by archival aerial photographs. The comparison of reed decline history with the reconstructed changes in water quality confirmed the coincidence of reed decline and eutrophication. Consequently, eutrophication cannot be excluded as a potential cause of reed decline in any lake in this study.