During the last few years, lake acidification has become a topic of international interest because of the detrimental effects of this problem on lake ecosystems. The stratigraphic record of diatoms and other paleoindicators in lake sediments has been used increasingly to document past limnological conditions. Because many diatom taxa are sensitive indicators of lakewater pH, this approach is especially useful in assessing impacts of atmospheric pollutants and watershed land use on lake pH. The idea that a book be prepared on this subject originated at a workshop entitled 'Reconstructing pH...