3 Reading the Records Stored in the Lake Sediments: A Method of Examining the History and Extent of Industrial Damage to Lakes Sushil S. Dixit, Aruna S. Dixit, John P. Smol, and W. (Bill) Keller In this chapter, the effects of air pollutants from the roasting beds and smelters on Sudbury area lakes are examined. A rather novel approach has been used to track the lake water quality changes that occurred in the past century. This approach uses the rapidly expanding science of paleolimnology, the study of the fossil record in the lake sediments. In the absence of long-term data, paleolimnological techniques using bio- logical remains in lake sediment cores are being used extensively to provide quantitative assess- ments of past water quality in North, America (Charles et al. 1990; Dixit et al. 1987, 1992c) and Europe (Battarbee et al. 1990). A large area around Sudbury is character- ized by a geological environment that is highly resistant to chemical weathering (see Chap- ter 1). As a result, many lakes have low acid- neutralizing (buffering) capacity, making them vulnerable to inputs of strong acids. The wide- spread acidification and metal contamination of area lakes are major environmental prob- lems resulting from metal mining and smelt- ing activities near Sudbury. Acidification is also a global concern (Fig. 3.1). The very acidic nature of some lakes in the Sudbury area was observed as early as the late 1950s (Gorham and Gordon 1960). Evidence of fish population disappearance (Beamish and Harvey 1972; Keller 1978; Kelso and Gunn 1984) indicates that the acidification of many Sudbury area lakes was severe by the 1950s and 1960s. However, long-term water quality data are lacking, because the actual monitoring of water chemistry of some Sud- bury lakes only began in the 1970s. Recently, it has been estimated that lakes in a 17,000- km 2 area (Fig. 3.2) have been measurably af- fected by the Sudbury emissions. If pH 6.0 is considered the acidity level at which signifi- cant damage begins to occur to the most acid- sensitive components of lake communities (e.g., some aquatic insects, crustaceans, and small fish species; see Fig. 5.2), then more than 7000 lakes within this zone have likely suffered bio- logical damage (Neary et a1. 1990). Paleolimnology and Environmental Assessment Paleolimnology uses the physical, chemical, and biological information contained in lake sediments to assess past environmental char- acteristics (Smol and Glew 1992). This multidisciplinary science has made a unique contribution to environmental assessment studies by making data available that wouJd otherwise be unattainable. It has provided an- swers to questions such as (1) Has there been a change in the lake? (2) If so, what was the magnitude and rate of change? (3) Is the ob- served change greater than the natural vari- ability? and (4) What caused the change? 33 J. M. Gunn (ed.), Restoration and Recovery of an Industrial Region © Springer-Verlag New York Inc. 1995