into the lake (Garrison et al., 1992). Ground water is typically high in hardness and alkalinity. This is especially true of ground water in limestone aquifers, but even surficial (water table) aquifers in unconsolidated soil (e.g., glacial till) have higher hardness and alkalinity levels than do surface waters in acid-sensitive regions. Advantages of this approach involve low cost (no chemicals need be added to the lake) and ease of repeating the additions to maintain lake pH in the desired range. This method would not be useful in areas where ground water supplies are very limited (e.g., where granitic bedrock is near the surface).
Elimination or reduction of the input of contaminants (synthetic organic compounds and heavy metals) is necessary for remediation of contaminant effects. From a technical standpoint, input reduction is straightforward when point sources predominate. Where nonpoint inputs are substantial (see Lake Michigan case study, Appendix A), input reduction is much more difficult and costly.
Decontamination of lake ecosystems is most straightforward when contaminants are locally concentrated in sediments that can be removed by dredging. In other cases, contaminated sediments can be covered to retard recycling of contaminants to the overlying water. Where aquatic macrophytes concentrate metal contaminants, harvesting of the plants provides a means of biological decontamination of the system (Clark et al., 1981).
In many cases, contaminants are widely dispersed in lakes, and sediment or macrophyte removal is impractical. There is considerable interest in developing bioremediation techniques for dispersed organic pollutants. Bioremediation involves development of natural or mutant microbes that metabolize organic contaminants to nontoxic or less toxic compounds. These microbes can then be introduced to contaminated sites to degrade specific pollutants. Considerable research is under way concerning the use of altered microbes in ecosystems (Tiedje et al., 1989).
Remediation of chemical contaminants in lakes relates directly to management of fish and wildlife. Certain contaminants, such as halogenated hydrocarbons and methylmercury, are bioconcentrated, and they accumulate at increasingly higher concentrations in the tissues of organisms higher in the food chain. Consequently, piscivorous fish, birds, and mammals can develop in their tissues concentrations several orders of magnitude greater than those found in water (Thomann, 1989). Fish species differ widely in their tendency to