remained with no impairment of motility or other functions. If such survival is attributable to intraspecies variation in tolerance to copper, such genetic variation may contribute to the annual recurrence of this nuisance species in the reservoir.

Another example related to water quality is the development of toxic blooms of cyanobacteria (blue-green algae). Studies have shown that within a population, some strains produce neurotoxins and others do not. Toxic blooms occur when neurotoxin-producing strains become dominant. Occurrence of toxic blooms in farm ponds can cause severe illness or death in livestock drinking at the pond. Understanding the circumstances that favor toxin-producing strains would be useful in managing this problem.

Question: Can generalizations be made about genetic variations within particular classes of organisms?

There are many potential directions for research on genetic variation. Tolerance and bioaccumulation of contaminants is an issue for organisms at all trophic levels. If there are general patterns of genetic variation, such as more variation in tolerance in diatoms compared to cladocerans (water fleas), knowledge of these patterns would help in understanding ecosystem response to environmental stress.

Natural Water—A Chemical World

"Water quality" is a phrase used commonly in discussing water resources, but the meaning of water quality can be a source of confusion. Quality has many meanings, the principal ones being "peculiar and essential character" and "degree of excellence." The first refers to objective features of water; the second, to value judgments about the water for particular human uses (Averett and Marzolf, 1987). This distinction acknowledges that scientific inquiry into water quality issues (first meaning) is essential for the appreciation, definition, and management of water's utility for human uses (second meaning). The topics discussed below address water quality issues from the second perspective; specifically, they address the "so-what" question that can be asked about data sets of water quality parameters.

Major Cations, Anions, and Alkalinity

The major cation and anion concentrations vary greatly among inland waters, from saline to very dilute. There are many potentially significant questions. Addressing them could yield important insights and allow for a meaningful interpretation of the extensive water quality data that routinely are collected around the country and archived in computer data

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