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WATER-QUALITY CHARACTERISTICS Spatial and temporal changes in water quality often occur in lakes and reservoirs. Although this report is about a reservoir, the term "lake" more commonly is used in general literature and, therefore, sometimes is used in this report where discussing general properties and processes. Many of the explanations for water-quality characteristics presented in this report for Kenney Reservoir represent phenomena known to occur in lakes and reservoirs and are the likely reasons for the observed conditions. However, newly con- structed reservoirs characteristically undergo dynamic change in water quality during, and immediately after, the reservoir is filled. A new equilibrium condition in regard to its hydrologic, sediment, nutrient, and other properties usually is not achieved immediately. The filling water inundates the reservoir basin, causing sediments and other materials to enter the water column and undergo chemical and biological reactions and interactions. An enhanced biological productivity often occurs, which can cause tastes and odors, clog intake screens in water-treatment plants, produce slime conditions, and be toxic to animals (Palmer, 1977). Eventually, however, the water body will reach an equilibrium state and exhibit relatively stable water quality. Given the postconstruction sampling period for Kenney Reservoir, therefore, the water-quality and trophic characteristics measured during this study will not necessarily describe the conditions likely to exist over the long term, even considering the relatively rapid flushing rate of the reservoir. Although many physical and biological variables are involved, changes in water quality occur most noticeably when solar heating during summer causes nonuniform water-temperature distributions to develop within the impounded water. Temperature not only controls the rate of chemical and biological processes, but also, because the density of water is a function of temperature (water is densest at approximately 4 OC), nonuniform temperature (thermal) distribution in water is the primary cause of most stratification in lakes and reservoirs. A less common form of stratification can occur when large concen- trations of dissolved solids that increase water density become nonuniformly distributed within a lake. Depending on wind conditions, reservoir morphology, hydraulic residence time, and release patterns at the dam, various forms of thermal stratification may develop. Summer thermal stratification commonly is characterized by (1) an upper zone of uniformly warm water (epilimnion), (2) an intermediate zone of transition where temperature decreases rapidly with depth (metalimnion), and (3) a lower zone of uniformly cold water (hypo- limnion). The thermocline, as defined by Wetzel (1983), is the maximum rate of change of temperature with depth. The seasonal thermal profiles and circu- lation patterns of a temperate-zone lake are shown in figure 5. Hutchinson (1957) termed lakes that circulate twice a year in this manner as dimictic. Kenney Reservoir is an example of a dimictic lake. When thermal stratification is stable, the various metabolic activities of aquatic animals, phytoplankton, plants, and bacteria can alter and recycle dissolved gases, nutrients, and othet chemical constituents. As these activ- ities progress, the thermocline acts as a barrier between the upper warm- water zone and the lower cold-water zone, decreasing the exchange of heat and dissolved substances and, also, acts as a biological barrier that affects the movement and dispersal of many aquatic organisms. As a result, water zones that have different chemical characteristics may develop. The environments of these physical, biological, and chemical zones are discussed in Hutchinson (1957) and Odum (1971). 12