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<br />002393 <br /> <br />.1. Introduction to Limnology <br /> <br />Interpreting the trends and history of Lake Powell's requires the grasp of some basic limnological <br /> <br />principles as well as some specifics peculiar to Lake Powell (Wetzel 1975, Cole 1994). There are a <br /> <br />few components that drive the seasonal and yearly patterns of the lake; resulting in fairly <br /> <br />predictable horizontal and longitudinal stratification (Figs. I ,2a, 2b, 3a and 3b; Merritt and Johnson <br /> <br />1979, Gloss et al. 1980, Edinger et al. 1984, Stanford and Ward 1986, Potter and Drake, 1989, <br /> <br />Thorton et al. 1990). <br />It is important to first become familiar with the most common and pertinent limnological <br /> <br />terminology, then to build an understanding ofthe basic processes that drives the conditions found <br /> <br />in the reservoir. Only then can valid conclusions be drawn that differentiate inflow processes from <br /> <br />discharge dynamics. <br /> <br />a. Stratification: <br /> <br />1) VerucalStratij1cauon <br /> <br />Lakes exhibit vertical stratification based on density gradients. (Fig. I) <br /> <br />Epilimnion: The surface layer of the lake characterized by the least dense water resulting from <br /> <br />warmer temperatures and lower conductance. It is the most biologically active portion of the lake <br /> <br />due to light availability and higher oxygen concentrations. <br /> <br />Metalimnion: A boundary or steep. gradient between the epilimnion and the hypolimnion. <br /> <br />Hvpolimnion: The dense, cold, saline water at the bottom of the lake. It is fairly stable and <br /> <br />resistant to mixing. It is dark and has low oxygen levels; consequently bacteria tend to be the <br /> <br />dominant life form. <br /> <br />Thermocline: A thermal boundary or gradient between water masses of different temperature. <br /> <br />Chemocline: A chemical boundary or gradient between water masses of different salinity. <br /> <br />06/02/98 <br /> <br />DRAFT <br /> <br />Page 16 of 62 <br />