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<br /> <br />Values of 5-day BOD in Kenney Reservoir ranged from 0.7 to 2.3 mg/L <br />(tables 13 and 14 in the "Hydrologic Data" section). The daily values and <br />ranges of BOD values determined from 20-day incubations for Kenney Reservoir <br />for two depths at site 1 and for the White River at site 3 are compared in <br />figure 9. Although BOD generally was slightly greater in the White River <br />(site 3) than in Kenney Reservoir (fig. 9), one important exception occurred <br />during the phytoplankton bloom in June 1987. Two selected samples collected <br />near the center of the reservoir on June 9, 1987, from the l-ft depth within <br />localized growths or patches of phytoplankton had I-day BOD values that were <br />greater than 5.0 mg/L. These values extrapolated to 5-day BOD estimates that <br />were greater than 25 mg/L. Although not representative of the general water <br />column in the reservoir, these large BOD values indicated that rapid respira- <br />tion (oxygen consumption) rates from phytoplankton growths can occur in the <br />reservoir. If the biomass from phytoplankton blooms remain in the reservoir, <br />substantial additional BOD may further decrease dissolved-oxygen concentra- <br />tions at depth as microbial decomposition of the sinking biomass occurs. <br /> <br />Light Penetration and Turbidity <br /> <br />Nearly all biological activities in a lake depend directly or indirectly <br />on sunlight. Photosynthesis by phytoplankton and other plants is related to <br />the quantity of available sunlight. The depth to which light penetrates a <br />lake is dependent on latitude and season, lake surface area and morphometry, <br />turbidity, phytoplankton characteristics, and the transmitting and absorbing <br />characteristics of the water and its dissolved material. <br /> <br />Turbidity is a qualitative measure of the light reducing or scattering <br />capabilities of the suspended and colloidal matter in water. Where turbidity <br />becomes large and light penetration is decreased, the following conditions <br />may occur: (1) lowered water temperature at depth, (2) decreased photo- <br />synthesis and primary production, and (3) disruption of feeding patterns and <br />physiological functions of benthic organisms and fish. Extreme turbidity <br />levels can be directly lethal to some aquatic organisms (McKee and Wolf, 1963, <br />p. 290-21). <br /> <br />Secchi-disk measurements in Kenney Reservoir (tables 13 and 14 in the <br />"Hydrologic Data" section) ranged from 11 to 144 in. at site 1 and from 2 to <br />46 in. at site 2. A comparison of Secchi-disk measurements (fig. 10) <br />indicates that substantial increases in light penetration (referred to as <br />transparency in tables 13 and 14) occurred from the inlet (site 2) to the dam <br />(site J). Light penetration generally was least during periods of snowmelt <br />and storm runoff when concentrations of suspended solids were large and <br />greatest during late summer when streamflow and concentrations of suspended <br />materials in the water column were small. <br /> <br />Turbidity, expressed in nephelometric turbidity units (NTU), measured <br />from the 2-ft depths (tables 13 and 14 in the "Hydrologic Data" section) <br />ranged from 1.2 to 45 NTU at site 1 and from 6.0 to 220 NTU at site 2. <br />Turbidity measured in the White River at site 3 ranged from 5.0 to 210 NTU. <br />The pattern of change in turbidity values within the reservoir was similar to <br />the Secchi-disk pattern--turbidity decreased and light penetration increased <br />from the inlet to the dam. These relations indicate that light attenuation by <br />phytoplankton in Kenney Reservoir was minimal. <br /> <br />20 <br />