ZOOPLANKTON COMMUNITIES OF A NEW PUMPED STORAGE RESERVOIR¹

Abstract

Zooplankton colonization was followed for 16 months in Lake Oconee, Georgia, a new pumped storage reservoir. Data were interpreted to identify differences among stations and seasons, as a function of the reservoir's early stage of development and of pumped storage operations. Colonization was rapid, and the zooplankton community was characterized by a high species diversity; approximately 40 rotifer species and 14 cladoceran genera were recorded. Zooplankton density varied along an environmental gradient from riverine to lentic conditions. Rotifer abundance varied from 104‐106 individuals/m3, with maxima in the summers Copepod and cladoceran densities ranged from 103 to nearly 105 individuals/m3; maxima for stations other than the dam were observed in the summer and early fall, but high values at the dam station occurred throughout winter 1980. When pumped storage operations began in December 1979, zooplankton densities increased at the dam station. Pumpback decreased the intensity of the environmental gradient from riverine to lentic conditions, and led to a more similar zooplankton community structure throughout the reservoir.

CHANGES IN PHYSICAL AND CHEMICAL VARIABLES IN A NEW RESERVOIR DUE TO PUMPED STORAGE OPERATIONS1

“…Less oxygen stratification occurred after pumpback operations began, and hypo- Secchi disc visibility varied from 0.125 to 2.5 m. It was generally greatest at Station I and lowest at Station 111. Light penetration was maximum during August 1979 and at a minimum during times of high discharge (April 1980see also Potter and Meyer, 1982). The percent organic content of sue pended solids was consistently similar (-20 percent) at all stations only after the initiation of pumpback.…”

“…In summer 1979, a distinct thermocline was noted at all stations, while only partial stratification occurred during June 1980 (A < 7 C). Light penetration was maximum during August 1979 and at a minimum during times of high discharge (April 1980see also Potter and Meyer, 1982). In contrast, vertical differences prior to pumping were A 5-13 C. During summer 1979, stratification was most pronounced at Station I; however, when there was slight stratification in late summer 1980 during pumpback, it was most developed at Stations I1 and 111.…”

“…These data can be used in interpreting patterns of development in the biological community of the lake (Potter and Meyer, 1982). Our mainobjectives were: (1) to determine if the decomposition of flooded organics and plankton settling into the hypolimnion would create a severe biological oxygen demand and result in hypolimnetic oxygen depletion and chemical stratification, and (2) to examine the impact of pumped storage operation on thermal and nutrient stratification throughout the lake.…”

“…Our mainobjectives were: (1) to determine if the decomposition of flooded organics and plankton settling into the hypolimnion would create a severe biological oxygen demand and result in hypolimnetic oxygen depletion and chemical stratification, and (2) to examine the impact of pumped storage operation on thermal and nutrient stratification throughout the lake. These data can be used in interpreting patterns of development in the biological community of the lake (Potter and Meyer, 1982). Although this information is essential to understanding pumped storage effects resulting from an exchange of water masses between two reservoirs, it can also be applied to the overall study of artificial destratification procedures employed to improve existing lake water quality.…”

“…Trees and vegetation were left in situ to provide protective fBh habitats in 50 (0.2 km2) areas throughout the lake. For a more complete quantitative description of the lake see Potter and Meyer (1982). The purpose of reservoir construction was to provide the upper portion of a hydroelectric generation facility; a previously existing impoundment, Lake Sinclair, lies 27 m (106 m above msl) below Lake Oconee.…”