Critical loads are a potentially important tool for protecting ecosystems from atmospheric deposition

Information on biologically important physical and chemical variables is presented for Lake Oconee, a newly impounded pumped storage reservoir in Georgia. During its first summer, when no pumping occurred, temperature, oxygen, pH, inorganic nitrogen, and phosphorus were vertically stratified with severe hypolimnetic oxygen depletion. During the second summer, when pumped storage was in operation, more homogenous vertical profiles, generally higher oxygen, and lower dissolved nutrient concentrations were observed. These pumped storage effects were observed at all stations, rather than being confined to the immediate vicinity of the dam.

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.

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