Assessment of Thermal Discharges on Zooplankton in Conowingo Pond, Pennsylvania

Abstract

Assessment of the impact of power station operation on zooplankton communities requires separation of natural variations from those due to the facility. Analysis of covariance (density of zooplankton at control station, ambient water temperature, and average daily river flow as covariates) proved powerful in separating the natural variations from those due to the operation of Peach Bottom Atomic Power Station (once-through cooling system) in Conowingo Pond, a 35.8-km2 impoundment on the lower Susquehanna River. The covariance technique overcame some of the problems associated with using ratio of density at control station to the density at an affected station to adjust for ambient variations. Significant differences in adjusted preoperational and postoperational means occurred but were not attributable to station operation. Multiple regression analysis indicated that an increase in zooplankton production, particularly in winter, would result with addition of heated water when river flows are < 280 m3/s. The zooplankters were subjected to an average ΔT of 10.0 °C in winter and up to 8.0 °C in summer. Zooplankton population showed a great amount of resiliency in Conowingo Pond.Key words: zooplankton, heated effluents, statistical analysis, power plant impact