PREFACE vii 



communities (Marshall and Mellinger). Generalizations 

 about the uptake and toxicity of various trace metals 

 are difficult to make because of the specificity in action 

 of individual elements. However, current efforts in this 

 area center on similarities in uptake and toxicity in 

 relation to atomic structure of the elements and to the 

 chemical requirements of the biota being studied. 



Two of the previous volumes in the Savannah River 

 Ecology Laboratory Symposium Series on Ecological 

 Research, and approximately half this volume, are 

 devoted to studies of the response of organisms and 

 communities to thermal effluents. The papers in this 

 section of this volume are roughly grouped by their 

 emphasis on functional (i.e., primary productivity, 

 growth, genetics, reproduction, and behavior), struc- 

 tural, and toxic ological aspects of thermal ecology. The 

 diversity of these studies demonstrates that thermal 

 effluents have a comprehensive effect on most func- 

 tional and structural aspects of aquatic systems. 



Difficulties in design and analysis have impeded the 

 spread of studies on multiple and synergistic stresses, 

 and yet, in most of our "less-than-pristine" environ- 

 ments, the simultaneous presence of various stressors is 

 undoubtedly the norm rather than the exception. 

 Vernberg's review of recent research on the effects of 

 multiple stressors shows the reduction that can occur in 

 an organism's zones of lethality and compatibility as a 

 result of previous or concurrent exposure to multiple 

 stressors. Three papers demonstrate differential effects 

 on fish or Cladocera from multiple stressors associated 

 with entrainment (Poje, Ginn, and O'Connor and 

 Buikema etal.) or presence near the discharge (Cherry 

 et al.) of fossil-fueled or nucleair power plants compared 

 with the effects of single factors. This multiple-factor 

 effect is also shown for the benthic macroinvertebrates 

 in streams in Ohio (Beckett) and Pennsylvania (Bradt) 

 which had been subjected to a variety of physical and 

 chemical stressors as a result of channelization and 

 urbanization. 



We see a need for additional symposia that will serve 

 as forums for comparing and contrasting the effects of a 

 variety of stressors rather than focusing on individual 

 perturbations. The task of selecting the energy source 



