EFFECTS OF POWER-PLANT OPERATION ON ZOOPLANKTON 637 



TABLE 4 



ANALYSIS OF VARIANCE TESTS FOR 

 HOMOGENEITY OF PTYGURA SPP. 



*Explanation of symbols: 



S5, significant at the 5% level. 

 SI, significant at the 1% level. 

 NS, not significant. 



the 19 taxa. Table 5 lists the results of all tests and their 

 interpretation. 



An increase in spatial homogeneity was indicated if the signifi- 

 cance of station as a variable declined from year 4 to year 6. This 

 occurred for 13 of the 19 taxa tested and indicated that power-plant 

 circulation may have brought about an increase in spatial homoge- 

 neity (station similarity). 



An increase in seasonal homogeneity was indicated if the station 

 X month interaction term was significantly less in year 6 than in 

 year 4 or year 5 (year 6 was the year in which the power plant was 

 fully operational with both units on line). This occurred for 12 of 

 the 19 taxa tested. An increase in seasonal homogeneity for this 

 many taxa indicated that power-plant circulation may have brought 

 about an increase in seasonal homogeneity among stations. Tests 

 among the Cladocera, Copepoda, and Rotifera were not as conclu- 

 sive. The sensitivity of the analysis was lost owing to the high degree 

 of variation between the species that were pooled within each group. 



SUMMARY 



The densities of 19 zooplankton taxa at 8 stations were 

 examined separately by analysis-of-variance techniques to determine 

 significant differences in two ways. The yearly density of each 

 species at each station was compared among the 3 years of study. All 

 stations were then pooled within a year, and the density of each 



