-2 



-I 







AXIS I 



Figure 24-6. A Stepwise Discriminant Analysis of Data on 



Concentrations of Zoopiankton Biomass, Chlorophyll, Ammonia, 



Nitrate Plus Nitrite, Phosphate and Silicate in 9 MERL Microcosms 



and Bay Input Water from August 17 to December 6, 1976, 



was Used to Prepare this Plot of Centroids in Reduced Space. 



NOTE: Detailed information on the Analysis is presented in Table 24-5. 



A comparison of microcosm data and bay data allows us to determine 

 whether the greater variability of some of the microcosms makes them truly 

 different from the bay. A second discriminant analysis was preformed with the 

 same microcosm data set (nutrients, phytoplankton, zoopiankton), and a 

 similar set from the 1972-73 bay survey at 13 stations around the bay for the 

 same period of the year (Figure 24-1 , Table 24-2). In Figure 24-8, the bay 

 stations are found positioned in a roughly linear arrangement, parallel to the 

 first axis, which corresponds approximately to the eutrophication gradient in 

 Narragansett Bay. Stations at the clean mouth of the bay and in the deeper east 

 passage are positioned to the right. Stations in the west passage to the upper 

 bay are progressively positioned to the left with the Providence River on the 

 extreme left. All the microcosms, including those which exhibit more divergent 

 behaviour, are positioned in mid-bay locations. Microcosm 2 appears 



374 



