2 
84% VARIATION EXPLAINED 
c\J 
X 
< 
3 
BAY 
-2 1_I_I_I_I_ 
-2-IOI2 
AXIS I 
Figure 24-6. A Stepwise Discriminant Analysis of Data on 
Concentrations of Zooplankton 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, zooplankton), 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 
372 
