24 



Sixteen out of 65 stations in CLIS had mean OSI values of < +6 (Figure 3-16). 

 These values reflected shallow RPD depths (<3 cm), the presence of Stage I organisms, 

 and, at one station, the presence of methane (Figure 3-17). Eleven of the stations with mean 

 OSI values of < +6 were near the CLIS-89 disposal buoy. Low OSI values at the remaining 

 five stations resulted from the absence of Stage III taxa in one or more replicate REMOTS® 

 photographs combined with relatively shallow RPD depths. Mean OSI values exceeded -f-6 

 at the remaining disposal site stations and at all three reference areas. 



The frequency distribution of reference station OSI values had a major mode at 1 1 , 

 while the distribution of OSI values at all 65 stations within the CLIS boundary had major 

 modes at 7 and 9 (Figure 3-18). There was a significant difference in OSI values at the 

 disposal site stations versus the pooled reference stations (Mann-Whitney U-test, p <.001). 



3.3 CTD and Dissolved Oxygen Sampling 



CTD profiles obtained at the center of each reference area and at the CLIS-89 buoy 

 location (center and 300 m north, south, east, and west) all had a distinct layer of water with 

 high temperamre, low sigma-t, and low salinity to a depth of approximately 7 m (Figures 3- 

 19 and 3-20). Below 7 m the temperamre and salinity remained constant to depth. This was 

 consistent with CTD profiles from previous CLIS surveys (SAIC 1990a). 



Dissolved oxygen concentrations for water samples 1 m above the bottom ranged 

 from 4.02 to 4.33 mg 1"' around the CLIS-89 buoy location and from 3.4 to 6.34 mg 1"' at 

 the center of the three reference stations (Table 3-1). 



Moniioring Cruise at the Central Long Island Sound Disposal Site, July 1990 



