5£ 



3.4 CTD and Dissolved Oxygen Sampling 



Depth gradients of temperature, salinity, and DO at the reference areas and the active 

 disposal point are shown in the Appendix. Surface salinity at each of the four sampling 

 locations was approximately 27 ppt, increasing slightly (0.5 ppt) with depth. A well-defined 

 thermocline at 10-15 m water depth was present at each site. Surface temperatures varied 

 from 20.0° C to 21.5° C and decreased to about 18° C within one meter of the bottom. 



Dissolved oxygen concentrations measured by the Seacat Model SBE 19-01 CTD near 

 the surface ranged from 7.5 to 9.2 mgl 1 (SOUTH and WLIS "E," respectively; Table 3-5). 

 Near-bottom DO levels ranged from 4.2 to 4.7 mg l" 1 (WLIS "F" and EAST, respectively). 

 Dissolved oxygen concentrations, as determined by Winkler titration, differed slightly from 

 the CTD measurements. Near-surface concentrations ranged from 7.7 to 9.6 mg l" 1 

 (SOUTH/2000W and EAST, respectively) and near-bottom concentrations ranged from 3.6 to 

 3.9 mg T 1 (WLIS "F" and EAST, respectively). Differences between the CTD and the 

 Winkler titrations were attributed to small shifts in the CTD DO calibration. All measured 

 dissolved oxygen concentrations were within the aerobic range as defined by Tyson and 

 Pearson (1991) (Table 3-6). 



3.5 Benthic Habitat and Sediment Toxicity Assessment of Selected Stations 



Five stations (D200N, D100S, D300S, D100W, and E400W) occupied during the 



1991 survey had conspicuously dark sediment profiles and low OSI values. These stations 

 were reoccupied during the 1992 survey to assess benthic habitat conditions. The 1992 

 REMOTS® OSI values for four of these stations (D100S, D300S, D100W, and E400W) were 

 similar to values calculated during the 1991 survey. The median OSI value for Station 

 D200N increased from +5 (1991) to +7 (1992). Apparent RPD boundary layer depths 

 increased slightly (about 0.3 cm) at all stations except D100S, where apparent RPD depth 

 decreased from 1.2 cm to 0.8 cm. The benthic successional seres present for both years ( 

 were identical, with all stations having either Stage I or Stage I on Stage III. Although the 



1992 sediment profiles did show some variability among the replicate REMOTS® 

 photographs at each station, subsurface sediments from the 1992 survey did not appear as 

 dark as noted in 1991. 



The results of the amphipod 10-day bioassay showed no significant toxicity in the 

 three WLIS sediment samples (reference area 2000W; WLIS "A," Station E400W; and 

 WLIS "D," composite of stations D200N, D100S, D300S, and D100W) relative to the 

 percent survival of the laboratory control sample (Table 3-7). Mean percent survival values 

 for the 2000W and WLIS "A" samples (94 and 93%, respectively) were higher than the 

 control percent survival (89%). Mean percent survival for the WLIS "D" sample was 71% 

 and ranged from 95 to 25%. 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1992 



