10 



developed RPD and Stage III infaunal taxa at the center of the "D" mound indicated 

 that rapid recolonization of the recently-deposited dredged material had occurred. 

 Based on the results of past REMOTS® surveys, OSI indices of +6 or less indicate 

 chronically-stressed benthic habitats and/or those which have experienced recent 

 disturbance, such as erosion, dredged material disposal, or hypoxia, etc. (SAIC, 

 1990a). Therefore, the 1990 median OSI value of +7 at the disposal site stations 

 implied that dredged material had only a minor effect in terms of the benthic 

 biological community. 



Many stations along the fringe of the "D" mound exhibited exclusively Stage I 

 organisms and shallow RPD depths (OSI < +6) and possibly accounted for the 

 statistical difference of on-site versus reference station OSI and RPD parameters. 

 The dark, low-reflectant nature of sediments at these stations was typical of newly- 

 deposited, organic-laden sediments with a high oxygen demand. Camera 

 overpenetrations precluded OSI and successional stage determination at stations 

 100E, 200E, 100SE, and 200SE, indicating the loosely-consolidated nature (high water 

 content) of the sediments in this region of the mound. One would expect that 

 subsequent Stage III recolonization and further development of the RPD boundary 

 are likely to occur at these stations, given the level of recolonization at the center of 

 the "D" mound. 



Although a different survey grid and station spacing were used for the 1988 

 and 1990 surveys, thereby precluding direct (station versus station) statistical 

 comparison of the 1990 and 1988 onsite REMOTS® data sets, REMOTS® parameters 

 reflected a general improvement in the condition of the benthic habitat near the "B" 

 mound. Mean apparent RPD depths increased to greater than 3.0 cm. In addition, 

 OSI values near the "B" mound exhibited an increase from +3 (1988) to +11 (1990). 



As in the 1988 survey, the 1990 frequency distribution of OSI values in the 

 reference areas had a major mode of +11. Likewise, Stage III infaunal activity was 

 apparent in 63% of all replicate reference station photographs, compared to 61% in 

 the 1988 survey, indicating that a relatively stable and healthy benthic habitat exists 

 within these regions. 



4.3 CTD and Dissolved Oxygen Sampling 



The objective of the CTD/DO sampling at WLIS was to assess near-bottom 

 dissolved oxygen concentrations in relation to benthic habitat conditions at and near 

 the site. Near-bottom dissolved oxygen concentrations measured at selected disposal 

 site and reference stations were within the aerobic DO range (Table 4-1). In 

 addition, the 1990 REMOTS® analysis suggested that a relatively healthy and stable 

 benthic habitat persisted within the three reference areas and that infaunal 

 recolonization of the recently-deposited dredged material was proceeding rapidly at 

 some on-site stations. In conjunction with near-bottom DO concentrations, the 1990 

 REMOTS® analysis indicated that no recent or significant stress relating to near- 



Monitoring Cruise at the Western Long Island Sound Disposal Site 



