134 



disposal mounds measured as volume in bathymetric depth-difference calculations has been 

 stable over a period of at least twenty years. 



A three-dimensional view of the master bathymetric survey showed lower 

 topographic relief south of the NL-RELIC Mound, in a depression surrounded by historical 

 dredged material disposal mounds (Figure 3-49). The practice of using the periodic 

 disposal of dredged material to develop topographic barriers was first discussed in relation 

 to NLDS (SAI 1980). This practice was a successful management method during the 

 formation of the NHAV-93 mound at the Central Long Island Sound Disposal Site (Morris 

 1996). In that study, a topographic depression was used to site the disposal of a major 

 dredging project (New Haven); the disposal of the dredged material in this "bowl" served 

 to restrict its lateral spread. The depression located south of the NL-RELIC mound 

 represents a potential area for similar future management of material at NLDS. However, 

 the location of this bowl directly beneath the U.S. Navy Submarine corridor may place 

 limits on the effective use of this area for dredged material disposal. Buoys located in this 

 corridor are a hazard to submarine navigation and mound height would need to be limited, 

 in order to ensure water depths greater than 14 m. Other topographic low areas are near 

 the margins of the disposal site and include the trough in the southwestern quadrant of the 

 site, which is associated with the natural ridge southwest of the site. 



4.2 Biological Response to Disposal at the NLDS 



The REMOTS® sediment profile data collected from reference areas and within the 

 disposal site provide an opportunity to compare and contrast the biological response to 

 disposal activity over a six year period (1992-1998). Throughout this period the fresh and 

 recent (1-6 years old) dredged material showed a rapid recovery from a disturbed surface 

 to a healthy benthic assemblage. Areas of historical dredged material (over 6 years old) 

 were not specifically targeted for investigation, but were sampled around the margins of 

 new disposal mounds. These areas all supported a healthy mature benthic community. 

 Reference areas appeared to be recovering in 1992 from some patches of disturbance in 

 1991 but also recovered rapidly and returned to a more uniform mature benthic community 

 in 1995. All reference areas experienced some limited patches of disturbance (presence of 

 recolonizing Stage I organisms, eroded tube mats, shallow RPDs) at various times within 

 the survey period. None of the individual reference stations exhibited consistent 

 disturbance, that is, the patches were in different places each year. Overall, the reference 

 areas supported a healthy benthic assemblage and displayed typical features of seasonal 

 settlement and disturbance (see below). 



Assessment of the health of the benthic community at NLDS requires the ability to 

 separate site-specific characteristics from regional environmental characteristics. During 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



