41 



4.0 DISCUSSION 



The following discussion addresses the four major objectives of the 1991 DAMOS 

 CLIS survey: to define the topography and footprint of the active disposal mounds, to 

 evaluate the successional status of active and inactive disposal mounds, to collect sediment 

 chemistry information at the three reference areas, and to determine the potential role of 

 bottom water dissolved oxygen as an ecological variable. 



4.1 Disposal Mound Topography 



The objective of the combined REMOTS® and precision bathymetric surveys was to 

 delineate the extent and topography of the deposit resulting from dredged material disposal at 

 CLIS since the 1990 survey. At the CS-90-1 buoy location, material released in 1989 had 

 been capped since 1990. The CLIS 1991 survey was also designed to detect any of the 

 material released at CS-90-1 since 1989. The bathymetric survey showed a significant 

 accumulation of dredged material near the CLIS-90 disposal buoy and smaller amounts at the 

 CS-90-1 buoy. However, the radius of the CLIS-90 disposal mound detected by the 

 bathymetric survey (>20 cm thick above ambient bottom) was 100 m rather than the 

 predicted 200 to 250 m (Figure 3-3). Based on the detection of dredged material by 

 REMOTS® (< 20 cm), "fresh" and relic dredged material is present over the whole survey 

 area. "Fresh" dredged material extends more than 100 m south of CS-90-1 and north and 

 west of CLIS-90. 



The distinction made between "fresh" or recent dredged material, and relic or older 

 dredged material, is based on a "fresh" signature exhibiting thin or patchy RPDs (redox 

 potential discontinuities), physical layering or chaotic sedimentary fabric near the surface due 

 to a lack of bioturbation, and high boundary roughness. The "fresh" appearance to the 

 material in these areas may be due to the low metabolic rate of infauna over the winter 

 (including bioturbation rates) resulting in thin or patchy RPDs. A plot of reported barge 

 release points for the 1990/1991 disposal season at CLIS indicates that most of the barges 

 released dredged material within 250 m of the CLIS-90 and CS-90-1 buoys (Figure 4-1). 



The presence of dredged material at all REMOTS® stations in the main 1991 survey 

 grid reflects the extensive use of this quadrant of CLIS for dredged material disposal over the 

 past few years. A disposal mound has been formed within the 1991 survey area every year 

 since 1987. Previous surveys have noted dredged material disposal away from the intended 

 locations (Germano et al. 1993). At CS-90-1, however, the material was intentionally 

 released at various locations away from the buoy to spread cap material around the CS-90-1 

 mound. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, June 1991 



