39 



4.0 DISCUSSION 



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

 WLIS survey: to define the topography and footprint of the active disposal mound and the 

 status of the inactive mounds at WLIS, to assess the extent of infaunal recolonization at the 

 active disposal point and compare it with reference area benthic habitats, 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 



One objective of the REMOTS® sedunent-profile survey and 1200 x 800 m 

 bathy metric survey was to delineate the extent and topography of the dredged material 

 deposited during the 1990-1991 disposal season. Based on the recorded disposal volumes, 

 approximately 86,462 m^ of dredged material was deposited at WLIS during that period. 

 The bathymetric analysis showed well-defined accumulation of dredged material at the 

 designated disposal point. The previous 1990 bathymetric survey of WLIS (800 x 800 m) 

 did not include the 1990-1991 designated disposal point; therefore, a depth difference 

 analysis (comparing the 1990 and 1991 surveys) could not be used to determine the height of 

 WLIS "E". Instead, the height of WLIS "E" was estimated to be 3.0 m based on 

 comparison to the surrounding ambient bottom depth of 32.75 m. This mound was an 

 elliptical deposit with a maximum diameter of approximately 200 m and a minimum diameter 

 of 150 m. Although the diameter of WLIS E fell within the predicted diameter (200 m), the 

 mound was higher than predicted (3 m versus 2.7 m). This is widiin the combined error of 

 the disposal simulation model and the bathymetry. 



Due to the proximity of the five WLIS disposal mounds, the volume of dredged 

 material deposited since 1982, and the proximity of the discontinued Stamford and Eaton's 

 Neck disposal grounds, virtually all stations within WLIS (except E400N) provided evidence 

 of past disposal operations. Relic/buried RPD boundary layers and physical layering of fine 

 sands and mud (4-3 phi) associated with dredged material can be distinguished from the 

 homogeneous, deeply biomrbated sediment profiles of ambient silt/clay materials (>4 phi) 

 typically found in this part of the Sound (i.e., E400N, Figure 3-3). Such dredged material 

 signamres can persist for years in the low energy, nondispersive regime which characterizes 

 WLIS. 



Individual REMOTS® parameters (i.e., RPD depth, successional stage, and boundary 

 roughness) did not allow unique identification of 1990-1991 dredged material relative to 

 older dredged material deposits. Several stations adjacent to the WLIS "E" moimd apex had 

 RPD depths greater than, or equal to, the on-site mean of 2.2 cm, and the distribution of 

 infaunal successional stages showed evidence of Stage HI activity at six of eight stations 

 within 100 m of the mound center. In addition, grain sizes of dredged material deposited at 



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



