45 



According to log estimates, barges deposited 88,588 m 3 of dredged material at CLIS 

 during the 1990/91 disposal season. A volume calculation based on the depth difference 

 between the July 1990 and June 1991 bathymetric survey at CLIS was 39,503 m 3 of material. 

 The depth difference between 1990 and 1991 includes not only material added to the area 

 during that time but also any compaction of material that has occurred. 



Tavolaro (1984) showed that volume estimates based on barge logs overestimate the 

 amount of transported dredged material because of the significant amount of interstitial water 

 associated with the material in the barges ("fluffing"), and the detection limitations of 

 bathymetry. He calculated that "depth difference" volume estimates based on successive 

 bathymetric surveys can be as much as 41% less than the barge log volume estimates. The 

 discrepancy was attributed not only to log inaccuracies (due to limitations inherent in 

 measuring dredged material volumes in the barge) but also to compaction of dredged material 

 on the bottom following disposal and the significant volume of material that is deposited on 

 the flanks of the mounds in layers too thin to be detected acoustically. Applying the 41% 

 factor to the log estimate of 70,624 m 3 for dredged material actually released at CLIS 

 resulted in a corrected barge log estimate of 41,668 m 3 . This corrected estimate is 100.5% 

 of the volume of material detected by the bathymetric survey (39,503 m 3 ). 



4.2 CLIS Successional Status 



The predicted recolonization status at CLIS was Stage I on the CLIS-90 and CS-90-1 

 mounds, progressing to Stage IJJ on the inactive mounds. Both the CLIS-90 mound and CS- 

 90-1 mounds had Stage I taxa at the center, but stations around these mounds have apparently 

 retained a Stage III status. Burial of Stage HJ taxa by thin layers of dredged material does 

 not kill these organisms as they are capable of burrowing upward through the deposited layer 

 to reestablish connection with the new sediment- water interface (Goldring 1964, Kranz 

 1974). 



Stage m organisms were expected at all of the reference areas and inactive mounds. 

 At the reference stations, Stage HI taxa predominated with only 2500W-REF, station 100W, 

 having only Stage I infauna. On the inactive mounds, CS-1, CLIS-88, CLIS-89, NHAV-74, 

 and FVP all exhibited Stage IJJ seres. This observation supports convergence between the 

 successional status of old inactive disposal mounds and the ambient bottom. The exception 

 was CS-1, 300E, that had only Stage I. The scattered locations where Stage JJJ was not 

 detected may have been mischaracterized, or a consequence of natural benthic patchiness as 

 also observed at 2500W-REF. The recognition of Stage HI seres in REMOTS® photographs 

 depends on the development of subsurface feeding voids. The CLIS 1991 monitoring survey 

 was conducted in the late spring when low sediment temperatures depress the metabolism and 

 feeding rate of Stage HJ worms (D. Rhoads - pers. comm.). This results in less well- 

 developed feeding voids at depth in sediments and can result in inaccurate successional stage 

 characterization. 



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



