46 



4.2 Recolonization Status at the New London Disposal Site 



Benthic recolonization at the active disposal area was predicted to be mostly in Stage I 

 in the central portion of the mound, while the margins were expected to be at or progressing 

 to Stage III. The majority of the disposal site stations and NE-REF were dominated by Stage 

 II, Stage II on III, or Stage III assemblages. Much of NLON-REF was dominated by torn 

 tube mats of Stage II organisms resulting from decomposition, erosion (if the mats were 

 formed during the 1990 summer-fall period), or possibly a trawling disturbance. Stage I 

 only assemblages were present at just three disposal site stations which were in areas of 

 active bedforms and/or deposits of fresh dredged material. Stage II represents a transitional 

 sere between Stages I and III and is associated with recovery of a disturbed benthic habitat 

 (Rhoads and Germano 1986). Organism-Sediment Indices were variable and indicative of a 

 patchy benthic environment (Figure 3-19). 



In comparison to the June -July 1990 survey of the New London Disposal Site, the 

 RPD values measured in the present survey were lower at both the NL-TR survey area and 

 surrounding reference areas. The difference in RPD values for the 1990 and 1991 surveys is 

 largely due to the fact that the 1991 survey was done earlier in the season than the 1990 

 survey. Between June and July, bioturbation rates in Long Island Sound may increase 1.2 

 times the initial low rate in June due to rapid changes in bottom water temperatures (Rhoads 

 1992). Bioturbation by benthic biota directly affects development of the RPD layer; a 

 significant increase in bioturbation between June and July will be accompanied by an increase 

 in depth of the oxygenated sediment layer. In addition, lack of penetration and apparent 

 RPD data collection at the WREF reference area lowered the combined RPD values for the 

 reference areas. 



4.3 New London Disposal Site Sediment Chemistry 



Analysis of sediment grain size correlated well with the mapped distribution of grain 

 size as determined from REMOTS® photographs. Sediment grain size is commonly 

 correlated with both metallic and organic contaminants in sediments. Studies of both natural 

 and polluted sediments have demonstrated that higher concentrations of contaminants are 

 invariably associated with the silt/clay fraction (Forstner and Wittman 1983, Pequegnat et al. 

 1990, Kennish 1992). Particulate and colloidal organic matter, because of its fine grain size, 

 surface charges, high surface area to volume ratio, and microbial coatings, serves to adsorb 

 or chelate organic and metallic contaminants. The percent silt/clay and TOC were greatest at 

 NE-REF. Silt/clay fractions were similar for WREF and NLON-REF with percent TOC 

 greater at the WREF (Table 3-1). 



Heavy metal contamination is of concern because of the tendency for metals to 

 bioaccumulate in the foodchain. Of the three metals analyzed, Cd and Pb have no known 

 biological functions while Zn is a trace element necessary for life processes. At elevated 



Monitoring Cruise at the New London Disposal Site, June 1991 



